Ok, i got my rear end off a 95 TA. It has 3.42's Posi and Disk brakes. And i see how much wider it is than my 3rd gen. SO i was wonderin, could i transfer everything from my 4th gen rear to my 3rd gen, so i won't have the vato style tires sticking out past the fenders in the back.

Questions
1. Will 4th gen gears fit in my 3rd gen rear (89 rs. 3.08's non posi)
2. What about the posi unit, will it fit too?
3. Will the disk brakes bolt on?
4. Has this been done before?

thank you all for reading.

john

1 yes
2 yes
3 maybe, i'd guess they would
4 i'm sure someone has

It doesnt look horrible with the 4th gen rear, but its bad enough for me to get 4th gen rims and spend $150 on spacers for the fronts. It'll cost you a lot to swap the internals unless you can do it yourself, and from what Ive read to go from drum to disc is a hard swap.

I will probably, do the gear swap myself, and the posi trac swap too, just for the learning experience. i just want to make sure that they will fit for sure before i start tearing apart my rear end.

as long as my drum brake rear has the same bracket on the ends of the axel tubes, it should bolt right on. i will be getting a new master cyclinder and proportioning valve for a third gen with rear disks so the braking should be balanced.

ANd does anyone know who has done what i am talking about?

john

Email sent

thank you very kindly for the emailed info, it will be of great help.


Next question, will my stock 15 in third gen rims fit over the rear lt1 disk brakes?

john

Yes.

Umm... are we sure that both rears are 10 bolts?

yes i believe both are 10 bolts, but they may be different size diameter of gears though. Not sure.

john

OK, lets be clear here: All third gen 10 bolts are 7.5-7.625" in size, "the same" so the diameters can't be different. The 9 bolt however is 7.75" in diameter. Are you sure you don't have a 3.08 9 bolt back there? Please count the number of diff cover bolts for us to be sure.

Ed

yes they are both 10 bolts, just checked.

While i was under there, i was looking at the plate welded on to the end of the axel tubes, where the drum brake assembly bolts on. It is different than the one on the lt1 rear end. So that tells me that they wont bolt onto my 3rd gen rear. does that sound right to you all.

also, i did a small burn out the other day, and left 2 black marks, doesn't that mean i have posi? but my code of 6 hk on my rear axle crosses with a 3.08 geared open diff? what gives?

john

Didn't realise you had a 3rd gen "drum brake axle" that you wanted to put discs on. Whether you install 3rd gen disc or 4th gen disc (both the same) you have to modify the drum brake flange. Drum and disc flanges are different- but the drum axleflange can be EASILY modified to work (one cut and two holes drilled) https://www.thirdgen.org/newdesign/t...reardisc.shtml

Jack up the rear and spin one wheel (in neutral) If the other side spins the same direction- You have posi. If spins the opposite direction- open diff.

I thought that i had did the idiot posi check before and they spun opposite.. I might just be a rock.

Now onto modifying my drum brake brackets to fit the 4th gen disk brake brackets. Will the axels stick out the perfect amount so that the rotors set perfectly in between the pads on the caliper? or will i have to shim?

john

Sorry I missed this question from a week ago-
Anyways, Yes the offset is perfect. Both 3rd gen and 4th gen rears run a 2.75"offset from flange to axle. So the brakes are compatible without shimming.

I am in the process of doing a rear disk swap as well. However I am taking the whole axle assembly too. I chose to use a 98 rear disk axle, only for the 12" rotors and seperate parking brake assembly. The things that you will need to do with your year of car are as follows.....New master cylinder, proportioning valve, and if there is a rubber brake hose between the caliper and the axle housing. I know 91 and 92 used the same master and prop. valve for rear disk or rear drum. However you will find that your brake fittings are not the same...gotta love GM for changing the little stuff If I were in your position, I would pick up a set of 4th gen rims and a set of spacers and just install the whole axle assembly....but then again, I like to try doing things the hard way!! Good luck, either way you do it, it should turn out great!

im pretty sure that the master cylinder for the drum brake set up is the same one used for the later style disk set up, which was like '87 and up i think. i also believe it was only the first couple years that had sae threads on the lines

I recently put thirdgen PBR's on my thirdgen 10-bolt J65. Shimming was necessary on one side to center the rotor in the carrier. Without the shim the rotor would have drug on the carrier.

Note: The axel shaft does have some play, so after putting the axel back in the tube, inserting C-clip, replacing the cross shaft bolt, and bolting on the backing plate and carrier, grab the rotor and push/pull. You may find interference in this fashion.

JamesC

I will do some digging when I get into work this morning about the master. I know that the rear disk master ended up taking the place of the drum master in 89 or 90...can't remember. As for the thread change, not sure what year they did that either, remember reading it in a tech page somewhere. I will see what I can find on that today too. I will also try to post some part numbers for them.

All the prop valve and master info is right here, including the part numbers and year applicability:

http://www.ws6transam.org/1LEbrake.html

Ed