Differential Rebuild

[cirrusblau325i]

I am planning on rebuilding a used 3.73 LSD that I picked up a little while back. I know the general procedure for a rebuild and have the tools, etc. to do a proper rebuild.

However, I do not know the original factory specifications. Does anyone know the proper shaft end play (axial play) or rotating torque, or similar?

Thanks in advance
Matt

[Teaguer]

Do you have the tools and ability to torque down the pinion gear nut without crushing the input bearing ??

BMW diffs are not something the DIY'er home mechanic can rebuild .

[cirrusblau325i]

I have a 2' long breaker bar that should do the job quite nicely, with a pipe on the end if absolutely neccesary. I am not familiar with the exact setup of the differential, but my understanding on the pinion crush nut is that you tighten it until endplay is within specifications. So long as I do not go below the specified minimum endplay, the bearing should not be crushed or otherwise damaged.

I will be attempting the rebuild. It is a spare dif, so I have plenty of time. I will work on it slowly and carefully, particularly since it would be my first differential rebuild. I have no reason at this point to doubt a successful rebuild.

If anyone has rebuilt a differential (or knows anyone who has), I'd appreciate hearing from you.

Matt

[moberg12]

Most people don't rebuild them, if a diff goes bad just replace it with a known working diff. Seems like rebuilding one would be a waste of money!!! Does the one you are planning to rebuild need a rebuild if not just keep it as a spare, and save your time and money for more important projects. Of course if you are like me you might want to do it just for fun!

[cirrusblau325i]

This is certainly not about the money, and at the moment it is not a necessity. I am doing it somewhat for fun, but also to guarantee that I have a well sorted dif in my driveline. Even the best kept used dif is running on borrowed time at the this point (unless the car has been driven only occasionally over its life).

Also worth noting is that the previous owner of the dif said it had a bit of a whine develop while running leak free at proper fluid level. I got the dif cheaper than a good condition one. When I buy the bearings, spacers/shims, gaskets and crush washer I'll come out about equal cost to a good-very good used LSD.

[TXBDan]

Actually, IF you're using the stock gearset and housing, its quite straightforward. I just finished rebuilding mine and putting it back in the car last weekend. I could rebuild it in a few hours no problem.

The carrier is pretty simple. Take everything a part and lay it out in order paying attention to what face faces which way. There is a good writeup w/ pics on r3vlimited.com. I replaced the clutches w/ the ones from bimmerworld. Clean everything and rebuilt it like how it was w/ the new clutches. You should also flip the dogged washers that the clutches rub on to provide a fresh surface.

Note, its probably easier/smarter to replace the output bearings before you rebuild the carrier.

I got the output bearings off w/ a gear puller. All the races in the housing and tranny sides can be tapped out w/ a hammer and tap. Always tap the new races in by tapping the old race against the new one to prevent damaging the new race.

You'll need a press to press the pinion bearings on/off. There is a shim behind the inner bearing race. This is important and goes w/ your housing, don't forget it. Its what sets the pinion depth. Press the inner pinion bearing on and put it in the housing from the inside. don't forget the crush sleeve. Then you gotta sort of hold it as you start the outter bearing by tapping it. Then you'll need to press it on until it snugs up against the crush washer. Then you put the input flange on and the nut and slowly torque down on the nut to crush the crush sleeve until you get the correct drag torque and/or feel. spec is around 15-20inoz. I crushed the sleeve until i got around 16inoz of drag and an experienced friend agreed that it felt right. Note, you do this without the input seal first because the seal creates a lot of drag when new. So do this all to crush the washer, then take the nut and flange off, tap in the seal, and put the flange and nut back on.

Then you put the carrier in. Slap on the tranny sides (don't forget the shims) and you're rolling.

Really, its not hard and costs under $250 in parts for all new clutches, bearings, seals, etc.

[eshghehBMW]

If you go forward with the rebuild....
consider if you can do me a favor and post some pics. along with a DIY of some kind.
if you can't then consider just posting some pics along the process...they may prove to be self explanatory.

Thanks

[billyfiction]

Actually, IF you're using the stock gearset and housing, its quite straightforward. I just finished rebuilding mine and putting it back in the car last weekend. I could rebuild it in a few hours no problem.

The carrier is pretty simple. Take everything a part and lay it out in order paying attention to what face faces which way. There is a good writeup w/ pics on r3vlimited.com. I replaced the clutches w/ the ones from bimmerworld. Clean everything and rebuilt it like how it was w/ the new clutches. You should also flip the dogged washers that the clutches rub on to provide a fresh surface.

Note, its probably easier/smarter to replace the output bearings before you rebuild the carrier.

I got the output bearings off w/ a gear puller. All the races in the housing and tranny sides can be tapped out w/ a hammer and tap. Always tap the new races in by tapping the old race against the new one to prevent damaging the new race.

You'll need a press to press the pinion bearings on/off. There is a shim behind the inner bearing race. This is important and goes w/ your housing, don't forget it. Its what sets the pinion depth. Press the inner pinion bearing on and put it in the housing from the inside. don't forget the crush sleeve. Then you gotta sort of hold it as you start the outter bearing by tapping it. Then you'll need to press it on until it snugs up against the crush washer. Then you put the input flange on and the nut and slowly torque down on the nut to crush the crush sleeve until you get the correct drag torque and/or feel. spec is around 15-20inoz. I crushed the sleeve until i got around 16inoz of drag and an experienced friend agreed that it felt right. Note, you do this without the input seal first because the seal creates a lot of drag when new. So do this all to crush the washer, then take the nut and flange off, tap in the seal, and put the flange and nut back on.

Then you put the carrier in. Slap on the tranny sides (don't forget the shims) and you're rolling.

Really, its not hard and costs under $250 in parts for all new clutches, bearings, seals, etc.

`

[TXBDan]

Here are the pics i was talking about:
http://www.r3vlimited.com/board/showthread.php?t=92714

[cirrusblau325i]

TXBDan, where did you get your drag torque spec? Are there any other specs, or is that it?

[TXBDan]

i got it from searching around the internet and from a few experienced BMW ppl. All in that ball park, 15-25inoz. Mine felt good and tight at about 1inlb so we stopped there.

Thats the only spec i used and needed. Nothing else is critical. I used red locktite on the carrier top bolts which are pretty soft and don't need a whole lot of oompth. The only other bolts are the tranny sides and diff cover which arent critical.

btw, here is my parts list:


Pelican Parts

Part # Description Qty

23 21 1 490 120 securing plate 1 1.5 $1.50
33 10 1 214 099 shaft seal (pinion) 1 $9.75 $9.75
33-12-1-468-892 tapered roller bearing (pinion, superceded?) 1 $18.75 $18.75
33-12-1-468-893 tapered roller bearing (pinion) 1 $25.00 $25.00
33 12 1 744 368 clamping bush 1 $11.25 $11.25
33 10 7 505 602 shaft seal (output) 2 $7.50 $15.00
33 13 1 213 893 tapered roller bearing (output) 2 $17.25 $34.50
33 11 1 214 144 o-ring 2 $2.25 $4.50
33 13 1 207 280 lock ring 2 0.5 $1.00
33 11 1 210 405 diff cover gasket 1 $4.00 $4.00


bimmerworld

LSD clutch 2 $65 $130.00



TOTAL: $255.25

[cirrusblau325i]

TXBDan, thanks for the parts list and specs - should come in handy. One last question: have you run your rebuilt dif in your car yet? If so, has everything been okay so far?

eshghehBMW - I will certainly be taking a bunch of pictures while I do the teardown and rebuild. I might do a DIY write up depending on if I have time and if things go as planned. Bear with me, however, as it may take some time to complete this project as I am still planning things out. I have not yet ordered parts or taken apart the old dif.

[TXBDan]

Yeh its in the car, but it only has about 25 miles on it so far.

so far so good, though. its about 10% as loud as it was before. it was unbearably loud before. Itd whine so loud it'd give my headaches while driving to/from the track, etc. I'd have to crack the windows in the winter just to get some noise in the car to help drown it out. Note i have solid subframe bushings and a poly diff mount so it was especially loud.

Now its is a nice quiet shhh like it should be w/ such mounts. I bet itd be dead silent in a stock car.

But yes, we'll see how it holds up long term.

[M3Rob95]

If someone has the time to make a DIY that would be awesome!

I am planning on replacing just the clutches and am trying to do some research before tearing into it...

PM me if you can help

[prestonquirk]

so if my 4.10 leaks a 1" dia drop twice in one day when I run it hard at the track, and does have some leakage on it from normal street use (does not leak in drive at home), do I likely need to replace a gasket on the cover? I don't think it is leaking at the shaft seals. I was thinking of rebuilding it, but not sure I want to tackle that job right now. Otherwise it works well.

[subdewd]

Do it, people read those warnings in the manual and take it as gospel.
hell when i was 16 I rebuilt 68 volvo (borg warner) automatic.
When I went to try and buy parts the dude who ran the tranny shop
quizzed me a bit kinda laughed when he saw I knew what I was talking about
and gave me the parts free!! Of course that was the old days.
Good for you..

[aljaz11]

I would like to learn one thing: first, I tighten down the pinion nut to a specified rolling resistantance (aka crush the crush sleeve) without the seal. When I reinstall the input seal how do I know how much do I need to tighten the nut? Or is there a specification for rolling resistance with the input seal installed?

Thanks a lot!

[estoguy]

Before you take that nut off, you need to mark the nut and shaft. You don't tighten past that Mark. It's also noted in Bentley.

Once thing that is wrong though is through torque value. Just go by the position. Learned this last summer doing the input shaft seal. My buddy and I used an impact gun on low power. No problems.

[cirrusblau325i]

I'm no dif builder, but I guarantee you an impact gun is not the way to do it. From my understanding, proper method is to use a tool to hold the input flange and tighten until the drag torque is in spec. Remember, you're setting the preload on the bearings and too much or too little may not affect it now, but it could make the difference between the dif lasting 1 year or 10.

Before you take that nut off, you need to mark the nut and shaft. You don't tighten past that Mark. It's also noted in Bentley.

Once thing that is wrong though is through torque value. Just go by the position. Learned this last summer doing the input shaft seal. My buddy and I used an impact gun on low power. No problems.

[estoguy]

All we did was the seal. Honestly the nut on it wasn't too difficult to remove. The torque spec in Bentley didn't make sense (page 11:18). It said the torque for the collar nut is supposed to be 229 ft lbs. There's no way it was on that tight - it came off and went back on pretty easy. It was back in exactly the same spot as it came off.

[cirrusblau325i]

Ah, okay. Yeah, for just replacing the input seal, just mark the nut, remove,replace the seal, and reinstall to the mark. When you replace the pinion nut, you're not compressing the crush sleeve which is why it takes less torque, but I would not go by the Bentley torque spec anyway. You're preloading a bearing and pinion nut torque is not a reliable metric. Input shaft drag torque is.

Installing a pinion input shaft is more involved than simply replacing the seal.