Hi Team

we own the above mentioned car which according to the build codes was a fully optioned car with 4 wheel disc brakes. I currently has a 4th Gen Camaro fitted by the previous owner. It looks terrible with the factory wheels fitted back on so swapping out for an 3rd Gen diff now. According to online info, the factory fitted 1982 only

4 wheel disc rear end had opposed brake callipers & a posi diff fitted. Can anyone confirm this for me please?

I have just purchased a used 4 wheel disc 3rd Gen diff with limited slip diff (posi) which I’m about to strip to replace bearings & seals etc as well as check the diff head for any servicing to be done.

 

"Online info" is wrong. No idea where that misinformation might have come from; certainly not from here, where there are plenty of people who actually know these cars. The 82s, pace cars included, got the same rears as any other F body of the time.

The 82 cars also all had the 10-bolt rear, whereas the 9-bolt was introduced in 85.

The "opposed" rear disc calipers are the crappy old cast-iron Delco-Moraine system, used on all 3rd gens with rear discs from 82 to 88, that hardly ever works or even does anything. In 89 they switched to the far superior aluminum PBR calipers, much like those on the 4th gen rear. If your just-purchased one has cast-iron calipers then it matches what would have come in your car originally as far as that goes. Both 9- and 10-bolt rears came with the same brake systems, year for year. Likewise, the posi systems in all 3rd gens, are likely to be worn out; what would have come in your 82 was probably the Auburn, which is a steaming bucket of dog plop, although many of these cars in their early years (82 - 84 mostly) got the Eaton Gov-Bomb which is even worse butt in a different way. The posi in the 9-bolt is completely different again, butt also subject to wearing out and doing nothing.

I agree, a 4th gen rear in one of our cars with the stock 3rd gen wheels on it, DOES look rather derpy.

 

Thanks for your comments. the rear end we have purchased is a 9 bolt posi disc brake diff with alloy callipers so not sure which year car this is from? I plan on stripping it down & replacing all bearings & painting it etc before fitting to the car. I’ll need to confirm ratios as well.
looking forward to our car looking right & not wide in the back end. Hopefully we can get some cash for the 4th Gen rear end we take out.

 

Is the Borg Warner Aussie 9 bolt (BTR/BW M78) a cast iron caliper Delco-Moraine disc brake rear end or a PBR aluminum caliper disc brake rear end?

Is the GM 10 bolt 4th gen rear end a 1993 to 1997 with PBR aluminum caliper disc brakes or a 1998 to 2002 with GM LS1 aluminum caliper disc brakes?

 

The 9-bolt isn't "right" for the car, since it didn't come in the Camaro until 87 (Firebirds starting in 85), but should work fine.

Be aware that one of the axle seals for some of those, the right one I think it is, is EXTREMELY hard to source. Fortunately for you, since you're in N Zed, the primary source for parts for those, is in Australia, since it was used in Holdens so much. Left and right sides are different for some reason. Yeah not my idea but It Is What It Is. Be absolutely positively 100% CERTAIN that you have the right seals for YOUR rear in your hands before tearing it down. I'm not sure how to tell for sure which one you need; there are 2 that it could be though, might even be worthwhile to have 1 of each on hand before you disable the axle.

 

Idk if Rock Auto ships to New Zealand but they have the axle seals for the 9-bolt (just ordered them).

I've had a 9-bolt with the iron calipers under my 83 Z for over a decade now, it's a great unit.

 

The seals are handed because they have directional grooves or ridges in them that pump oil down the axle tube toward the center of the rear end. Put them on the wrong side and they try to pump oil out the end of the axle tubes. One of the seals seems to have the correct part number for its handed side but in the bag or box is the wrong seal, not the wrong handed seal just the wrong seal. Two correct but opposite sided axel seals will be mirror images of each other on both sides but the directional oil pumping grooves/ridges on the seal with be pointing in opposite directions when viewed from the same side of both axel seals.

 

Thanks for your comments. I purchase most of my car parts from Rockauto & love their range & service!

 

The 9 bolt 3rd Gen diff is posi with PBR alloy callipers disc brake.

 

That rear would be from a 1989 Camaro or Firebird. It's the only year with the 9-Bolt and aluminum PBR calipers. Should bolt in just fine and as was previously stated, the service parts for the 9-Bolt are available from Australia.

You will need different park brake cables for the PBR calipers and may need to adapt the brake line fitting in the rear, but should be relatively straightforward.

 

Nice thing is the M78 rear end and the PBR brakes are Aussie so parts may be easier for him to get over there than for us to get over here.

Depending on which year his 4th gen rear end is it might have PBR discs too

 

Hi Team

I finally got around to dragging this diff I purchased into the garage to clean up & check out. I can confirm it is a Posi rear end & tested it to 85 foot pounds before the axles release. When I opened it up, the oil was like brand new with no moisture. The gear ratio is 3.27 which I’m hoping will be ok in our car? FYI we have a 1988 305 roller rocker engine coupled up to a TH350 trans. We are running the factory 15” wheels. The brake calipers are PBR aluminium finned.
looking in my Haynes workshop manual, I’m not sure which year this diff is from. Based off the ratio & being posi, the only options I see are either a 4EU 1987 or GW6 1988-89 or a 9EQ from a 1990 car.
I hope someone can shed some light please?

 

9-bolts in these cars are virtually ALL posi. I would say "all" butt I've seen a photo of ONE that wasn't, so...

There's no valid ID info in it being a posi.

I wouldn't bother with "codes" and "Haynes". Sounds like a bunch of monkey-spank to me. You can get far more complete and accurate info on this forum than ANY of that ... other.

Since the rear has 89-up brakes, it isn't from 87 or 88. Since the 9-bolt was discontinued starting in 90, it's not a 90 91 or 92. (except for a very few early-production 90s that got leftover old stock)

Since 89 was for all practical purposes the only year that that rear with those brakes existed, you can be about 99% sure it's a 89.

3.27 was the ratio used in 350 TPI automatic cars with RPO G92 "performance axle ratio". It may have been used in some 305 TPI cars as well. Butt 350 auto G92 was the most common driveline associated with that ratio in that year AFAIK.

Not sure 15" wheels will fit over those brakes. No cars with those brakes ever came with 15" wheels in any case. Best to verify the fit CAREFULLY before swapping it in if you want to keep those. You might find that someone did some grinding on the fins, or some other sort of shadetree hacking, to get the 4th gen rear to fit under the tiny wheels.

The rest of the brake system (master cyl & combo valve) were different between the 2 disc brake systems. The hydraulic requirements of the PBR calipers are more similar to drum brakes than to the old Delco-Moraine discs. Whether the brakes will work "right" leaving the old MC & CV is doubtful (or for that matter, whether the 4th gen ones are really working "right" now, even if they seem to work "well enough"). Problem there is, your 82 has SAE fittings and SAE diameter metal lines throughout the brake system with SAE 45° flares, whereas 85-up used all metric fittings & lines with "bubble" flares. Therefore changing out the MC & CV to match would be an ordeal; and coming up with the 82-84 combo valve is quite difficult in any case these days. Considerable creativity is needed where the rear rubber line connects to the chassis, and you might be horrified to see however whoever did whatever they did to get the 4th gen rear in the car (same problem). When I put a PBR-equipped 10-bolt from about 91 or 92 into my 83, I was able, JUST BARELY, to put a ¼" SAE flare on a short piece of 6mm metric bubble-flared line which took several tries using various alternative engineering techniques to get the flare tool to grip the too-small line, and then use a ¼" SAE flare union to join that to the existing line in the car, so that I could then use the right hose for the rear, with its metric fittings. The 89 brakes may well work better than the cast-iron garbage though, even if they don't perform as well as they could. They should work overall about the same as the ones you have in it now. You may also find surprises when it comes time to make the parking brake work, again, depending on whatever whoever did to whatever to get that 4th gen rear into the car.

 

Your BW "Aussie" 9 bolt rear end is a 1989 model. 1989 was the first year you could get PBR discs on the rear and the last year you could get a BW 9 bolt in a third gen.

You have a one year only rear end. That rear end came out of an 89 IROC-Z with the L98 engine, no factory T-tops, and the G92 Performance Axel Ratio Package or it came out of an 89 Firebird Formula 350, Trans Am with the L98 engine, or a GTA with the L98 engine.

 

My 9-bolt also has 3.27 gears, I'm running a 28" rear tire. Currently have a t-5 manual but prior to that had a hopped up TH350, it drove well then and drives well now. Hope that helps.

 

Agreed that based on the info provided, it's a 1989 rear and the 3.27 ratio would have been a 350TPI with the performance rear gear ratio option. This was the setup in my GTA.

As far as 15" wheels fitting with the stock PBR brake setup, yes they do. I used to run 15" thirdgen Z28 wheels and also 15" American Racing wheels as my winter wheels with snow tires back when I daily drove my GTA.

 

Seems like that 9 bolt rear also ran different offset rear wheels than the fronts. Your wheels might stick out some like they already do? Might want to do some measuring to see.

 

3rd gen rears are all the same length, flange-to-flange. There's a slight difference between the thickness of drums vs rotors butt that's less than ¼". The factory put a spacer on some cars to make them the same width; if I were to guess, the reason was probably something having to do with automated assembly or MH eqpt.

There was also a problem (excuse me: [corporate_jargon] opportunity for a solution [/corporate_jargon]) out in our world wherein on some rears, mostly early ones AFAIK, the axle flange for disc rears was a slightly smaller diameter, again something around ¼", such that on some drum rears, a rotor won't fit over the axle flange properly, requiring an extra step for a drum –> disc conversion.

The 2 different wheel offsets are on various of the 16" wheels on 85-up cars, to clear the fender lips and/or various suspension parts. The difference between front & rear was something around ½" or so. I don't remember the details and I sold off the last of those small wheels that I had back about 20 yrs ago so I can't measure any. The 15"s however were all the same offset on all cars that used that even smaller size.

As long as the OP decides to retain the old little 15"s he won't have to worry about their offset.

 

Nothing wrong with old little 15’s OP, lots of us still run them 😎

 

New used Posi diff calliper mount seems very thin

Near new rotors the same diameter as what’s currently on the car

The current arrangement of the 4th Gen open diff

Thicker calliper mounts currently on the car

Same size rotor as what is currently running on the car

 

Hi Guys

As per the photos, I have measured the new used posi diff between the rotors & measured the 4th Gen diff currently on the car. The posi diff is approx 3.38 inches narrower than the diff on the car. That confirms I have a suitable diff & the rotors are the same diameter than the rotors currently in the car. I have decided to transfer the callipers, brake lines & hoses currently on the car to the new diff. I know they will be longer but easy enough to bend an expansion U in the tubing.

 

That's pretty much exactly what would be expected. The usual number quoted is 3-3/8", which is 3.375". So, ... yeah.

The 93-97 brake system used the caliper as the parking brake. The 98-up system had a little "drum in hat" parking arrangement; shoes rather like old drum brakes, and the "drum" was part of the rotor. Looks like you have the 93-97 version. Those are actually almost the same as the 89-92 style. Not "exactly", butt, real close. Rotor dia (11.8", or 300mm, more or less) and stuff like that for example.

The steel lines, you can just go to the parts store and buy acoupla sticks of line with the flare already made onto them; and just bend em up to fit the rear. I think that would be better than transferring over the old other lines. If nothing else, you get new, un-rounded-off flare nuts that way. Never had Vise-Grips used on em. I'd also STRONGLY recommend new hoses: those are well and widely known for failing after they've been so much as TOUCHED after 40 yrs or more.

Brakes in an overall general sort of way were considered much less important "back in the day" than they are now. As time has gone on, people have been steadily putting more of a priority on them. Mfrs included. So I'm not surprised that the 4th gen system "looks" more robust than the 3rd gen; after all, the car mfrs had started losing LOTS of lawsuits for inadequate braking by then. I don't know, butt it MIGHT BE possible to put the 4th gen brackets on the 3rd gen rear. No idea butt it could be worth looking into, as you propose. Just make sure you have ALL the replacement parts you'll need - seals, bearings, etc. - IN YOUR HAND before you take anything apart, lest you be unable to put it back together at all ever. Bear in mind that brake parts HAVE TO BE available for purchase BY LAW at least in the US, butt seals and bearings aren't included in that. Brake parts, you might have to wait a few days; that other stuff, "they" can just discontinue altogether if "they" think they're not selling enough of em.

 

can anyone tell me the best place I can get a replacement Diff cover plug for this Differential?

I have fitted new wheel bearings & seals, now ready to replace the gear oil.

 

It's the same plug that fits Dana rears. Cheeps for example, like late 90s Bland Cherokee.

Alternatively you could do something that actually makes sense. Tap it for ½" pipe, just barely and NOT ALL THE WAY DEEP because the hole is already on the edge of being too large for that thread, and use a brass pipe plug with Teflon thread sealer on the threads so it doesn't leeeeeek even when brand new like the stuuupid rubber crap does on every rear that uses that stuuuuuuuupidity.

Come to think of it, a Holden might use the same plug.

 

A T/A Performance aluminum diff cover would also be a good option.

 

Thanks for your comments.

After I posted this I thought why don’t I weld a fine thread nut on the housing with a short bolt & copper washer duh. Easy fix!

looks pretty good I reckon!



cheers

 

fully rebuilt the callipers from the new old diff. Now just got to fit the new brake lines.