saif najd
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How to: NBS master cylinder swap for firm brake pedal
- Thread starter _Dylan_
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nomad
Member
NBS vs OBS: Additional Info and test results
In a previous post I mentioned I replacing the OBS MC with the NBS MC from an 01 Silverado because of the success posted in this tread.
As I had mentioned the results where not great and though it could be an ABS computer issue. Here are the final findings and some hard numbers.
Using a GM Tech 2 tool I ran diagnostics and cycled the 4wABS unit. It passed without errors and had no codes set. After running the test the brakes were somewhat better but still not what I thought they should be. I again bled the brakes (2 person method) and cycled the ABS unit with no change. Obviously if I still had air in the line the pedal would not be rock hard.
I made some test passes then re-installed the obs MC and tested again.
Test findings:
1. The NBS MC provided a harder/stiffer pedal with less "mushy feel". This is misleading because even though the pedal travels less the actual braking amount is less when the same effort is applied.
Actual test 1 60 mph:
Standard one foot hard stop; braking using and equal amount of depression force with both MC's the Tahoe required an additional 12 feet extra space to come to a stop with the NBS, result: OBS stopped in less distance, no lockup or antilock activity was noted.
Actual test 2: 60 mph:
Panic stop, both feet; jamming both feet quickly on the pedal with high pressure the results are a little different, the NBS MC would lock up the brakes faster resulting in a 4 foot better stopping difference on the OBS MC. Antilock system was activated.
In both tests the OBS MC stop had much more pedal travel then the NBS MC.
Also, it appears there is less nose drive with NBS MC probably because the larger rear bore allows the rear brakes more fluid.
Based on those results one might say the NBS MC is better because you can get a lock up faster but I disagree, granted the NBS MC provides a nicer firmer pedal but what good is it when you have to push it so hard to get the equivalent stopping power.
Finally, the Wife test: Since my wife drives my Tahoe all the time I tried the following: I did not mention to her what I did, I pulled onto a back road and told her to drive, I told her I wanted to listen to something while she drove. I had her make a number of stops. Her first question was "is there something wrong with the brakes? She went on to say the pedal is really hard and it doesn't seem to stop as good as it used to. After I explained what I did her answer, "you ruined it, put it back the way it was".
Final conclusions:
At this point I am thinking of leaving the OBS MC in place and returning the NBS MC. I still cannot explain why the OBS MC appears to be a 40mm bore though I haven't pulled out the piston to verify the bore is actually that size. Perhaps someone has an answer for this.
Is the NBS MC the answer to a mushy pedal, In my opinion, no, true it will give you a hard pedal but what good is it if you really have to mash it on a hard stop. To me it somewhat degrades the driveability.
What would be the Possible solution? If you had a stronger Vacuum assist or Hydroboost unit giving you the extra force thus removing it from the driver that might be the ultimate answer. Both a non mushy brake that activates without a great amount of pedal force.
Bottom line and again my opinion, what constitues "good braking" is a matter of perspective. Some feel a rock hard pedal that locks up when you stand on it is better then a soft squishy pedal that only requires moderate effort with greater pedal travel. For men, maybe so, but for your wife, maybe not.
I am hoping SunlitComet can provide some input after he completes his hydroboot upgrade with NBS MC.
Constructive Comments Welcome!
Dan
In a previous post I mentioned I replacing the OBS MC with the NBS MC from an 01 Silverado because of the success posted in this tread.
As I had mentioned the results where not great and though it could be an ABS computer issue. Here are the final findings and some hard numbers.
Using a GM Tech 2 tool I ran diagnostics and cycled the 4wABS unit. It passed without errors and had no codes set. After running the test the brakes were somewhat better but still not what I thought they should be. I again bled the brakes (2 person method) and cycled the ABS unit with no change. Obviously if I still had air in the line the pedal would not be rock hard.
I made some test passes then re-installed the obs MC and tested again.
Test findings:
1. The NBS MC provided a harder/stiffer pedal with less "mushy feel". This is misleading because even though the pedal travels less the actual braking amount is less when the same effort is applied.
Actual test 1 60 mph:
Standard one foot hard stop; braking using and equal amount of depression force with both MC's the Tahoe required an additional 12 feet extra space to come to a stop with the NBS, result: OBS stopped in less distance, no lockup or antilock activity was noted.
Actual test 2: 60 mph:
Panic stop, both feet; jamming both feet quickly on the pedal with high pressure the results are a little different, the NBS MC would lock up the brakes faster resulting in a 4 foot better stopping difference on the OBS MC. Antilock system was activated.
In both tests the OBS MC stop had much more pedal travel then the NBS MC.
Also, it appears there is less nose drive with NBS MC probably because the larger rear bore allows the rear brakes more fluid.
Based on those results one might say the NBS MC is better because you can get a lock up faster but I disagree, granted the NBS MC provides a nicer firmer pedal but what good is it when you have to push it so hard to get the equivalent stopping power.
Finally, the Wife test: Since my wife drives my Tahoe all the time I tried the following: I did not mention to her what I did, I pulled onto a back road and told her to drive, I told her I wanted to listen to something while she drove. I had her make a number of stops. Her first question was "is there something wrong with the brakes? She went on to say the pedal is really hard and it doesn't seem to stop as good as it used to. After I explained what I did her answer, "you ruined it, put it back the way it was".
Final conclusions:
At this point I am thinking of leaving the OBS MC in place and returning the NBS MC. I still cannot explain why the OBS MC appears to be a 40mm bore though I haven't pulled out the piston to verify the bore is actually that size. Perhaps someone has an answer for this.
Is the NBS MC the answer to a mushy pedal, In my opinion, no, true it will give you a hard pedal but what good is it if you really have to mash it on a hard stop. To me it somewhat degrades the driveability.
What would be the Possible solution? If you had a stronger Vacuum assist or Hydroboost unit giving you the extra force thus removing it from the driver that might be the ultimate answer. Both a non mushy brake that activates without a great amount of pedal force.
Bottom line and again my opinion, what constitues "good braking" is a matter of perspective. Some feel a rock hard pedal that locks up when you stand on it is better then a soft squishy pedal that only requires moderate effort with greater pedal travel. For men, maybe so, but for your wife, maybe not.
I am hoping SunlitComet can provide some input after he completes his hydroboot upgrade with NBS MC.
Constructive Comments Welcome!
Dan
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SunlitComet
OBS Jedi-Do Good
With just the NBS MC you are changing the fluid volume in MC. The NBS unit may not be able to create enough hydraulic force because the cylinders bores are bigger. Physics require you to use more pedal force to get the same wheel force as the old one did. You need a stronger booster at least. When my hydroboost is done(This Saturday I hope), I will have a hydroboost obs MC that matches the booster and PS pump(OBS Suburban JH6 system). The MC will not be changed just yet because when I convert the rear drum to disc later it will have a MC in the kit. While a hydro boost can make the NBS MC work easier I can can not provide my own results yet. just those of who I have read have done it on an OBS burb. For now anyway.
The OBS MC has a dual bore, 40mm and 28.6mm. You're measuring the 40mm portion. The NBS MC has both front and rear bores equal. The reason for this is that the NBS MC is for a Disc/Disc system, the OBS MC is designed for Disc/Drum brakes. Not only are the bore sizes not balanced for Disc/Drum on the NBS MC, but it lacks a residual pressure valve for the rear brakes. Disc brakes don't need a residual pressure valve, drum brakes do need them.
You mentioned earlier that you have the 11" rear drums and the 14 bolt SF axle. When you did the swap, did you swap out the brake combination valve--the proportioning valve? I know on yours it looks like you don't have one, but you do. It's bolted to the output side of your ABS unit, and is replaceable.
nomad
Member
Nak, thanks for your reply,
In answer to your question no changes were made other than an axle swap, at the time when I swapped the rear axles the only real differences brake wise between the 10 bolt and 14 bolt was an extra inch in shoe sizes, the wheel cylinders were just about the same. I also did not notice any difference in braking when I swapped the rears.
Another interesting fact I just discovered, I went back to the maintenance records of the original owner and saw that he had the MC replaced, I guess when they replaced it they used a Hydroboost MC and not the standard Vacuum MC. This explains why my old mc was 40mm.
The original owners complaint was "Mushy and excessive pedal travel". I needed to know for sure so off to NAPA.
I had the NAPA person pull both the recommended Vacuum MC and a hydroboost MC, sure enough my old MC was a hydroboost type. Perhaps this was done on purpose, to satisfy the original owners complaints.
This leaves me with a delima on what to do from here, from your post I gather the NBS MC will really not provide the balanced fluid needed for the rears unless I convert to discs. I have not been able to find any kits to accomplish this (though I have spent much time looking). You can buy a disc brake conversion for 14ff all day long, not so with 14sf. And it looks as though going backwards and putting in the correct Vacuum MC would make things even worse!
At this point it looks I have 2 options, 1 is to update to hydroboost with a matching OBS MC to make everything work correctly, or, 2 dump the abs, re-plump the system with a standard drum combo/prop valve.
As always, comment are welcome!
Dan
In answer to your question no changes were made other than an axle swap, at the time when I swapped the rear axles the only real differences brake wise between the 10 bolt and 14 bolt was an extra inch in shoe sizes, the wheel cylinders were just about the same. I also did not notice any difference in braking when I swapped the rears.
Another interesting fact I just discovered, I went back to the maintenance records of the original owner and saw that he had the MC replaced, I guess when they replaced it they used a Hydroboost MC and not the standard Vacuum MC. This explains why my old mc was 40mm.
The original owners complaint was "Mushy and excessive pedal travel". I needed to know for sure so off to NAPA.
I had the NAPA person pull both the recommended Vacuum MC and a hydroboost MC, sure enough my old MC was a hydroboost type. Perhaps this was done on purpose, to satisfy the original owners complaints.
This leaves me with a delima on what to do from here, from your post I gather the NBS MC will really not provide the balanced fluid needed for the rears unless I convert to discs. I have not been able to find any kits to accomplish this (though I have spent much time looking). You can buy a disc brake conversion for 14ff all day long, not so with 14sf. And it looks as though going backwards and putting in the correct Vacuum MC would make things even worse!
At this point it looks I have 2 options, 1 is to update to hydroboost with a matching OBS MC to make everything work correctly, or, 2 dump the abs, re-plump the system with a standard drum combo/prop valve.
As always, comment are welcome!
Dan
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SunlitComet
OBS Jedi-Do Good
hydroboost it.
The extra inch in shoe size is actually a big deal...
Our 10" drum brakes are called "Leading/Trailing brakes while our 11" drum brakes are "Duo Servo". Duo servo brakes are far stronger. That's why the 11" brakes are much stronger than the 10" brakes even though the 10" brakes have much bigger wheel cylinders. (The larger diameter of the brakes adds 10% as well, but the duo servo adds more.) That's why the 11" brakes are a great upgrade for our trucks. They need less fluid and pressure to operate than the 10's, so brake feel and force are both improved. But you have to change more than the rear brakes to see an improvement. By themselves, the 11" drums will dangerously destabilize your rig. That's why you should change the combination valve if you upgrade your rear brakes.
If your brakes are functioning properly, you should have noticed a big difference with the 11" rears. The wheel cylinder on the 11" brakes is 1", where as the 10" has a 1-3/16 wheel cylinder. That's a lot less fluid required, so you should have seen less brake pedal travel and more firmness immediately. If you didn't, something is wrong. Check out the rear brakes, are they assembled correctly? The previous owner may have screwed up a brake job. The wheel cylinders may be the wrong size. Visually, I don't know how to tell the difference between 1" and 1-3/16" wheel cylinders without tearing them down... Did you power bleed the brakes? I tried bleeding mine for hours the manual way and never got a firm pedal. I took it in to a shop to get pressure bled and flushed--instant firm pedal. When you bled, did you use the little tools to open all of your valves on the ABS? I'm not sure if your Combi valve has one, it should. Did you bench bleed your MC? Are you sure the rear shoes are adjusted correctly?
If you haven't changed your proportioning valve your brake distances will go up. In fact, your ABS is preventing a very dangerous situation. But it won't save you in all conditions. You have way too much pressure going to the rears for the 11" brakes. They'll lock up way too easy and well before the fronts. If your rears skid before the fronts, the truck wants to swap ends. The ABS is preventing that, but you probably hear the ABS working on moderate braking on wet roads. Even medium braking in a turn on a wet road is dangerous though. Too much rear bias.
Hydroboost is absolutely the best braking you can get. But I have to say my vacuum brakes are rock solid and plenty powerful after going to 11" rears. Before I switched the Combi valve though, my braking distance went to hell with the 11" brakes. It felt really good with light braking, because the rears are so effective. But add wet roads or downhill braking and I could hear the ABS cycle way too early. That was because the rears were trying to lock up. You can verify this pretty easy. Open your window and brake moderately going down a damp hill. You'll be able to hear the rear brake start to lock up, then the ABS will kick in. You can hear the same thing in other conditions, but a damp hill lets you do this at slower speeds. Do this with no other vehicles or people around obviously.
If it were me, I'd get a new ACdelco or GM master cylinder, OBS and vacuum specified. Way too much Chinese junk around that is bad right out of the box. Also, I'd change my combi valve to the one specified for JB6 brakes, as that is what you now have if you have the 11.15"x2.75" rear drums. Be absolutely 100% sure your rear brakes are assembled correctly and you have the proper wheel cylinders. You never know what idiotic thing a previous owner may have done. Get your brakes pressure bled at a good shop. Vacuum bleeding won't bleed the ABS, and in my experience neither will manual bleeding. You have to start from a known good brake system to try and diagnose any issues. Way too many variables otherwise. My guess is after you do these things, your brakes will be great. If not, you'll be able to figure out the problem a lot easier with the system in a known good configuration.
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nomad
Member
The plot thickens
Nak, Seems the more I look into this the more confusing it gets.
Here are a couple of things I found out today,
I pulled the rear drums today, all parts are in the right place, and shoes are showing even wear and the correct wheel cylinders are in place. I did a little testing today on a wet road, my fronts lock up well before the back and the abs takes over. On a dry road forget it, just about impossible to get a lockup. The pedal and brakes are about the best it has been (even though they are not great), I mentioned I did not really notice a difference when I swapped out rears but then again I had just replaced the rear brakes at the same time, I usually am very easy on new brakes so I really didn't put them though a proper test. Next,
I looked into replacing the Combi/Prop valve you suggested. The problem is that it has limited availability and to get the correct part you need the following info: Vehicle VIN and the code that is stamped on the valve itself. As I have been told there are many different valves used even for a specific vehicle. So without a code from a specific application (one that matches mine) replacing the valve would be a shot in the dark.
I also did some research on MCs as well and according to GM the Tahoe and Burb both use pn 19209221. This MC is for used in vehicles with RPO code JB5 (2dr Tahoe, Vacboost with 10" rear drum) and RP0 code JB6 (4dr Tahoe, Burb with 11" rear drum). These master cylinders have a 40mm bore size with 1.125 bore (dual diameter bore)
Another MC pn 18029968 is used in 4dr Tahoe’s and burbs with RPO code JB7 (Vacboost with 13" rear drum, my guess is ff14 rears. and Tahoe’s with police packages) These master cylinders have an approx 34mm bore size with 1.125 bore (single diameter bore) This part number is also used with brake codes JD6 and JD7 (hydro boost)
OK, now comes the interesting part, the Kelsey/Hayes Antilock controller has the same part number for all of the applications above. You would think there would be different part numbers (unless the combi/prop valves are not part of the assembly?) I would ask you to give me the number of your valve but unless you have the same ABS configuration it probably would not fit.
I have just about come to the conclusion what I need to find is an obs 3/4 ton burb with hydro boost and pull everything out, booster, master, brake pedal and rod, ps pump and the 4wabs unit. Equipped with the VIN and all the hardware I should be able to get everything to work as it was designed. Now the challenge is to find one, I spent most the afternoon with salvage yards. So far no go.
Worst case I will just replace the master with the correct part, pressure bleed and just live with it. Not my first choice!
Dan
Nak, Seems the more I look into this the more confusing it gets.
Here are a couple of things I found out today,
I pulled the rear drums today, all parts are in the right place, and shoes are showing even wear and the correct wheel cylinders are in place. I did a little testing today on a wet road, my fronts lock up well before the back and the abs takes over. On a dry road forget it, just about impossible to get a lockup. The pedal and brakes are about the best it has been (even though they are not great), I mentioned I did not really notice a difference when I swapped out rears but then again I had just replaced the rear brakes at the same time, I usually am very easy on new brakes so I really didn't put them though a proper test. Next,
I looked into replacing the Combi/Prop valve you suggested. The problem is that it has limited availability and to get the correct part you need the following info: Vehicle VIN and the code that is stamped on the valve itself. As I have been told there are many different valves used even for a specific vehicle. So without a code from a specific application (one that matches mine) replacing the valve would be a shot in the dark.
I also did some research on MCs as well and according to GM the Tahoe and Burb both use pn 19209221. This MC is for used in vehicles with RPO code JB5 (2dr Tahoe, Vacboost with 10" rear drum) and RP0 code JB6 (4dr Tahoe, Burb with 11" rear drum). These master cylinders have a 40mm bore size with 1.125 bore (dual diameter bore)
Another MC pn 18029968 is used in 4dr Tahoe’s and burbs with RPO code JB7 (Vacboost with 13" rear drum, my guess is ff14 rears. and Tahoe’s with police packages) These master cylinders have an approx 34mm bore size with 1.125 bore (single diameter bore) This part number is also used with brake codes JD6 and JD7 (hydro boost)
OK, now comes the interesting part, the Kelsey/Hayes Antilock controller has the same part number for all of the applications above. You would think there would be different part numbers (unless the combi/prop valves are not part of the assembly?) I would ask you to give me the number of your valve but unless you have the same ABS configuration it probably would not fit.
I have just about come to the conclusion what I need to find is an obs 3/4 ton burb with hydro boost and pull everything out, booster, master, brake pedal and rod, ps pump and the 4wabs unit. Equipped with the VIN and all the hardware I should be able to get everything to work as it was designed. Now the challenge is to find one, I spent most the afternoon with salvage yards. So far no go.
Worst case I will just replace the master with the correct part, pressure bleed and just live with it. Not my first choice!
Dan
Hey Dan!
You mentioned doing tests with both NBS and OBS Master cylinders; I assumed you reverted to the OBS MC? If you're using the NBS MC, I can't say what your brakes will do because of the non-spec MC. Like I said, I'd go back to a known configuration before anything else. Once you introduce more than one variable it get's real difficult to diagnose things...
If you are using the OBS MC, Start by taking the rear drums off. Have a helper push slowly on the brakes while you watch the brake shoes. Take off one drum at a time. Be very careful, because you can over extend the wheel cylinders. I did this after multiple bleeding attempts and the rear shoes didn't even move. That's when I gave up manual bleeding and took it in for a pressure bleed. After that, my brakes were rock solid and I found out how overpowered the rears were. Check adjustment of the rear brakes. The manual says to adjust the shoes until their is moderate resistance to moving the wheel. Then back off the adjuster 33 clicks.
All I can say is that if your brakes aren't rock solid with the 11" brakes and the OBS MC, there is something wrong with your brakes. Going to the 11s basically does what people are trying to do with the NBS MC swap. The smaller wheel cylinder needs less fluid, so you don't run short of MC capacity. That, and having more of your effort going to the front brakes should be a vast improvement over your old brakes. But it's all out the window with a NBS Master.
The 11" brakes should really improve your brakes, both front and rear. It was explained to me this way. When you push on the pedal, you are activating four brake mechanisms, two front and two rear. Your effort--and the booster's effort--is divided into four parts. Since the 11" Duo Servo brakes require much less pressure and fluid to activate than the 10" drums, there is more pressure left to put to the front brakes. I believe this, because I used to have to put two feet on the pedal and really push to lock the wheels--activate the ABS. Now, good pressure with one foot will get all four wheels cycling the ABS.
I got the same info as you, the front brakes, the MC and the ABS are all the same for JB5 and JB6 brakes. The difference is the rear brakes and the combination valve. The combination valve is bolted to the ABS, but it is not listed as a part of it. It is separate. The way I got the part number is I found the online GM parts dealers and looked up the parts. I use GM Parts East :
http://www.gmpartseast.com/Page_Pro...ctionDate=&VehicleInfo=&CatalogCode=53C&Year=
They don't want you to use their charts to look up part numbers, so they use XX in place of the first two numbers. 12 I can't tell you what number to use, 12, that would be wrong.
Anyways, it says Combi valve not available, but go down to the kits at the bottom. It is available as a kit, which is the valve and the connector for the ABS module I think. Look at the part number for JB5 brakes and the different number for JB6 brakes. BTW, GMPartsEast has great prices, but if they don't have the part you can google it, it's still available. BTW, "COMB" is short for "Combination"
It's interesting, because even though the valves for your year and mine are different, they are still both marked the same. Under "Kit 3" for your truck, you can find both the JB5 and the JB6 valve, and they are stamped "D" and "A". Precisely what my valves are stamped for the same options. (Although on mine it's a sticker, not actually stamped. ) My guess is the letter designator is for the springs inside that control the pressure differential.
The parts guy couldn't help you, because there is no way he knows the parts for a 20 year old truck. All he can do is use the VIN. By studying the parts charts you can learn what parts you need. If you have problems reading a chart, print it out and find a Parts guy who doesn't mind helping you figure it out.
You mentioned doing tests with both NBS and OBS Master cylinders; I assumed you reverted to the OBS MC? If you're using the NBS MC, I can't say what your brakes will do because of the non-spec MC. Like I said, I'd go back to a known configuration before anything else. Once you introduce more than one variable it get's real difficult to diagnose things...
If you are using the OBS MC, Start by taking the rear drums off. Have a helper push slowly on the brakes while you watch the brake shoes. Take off one drum at a time. Be very careful, because you can over extend the wheel cylinders. I did this after multiple bleeding attempts and the rear shoes didn't even move. That's when I gave up manual bleeding and took it in for a pressure bleed. After that, my brakes were rock solid and I found out how overpowered the rears were. Check adjustment of the rear brakes. The manual says to adjust the shoes until their is moderate resistance to moving the wheel. Then back off the adjuster 33 clicks.
All I can say is that if your brakes aren't rock solid with the 11" brakes and the OBS MC, there is something wrong with your brakes. Going to the 11s basically does what people are trying to do with the NBS MC swap. The smaller wheel cylinder needs less fluid, so you don't run short of MC capacity. That, and having more of your effort going to the front brakes should be a vast improvement over your old brakes. But it's all out the window with a NBS Master.
The 11" brakes should really improve your brakes, both front and rear. It was explained to me this way. When you push on the pedal, you are activating four brake mechanisms, two front and two rear. Your effort--and the booster's effort--is divided into four parts. Since the 11" Duo Servo brakes require much less pressure and fluid to activate than the 10" drums, there is more pressure left to put to the front brakes. I believe this, because I used to have to put two feet on the pedal and really push to lock the wheels--activate the ABS. Now, good pressure with one foot will get all four wheels cycling the ABS.
I got the same info as you, the front brakes, the MC and the ABS are all the same for JB5 and JB6 brakes. The difference is the rear brakes and the combination valve. The combination valve is bolted to the ABS, but it is not listed as a part of it. It is separate. The way I got the part number is I found the online GM parts dealers and looked up the parts. I use GM Parts East :
http://www.gmpartseast.com/Page_Pro...ctionDate=&VehicleInfo=&CatalogCode=53C&Year=
They don't want you to use their charts to look up part numbers, so they use XX in place of the first two numbers. 12 I can't tell you what number to use, 12, that would be wrong.
Anyways, it says Combi valve not available, but go down to the kits at the bottom. It is available as a kit, which is the valve and the connector for the ABS module I think. Look at the part number for JB5 brakes and the different number for JB6 brakes. BTW, GMPartsEast has great prices, but if they don't have the part you can google it, it's still available. BTW, "COMB" is short for "Combination"It's interesting, because even though the valves for your year and mine are different, they are still both marked the same. Under "Kit 3" for your truck, you can find both the JB5 and the JB6 valve, and they are stamped "D" and "A". Precisely what my valves are stamped for the same options. (Although on mine it's a sticker, not actually stamped. ) My guess is the letter designator is for the springs inside that control the pressure differential.
The parts guy couldn't help you, because there is no way he knows the parts for a 20 year old truck. All he can do is use the VIN. By studying the parts charts you can learn what parts you need. If you have problems reading a chart, print it out and find a Parts guy who doesn't mind helping you figure it out.
nomad
Member
Nak,
Thanks for providing the chart and I get what your saying!
Obviously you did a great deal of homework when you installed your sf14. I do have one question, did you try your brakes before your replaced the valve, or was the valve replacement because of the over active rear brakes?
My obs mc was put back in place almost immediately after I tried the nbs and have been using the truck that way. I going to have a friend come over and do the rear test you mentioned.
Based on your results I am thinking my original obs mc might be no good, cant really test it without a high pressure gauge. One note, when I bought this truck it had been sitting in a garage for 2 years and didnt move, it also had low miles for the year. It is possible its been bad from the start just from sitting.
Based on testing results today I might just purchase a new obs mc (jb5/6), have the brakes pressure bled, verify proper operation of the rears and nail down the combi/prop valve. I have already thrown some money at this, whats a little more for good brakes!
I greatly appreciate your effort and suggestions.
Dan
Thanks for providing the chart and I get what your saying!
Obviously you did a great deal of homework when you installed your sf14. I do have one question, did you try your brakes before your replaced the valve, or was the valve replacement because of the over active rear brakes?My obs mc was put back in place almost immediately after I tried the nbs and have been using the truck that way. I going to have a friend come over and do the rear test you mentioned.
Based on your results I am thinking my original obs mc might be no good, cant really test it without a high pressure gauge. One note, when I bought this truck it had been sitting in a garage for 2 years and didnt move, it also had low miles for the year. It is possible its been bad from the start just from sitting.
Based on testing results today I might just purchase a new obs mc (jb5/6), have the brakes pressure bled, verify proper operation of the rears and nail down the combi/prop valve. I have already thrown some money at this, whats a little more for good brakes!
I greatly appreciate your effort and suggestions.
Dan
