Differential rebuild experience

[MINIzguy]

Does anybody have differential rebuild experience in the Morris County area?

I have a 318ti manual with a 3.45 open differential. I just purchased a 4.44 LSD differential from a parted out 318ti. I want to replace the clutch disks, but more importantly swap ring gears to have a 3.45 LSD differential. Adjusting preload and backlash sounds a little daunting to me, and while I can follow enough online guides, I would like to have some help in this rebuild. I don't want to send it out to a shop because I prefer to have the experience. Does anybody local know somebody/can assist me with this task?

In a last resort situation, what are some shops that can do a job like this?

I will also need to drop my rear subframe to do this job. Does anybody have a home press that I could pay to use, instead of going to a shop where I may get overcharged to just use a simple machine?

[warrenbrown]

I was online and wondering something similar. I have an E30 small case LSD that is trashed but the LSD is probably as good as any 200K LSD. I also have a 318ti with an open diff. After poking around on the internet I found BimmerDiffs.com http://www.bimmerdiffs.com. They had a bunch of guides and info that you might be interested in.

I've never done any diff work, it sounds fussy and perhaps something that you need experience before starting. I asked about swapping in a LSD to an Open diff, they claim it is doable, here is the response...


Hi Warren,

Thanks for the email and sorry about my delayed response.

The short answer is that yes, you can use the 168mm LSD spool in a open ti differential. The process is not complicated, but you may need to shim the carrier/ring towards or away from the pinion. I have some used shims on hand also if you do need to reshim. Bearings and seals obviously should be replaced and I'd be happy to quote you all the parts needed as I stock all.

If you're still interested in doing this, let me know and I can get more information over to you.

Best,

Jonathan Thayer


Maybe in another 100 years I'll find some time to try this modification. Right now my 21 year old daughter drives the Ti, it doesn't stop, I have to do oil changes on the move, so there is like no chance I'd be able to tie the car up.

You asked about removing the subframe to get the diff out. On an E30 as I recall, I lowered it some and was able to get the diff out and back in. I would imagine a Ti is about the same, the look pretty close.

I have a press, you are welcome however I'm in Mommouth county (exit 117 or 120).

Warren

[MINIzguy]

That sounds great Warren!

I did some more research and the process seems much easier now that I've read a few guides and watches a few videos on the subject. Since I will not be touching my pinion gear, I will not worry about the pinion preload, and as a result, not worry about my carrier preload.

Setting my spacing and backlash is the only complicated part, but can be done carefully and by double checking everything. I will buy a Harbor Freight dial indicator and mount for it and use that. Spacers are still available from BMW, so that is not an issue. Diffsonline also sells the clutch discs for $65.

I plan on removing the entire subframe to also do the bushings and rear trailing arm bushings. The rubber parts aren't too expensive if I buy the Febi branded ones. I just need access to a press to get them removed and installed.

I am 100% set on doing this job in the summer. I just have to find time in-between whatever job/internship I manage to get in the summer.

[victory1auto]

If you are putting a carrier into a different case, then I think you will need to address the carrier-bearing preload. I always did.

[MINIzguy]

Isn't carrier preload dependent on pinion preload?

The pinion preload will not be touched by me, so it will still be set to factory BMW specs. I'll tighten the the carrier bearings to the proper torque and then the total diff preload will be within spec. By deduction, won't carrier bearing preload be within spec too?

I'm using this formula:

Total preload (in/lbs. with the unit totally assembled) minus the pinion bearing preload (with only the pinion assembly) multiplied by the gear ratio = side bearing preload.

[victory1auto]

You may be confusing how to measure the carrier preload with what affects it. The preload on the carrier bearings is affected by the differential-case-dimension tolerances, so if the carrier is moved to a different case the carrier-bearing preload can affected and should be checked/reset.

The pinion-bearing and carrier-bearing preloads do not affect each other. The pinion position, however, affects the gear-contact pattern. This should not be an issue if you are only changing the carrier, and reusing the ring gear. The pinion/ring gear backlash will be affected by changing the carrier, however, so you would first set the carrier preload then check/reset the backlash.

HTH

[MINIzguy]

Ah, I guess I'm still underestimating the difficulty of this project.

I may just have to have a shop do the work if it is cheaper than having to buy a dial torque wrench.

[victory1auto]

You can make an inch-ounce-measuring device with a ruler and some fishing weights or large nuts and washers of known weight. Bolt it to the pinion flange and set preloads to your heart's content.

[edw1]

You can find very reasonably priced used torque watches and dial torque wrenches on Ebay. Make sure the range is sufficient for BMW diff bearings.


Look up pricing on new torque watches if you want a good scare.

[MINIzguy]

Okay, while bored in class I did some more reading on the subject. This is the torque wrench I plan on using to finish the job; I can't find a dial type (new or used) for the same price on eBay.
http://www.ebay.com/itm/GearWrench-2955 ... ls&vxp=mtr
Is this the right process:
Using the 3.45 case, leaving the 3.45 pinion in place and using the LSD unit with 3.45 ring, I will use the 4.44 carrier shims as a baseline.
Check carrier preload.
If in spec, check backlash.
If not in spec, add shims to make carrier preload in spec.
Check backlash. Move shims around to make backlash in spec, but keep total shim thickness the same.
Check final carrier preload.
Reassemble.

The one thing I have reservations about are the pinion preload and carrier preload specs. Listed here:

How can the preloads be so similar when the carrier preload essential has more drag (pinion drag, carrier drag)? Is it because of the gear reduction (3.45:1) keeps the preload down over the apparent increase in drag?

[edw1]

I check the output bearing preload with no pinion installed. Find the total shim height (L + R) that gives you the desired bearing drag and write that magic number somewhere. Remove the center section then do the pinion work. When it is time to move the center section to adjust contact pattern, keep the L + R total the same. Whatever you take out of one side has to go into the other side.


One more tip:
Somewhere on the interwebs, I read about some shop that ground down the OD of an inner pinion bearing race so it could slip in and out of the case by hand to make pinion shimming easier. Once you find the right shim, press in an unmodified race.

[MINIzguy]

Would measuring the carrier preload of my complete 3.45 open and 4.44 lsd, and using an average of the values be okay? If I aim for the same assembled carrier preload, will I be able to get away with not removing the pinion?

I'm trying to not remove the pinion to reduce the amount of work I need to do.

[edw1]

Would measuring the carrier preload of my complete 3.45 open and 4.44 lsd, and using an average of the values be okay? If I aim for the same assembled carrier preload, will I be able to get away with not removing the pinion?

I'm trying to not remove the pinion to reduce the amount of work I need to do.

Don't forget to add a couple in-oz drag for new seals.

[victory1auto]

Although Ed is absolutely correct that the carrier preload is best set with the pinion out, you can get by with it in. Measure the total torque to turn the pinion with the old carrier in, then set the preload on the new carrier to match the torque value you recorded with the old carrier in place. Of course this assumes that the preload of the old carrier was set correctly, but the short-cut procedure has been proven to work.

[MINIzguy]

This is coming back into the realm of "I can do it" possibility.

Fairly certain none of my differentials have been opened up. I finally get the entire process and will try to knock it out this summer. Hopefully I have the time to do so.