4th gen rear in 3rd gen car

**davegz28** · 03-02-2006, 05:45 AM

anyone know what needs to be done to put a 4th gen rear in a 3rd gen car. can you use th 3rd gen brakes

**Anniversary-Z** · 03-02-2006, 01:08 PM

I've got a 4th gen rear in my '92 Z. All the stock suspension pieces are universal and will work for either. I recommend relacing the stock rubber brake lines with some SS braided ones. I'm fairly sure the brakes will work fine too, although I'm not 100% as I've got Baer's.

Do a search on TGO or check the tech articles for swap info.

- Joel

cmadams4 · 03-02-2006, 01:45 PM

Are the 4th gen rears any better? I thought they both are fragile when you start to beat on them.

**Anniversary-Z** · 03-02-2006, 03:25 PM

The only real difference between the 3rd and 4th gen rears is the 4th gen rears are 2" wider on both ends to accomodate the different rims back spacing. So in my case since I have SS rims I have the 4th gen rear to eliminate the need for spacers in the rear. Plus you can build up the rear to handle some decent power. Here are some things I've done to beef it up:
Weld axle tubes to center pumpkin
weld angle iron along the axle tubes to prevent flex
Cryo treated SLP gears
HD Zexel/Torsen differential
1350 series pinion yoke
ARP main studs
LPW alum. rear girdle cover
Moser axles

- Joel

**davegz28** · 03-03-2006, 04:04 AM

the main thing I need to know is will the 88 stock drum brakes work on it. I have a spare rear for my 98z that we want to put in my cousin's 88 305 with 175k on it I'm not woried about him braking it. the 98 rear is probaly stronger than the 88 car.

thanks for the info : Dave

**Anniversary-Z** · 03-03-2006, 09:24 AM

Unfortunately I couldn't tell you about the drums....I'd take a look at both rears and maybe take some measurements at the hubs to see if the drums will swap over and it the ends on the stock rear are identical to the 98Z's.

**Marc 85Z28** · 03-05-2006, 02:31 PM

From my experience with swapping in a 02 TA rear into my 85Z, here is what I found:

1. 1993-1997 rears are almost 4" wider than the 3rd gen rear, and 1998-2002 are shorter, just over 3" wider.

2. The difference between the the 2 4th gen rear widths is all about the brake setups. Due to the later "drum in hat" style parking brake, a different backing plate offset was needed. I did not attempt to install my original drum setup on the rear as I had an LT1 rear brake setup. The drums looked like they would not have worked, as the backing plate bolt pattern and rear axle tube mount bolt patterns did not match - not a direct bolt-on.

3. The parking brake cable issue. There are a lot of variables here, so you will need to sort out what rear brake setup you will want to run.

4. Your factory wheels will now have the incorrect offset and backspacing and will stick out much further (even with or past the wheelwell lip). Some like this look, however I do not.

5. The 4th gen rear center section is casted differently. A close inspection will reveal additional and better designed bracing on the later rears - which is a good thing as flex is the #1 killer of the small 10 bolt.

6. All suspension pieces, driveshaft included, bolt right up.

Finally, I would highly suggest a rear disc swap. LS1 rear disc setups are getting cheap, and work very well. An LT1 brake setup will work on an LS1 rear with modifications. A stock master cylinder and combo/prop valve from a front disc/rear drum car works very well (so leave it alone), while a factory front and rear disc MC and valve are less than ideal.

**91_RS_LS1** · 03-06-2006, 04:31 PM

I did a 4th gen rear into my 3rd gen car. It was no touble. The thing I did with the brakes (I had rear drums as well) was to get a 3rd gen all wheel disk porportioning vavle and use the brakes on the rear.
It is wider and I still have the stock 91 wheels, so I have some rubbing problems when I have more than 1 passenger in the car or hit a bump hard at higher speeds. I have Eibach Prokit, and because they are stiffer than the worn stockers,the rubbing isn't as bad as it was. Hope this helps.

**davegz28** · 03-07-2006, 02:44 PM

thanks alot, great info. Helps alot to hear from from someone that has done it before you try it. I just want to have what I need to finish the job before I start it.

**91_RS_LS1** · 03-07-2006, 03:21 PM

Oh, one thing I forgot. You will need to get the parking brake cables from a disk car. I tried to use the ones from the drum rear, but the rear pair are shorter in the disk setup. I can't really remember, but I think that it will be best to buy the single one that goes from the handle to where it splits. They are HARD to find, and I had to pull mine from a wrecked IROC. Got the porportioning valve from the same car. Both parts were $20. None of the local (or not so local) parts stores had them in stock, and 4 weeks later, they still didn't have any. Didn't try the dealership, but I am sure you could get one there.