mullery

I have a 1989 IROC with a 5-speed and the 9-bolt rear-end. It has 170,000 miles on the clock and the rear is making some noticeable noise. The noise can best be described as a light grinding, especially while coasting in gear or accelerating. I have checked the posi by lifting one side and turning the tire by hand. It turns very easily, telling me the pos is worn out. I assume that with the noise, the worn-out posi, and the mileage a rebuild of some sort is necessary. It seems there are different stages of rebuild from rebuilding just the carrier to replacing the pinion seat, but, crush sleeve, etc. I've been reading-up on the process of rebuilding these units and I have some questions for the experts:

If I plan on keeping the stock 3.45 ratio and therefore don't necessarily need to replace the pinion gear, is it necessary to replace the pinion seal, crush sleeve, etc? What can I look at to determine that the pinion gear is worn? If the pinion gear is fine, can I just remove the carrier and rebuild it? The rear does not leak at all and I'd like to keep the repair as simple as possible.

I've never disassembled a carrier and overhauled it. Might I be better-off buying a replacement carrier or is this something I can do with some time and care? I have good mechanical skills, mostly engines, suspension, etc.

If I chicken-out and decide to have it rebuilt professionally, what should I expect to pay? How much can I expect to save if I removed the axles and carrier and take those to the shop myself? What kind of shop should I look for to rebuild on of these?

Thanks for you advice,
Matt

Z2887

Get yourself a 10 bolt and stick in it.

mullery

I should note that I also want to keep the car as original as possible to improve its resale value as an original in a few years.

Z2887

That wont hurt the resale value. Noone will ever know unless its someone thats goint to build it. Then they will rather have the 10 bolt. They were stock in most 3rd gens

built91Z28

I agree with just sticking in a 10 bolt. If anything it may help resale value as parts are extremely easy to find for the 10 bolt.

However, if you decide to rebuild the axle there is only one proper way to do it. Replace everything. You dont have to buy a new carrier. You could see if you can find just the clutch packs and replace that. Other than that, you would need a ring and pinion set, pinion bearings and carrier bearings, and crush sleeve. I do this for a living. Trust me, replace everything or you will hate yourself later. The only part you may not have to replace, although it could be your noise, is the outer axle bearings. If that is your noise, then you may need a new axle as well. Regardless though, if you rebuild the axle then I would replace the axle bearings as well. They are not that expensive. Dont forget though that you need a few special tools to do this.

Z2887

Agreed. If you have to have it done, its not that cheap either. Unless you have a connection at a shop. IMO, I would find a lower mile 10 bolt and stick the whole thing in. You can do that easily yourself. You could do that and change the gear cheaper than having yours rebuilt probably. With that many miles you should change the ring and pinion anyway. Like he said. replace everything, or you could regret it later, and have to have it done twice. Dont forget to see what gear is in it(or put a new one in), and change the speedo gear accordingly. Stick some 3.55, or 3.73 in it. Might as well upgrade while your in it. It wont affect your MPG enough to notice. With a 5 speed especially. With 3.55's your speedo wont be off much from a 3.45 anyway. If you want it perfect change the speedo gear though.

jwscab

the 9 bolt doesn't have clutch packs that can be replaced. There is tons and tons of info on these boards regarding the 9 bolt. try searching for borg warner axle.

there are a few people that sell a full rebuild kit, which is what i recommend, IF the posi can be rebuilt. this involves grinding off a small amount of the end of the cones. alternatively, I beleive you can still buy parts (cones)provided the carrier isn't shot. this is definitely a hard axle to find parts for, but this is the right place to dig around and find info.

I just saw something recently regarding the cone replacement, within the past couple weeks.

regal301

throw the 9 bolt in the trash.

swap in a 10 bolt.

end of story.

jwscab

correction:

sell 9 bolt for 100 bucks as is

swap in 10 bolt

end of story

mullery

Wow, it sounds like there are a lot of 10-bolt fans out there. I would prefer to keep the car as original as possible, meaning I would rather keep the 9-bolt and either overhaul the carrier assembly, bearings, etc. or put a rebuilt carrier in it. It's worth a little extra $$$ to me to keep the car original.

It's a 1989 IROC 5-speed with the G92 option, which isn't a common setup. The car is all original, but with high mileage. Keeping it original might improve it's value some day. I'm going to slowly restore this car, reconditioning the existing parts on the car when possible, swapping them for the same part from a donor car if necessary, and as a last resort swap them for parts that aren't a match for the G92 option package.

Thanks to all your advice. If anyone else has some pearls of wisdom to share on getting my 9-bolt back into good running condition, I would appreciate it. I have poured through the message boards and read everything I can find. I have a good grasp on the process of rebuilding the carrier assembly (machine the cones, add shims, etc). Where I am lacking in knowledge is in the tools and techniques to do the rest of the job (axle bearings, pinion bearings, crush sleeve vs solid pinion spacer, bearing preload, pinion preload, etc). I've never rebuilt a rear, but I am willing to give it a try. The car is not a daily driver and can sit on stands while I work through this process.

Thanks,
Matt

Killert

iTrader: (9)

for parts go to http://9bolt.com/

regal301

setting up a ring and pinion is not like putting on a set of brake pads.
do it wrong and shred the gears in 50 miles.most shops for a ring and pinion swap and limited slip install will run you $800-$1000 and thats for a chevy 10 bolt(10 bolts are cheap and easy).add in the price of parts and machine work for a 9 bolt and find someone that will work on it and your going to spend more than your car is worth.do it yourself and your going to spend several hundred on the tools and dial indicators ,and do it wrong and kiss most of the parts goodbye..............

i own 2 third gens myself...........

but there not GTO's,TURBO TA's or GNX's

no ones going under a 305 camaro to check that part numbers match

but, do what you want with your car.

(but keeping that 9 bolt wont do you any good.)

8t2 z-chev

years ago,i tried 9bolts in my car but discovered the posi
was bad,so tried 2 others-bad posis there too,and this
was in the mid-'90s gave up on those and went back to
10 bolt. If i had a good 9-bolt i would put a drain plug
in it and change the oil every time it gets a bit dirty
-tiny iron particals wearing off the cones contaminate
the oil,gauld and gouge the cones further,damage the
bearings.
'89-92 10 bolt with disc should be virtual bolt -in

built91Z28

What about putting a 10 bolt in now so you can get driving and then you can change gears in and not feel guilty. Then keep the 9 bolt in the garage or somewhere so if you sell the car you still have the original rear axle.

mullery

built91Z28, I like your idea of keeping the 9-bolt around and maybe working on it on the side. I'd have to convince my wife to let me keep it in the garage!

regal301, No offense, but I am not a total noob when it comes to working on cars. I have rebuilt engines, installed steering and suspension parts, etc. I am familiar with the use of specialty tools and precision instruments (micrometer, calipers, dial gauges, pullers, presses). I have just never rebuilt a rear end before.

The common sentiment among the posters to this thread is that parts and labor are cheaper for the 10-bolt than for the 9-bolt. This is no doubt true. Here's my concern. Everyone seems to think I can buy a used 10-bolt and simply bolt it in to solve my problem. Won't I run the risk of having to rebuild the 10-bolt as well? It seems like I won't know what kind of shape it is in until I install it and drive the car.

If I need to rebuild a used 10-bolt, why not just use the $$$ I would spend on a used 10-bolt toward getting the 9-bolt I have rebuilt? Aside from the posi carrier in the 9-bolt what else is so different and costly about the 9-bolt to rebuild that is cheap and easy on the 10-bolt? Is it just the posi carrier that everyone is so concerned about? What special tools do I need to but to rebuild a 9-bolt that aren't necessary to rebuild a 10-bolt?

Again, I welcome all your opinions. This information is very helpful in determining what direction I should take.

rayar

iTrader: (1)

Wasent there a thread somewhere about useing a 28 spline ford 9 inch center section with the 9 bolt axles and tubes. I guess the 9 bolt axles are the same size, 28 spline and the correct length that would be required for the 9 inch center section conversion. Lots of LS options with the ford center section. If I had a 9 bolt I think that is what I would do.

87350IROC

iTrader: (2)

I'm not sure whats up with all the 9 bolt hate in here. Its a fine diff but like all will require a rebuild after many miles. If you want to keep the car stock, I appreciate that, and the money spent on the 9 bolt will be worth it. Sure the 10 bolt will be cheaper but not better. Some people just take the easy and cheap way out. Lots of guys going fast on 9 bolts. Good luck.

rayar

iTrader: (1)

I wouldn't say hate, just hard/expensive to get parts for, limited gear selection and no LS options

regal301

you said it not me.............


that's why the friendly warning about setting up your own rear


run a search on ebay or http://car-part.com/ then you have a good rear with a warranty. mine came from f-parts on ebay

check craigslist,but then your gonna have to check it yourself.(pull the cover)

IROC212

iTrader: (1)

I helped rebuild my friend's 9 bolt about 10 years ago in his GTA. We had to replace the ring and pinon, carrier bearings, both axle bearings....basically everything. There is a fixture to measure pinion depth we borrowed from a friend at a Chevy dealer. The Clutch cones were in pretty good shape so we left them alone. As far as actual labor goes, it wasn't any more difficult than a 10 bolt, or any other car axle. The price of parts was about double that of a 10 bolt. The axle now lives in another car, and is still going strong.
Like others have said, setting up ANY diff is challenging. You don't want to invest a lot of money, put it together and have an axle that whines or clanks when you shift.
I'm not a 10 bolt fan at all since I've broken 2, but there are tons of them out there for cheap.

mnorton

Find someone who rebuilds rear ends for a living and have him do it. These carriers have to be shimed properly, and the ring & pinion have to be set to mesh properly or the gears will wine and drone when you run it. Expect to spend $1000 for parts and labor.

Buy a rebuild kit with new carrier bearings, shims, etc. and replace the axel bearings while you have it apart. Clean an paint the whole thing. Replace the brakes too while you're at it. If you do need to replace the ring & pinion, you can buy a new set from Dana/Borg-Warner in Australia. Even more $ if you buy a new ring & pinion.

Here's some info:
9-Bolt:
The 9-bolt years are 87-89 in Camaros and 85-89 in Firebirds.
__________________
The Borg Warner 9 Bolt Rearend is actually called the M78 Rearend or "78 series". It has been made since the late 60's in Australia by a company called BTR Engineering Ltd. BTR was bought out by Borg-Warner under which company name the rears were produced for our cars. In the last few years Borg-Warner was bought out by Dana Corp. and the rears are still produced by Dana today in the same BTR factory under the "Spicer Axles Australia" name. www.spiceraxle.com.au/products.htm#srd
CHECKING & SHIMMING THE POSI:
Here is some info on checking and tightening them up by using shims. This info is from a post originally done by Karl Hunter and info provided by Miles from 9bolt.com.
The posi units of 9 bolts will wear. One of the most common reasons a 9 bolt fails is due to excessive backlash between the ring gear and pinion (usually due to worn out pinion bearings or improper pinion preload) or between the side gear and the pinion gears (usually due to worn out brake (ie posi) cones). Either of these usually results in broken gear teeth.

TESTING THE POSI
1. Place transmission in Park (or low gear for manual transmission).
2. Raise rear tires from the ground.
3. Lock one wheel from rotating.
4. Measure torque required to rotate opposite wheel.
5. If torque is less than 35 lb ft unit should be replaced or rebuilt.

CARRIER SHIMMING
First you need to find shims. There is no G.M. part for this, you just have to use whatever is available.

You need a variety of thickness of shims ranging from .010" to .050" in .005" increments. Some types of differential pinion bearing shims will work for this purpose, but use ones with a Max Outside Diameter of 2.5" and a Min Inside diameter of 1.5"

Mount one axle in a LARGE bench vise with splined end pointing straight up. The vise must be securely mounted to a strong table or work bench.
Place the differential carrier over the splined end of the axle with the ring gear teeth facing downwards.
Mark the 2 halves of the housing for alignment during re-assembly.
Loosen the bolts that hold the housing together. (the ones with the 7/16" head) It is not necessary to remove the ring gear, however if it is to be removed it should be marked prior to disassembly for proper re-alignment.
Once all the bolts holding the housing together have been fully loosened remove the upper carrier housing from the assembly. All the internal parts for the differential are now accessible. Each half of the carrier houses a friction cone and a side gear. All parts must be kept in order. Place match marks on the cross shaft and spider gears prior to removal. There should also be a spring pack in the centre of the assembly, which should have 3 springs together. G.M. recommends replacing these springs anytime the differential is apart, but if they are not broken this should not be necessary. If any other parts are broken it is recommended to find a complete replacement for the carrier, however single parts such as side gears or spider gears may be replaced individually in emergency situations. If a friction cone is worn to the point where the end of the cone is contacting the housing at the inner most point (it will be evident by the wear pattern) then the carrier must be replaced.
Place the friction cone in its respective half of the housing and insert a shim between the side gear and the cone. Place the cross shaft with spider gears on top of the cone and gear in the housing. If the cross shaft seats fully into the housing and there is play between the spider gears and the side gear then use a larger shim. The idea is to remove all play in the gears while still allowing the cross shaft to seat fully in the housing. If too big a shim is used then the cross shaft will not seat properly and the assembly will bind causing the differential to act like a spool or possibly cause premature failure.

Install brake cones in the differential case. Measure the distance from differential case mating surface to flat surface on brake cone when it is fully seated. This is done to determine the size brake cone shim required.

Distance Measured In.(mm) Shim Size In.(mm)
1.155-1.162 (29.34-29.51) No shim required
1.163-1.167 (29.54-29.64) .005 (.13)
1.168-1.172 (29.67-29.77) .010 (.25)

ADVANCED SETUP- SOFT FEEL shim each side until all play is removed and cross shaft seats properly in case, then remove .005 to .010 inch of shim.

ADVANCED SETUP- HARD FEEL shim each side until all play is removed and cross shaft seats properly in case and add up to BUT NO MORE THAN .005" of shim per side. This will provide additional preload to the differential that is not possible unless the gears themselves are loaded. RECOMMENDED FOR RACE USE ONLY. If the vehicle is to be street driven on a regular basis it is not recommended to preload the gears.

The optimal amount of shim for Street-Race use is the point where all play is removed from the side gears and the cross shaft and spider gears seat properly in the housing. All one wheel peel will be eliminated and the differential will still operate normally.

RE-ASSEMBLY (This part is easier with 2 people)
Place components into case half without ring gear and place onto axle mounted in vise. It is important to re-assemble the case using the axles to align the internal components, otherwise the splines on the side gear and the friction cone may not be aligned and it will be impossible to insert the axle when the case is tightened.
Place cross shaft with spider gears into lower half of case and insert preload springs and spring plates.
Place other side gear on top of spider gears, then place the correct shim on top of the side gear then place the friction cone on top. All components should now be in place and in correct alignment. Double check to make sure there are no left over parts.
Place other case half over the assembly. Make sure the alignment marks line up.
Insert all bolts and hand tighten. The case may not seem to go together at this point, don't worry, the preload springs have not been compressed yet.
Insert other axle shaft into upper case half and align friction cone and side gear. Do not remove axle shafts until carrier is re-torqued.
Tighten bolts little by little in a cross-pattern until the 2 case halves seat together then torque to 29 Lb.Ft.
Remove axle from upper case half (you may have to hammer it out) and remove carrier from axle mounted in vise.
Re-install carrier into housing making sure all parts are re-installed in original order. It will be a tight fit, one side bearing shim will have to be GENTLY tapped into place with a hammer, preferably a brass faced, or use a brass drift. Install all components except one side gear shim, then do the remaining side gear shim last and gently tap it into place.
Install bearing caps in original positions and torque to 40 Lb.Ft.
Install axles. They may need some persuasion with a hammer to fully seat. Tighten axle retainer bolts to 36 Lb.Ft. Don't forget the caliper mounting plates.
SET-UP SPECS:
TORQUE SPECS:
Pinion Bearing Preload-Inch Lbs. NEW 12-15 USED 6-7
Ring Gear Bolts-Ft Lbs. 65
Bearing Cap Bolts-Ft Lbs. 45
Axle Retainer Bolts-Ft Lbs. 36
Rear Cover Bolts-Ft Lbs. 25
Carrier Half Bolts-Ft Lbs. 29

Fluid Capacity with stock cover 1.7 qts

Backlash-.006-.010 inch

One of the most common reasons a 9 bolt fails is due to excessive backlash between the ring gear and pinion (usually due to worn out pinion bearings or improper pinion preload) or between the side gear and the pinion gears (usually due to worn out brake (ie posi) cones). Either of these usually results in broken gear teeth.

Set up the gear sets with a little more toe pattern and on the low side for backlash (preferrably between .006-.008). This is a little stronger, but also makes more noise. Also, if the backlash is set too low the gears will bind up when hot.

Here's a link to Slow89Iroc-Z's post on his setup experience AND the exploded views and pn's of the 9bolt rear from the GM parts catalogs:
https://www.thirdgen.org/techbb2/sho...hreadid=239424


tighten your 9 bolt posi!
shims for sale.
larryburd@mail.com