alright its my understanding that this is the 89-92 style rear disc brake rear end, a few questions, what is most likely the gear ratio in this, 3.42? also is there any sort of matniance i can do to to the diff? how would i go about putting new wheel bearings in here? and generally, what the heck am i looking at.

 

alright, since you have the cover off, count the ring gear teeth, then try and count the pinion gear teeth, and divide. (the pinion gear teeth are pretty hard to count with the ring gear in, but give it a shot.)
so if you have, 42 teeth on the ring, and 13 on the pinion, 42/13 = 3.23xxx so it'd be a 3.23 ratio.

i'm not sure why the inside of the case is red...?

I think you should clean it up, wire brush it, and paint it first off. Maybe weld the axle tubes to the housing if you have a welder.
I think those rotors are toast.
maybe replace the wheel bearings and axles, or if you think you need to, replace all the bearings and seals in the rear altogether. (buy the kit)

do you want to strengthen it for performance, or just maintenance?

 

pictures of my rear end rebuild a month ago or so, in case you were interested:

link

 

From looking in the housing it looks like you got yourself a 9-bolt. Welcome to the hell that is finding parts for it

Suposed to be a good rear though. Mine is holding up well.

 

the brakes, i'm just going to totally overhaul what i got, new everything brake wise.

how would i go about puting new wheelbearings in it anyhow. i'll have to count the gears and find out what its got.

my only rear eperience is old chrysler peg leg rears, so this is a very different animal to me here.

also what year car would this have been out of origionally?

 

9 bolts typically have the gear ratio stamped onto the rear gear just spin it over until you find it.

2.77
3.27
3.45
3.70

those are your factory choices.

 

Brakes are the easiest thing to do on this rear because they're the same as what come on the 10 bolt minus the backing plate. In other words, they’re the only easy to find thing for this rear.

Wheel bearings - they have to be pressed off and new ones pressed on. Might as well do the seals while you're at it but they're a major pain to track down because they're so rare. After all, the rear was only made for 4 years. Also, each side has a different seal.

Year - I know 88/89 had them. I'm not sure what others did but with those brakes I'm guessing a 91/92 unless someone swapped to them like I did.

 

Are axle seals leaking?? Why do you want to change the bearings? Those rotors can be resurfaced. or just install the rear buy the time you go through a tank of gas they will be cleaned up,then change the pads.

 

wow... just called the parts store, $90 each for rotors is a little pricy, i may end up getting these turned.

also is there any way to test the posi unit prior to putting it in the car?

and what kind of oil should i use in it. i was thinking about 75w140 synthetic with a addative of some sort

 

that rear had to come out of an 89 because it has the PBR calipers.that was the first year for those calipers and the last year the 9 bolt 7 3/4 rear end was offered in a f-body.

here's a couple threads that may be helpfull
pinion bearing replacment
axle bearings and seals

 

yea, that`s a rare one...good find

 

ok, so i'm starting to get this ready to go in the car, had to beat the old rotors off with a hammer, i'll probably clean it up abit and throw a coat of paint of it.

what oil should i use, i was told 75w-140 i think, and should i use a addative?

 

I run 75w-90 in mine. You don't really need an additive because it's a cone style posi unit (clutches are the ones that need the additive) but you can add one if you wish for peace of mind.

 

1989 IROC-Z's were the only cars with the optional rear disk brakes however there are still 3 options for gear ratios depending on engine and tranny. The gears could be 3.45, 2.77 or 3.27.

You've got a good strong diff with the better PBR calipers and larger rotors however finding any good performance parts will get very expensive.

 

Yes, 1989 9-bolt with the 11.655 rotors and aluminum pbr calipers. On a side note another 9-bolt painted red on the inside of the housing.

 

i have two 9 bolts sitting in my garage both are painted red inside.

 

At one time someone on the board swore up & down that no 9-bolt came painted red on the inside of the housing. So I just pointed out the picture.

 

yes I would like to see one that is not painted inside


as far as the years pbr 9 bolts were brought into production in mid 88 model run and were used until a undisclosed number of plant stock was used up some time in 1990. (still leaving units for warr. replacment if needed)

a very common ratio for that rear would be 3.27 or 2.77 and a harder to find but not "rare" 3.45 ratio for a pbr 9 bolt

2.77 common
3.08 very very uncommon (for a 9 bolt) but are out there
3.27 common
3.45 often found in 5-speed cars with tpi which is why it is harder no find but far from rare
3.70 in l69 cars (the real H.O. cars)

 

mine's not painted on the inside at all. i feel cheated...lol.

 

Is it just the aftermarket performance stuff thats not available for the 9 bolts? I mean can you find the basic rebuild stuff like bearings, seals, axles. What about the posi unit it self?

I replaced my 10 bolt with a 9 bolt its only got 27,000 original miles on it so it should last awhile. But never realized that the parts were so hard to come buy. Its sounds like its stronger then the 10 bolt. But seems like aot of people are swapping from 9 bolts to 10.

 

i bought all my bearings and seals at AutoZone.

 

my 88 formula 9 bolt wasn't red on the inside it had rear disk 3:27 gear the posi went bad i got my complete ls1 rear for alot cheaper than the posi unit costed

 

Thats good to know thanks....i guess its the aftemarket stuff thats not there.

 

I have a 1989 9 bolt with same PBR's. The calipers are expensive. To save money, I bought rotors for a 1995 camaro for around 20.00 each, and they fit perfectly, I've had no problems with them. There are lots of threads on it on TGO.

 

maybe i missed something...but how do i check if i have the pbr calipers? i picked up a 9 inch from the junkyard with disk brakes but havent worked on it yet. plan to do so, and kinda wanna know what to look for si that i know what i got. thanks!

 

see the callipers on the rear that i have, those are the PBR ones. if yours look like mine, then your good.

and is there any way to test the posi unit before i put it in the car?

 

thanks! ill check and compare the pics to mine. about checking the posi unit i dont know. but i opened mine up and i have the 3.27 gears and my rear is also painted red on the inside.

 

PBR calipers are also Aluminum.

 

What??

 

wow you guys have pictures? I have seen countless ones apart and never yet saw an unpainted one. were yours stripped clean or are you guys the first ones in there

 

alright, small update.

i just picked up the 80w-90 synthetic blend gear oil, posi addative, and a gasket for it, and i'm going to hope for the best when i put it in.

does anyone have pictures of how the brake lines are supposed to be setup on this rear end? someone over the years put stainless steel braided brake lines where all the stock stuff was, and i'd like to know how it was setup "correctly".

i also have the 3.45 gears in it, and the car i gor it from was a 305TPI/5 speed car. and overall it seems to be in prety good shape considering the rest of the car was totally shot.

and someone mentioned useing rotors for a 95 camaro in place of mine? any truth to that?

also, i believe i have 2.73 gears presently, what spedometer gear will i need with the 3.45s? and what kind of RPMs am i going to be running on the highway now with a 3.45s and a 700r4

 

Hey, I figured I would let my first post be a helpful hint post.. If you have access to an Oxy/Acetalene torch, you can just heat the bearings up and slide them off/on, you just have to be careful to not heat them up too much, because you will Un-Temper the hardened races of the bearing. I use this trick all the time and it works great if you just heat it up enough to get it to slide over the spindle. Make sure you look up the endplay spec and measure that with a dial indicator too. If you don't run enough endplay, you're going to spin a bearing and toast your spindle, and maybe even have a wheel off! if you run too much endplay the same can occur. Typically the endplay spec for most wheelbearings is between .001" and .005"

_bR3T7

 

Heres a couple very handy equations:

RPMS = MPH x (final gear ratio) x 336
............________________________
............Tire diameter in "s

example =
65mph x (.085x3.73) x 336 = 69243.72
divded by.. tire size, lets go with 28"s

2472.99
so about 2500 rpms going 65 in OD with 28"s

A few more really helpful ones:

If you want to figure out what gear ratio you want to run by aproximating your RPMS and MPH, use this:

Ratio= RPM x Tire dIameter in "
...........____________________
........... MPH x 336
so... 2500 x 28 divided by 65 x 336 = 3.20 Now keep in mind that this is final gear ratio, so whatever reduction is coming out of your tranny multiplied by the ratio of your rear end. so in 4th, 1 x 3.73 if you are running 3.73's I think OD in 700R4's is .85:1 so just multiply that by your rearend ratio and there you go. on 4x4's just add in your Xfer case and mulitply out.. ta da

If you have any questions PM me

 

Mine's NOT painted red inside......