No more r3vtard assist

[e30leigh]

oh man. thats awesome. those pics made everything real clear!!! thanks heaps. should be tonnes easier now.

[NigelStu]

I was hoping that the pics could help someone. :D

[th3blue]

^
awesome pics... I really needed those to visualize what I will be doing.

[NigelStu]

Thanks for the write-up! Finished rebuilding the spare diff into a 3-disc setup, and replacing the broken bits, by scavenging parts out of my 'ES' diff. It was easy. Took me 2.5 hours to completely disassemble the 2 units, clean parts up, measure and reassemble the 1 unit. And now I have a good spare :)

A few pics from the process - first up, what came out of the 3.73. Notice the spider gears/shafts.... oops.




Parts measured up right, spacer that gets pulled and the disc/plate can that goes back in.


Thickness shot -



The mess of parts from both LSD units, laid out in 2 sets of rows - bottom rows are bottom of LSD unit from spacer/washer to spider gear carrier, top 2 rows is top of spider gear carrier to the top spacer washer - all match up. I measured up all the clutch disc/plates and used the 3 best - signified by the "O"s. The large spacer that gets replaced by the extra disc is the first large disc on the bottom row.




And the finished product.

[Wanganstyle]

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[shiboujin]

wha? nah. each clutch stack is about 2mm thick (if you don't get thicker plates). So you just need to machine off the cap 4mm. Course, you could machine off less for more preload.

[e30leigh]

cool. thanks for that. that clears that up for me before i even get into it.

im assuming. for argument sakes if the added steel and disc are 6mm in total thickness. i need to machine 3mm off each side bearing to keep it all centre?

[shiboujin]

you machine what's touching the table in this picture

[e30leigh]

would it be possible to see a picture(s) of what needs to be machined in a lathed for the 4 disc mod? i found a 188mm diff sitting at work. its condition is unknown. and i might not even be able to use it. as i have a feeling its one of the spares for the company race car.

i have a feeling it will all become painfully obvious what will need to be done once i get into it. but id just like to be confident first. and im assuming all that comes off is the exact difference of the added steel and friction disc that is going in?

thanks, leigh

[Wanganstyle]

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[NigelStu]

Thanks - it sounds like I should have no problem swapping the internals of the LSD unit from the 2.9 to the 3.7, which will give me a good usable spare. I plan to build the other current good unit (with worn clutches) into the 2/1 setup. Is there any big performance advantage to going to the Bimmerworld motorsports clutch discs over the OEM organic ones? And to confirm, are the BMW OEM discs same as Porsche ones (I have only been able to find part # for Porsche - 95133255100)




That broken diff was in our ChumpCar, broke during a 25 hr race. Started with worn discs and low % lock-up, which slowly wore as the race went on and lock-up reduced even more. It was acting pretty much like an open diff by the 12 hour mark, and we kept going on it (at that time the spare was the 2.9 diff). Eventually, it changed itself to a locked diff (when the spider shaft broke and the gears lodged themselves in a way to lock the diff). My hypothesis on what finally broke that shaft was repeated banging back and forth due to accel/decel and the turns - the system taking up that bit of slack, which was increased due to lack of friction material.

[Wanganstyle]

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[NigelStu]

Question on ES 2.9x vs. IS 3.7x LSD units.


I have a good 2.9x LSD full assembly and a 3.7x LSD full assembly that has worn discs and a broken spider-gear shaft. Originally I was going to swap the LSD units between the 2 (put the 3.7 gear onto the 2.9 unit) to rebuild the 3.7 assembly, but it seems that cant be done.

So, what parts CAN be used from the 2.9 to rebuild the 3.7? Internals of the unit OK to swap over? Is there some combination of parts that would allow for an increased # of discs/plates to help improve lock-up for racing application?

[NigelStu]

3 clutch disc setting will change the side to side loading and have higher locking force on the bottom side as there are 2 disc/steel sets on one side compared to only 1 pair on the other.

How does this imbalance affect drivability? Does it change lock-up characteristics on left turns vs right turns? Or accel vs. braking?



Also, what is the % lock-up with this 2/1 setup?

[shiboujin]

One Drift setup trick is to use this thicker pre-load springs for more consistent actuation when clutch kicking the shit out of it between pendulum swings.

cup springs? IE bellvue washers? Where do you buy those?

Also, what do you do with the center sections that are scored from the abuse of the stock clutches? You can't really get new center pieces and since they are hardened steel, it's hard to machine that surface.