Diff Rebuild

#1

All:

Carlton and I bought the stock limited slip clutches to rebuild both our diffs. We’ve heard that the diff should get new clutches every season and that the finned cover should be used and that the fluid should be replaced every weekend.

I know that Brain just had his diff rebuilt and that it needed it. His clutches were "paper thin" according to his report and prior to the rebuild, he said that he could turn one side by hand, while the other side was sitting on the ground.

With all this to think about, Carlton and I pulled his diff and swapped the clutches. Interestingly, the clutches in the diff looked just as thick as the brand-new clutches. They didn’t look worn, burned, or scarred in any way. We did not do the hand-turn test before pulling it.

Regardless, after all of last season (about 7 race weekends and 5 school weekends) on the stock cover and one fill of the fluid, the clutches looked very good. And the diff clutches had not been replaced by him at anytime.

We had planned to do mine as well but after seeing his and not being able to turn a wheel by hand, I’m going to put it off until later in the year. For sure, a finned cover is a good idea and I’ll probably change the fluid every weekend but it looks like these diff clutches are more durable than I had thought.

Carter

#2

Carter, What is involved with swapping out the clutches. I was going to email James Clay to ask but now I don’t need to. I have a diff of unknown mileage and was going to put in the clutches as PM. while it is sitting in the shed

#3

The Stock Diff is supposed to be a 25% lockup. I have read that this number is 25% of the torque the car produces so in theory(haaaaaa!!!) one should be able to test this by applying torque to one side that exceeds the 25% of factory spec.(164 lb./ft).

#4

After experiencing A-LOT of inside wheelspin and being off the pace by 1-4 seconds in the dry (Vic’s fast but not that fast) I took a hard look at my Diff. I put the car up on the lift and with only the strength of my arms I could turn each wheel independant and opposite the other. My LSD was toast.

I went the expensive route and shipped my Diff off to Korman BMW for a full rebuild.

http://www.kormanfastbmw.com/

They do all kinds of rebuilds from stock to 75% lockup. Since the rules don’t really address Diff rebuilds, I chose the logical (and least expensive) option of having my Diff rebuilt to stock specifications with 25% lockup and factory torque settings. If you increase torque settings beyond factory specs it will increase your percentage lockup but isn’t in the spirit of the rules. I didn’t want to have to pull it later so I specifically asked for a maximum lockup of 25%.

Beyond 50% lockup, special machining is involved so that’s absolutely not allowed per the rules.

I asked them about Finned covers and they said they do make a small difference in temperature but are not nessesary for track use. Without a finned cover the fluid gets a bit hotter and will need to be changed more regularly. I have been changing my diff fluid once a year at the end of the season, and Ray Korman said that should be enough if all I run are sprint races. After spending the bucks on the rebuild I’ll probably swap fluid after every three weekends just to be safe.

And-Oh-by-the-way…Korman Autowerks did a super job! Fast turnaround, price was as quoted and when I got the Diff back it really looked like a brand new piece.

brain

Post edited by: brain, at: 2006/04/18 10:35

#5

Apparently Korman chooses not to put pricing on their online catalog, but I was curious to learn what you saved by doing it through them vs. getting a factory reman’d diff for the car…?

#6

The price list is there…a redo is like 785.00
re-mans are easily double that

Post edited by: nasaregistrar, at: 2006/04/18 16:45

#7

Oh, I forgot to mention that with my Korman Diff Rebuild it comes with a 2 year / 24000 mile warrenty.

Yes… $800 plus (with shipping both ways) is a fair amount of coin but not too much more than a set of new Toyo’s. A properly working LSD will help get the power down better.

#8

brain wrote:

[quote] Since the rules don’t really address Diff rebuilds, I chose the logical (and least expensive) option of having my Diff rebuilt to stock specifications with 25% lockup and factory torque settings. If you increase torque settings beyond factory specs it will increase your percentage lockup but isn’t in the spirit of the rules. I didn’t want to have to pull it later so I specifically asked for a maximum lockup of 25%.

Beyond 50% lockup, special machining is involved so that’s absolutely not allowed per the rules.
[/quote]

9.3.11.2 Factory limited slip differentials are permitted.

Brain is correct. It came from the factory with a 25% lockup so that’s what is legal. As wth other aspects of the car, it something other than factory stock was legal, it would be specifically described in the Spec E30 Rules.

Carter

#9

so it is to be 25% or completely welded, nothing in between, right?
thanks,
bruce

#10

I am curious why you would ever want to race with a welded diff? I am friends with some people in the drift scene, and they do it but it seems like it would be terrible while racing. Can someone explain this to me?

#11

leggwork wrote:

[quote]so it is to be 25% or completely welded, nothing in between, right?
thanks,
bruce[/quote]

Right.

Carter

#12

Brain - just curious, I’m guessing the rebuild included new carrier bearings, pilnion bearings, pilot, etc.? I just had the torsen diff in our 240z rebulit. The bearings alone were about $500!

Ed

#13

Year old parts pricing from a local dealer for everything but LS clutch parts:

23 21 1 490 120 securing plate 0.75
33 10 1 214 099 shaft seal 10.27
33 12 1 203 615 tapered roller bearing 37.87
33 12 1 203 616 tapered roller bearing 44.81
33 12 1 744 368 clamping bush 6.60
33 12 9 065 179 spacer rings set 26.44
33 12 9 065 180 spacer rings set 26.44
33 10 7 505 602 shaft seal 8.47 (qty 2)
33 13 1 213 893 tapered roller bearing 29.81 (qty 2)
33 13 9 065 734 spacer rings set 36.56
33 13 9 065 735 spacer rings set 36.56
33 11 1 214 144 o-ring 1.45 (qty 2)
33 13 1 207 280 lock ring 0.14 (qty 2)

That comes to a little over $300 in appropriate quantities including spacers which you probably don’t need if you are doing a straight bearing replacement/rebuild.

Post edited by: edw, at: 2006/04/20 10:42

#14

Ed,

To be honest, I can’t remember the specifics of what Korman told me they were going to replace. But essentially if it’s a wear item it’s replaced with new. All other parts were inspected and replaced as needed

brain

#15

Thanks Brain. Definitely something to think about. We have a relatively low mileage car, but when the diff goes bad, it really messes up the weekend!
Ed

#16

Welded diff would probably be a disadvantage in a low powered car like a spec e30, corner entry understeer would probably slow the car quite a bit. I used one in the M30/3.5 Cowvaria as welding the diff cost me $25 compared to NLA old CS style limited slip at $$$$$$$$$$, it worked good everywhere but Summit Point, you basically had to trail brake then stomp the throttle to get it around a corner, it always got a lot of comments from other drivers. I have an e30 welded diff and almost tried it out at VIR but the stock LS I have seemed OK…

Also Mark Donahue/Penske used welded diffs in everything way back when and did a lot of testing on a skidpad…but again everything they ran was mucho power…

Al

#17

Does anyone have a link to a writeup on replacing the LSD clutches? How involved is it? Does it involve messing with the gear set? Am I going to have to break out a dial indicator?

#18

I did mine this weekend and it is not real difficult. I did not mess with dial indicators and such bot others would tell you you need to. I just took it apart, replaced the clutches and put it back together. I also replaced the input and out put seals.

Basically, you pop out the output flanges, remove the output flange bearing hub. Remove the ring and stuff from the rear. Set it up and remove all the allen head bolts and unpack the LSD unit keeping track of the way it comes out. I removed the input shaft nut to replace the seal but if you don’t replace the input seal I don’t think you have to remove that nut. Make sure all spacers and such go back in just like they came out. This is the second one I have done. The first one I replaced the ring and pinion. BMW (or their supplier) makes them very well.

Michael O.

#19

Started my diff rebuild today.

Here is a good picture guide that i used ahead of time to see what i was in for: http://www.e30tech.com/forum/showthread.php?t=44131

Today i took all of the above apart, replaced the clutches, and flipped the dogged washers as recommended by Bimmerworld. Really it was pretty darn straight forward. I spent more time cleaning than anything else.

Its all buttoned up now and everything is clean and lookin’ sweet. B)

Next weekend i’ll go to a friend’s and he’ll pressing the bearings out and press the new ones in and help my set the pinion bearing preloud w/ his inoz torque wrench.

All the parts including clutches came out to $255. I’ll wait till i get it back in the car and working before i claim victory, but so far i feel like i’m making out like a bandit.

#20

Where are people sourcing the replacement clutches from?