Differential Equations

[tig]

I have a dilemma regarding the diff for my 87 528e that I'm doing a 5-speed swap on.

I found this 3.25 LSD in the bottom of Puget Sound and figured 3.25 would be nice for this car since that's the ratio that came on 5-speed 528es.

However,

1) I'm not really sure it's the ratio I want, especially if I actually do turbo charge this car some day.
2) While it spins freely and SHOULD be in fine working condition, I really feel I need to get the rust off and paint it. You know me.

Is it worth my time? Or should I just source another diff, maybe in a different ratio, that's in better cosmetic condition?






I was considering diving into cleaning it up today. But I have other things on my list, and frankly, while the hard work involved my the therapeutic, it's not really what I want to use my time on.\

What do the masses say?

[waynet1]

I can only assume that you have not gone here for the usual good information available.
Also there, is this.

[oldskool]

Throw that boat anchor back into the sound.
-And don't "sorry" me babe. Shake that tail when you walk . . . you're better than that.-

[tig]

I can only assume that you have not gone here for the usual good information available.
Also there, is this.

I'm not asking HOW to do it Wayne, but IF I should do it. That second link I had not seen. Gold. Thanks!

[trevmmeister]

That second link was an extremely interesting read. Learned a ton from that.

[waynet1]

I can only assume that you have not gone here for the usual good information available.
Also there, is this.

I'm not asking HOW to do it Wayne, but IF I should do it. That second link I had not seen. Gold. Thanks!

I wasn't suggesting you needed to no HOW to do the job. I was merely pointing to the wealth of good information for an 528e that is so often overlooked.
That second link is available, and copied, from the first.

[Mike W.]

Jeez, how many years was that thing in the sound? I've never seen one where the ribs were thinner due to rust.

Regardless, the rust looks cosmetic to me, pull the rear cover if you're worried and take a peek. Maybe use your existing flanges, but I don't see anything that would affect operation.

[tig]

Jeez, how many years was that thing in the sound? I've never seen one where the ribs were thinner due to rust.

Regardless, the rust looks cosmetic to me, pull the rear cover if you're worried and take a peek. Maybe use your existing flanges, but I don't see anything that would affect operation.

Yea, I don't either. The real question is do I want to spend the several hours of work required to de-rust the case, get the bolts off (!), and paint. Or do I just want to buy another 3.25 LSD that's in better cosmetic shape?

[wkohler]

I hadn't noticed the ribs the first time I saw it. Wow.

Looks fine inside though from what I can see.

[Mike W.]

Maybe see if the rear cover bolts turn? That would at least let you inside. But I think you answered your own question, if you want it to look nice I think you need to look elsewhere.

[tig]

Maybe see if the rear cover bolts turn? That would at least let you inside. But I think you answered your own question, if you want it to look nice I think you need to look elsewhere.

FWIW, here's what the insides look like.



Looks entirely serviceable. I've gone another route for this project, so this diff is 'available' if someone wants to make me an offer...

[tig]

After starting this thread I did the following:

1) I sourced a 3.46 LSD locally and installed that in Maytag.
2) Found another 3.25 LSD that's not a clump of rust.

Thus I have 3 diffs lying around: The 2.93 that WAS in Maytag, the rusty 3.25S, and the non-rusty 3.25S.

Today I decided to tear into making at least one good 3.25S that I could put in Maytag because the 3.46S is too short for my tastes.

I have questions. Please answer them.

First, I dove into the 2.93 non-LSD because neither of the 3.25s came with output flanges and I figure I can use them. Lame that sellers didn't include them!


I was surprised at how easy the diff came apart once the outer flange mounting cover thingies were removed. When I worked on the diff for my FJ40 it seemed way more complicated.


The input bearing in this case feels a little rough. It is the best case of the 3.


First question: I can't find the input-shaft/gear on RealOEM. Is there any difference between this part on LSD/Non-LSD diffs?

In other-words, can I just slap one of the LSD diff units into this case?

Next, I pulled apart the 2nd 3.25S that I bought. And dropped the cover, breaking the speed sensor. Which made me notice just how much gunk is on the speed sensor. Which made me think the speed sensor is actually a magnet and all this gunk is metal filings. Which makes me think this diff has not been wearing very well.



Am I right that the sensor is magnetic? And that this amount of metal is a bad sign? The other diffs I disassembled did not have anywhere this much gunk on them.

Compared to the rusty diff, this one just looks more worn. No obvious teeth missing or severe wear that I can see, just dirtier and the gears look slightly less crisp.




Should I bother replacing the bearings? I probably will for the input shaft since none of the 3 that I have feel smooth. Do the output shaft bearings wear?

FWIW, I have a rough idea of what it takes to put the diff back together. I need to set the ring & pinion backlash, preload the pinion and carrier, etc... Doesn't look too hard. I will need to buy some tools. Heh. Apparently there's a good thread on the Ohio Bimmer forum, but it requires registration/activation and that hasn't happened for me yet (this link: http://www.ohiobimmers.com/forum/showthread.php?t=3624). Should be fun.

[Gustav129]

When you refer to the input shaft, I take it you are refering to the pinion? Yes, if it's a little loose, replace the pinion bearing. Pinion bearing failures, get worse really fast and cause extensive damage if not taken care of. You will also have a bad vibration at low and high speeds.

As for putting a different unit in the case, I assume you are staying the same ratio? Ring and pinions are wear mated to each other and can cause premature failure by mixing ring and pinions from different sets.

[tig]

As for putting a different unit in the case, I assume you are staying the same ratio? Ring and pinions are wear mated to each other and can cause premature failure by mixing ring and pinions from different sets.

Thanks, so as long as I use the pinion that matched the LSD unit it won't matter what case I use? Cool.

[tig]

Were the outer ends of the output shafts painted/coated from the factory? In cleaning them I couldn't tell if what came off was old grease or paint. I think it was paint. Otherwise these would rust, because they are exposed, right?

[tig]

Once again, I'm foiled by a socket.

I didn't have a 30mm socket anywhere. Went to Harbor Freight and all they had was a full set of torque sockets that included a 30mm for $24. Got it. It's WAY too big.

Went to Sears. All they had was this socket. It's just barely too big.



Blarg.

According to a thread on rv3 this will work. Ordering now:

http://www.amazon.com/GearWrench-80826- ... B003L1ZZWS

[Alejandro G]

Just saying i recently resealed a diff and the harbor freight impact socket will fit if you shave the outside a little bit

[davintosh]

Once again, I'm foiled by a socket.

I didn't have a 30mm socket anywhere. Went to Harbor Freight and all they had was a full set of torque sockets that included a 30mm for $24. Got it. It's WAY too big.

Went to Sears. All they had was this socket. It's just barely too big.

Blarg.

According to a thread on rv3 this will work. Ordering now:

http://www.amazon.com/GearWrench-80826- ... B003L1ZZWS

If it's too big as in the wall is too thick to fit between the nut and the well it's in, grind down the outside of the socket. Carefully, and evenly.

The same 30mm thin-wall socket works on the Getrag output shaft nut too; I was able to get that same Gear Wrench socket at Advance Auto when I needed to replace the seal on mine during the clutch change. I think I paid a little more for it, but it was worth it.

[Jelmer538i]

You can mix a lot of parts just make sure that the ring and pinion stay together as a set. So mixing cases and LSD units is not a problem just make sure the R&p's stay together. Offcourse, a 2.93 pinion doesn't fit a 3.25 ring gear but you get the point. Replacing bearings on these diffs is a pretty big job because you have to set the R&P after checking tooth contact and you need a new crush sleeve which is not available from BMW.

[Soundstorm]

Did you already try to take the locking plate out? It's probably stuck good, but as you need to replace it anyway, you can destroy it to take it out. Socket should normally fit.

[tig]

Did you already try to take the locking plate out? It's probably stuck good, but as you need to replace it anyway, you can destroy it to take it out. Socket should normally fit.

Wait as second. The locking plate is not held in place by the nut? I thought it was like a washer.

[davintosh]

Did you already try to take the locking plate out? It's probably stuck good, but as you need to replace it anyway, you can destroy it to take it out. Socket should normally fit.

Wait as second. The locking plate is not held in place by the nut? I thought it was like a washer.

I thought the same on the trans output nut, and it looks like it's the exact same part used in both locations. http://www.realoem.com/bmw/partxref.do? ... series=E28

The locking plate fits around the flats of the nut and has a tab punched out on it that keep the nut from turning. Use a small screwdriver to pop it out.

[tig]

Did you already try to take the locking plate out? It's probably stuck good, but as you need to replace it anyway, you can destroy it to take it out. Socket should normally fit.

Wait as second. The locking plate is not held in place by the nut? I thought it was like a washer.

I thought the same on the trans output nut, and it looks like it's the exact same part used in both locations. http://www.realoem.com/bmw/partxref.do? ... series=E28

The locking plate fits around the flats of the nut and has a tab punched out on it that keep the nut from turning. Use a small screwdriver to pop it out.

Well, shit. Sure glad I learned that before I got a socket that fit and went to town with my impact wrench. That would have been a literal exercise in futility. I'm willing to bet that Craftsman socket I already bought will now fit. Will report back asap... wife is going on another trip so I'll have lots of garage time available. Tee-hee.

[tig]

Pure gold: http://www.bmw2002faq.com/_/technical-a ... -build-r74

Thanks to Jake @ ClassicDaily for pointing me at this.



This comment in the comments was useful to me too:

I'd only add that, if you're moving a pumpkin from case to case, start with the side- case shims that came with the pumpkin. The case tolerances in the later diffs are very very good, so the shims eventually

I plan on using the bearings (both pinion and both output) and pinion that came from the same diff the pumkin (what I was calling the LSD unit) I'm using came from (the rusty one). It's too bad I didn't measure the slip torque before I disassembled. I may quickly re-assemble the rusty unit and test it to double check that the pumpkin is in-fact ok and doesn't need to be rebuilt.

[tig]

Well, I guess I know which of the two pumpkins I have I will NOT be using.

In the pic above, see the one on the left, that I identified as being dirtier and more worn? I wish I had been more aware, and had taken pics of the other sides because it would have been obvious that ALL OF THE HEX BOLTS that hold it together were missing.

I discovered this once I popped the pinion shaft out of the case. Because a whole slew of hardware fell out when I did:



All I could do was giggle. I had set the pumpkin in a box, and this time when I picked it up, it fell apart in my hands. Tee-hee. (Hey, @Sam 84, 533i, you sold me a bum LSD. I'm going to hunt you down and make you smell used gear oil.)

Anyway, the reason I was removing the pinon from that case is I couldn't get it to come out of either of the other two cases. Many heavy whacks with a weighted rubber hammer had no effect. The link I pointed to above says "use a rubber hammer or, if needed a press". I don't have a press. I tried all three cases and this was the only one the pinion would come out of.

So now I need to go find a shop with a press who will push these out for me, unless someone has some other tricky DIY technique for pressing something out like this.

[tig]

Ok, as is usual, after I am stumped and post a message a solution comes to me.

I have a brass block and a sledge hammer. Set the brass block on the end of the pinion and a whack with the sledge hammer and the pinion popped out.

Now I have everything disassembled. From the rusty donor, all the important matching parts:

• Pinion
• Pinion bearings with matching races
• Pinion spacer washer (specific to each pinion & ring gear set)
• Pumpkin
• Side covers (from one of the better cases)
• Side cover shims from the rusty donor, marked for correct sides; match the pinion/pumpkin
• Cleaned cover
• Good case, to be cleaned & painted (also removed races from it)

Now I know precisely what to order:

• Securing plate
• Pinion shaft seal
• Pinon crush sleeve
• 2x output flange seals

I won't bother ordering any side cover spacers because (a) supposedly the ones I have will 'just work' because they are matched to the pumpkin and (b) I have 2 other donor sets that are all different sizes. When I reassemble, if I discover that lash can get set correctly with these spacers, I'll order other sizes.

I'm learning a ton. I hope you, dear reader, are too.

I'm also going to ensure all the fastners on the pumpkin are torqued correctly... maybe I'll pull them and put locktite on? Should I?

[Shawn D.]

Yikes. That ain't no good!

[Jelmer538i]

If your here, also order some new LSD parts:

http://thayermotorsports.com/collections/all

And make sure you check this:

[Mike W.]

I like this thread. Much like auto transmissions which aren't really all that difficult to work on, popular belief is that you need thousands of dollars worth of tools and diffs are impossible to set up correctly. Maybe, maybe not, I worked on a couple back in my air cooled VW days and both came out ok. Didn't put enough miles on them for a long term view, but short term at least they were fine.

[tig]

Painted the case today.