How to: NBS master cylinder swap for firm brake pedal

[SunlitComet]

mityvac sell several type of bleeder and if sold separately the adapters too. Amazon has the cheapest prices usually. Are you finding the pedal pressure harder to stop or the same but sinks and hardly stopping. You can also use a second person to depress pedal while you put a clear hose on bleeder and into bottle to do it that way. May not cost you any labor.

---------- Post added at 07:51 PM ---------- Previous post was at 07:44 PM ----------

If you want to pressure bleed, this kit can do it and you will either need the:

MVA811 face seal secured with double chains or, rectangular shaped master cylinders ranging in
size up to 3½" x 6" (90 mm x 150 mm)

MVA812

Rectangular shaped master cylinders ranging in
size from 3½" x 6" (90 mm x 150 mm) to 4¼" x 7¾" (108 mm x 200 mm)

I forget the size of MC at the moment.

---------- Post added at 07:52 PM ---------- Previous post was at 07:51 PM ----------

Could do a vacuum one too. Just need to understand what it does when bleeding.

 

[MarkD51]

Thank you SLC.

That looks like that would be what's needed. Not cheap though. I see NAPA makes an adapter too, which basically looks like a stock Master Cylinder Cover, with a hole drilled in its center, a fitting attached, and a bar brace at the top for securement. Again not cheap, more money than the vacuum unit.

I imagine one, with a little inventiveness, some hand tools, and some fittings could easily duplicate what would be needed. Could probably pick up a MC Cover at a junk yard for a few dollars, and convert it. Reckon the important thing would be insuring a tight positive seal at the MC.


Will this sort of pressure bleeding from the MC also insure that the ABS Unit is also fully bled too, or will codes, or other special tools still be needed for such to properly bleed the ABS?
Thanks again, Mark

 

[SunlitComet]

Just get a neighbor to push on the pedal for you. Less expensive. Some sections of the abs will be bled but not the areas normally cut off from the mine piping when brakes are locking up. You can induce lock-up to sorta mimic what the abs does when reacting to it but you will probably never new if you locked up both fronts and the rear. On top of that not only does it need to dump pressure the pump must also run to apply braking on its own and push the air into the distribution passages to push out air as well. There are six separate valves in the abs. If you did not get air in the abs while in active mode I would not worry about it so much unless braking force is uneven or you can have someone run the functional test on it.

 

[MarkD51]

Just get a neighbor to push on the pedal for you. Less expensive. Some sections of the abs will be bled but not the areas normally cut off from the mine piping when brakes are locking up. You can induce lock-up to sorta mimic what the abs does when reacting to it but you will probably never new if you locked up both fronts and the rear. On top of that not only does it need to dump pressure the pump must also run to apply braking on its own and push the air into the distribution passages to push out air as well. There are six separate valves in the abs. If you did not get air in the abs while in active mode I would not worry about it so much unless braking force is uneven or you can have someone run the functional test on it.

Stupid question maybe, but with a conventional "two man bleed", should the engine be running,or no? Does it make a difference?
Thanks, Mark

 

[SunlitComet]

engine off.

 

[MarkD51]

Just get a neighbor to push on the pedal for you. Less expensive. Some sections of the abs will be bled but not the areas normally cut off from the mine piping when brakes are locking up. You can induce lock-up to sorta mimic what the abs does when reacting to it but you will probably never new if you locked up both fronts and the rear. On top of that not only does it need to dump pressure the pump must also run to apply braking on its own and push the air into the distribution passages to push out air as well. There are six separate valves in the abs. If you did not get air in the abs while in active mode I would not worry about it so much unless braking force is uneven or you can have someone run the functional test on it.

Whether at some past point in time, I allowed air into the system by doing some unorthodox method of work, or bleeding, that's a possibility?

When I installed the two Stillen 3/4 Ton Calipers, Pads, Slotted Rotors, and the three Stainless Braided Hoses to the Tahoe, I first drained the MC Resovoir of old fluid. (simply with a Turkey Baster)

The mechanical Aspects of installation all appeared to go just fine. Everything buttoned up properly, and the only mechanical issue I had to rectify was the flexibility of the two front Braided Brake Hoses, that would've been rubbing the insides of the front tires, so I simply used two ultra heavy duty Tie Wraps to hold-tether the Hoses away from the Tires a bit.

After installation, and bleeding by myself with a Vacuum Type Bleeder, with Cup, then was the big moment, the test drive.

The brakes at first were pretty horrid, I had quite a bit reduced braking efficiency on the truck, and of course was shaking my head "oh boy, now what?"

Taking the truck on a deserted unused street in the area, I took the Tahoe up to about 40-45 mph, and pushed the pedal as hard as I could. I almost went through the windshield. The ABS activated, and the truck hauled down from speed very quickly.

Thinking back, I thought I might've drained the Resovoir a bit too much, virtually totally emptying it before I refilled with fresh?

The other, was that the Pistons within the Caliper Bores were slightly seized, or I didn't get a full bleed though all the lines?

Anyway, after that, the brakes did appear to work quite well. It seemed that the Slotted Rotors, and better composition of the Pads enabled the truck to stop much better than stock, especially after the Pads were warmed up a bit. Pedal feel was good, seemed firmer than before.

The truck with the new brake components worked flawlessly for quite many 1000's of miles across country towing a Cargo Trailer.

Until recently, currently, my brakes are working quite poorly.

I like doing work myself, and sadly have little in the way of help here in NM.
I just earlier ordered a Power Motive Power Bleeder Kit, with Tank, and Alu Square Plate Adapter. I'll again buy a qt or two of good fluid, and try again with a full system bleed, and go from there.

I see no leakage anywhere on the vehicle, and will do an update when I can.

At this point, I will of course hold every component on the system as suspect, the MC, Booster, and all brake parts at the wheels as possibly faulty. The ABS still appears to work correctly, no premature locking up, no brake lights, etc.
Mark

 

[SunlitComet]

no brake warning lights at all? not even at vehicle start?

 

[MarkD51]

no brake warning lights at all? not even at vehicle start?

At start up, yes, I get all the usual dash lights that come on, then go out. No unusual issues there. Bleeder should be here Friday, maybe this weekend I'll get to toy with the truck

 

[MarkD51]

Here's another small update, and some comments about how my brakes feel. I took the truck for some gas this morning, and traveled about 40 or so miles, combo of street, and highway.

The brakes actually don't seem as bad as they were. This could be due to the crappy "one man bleed" I did a few months back, and some removal-cleaning of the rear drum adjusters (11" drums) last week or so.

The brakes work positively, I did check for things this morning like booster bleed-off-leakage, and this seems to be OK. also no leaks anywhere.

The truck comes down well from any speed, stops no worse than it ever did, no pull, etc., ABS appears to be functioning perfectly, no issues there.

What I note, and what I particularly don't like, is that it takes about 2 or so inches of pedal travel before the brakes begin to bite, and with those top 2 or so inches of initial pedal travel, the pedal seems hard, and firm. I note this "firmness of intial travel seems to vary ever so slightly, that when initially applying after a while of driving, it is firmer than when again activating the brakes. Seems the second, or third time it is a little easier to depress the pedal.

Is this typical? Is this the infamous crappy OBS Brake' s signature qualities? Or?

Thanks again for any comments-help you folks can help me with.
Mark

 

[SunlitComet]

Hard to push pedals in the first couple of inches is the vacuum booster holding you back. your booster might have malfunctioning seal or valves inside the unit from your description of what is going on. your first push on the pedal should be easy.