keykey

I'm going to show you how I overhauled my BW 9-Bolt Posi with replacement of the cones and conversion of the housings to fit the new cones. Before I decided to do this I read a lot and studied every thread I could find, I'm so glad I can now contribute with my own thread!

It's a 3.27 Posi with the iron caliper disc brakes and before this job it hade no posi effect, one wheel peeling when taking off and doing burnouts.

This is where I started.



Checking the posi standing under the car up on a lift, I could easily move one wheel with one hand while holding the other with my other hand.

My first step was to order two new brake cones from 9bolt.com. The price for two cones was 154 AUD, shipping was 33 AUD, Swedish government wanted about 250 SEK (38 USD) taxes & customs when I picked them up. A total of about $211 US Dollars for getting the cones to me. Pretty cheap in my opinion.

Next, I looked around a lot for shims, at last I settled for standard shims from Tools Momentum, I bought 16 of them. Metric of course being I'm in Europe, i got four 0.5 mm, four 0.3 mm, four 0.2 mm and four 0.1 mm.
Total cost for 16 shims = 42 SEK ($6.38 USD)

Here is a picture of one of my new cones sitting on my bedside table with one of the shims on top.


Got the car up on jackstands with the axle hanging down fully, did this outside in the yard at work (on tarmac). I did it outside because I didn't want to feel any pressure to put it back together quickly during the process. I therefore had time to paint the diff cover and the brake disc hats and edges.





I removed the brakes, diff cover, right panhard rod bolt and moved the rod around to the back of the bracket so it got back a tiny bit from the diff. The hardest part was the right brake disc, I had to drill 2 holes through the hat and tap the holes with M10 threads, and use a M10 bolt to pull the disc off against an iron plate that I tucked in behind the disc. It was really stuck on there. Then I marked the axles L&R, and removed them with a small slide hammer, they came out easy.

I marked the bearing caps with a punch, two dots one one side and one dot on the other side. Then I punched the same dots in the axle housing beside the caps. Tadaaa, impossible to put them back wrong

To remove the diff, I used the method preferred in the FSM. I put the car in neutral, put a wrench on a ring gear bolt and turned the driveshaft with my hand until the wrench contacted the housing. Then I kept turning the driveshaft with a wrench stuck between the yoke and the driveshaft. The diff climbed out with almost no effort together with the shims.
Halfway out I had to use an aluminium prybar to pry the diff upwards a little since one ring gear tooth got stuck against the housing. Then I removed the right side bearing shim with my right hand while holding the diff with my left hand. I immediatly marked the shims and bearing races with zip-tied post-its saying "left side shim", "right side bearing race" etc. My car had two shims, one per side about 3-4 mm thick each.

Here is the diff on my bench at work together with my marked shims and bearing caps.



I put it on an axle mounted in the bench vice with soft jaws. One thing I did that no guides have mentioned you should do, was to put a wood block between the diff housing and the vice to prevent it from falling down around the axle when you remove the bolts completely.

Then I removed the housing bolts. For you Euro guys, in metric the bolts are 11mm hex head. Put my hand in between the housing halves to prevent the parts from falling out since they are only held in by the oil film.

Then i put everything on the bench in the order it sat. The only thing i screwed up was to not keep track of the spider gears orientation. I later googled for a guide and found a pic though (I'm not sure it matters, but I'll better be safe than sorry).



Cleaned up all the parts with brake cleaner and inspected closely. One of the spider gears had begun to seize on the cross shaft (I could see that the PO did a lot of one wheel peels from the uneven tire tread depth in the rear when I got the car).
I just used some emery cloth to clean up the seized part of the shaft and gear until it was easy to turn again.

Picture of the partially seized cross shaft



Spider gears and spring plate


Compression springs


Old worn, bottomed out cone VS. New cone from 9bolt.com


To install the new cones from 9bolt.com, you somehow have to remove the ridges in the bottom of the housing halves to convert the housing to fit the new design cones, since the cones are completely flat at the narrow end. Every thread and guide I've read says you have two options.

1. Machine the new cones on a lathe to look like the old design.
2. Remove the side bearings and machine down the ridge on a lathe.

The guy at 9bolt.com recommended NOT machining the cones, he said to remove the ridge. The reason for this is that if you machine the cone, you will remove splined contact area. The new cones have deeper splines than the old design and therefore makes the diff even stronger than stock, so why remove that reinforcement?

Another good thing I figured out with this new design is that when these new cones bottom out in the future, you can just machine them flat and remove as much as the inspection window's width, which doesn't require getting any measurements right. Since the splines goes are all the way through the new cone, you can machine them once and still have as much splines left as a stock cone.

I didn't want to remove the bearings to risk destroying them in the process. I also don't like other (potentially stupid) people screwing around with my stuff and risk them screwing something up, so letting someone else doing it for me was a no-no.

So I went with my own third option.

I masked the bearings with electrical tape, since you can stretch it to make it almost airtight.



Continued in the next post (reached maximum image count for one post)

keykey

I then stuffed the hole for the axle really tight with paper.



Then i took a dremel tool and ground the ridges down. If you make sure the whole ridge is down to the same level as the bottom of the case half or lower, when the cone one day bottoms out, it will touch the bottom first (the dark area between the ridge and the edge) and that area is completely flat.

Picture of my grinding process to the left is a huge sucking thingy to keep the burrs from hitting my face (don't know what it's called in english? evacuation fan?)


Picture of the tool used



This is how i checked for flatness in relation to the case half bottom


Ridge is gone, case cleaned out from burrs with brake cleaner and shop air (BEFORE removing bearing masking tape)



Now I could put the new cones in and check for cone clearance. I had as much clearance as the inspection window's width which is very good.

Right side new cone clearance check



Left side new cone clearance check



Then i shimmed the cones and side gears. I began with putting two 0.5mm shims in, the cross shaft didn't seat fully. Then i played around and ended up with one 0.5mm, one 0.3mm and one 0.1mm, so a total of 0.9mm. That made my gears have as little play as possible while the shaft still seated fully. Did the same thickness on the other side, and checked gear play, it was about the same as on the other side so I went with that.

Then i lubed everything with gear lube of the same type I was going to use later to fill, and assembled the diff with both axles fully seated. Torqued housing half bolts to spec. Hammered axles out with a rubber mallet.

Then i lubed the bearings and ring gear, and put the diff, bearing races and one side bearing shim back in the rear end. Then I used a brass punch to hammer the right side shim in. Put the bearing caps back and torqued to spec. Put both axles in and tapped all the way in to fully seated with a rubber mallet. Torqued axle retainers to spec. Put brakes, diff cover and panhard rod back together.
I filled my axle with 80w-140 gear oil and used one bottle of GM Limited Slip Additive.

My old fill plug was dry and hard and leaking, but I was really lucky and got hold of a NOS Genuine GM Rubber fill plug! (I've heard they're discontinued)



Picture of the rear end all put back together and filled up, ready for the test drive!



Then I went for a drive towards somewhere with little traffic to try it out with a burnout. On the way there i did some peel-outs when I had to stop to get the cones to seat fully in the housings.
When I did the first burnout it worked flawless! The two rear wheels felt completely locked together and it made two equally long black marks . When doing tight turns it's as quiet as an open diff. No popping or grinding noises.

I've been driving around and doing several burnouts and the posi works perfectly! The car is a LOT quicker from the red lights now when peeling away, I had a HUGE smile on my face after every green light!

The total cost of everything including cones, shims, cover gasket, additive & gear lube was exactly $300 US Dollars (1975 SEK).

The total time elapsed from raising the car up on jackstands to the test drive was 4 days.

I hope you guys enjoyed the read, and get motivated to fix your 9 Bolt Posis! It was easier than I thought, and here are the results (I'm gonna try to get a before+after video posted later)



Video:

stealtht/a

iTrader: (1)

Great pics! Thanks for posting complete with results.

big gear head

Nice work. You are pretty talented with that grinder.

Just one piece of information that I would like to add. I'm not criticizing your work, but this is something that I learned in my years of doing rear end work. The bearing caps are under a lot of stress. The left bearing cap carries a lot more of the load than the right one. I have seen bearing caps break under very heavy use, and when you make punch marks in the caps it creates a stress riser. This makes the cap weaker. When I mark the caps I only mark the right cap. There is no reason to mark both of them. I put one punch mark on the right cap in a location that I think is under the least amount of stress.

Did you put the axles back in the differential before tightening the 8 bolts that hold the halves together so that the axle gear splines and the cone splines would be lined up? That is how I have done them.

keykey

Thank you!

Oh, actually I didn't even think about that! Several people have told me that's how you mark bearing caps for crankshafts so I just went with it, I was afraid that if I'd have marked them with paint, I would maybe wipe the paint away by mistake. Will paint next time then :P

Yep, that's exactly how I did to align the splines and it worked well

big gear head

Paint probably will wash off when cleaning the parts. If you just put one small mark on the right cap it should be enough so that you can get them back in the correct location.

I must have skipped over the part where you said that you had the axles installed. I see it now.

DynoDave43

iTrader: (11)

Nice job! Thanks for sharing all of the photos.

InfernalVortex

iTrader: (4)

Where can I get these shims in the US? What size are they?

My 9-bolt posi is fine, but I'm starting to get ... "invested" in mine, I want a contingency plan for when the posi kicks the bucket.

big gear head

Contact Randy's Ring & Pinion and see if they have shims for it. I've got a lot of pinion shims from many different types of rear ends and some of them might be just what it needs. Randy's could sell them to you.

red rock

iTrader: (2)

You did a very nice job and brought another old 9 bolt back to life.

keykey

I looked at the shims today, they are outside diameter 50mm and inside diameter 40mm. The guy said they were "standard shims". Tools Momentum is an industrial store which sells bearings, seals, grease and so on and I would check stores like that.

Bullydawg

iTrader: (7)

I rebuilt mine before, and in the end wish I had just gone with a Torsen diff 4th gen rear with the bigger rear brakes. Just food for though!

jmd

iTrader: (4)

Nice work and write-up!

keykey

The only issue for me is that parts for american cars aren't as cheap here as they are in the US, if you can even find the parts you want for sale. I'd love a Torsen and beefier brakes but it will cost me, so for me right now this was the best solution. I also like that the car is still original!

big gear head

The 9 bolt parts come from Australia. You might try getting them directly from there instead of the US.

keykey

Oh I was talking about parts being expensive in general in Sweden compared to the US, referring to the discussion about doing a 4th gen rears/torsen diff conversion. I did buy my 9-bolt parts from Australia (9bolt.com).

keykey

I have now uploaded a video of some Posi Action

Base91

iTrader: (1)

I did one too and very happy with the results. However, I have a friend that machined the carrier halves so no Dremel work for me. Also machined the noses of the cones a little so didn't need new ones.

Horacioz28iroc

So what oil did you use? Also any additive?

GeneralDisorder

iTrader: (1)

It didn't last. He later (like me, and were talking very shortly later) replaced the cone type with Torsen carrier from Austrailia. When the manual and other sources say these cone types can't be rebuilt, they mean just that. You won't have success (for long). They suck intensely.

Look for my post on the Torsen install. KeyKey's too.

GD

jmd

iTrader: (4)

https://www.thirdgen.org/forums/tran...installed.html

red rock

iTrader: (2)

I have to disagree with you. I rebuilt a 9 bolt in 2010. Machined 3 series carrier, new cones, set the spider gears with maximum shim and a 3.70 gear. It was running behind a complete bolt on TPI, (Ported Edelbrock intake manifold, ported SLP runners, Ported Plenum, 52mm BBK TB, mild cam 1.6 RR, headers and Borla exhaust, custom tune) and stock 700r4 with a Transgo kit till 2013. Then I went 383 with a TPIS mini ram and custom dyno tune with 468hp at the crank, Probuilt Automatics street strip kit and Transgo kit with a Boss Hog 9.6 convertor. I just replace my gear oil last week and the 9 bolt looked great. Been running my 9 bolt hard for over 7 year, and now really hard for the last 4 years. If you set them up right, rebuilding will last. Now, I'm NOT saying the Torsen is not better, I'm just saying the 9 bolt will work on a rebuild. I am thinking on getting a full spool for more drag strip work though.

GeneralDisorder

iTrader: (1)

Well the rebuilt one I got from 9bolt.com was garbage and he's supposed to be the expert. I got less than 2500 miles out of it. I didn't have the desire to rebuild it myself. Everyone says the Auburn style is terrible.... The Torsen works amazing, its silent, never wears out, doesn't require additive, etc.

That's great that yours is working that well. But between your labor and parts what did the carrier rebuild cost? The Torsen came pre-assembled for about $500. That's not really much for guaranteed success and no labor, learning curve, or hard to source parts.

GD

red rock

iTrader: (2)

My labor was me, and the joy of doing it myself. I still have my original 9 bolt that came in the car sitting on a rack in the garage and it still works great. I bought a used 9 bolt and stripped it, cleaned it, and rebuilt it myself. The carrier came with the rear end, $20 for machining, and at the time i bought the cones, probably $200 shipped from Aussie land. I'm not in any way taking anything away from the Torsen set up. I think it's great that there is a replacement. I'm just saying, a proper rebuilt 9 bolt is one strong rear end. Now maybe with more track time, I may break or twist an axle, but it can also be upgraded to a 31 spline also. I'm just curious as to where you got the Torsen for about $500?

GeneralDisorder

iTrader: (1)

All the info on getting the Torsen is in my post here:

https://www.thirdgen.org/forums/tran...rg-warner.html

GD

red rock

iTrader: (2)

howie099

There is not much to rebuild in these diffs. All you have are the bearings, seal, sleeve and cones. I bought a used series 3 carrier with a good 3.70 to replace my 2.77 series 2. Had all the bearings pressed on, modified the diff for the new cones, and install. I had a guy put it in since I don't own the dial gauges and for $200 to do the bearings in both carrier & axles plus install you can't beat that price.

I was told the torsion style can't handle as much HP the cone type. Torsion is rated for 400HP and proper setup cone type can do 500HP. Do the axles I bet you can add more HP to it. Yes the torsion has less maint but with the new style of cones I don't see them wearing like the old design did.

GeneralDisorder

iTrader: (1)

Auburn (cone style) diffs are well known to be problematic - they wear, they make noises, and are questionably rebuildable.

I have not heard of anyone breaking the Torsen. Not that it can't be done, but there doesn't seem to be any evidence of them being weak or breaking. There are people running way over 500 HP on Holden Commodore VL's with these diffs in Australia. Also the 99 to 01 LS1 powered Trans Am's used the Zexel Torsen carrier in the GM 10 bolt so I don't think strength is an issue at all.

Mine is excellent. And cost was very reasonable. I've experienced the cone type and the Torsen and I wouldn't consider going back. And if you take a poll of people that have driven both, no one would choose the Auburn.

Just how it is.

GD

howie099

I have never seen anyone up here run a torsion style diff at the strip. Torsions I see on road racing and street use since you have less maint on them they are better in the turns. A GM stock 10 bolt it weaker than any 9 bolt for the third gens. For the track I am sure the torsions must not hold up to trans brakes and slicks or more people would have them.

The 9 bolt diffs don't look like a auburn (clutch) diffs. Most people if you don't have 9 bolt have never seen those wear cones. Guy who installed my 9 bolt never seen a style like that in over 30 years of doing them.

big gear head

The 9 bolt is a Borg Warner rear end and uses a Borg Warner differential, not an Auburn. The Borg Warner and Auburn both use cones and both of them wear the cones and the differential case. The Borg Warner can be reconditioned once, but the Auburn can not. The BOP 8.2 10 bolt rear end that was used in GM cars in the '60s and early '70s also used the Borg Warner differential.

GeneralDisorder

iTrader: (1)

It's "Torsen" as in TORque - SENsing. That's how the name was derived. There are at least three types of Torsen diffs and their strength depends on which design is used among other things.

Auburn (style) diffs are not clutch type. They are cone type also like the BW. The plate style (clutch type) is often refered to as Posi-traction or the Eaton plate style differential (Eaton makes Torsen diffs, Detroit lockers, and others).

If your guy had never seen an Auburn cone type in 30 years of working on diffs..... I don't know what to say about that. The BW is very similar - same basic theory of operation.

GD

howie099

I am not sure why he said the BW looked so different from Auburn design. They are very close in design. The BW looks stronger if you compare the same size of diff with auburn. The assembly and taking apart both diffs are totally different so that is what I am assuming why it was different.

He had no issues installing it took like 45 mins to do it. Shimmed and backlash was right on the money the first time. He doesn't even check the preload on pinion bearing. He goes all on feel.

scooter

iTrader: (11)

I've seen lots of people use a Torsen for the strip. I am not really sure why, but some people like to use them

Fran_Formula400

Hi Key-Key. Thanks a lot to take your time to share with us your job. I have a 2nd generation Firebird with a GM 8.5" 10 bolt Limited slip diff cone-type. I dicovered excessive rear axles play (2 mm in and out) and I decided to inpect the diff. Once disassembled, I confirmed the wearing in the brake cones and the housing is pretty similar that you show in your post. Then, thanks to you, I will try to repair them instead of to waste 500 or 600€. I have nothing to lost , except my time (that as you said is mine and I enjoy doing this things).

Please help. I have a main question about what gap or tolerance should exist between male and female cones after machining. I mean, depending of how much you turn the cone end the gap between male and female cones will vary...honestly I dont understand correctly this part of the process

Thanks again
Best regards

GeneralDisorder

iTrader: (1)

The cone type is garbage and KeyKey was not ultimately successful with this rebuild. It failed in short order and turned to a mess of cast iron slurry. He upgraded to a Torsen. Which is what you should also do.

GD

Fran_Formula400

Hi GD, Cone type diff were assembled in thouthand of muscle cars from 70's and still there are companies that manufacture them for new car models. one example is Auburn Gear. Honestly is difficut to beleveive this kind of differential design is still offered in the market if it result is so poor as you say...

GeneralDisorder

iTrader: (1)

Do more reading on this forum. The vast majority of people on here dislike them. GM went to the Torsen on the 10 bolt in 99. It's far superior. I got a rebuilt 9 bolt carrier from 9bolt.com and it was horrible. Made noises, wore out very quickly (2500 miles), and was generally just terrible.

They are not designed to be rebuilt and only some people have limited success doing so. If you want to gamble go for it. I had the so-called expert do mine and it sucked. KeyKey's didn't last. He went to a Torsen also. Look up his and my threads on the subject. My Torsen is abused in my 9 bolt every day. Works great.

GD

sofakingdom

iTrader: (1)

That's pretty naïve.

If I had a dollar for every product on the market that falls under that description, I'd be a VERY RICH person. Let's start with cigarettes; how about soft drinks; … the list could get REAL long REAL quick.

One of the fundamental assumptions in the field of economics is, that people act rationally, in ways that maximize value. Few assumptions are more WRONG.

There are 4 reasons why crap like … cone-type posi units … that DON'T LAST, are on the marketplace. (1) They are CHEEEEEEEP to make; (2) they can be sold to OEMs for ALOT more than they cost, i.e. they are profitable to their maker; (3) new-car buyers don't know any better, but they WILL pay extra for ANYTHING labelled "limited slip differential" or words to that effect, in the belief that it's "better" than an unlimited slip one; and (4) car mfrs are unscrupulous enough to take advantage of (1) through (3).

As GD points out, the original poster of this thread threw that worthless cone-type POS in the trash after it failed AGAIN after he put all that effort and $$$ into it. https://www.thirdgen.org/forums/tran...installed.html I don't know if he ever posted up exactly what had happened to the original thing that came in his 9-bolt when it failed the 2nd time, maybe he did and I just don't know about it, but it would be interesting to research it.

FYI, as I understand it (I could be wrong of course), Auburn was founded by some upper-mgmt people who left B-W for some reason, sometime in the mid to late 70s; I think it wasn't entirely voluntary, like, maybe it had to do with a plant closing, or elimination of a product line, or something along those lines. (not "quit" exactly, and not exactly "got fired" either) But however all that may be, they started a new company (Auburn Gear) making a product very similar to what they had been involved with at B-W. Has all the same weaknesses that the old B-W unit, which was later incorporated into the 9-bolt, had.

What was incorporated into cars 50 - 60 yrs ago, when they weren't expected to last more than 100,000 miles under THE BEST of circumstances, and the powertrain warranty was only 12 mo or 12,000 miles, was there for VERY DIFFERENT reasons that things are built like they are today. It's beyond foolish to compare the auto industry's mfg/mktg practices of the 2 eras.

Fran_Formula400

Sofakingdom and GD, thanks for your logical comments. All the weekend I have been reading a lot of information about it, and of course I have been applying the common sense... and finally I agree with you both; the Posi cone-type is a bull ****. The design concept is not bad, but the manufacturing no doubt. I mean, both male and female cones are manufacturing in casting steel, material really soft and inadequate for surfaces which are in contact transmiting high loads. I think if were manufactured in tempered steel and/or with a good hardenerd surface treatment...maybe!

Ok, what I have done in my diff? I have mechanized the cones base enough to let the surface cones to be again in contact. I have use shim washers to remove the play between planetary and side gears and reassembly everything. For the moments I have two good news: first the rear axial play have been reduced from 0.08" to 0.03". Second, the breakaway torque has increase from 50 lb ft to 140 lb ft!!!. The question now is how many time will stand in this condition...? we will see.

Of course, if the failure happend again I will sustitute it following your recommendation.

Cheers
You both have a cold beer waitng in the south of Spain

sofakingdom

iTrader: (1)

Be careful what you ask for: you might get it.

I may come to collect that reward someday.

keykey

I took it apart, realized the spider gear that was partially seized the last time, was even more seized and couldn't even be removed from the cross shaft. Cones bottomed out again. I took the cones to a friends machine shop and asked him to put the cones in the lathe to remove some material. I shimmed it up again and put it together, and kept it as a spare if something would go wrong with the torsen. Since it still works perfectly, the old "re-rebuilt" 9-bolt still sits in the box that the torsen came in, on a shelf in my spare parts closet.

Chevy86 IROC-Z

iTrader: (17)