Rear axel swap

[Gzes]

60s are cheap down here aswell. Matt find me a Dana 60 front cheap over there and I'll drive up lol

 

[mattluttrell]

60s are cheap down here aswell. Matt find me a Dana 60 front cheap over there and I'll drive up lol

I've seen a kingpin for $700 and ball joint for $500 recently. It's been surprising. I've been tempted to resell them. There are a couple fronts on the Oklahoma CL right now.

 

[Nak]

Cant you just Adjust the rear drums "loosely" to compensate for the extra Brake pressure? Im not calling you out I just don't see how the rear would be able to overpower the front unless you messed with the pressure system in some way . Ill definitely look into this and thank you for your information

Nope. The 11" drums are duo servo brakes, the 10" drums are leading-trailing brakes. Duo servo brakes require FAR less pressure to activate. That's why the 11" brakes have a much smaller wheel cylinder, only 1". Even then, as brake pressure increases, the 11"s produce significantly higher braking force than the 10"s. That's why GM uses a different C-valve with the JB6 brakes. They didn't specify a different valve just for the hell of it; they specified a different valve because the 11"s require a different valve. When you swap the 10"s for 11"s and fail to swap the C-valve, you're ignoring all of the knowledge, testing, and experience of the GM engineers. If you're going to do all of that, you should have a pretty good reason as to why.

Designing a brake system is a big deal. I know it's beyond me for sure. Very few people have the knowledge or the equipment to do it properly. For most of us, the answer is to mimic a factory system. Going with 11" drums is actually a pretty easy setup. The only difference between the JB5 and the JB6 brakes are the rear drums and the combination valve. It's not a big deal to replace the C-valve... Going to rear disc is harder, but still doable. You just need to make sure you swap out all the components for a factory system that came with the same rear disc.

Just swapping out a Master cylinder for one from a newer year, or changing out the rear brakes is a really bad idea. People get away with it when improving the front brakes, because in a skid the rig is more stable, not less. It still screws with the balance and increases your risk of spinning out of control in certain conditions, but not near as bad as massively improving the rears.

Vehicle brakes act as a system. Each piece is designed to work with the other parts in the system. When modifying brakes it's critically important to understand what you're doing and to modify the system as required to keep all the parts working together. You need to understand what you are doing and how it affects your brakes. If you don't, you just turn your rig in to a ticking time bomb that may just kill somebody some day.

 

[Symba_The_Lyon]

So is there a repo code for the gearing ratio? I have read some where that the one ton trucks have stock 4.10 gears and that is what i am trying to find, I talked to a guy from a junk yard and he say'ed that you can have a different gearing ratio in the back but you just cant use 4x4 i am wounding if this is true also with these bigger drums will they fit a 15 inch rim ?

 

[Gzes]

Meh out of my budget.. if you see a donor truck with one id be interested in it. Gonna prove you can sas for under 1k. There's 2 Dana 60 rears fir $250 each that havnt sold st all. I might offer $100 a pop on Em but they are about an hour away n I'd have to take my trailer for them but Idk yet

 

[Nak]

Yes, there is an RPO code for the gear ratio. I'm on the road right now and don't have accesss to my files on this though. I can post codes in a couple of days... I believe 3.73 gears are GT5, but I'm not 100% sure.

If you have different gears front and rear, you'll break something if you try and use 4WD. In the 1/2 ton Suburbans it seems like 3.73 was very common... Anyways I'd keep looking for one with the right gears. No 1 Ton is going to have the 14 Bolt SF rear end BTW. A light 3/4, or a Heavy Half will have it. You're looking for a rig with a GVWR of 7200 pounds. There's also an RPO code for that, but every rig I've seen had the 7200# GVWR paired with the JB6 brakes. The 7200# GVWR specifies the 14 Bolt SF rear end from what I can tell.

I know the 11" drums work fine with the 16" wheels, at least mine fit fine. I don't know about 15" rims though.

 

[Nak]

Here's the gear ratio RPOs:

GT3 AXLE REAR 4.55 RATIO
GT4: 3.73 Gear Ratio
GT5: 4.10 gear Ratio
GU6: 3.42 Gear Ratio

 

[Symba_The_Lyon]

So you can run two different gears in the front and the back safely but you just cant use 4x4?

 

[SunlitComet]

don't even think about it. one day you are going to forget something and WHAMO!. Instant drivetrain damage.

 

[Donnie Yukonie]

Gonna prove you can sas for under 1k

Not going to happen, the cheapest Ive seen it done was $19--.-- some odd dollars and that was with a Driver side pumpkin with "USED" everything The truck was NOT road safe by no means. Hell I would hesitate taking it on the trail to be honest . If you SAS do it right , Im not saying you need a $8k setup but you can at least test for 2k minimum and thats Fabbing your own parts and doing all the work yourself. Remember Saftey First I hate to sound like OSHA but Ive seen a lot of Avoidable Carnage and accidents because people cut corners .

So you can run two different gears in the front and the back safely but you just cant use 4x4?

You "can" Hell Im going to do it but I already Tagged out my 4x4 Until I rehear the front . Im going for 4.56s But as Sun stated It will Absolutely DESTROY your driveline . Binding up Gears and Transfer case . Hell it might even put some work on your trans . Put it this way you will quickly find out the weakest link in your Drivetrain there is

 

[Nak]

don't even think about it. one day you are going to forget something and WHAMO!. Instant drivetrain damage.

What he said!

 

[Symba_The_Lyon]

Hey there guys i just got my self a sf 14 bolt finally, They guy's at the junk yard opened the diff case and got the number off the ring gear and did the math and they stayed its the right ratio witch is 342, Now how do you find out the ratio when you open the case with the number on the ring gear i am just wanting to double check before i do the swap? @Nak when you did the swap did the drums make you're tire in the back stick out farther because of the drum sticking out so far??

 

[Nak]

For the ratio, count the teeth. Gear ratio is ring teeth divided by pinion teeth. The axle width, wheel mating surface to wheel mating surface should be identical between the 10 and the 14SF. My rear wheels stick out exactly the same as they did before.

 

[2wdr]

OK, I have read and reread this several times. I am looking to replace the rear end in my 1999 2wd 2dr with a 14 bolt. I understand to look for the brake size code JB6. And I need a GU6 3.42. But here is where I get lost a bit. I do not want the G80, soooo, what code do I need to look for?

G91 would be nice for me, but , is that still a Posi limited slip too?

I hope to find one in the vehicle and not have to open 12 to find one.

 

[livingez_123]

If the rear is bouncing, have you thought of better shocks to control the axle movement?
Have you also thought of using an NBS 3/4 ton axle and just changing the bolt pattern? the little stuff like spring mounts can be easily changed.

 

[Nak]

OK, I have read and reread this several times. I am looking to replace the rear end in my 1999 2wd 2dr with a 14 bolt. I understand to look for the brake size code JB6. And I need a GU6 3.42. But here is where I get lost a bit. I do not want the G80, soooo, what code do I need to look for?

G91 would be nice for me, but , is that still a Posi limited slip too?

I hope to find one in the vehicle and not have to open 12 to find one.

G91 denotes a 6.83 axle ratio according to the lookup I did?

JB6 is a good start, but I have seen some 10 bolt rear ends with the JB6 brakes lately... C5Z denotes 7200 GVWR, and that should definitely be a 14 bolt Semi floater. Y06 and Y07 both denote 9.5" ring gear, but I've seen 14 bolt SF rear ends in vehicles that did not have those RPOs listed. To avoid G80 just find a rig without it listed on the RPO sheet. However, it's always possible that someone could have swapped in a G80 unit at some point so it's important to pull the cover before buying. Also, measure the distance from outer brake drum to outer brake drum to verify. The 2WD and 4WD rear ends are about 4" different in width.

 

[jerryjoe28]

ok guys sorry to bring a old thread back to life. I just found a 94 1500 with a 14 bolt and 6lug. after reading this it sounds like it should be just a pretty straight forward swap?...... my question is what do you guys think about rear disk conversion kits? and any reccomendations on where to get one?

 

[Nak]

Yep, pretty easy swap. Just need a conversion rear U-joint; everything else bolts right up. Rear disc would be great for sure, but you might want to try the 11" rear drums that come on the 14 bolt first. It's a pretty big brake upgrade over what you have now. Fortunately, the proper combination valve is still available new. At first glance, it looks like it's part of your ABS unit, but it is separate and bolts directly to the ABS unit.

Anyways, I'd see how happy you are with the big drums first, you can always convert to drums later. My plan was to do the disc brakes as well, but the big rear drums improved brake feel and performance so much that I'm completely happy with them. Don't skip the new combination valve though, the 11" drums will put your rig's brakes dangerously out of balance without it.