No more r3vtard assist

[Sh3rpak!ng]

Just rebuild via tis to Oem
100% spec with 2 plates. It’s perfect for auto cross, if you have understeer its car or driver setup issues.

If you want the best turning diff for auto x it would be a torsen, sacrifice lock up on exit for max turn in speed and deal with the different style of suspension setup.

I have a torsen in one of my own cars currently, Autocrossed competitively back in 1999-2002, only circuit drive now.

Clutch type is king for circuit
For simple setup for autocross just feed the car a torsen and deal with the differences. If you are really seriously competitive (going for national championship) then a custom setup aftermarket clutch type lsd would be much better suited.

The Zf is good but is limited by ancient 1950’s dna.

Thanks for the input! Glad you're still around. No I'm not autocrossing or circuit driving for any serious competition. Just my own enjoyment for now, perhaps something more serious in the future. I have a good friend that used to autocross competitively and upgraded to a 3 clutch 30/60 ramp and used to (still does) rave about that LSD and what a difference it made for him. This was my inspiration to do nearly the same.

As I stated before the work to do the modifications will be free for me, or close to it so I figure why not? I'll have the rear subframe, trailing arms and axles out anyway.

Any chance you could comment on these questions? Or if you don't want to post here a PM?

Modifying ramp angles:

I have a full metals lab at my disposal to help reverse engineer surface finish, hardness, case hardness etc. but some tips here would save time. Biggest question I have is what kind of profile to cut and the difference between. What I mean is that I've seen ramps cut where each ramp is linear (similar to oem) making a "V" and also ramps cut where the trough is rounded making a "U". What's the difference?

Additionally, I assume that regardless of how the ramps are modified, I need to maintain the same stack height of the side gears and thrust rings.

Preload:

I found the TIS pages that detail stacking up the center section and how to measure the clearance to get proper preload setting for a standard setup 2 clutch 25% lockup diff, but I'm not clear on how to set it up further than that. If I want more or less preload, do I change thickness of the bellvue washers and maintain the same clearances stated in the TIS? What thickness washer equates to what static lockup %? If I want a 0 preload diff, do I remove all bellvue washers? What would the clearance be in this case? Or do I keep the bellvue washers but change the clearance?

[Wanganstyle]

deleted

[Wanganstyle]

deleted

[The Dark Side of Will]

Here's a photo of a 2016 bmw Motorsports ring gear with some runtime

[Sh3rpak!ng]

Bumping the thread from the dead...

I have recently been scouring the internet for information on rebuilding and upgrading the 188 LSD. I bought a 3 clutch rebuild kit on a group buy 2 years ago with the intention of doing a simple 3 clutch rebuild for my aging stock 188 LSD but have learned much since. Info seems to be few and far between but I've connected enough dots now to feel comfortable taking things to a higher level.

I have a unique opportunity to have most if not all of any machining, surface processing, heat treating done for free. I am the procurement manager for a large oem aerospace manufacturer and we do a shitload of business with aerospace machine shops and all associated finishing operations who've already expressed interest in helping me with my side projects :D

That said, here's where I'm at.

Modifying ramp angles:
I have a full metals lab at my disposal to help reverse engineer surface finish, hardness, case hardness etc. but some tips here would save time. Biggest question I have is what kind of profile to cut and the difference between. What I mean is that I've seen ramps cut where each ramp is linear (similar to oem) making a "V" and also ramps cut where the trough is rounded making a "U". What's the difference?

Additionally, I assume that regardless of how the ramps are modified, I need to maintain the same stack height of the side gears and thrust rings.

Preload:
I found the TIS pages that detail stacking up the center section and how to measure the clearance to get proper preload setting for a standard setup 2 clutch 25% lockup diff, but I'm not clear on how to set it up further than that. If I want more or less preload, do I change thickness of the bellvue washers and maintain the same clearances stated in the TIS? What thickness washer equates to what static lockup %? If I want a 0 preload diff, do I remove all bellvue washers? What would the clearance be in this case? Or do I keep the bellvue washers but change the clearance?

Lastly I'm just kinda looking for a sanity check on what I'm trying to accomplish and why. I'll preface by saying that I've only ever driven my E30S52 with a high mileage 100k+ stock 2 clutch diff. It's great fun but becoming a handful to manage autoxing having difficulty putting down power.

Here are my observations:

Massive understeer under braking and no throttle - trouble rotating the car through low speed tight turns (might be a driver mod needed here where I'm simply not getting my braking done in a straight line and still entering the turn too fast)

Difficulty putting down power anywhere but with car pointed straight (also may need driver mod to practice a lighter right foot)


So this is what I'm thinking. 4 clutch diff, little to no preload, ramp angles 30 acceleration, 60 deceleration (maybe higher deceleration?)


Any and all feedback is much obliged. I've got a spare low ratio (less than 2.93) LSD pumpkin on my shelf that I'll disassemble over the weekend to get started.

[Wanganstyle]

Deleted

[digger]

Not sure; perhaps consult with a materials engineer? Or ask ZF directly? I have a friend in the steering/knuckle department perhaps he can forward the query to a colleague -

Pinion doesn't seem to be coated
Ring is coated;

here is a bmw 3,91 Motorsports gear set (newest 2016 version).

Finish is very different between the pinion and ring

looks similar to phosphate (parkerize) which is used for breakin which wears off

[rcfanatic]

I have a Z3M diff that's in need of rebuilding. Production month 05/99, S52 engine car. Can anyone speak to whether the internals match the other 188mm diffs? 45/45 ramps, 2 clutches, extra spacer on right (bottom) side, etc.. ?

Also, can anyone describe how dramatic the power and coast understeer is on 4 clutch, 60% lock diffs? Will it increase lap times, or can suspension be configured to counter it?

Anyone have experience with the 60% lock characteristics?

[rcfanatic]

I have a Z3M diff that's in need of rebuilding. Production month 05/99, S52 engine car. Can anyone speak to whether the internals match the other 188mm diffs? 45/45 ramps, 2 clutches, extra spacer on right (bottom) side, etc.. ?

Also, can anyone describe how dramatic the power and coast understeer is on 4 clutch, 60% lock diffs? Will it increase lap times, or can suspension be configured to counter it?

[The Dark Side of Will]

Is the coating still adhered to the contact areas of the teeth (particularly the drive side) after use?

[Wanganstyle]

Deleted

[The Dark Side of Will]

do you want durability or not? this is racing; BMW motorsport obviously knows how to make racing products for BMW's

There's a whole world of racing outside of BMW's. Gear polishing figures prominently into a whole lot of the techniques used in that world.

Example: http://www.tigerrearend.com/

http://www.hotrod.com/how-to/transmission-drivetrain/ctrp-0902-quick-change-rear-end/

So you've mentioned a chemical coating, what chemical coating do they use?

There's basically nothing but casidiam/DLC (typically used on wrist pins in engines) that can take the kind of contact loads that rear end gears see without wearing away right quick.

[digger]

So you've mentioned a chemical coating, what chemical coating do they use?

[Wanganstyle]

Deleted

[The Dark Side of Will]

Seeing a photo of a gear in which one looks polished, one doesn't, and thinking the one that looked polished had been polished because Dinan was mentioned was an erroneous, but perfectly reasonable assumption. Allowance for the error of that assumption is why I used the word "appears".

REM polishing is worthless. Causes increase in tolerance and fractures from gear cutting root;

This is nonsense.

I never claimed that REM makes gears stronger. I am stating that your claim that REM causes them to break is in error.

Run a cooler if you want less temps

Coolers (and pumps, since BMW's run independent) have weight. Fluid has weight. Fluid has viscous drag. Polishing has neither weight nor drag.

Is it racing or not? If it's not, run a cooler. If it is, save the weight and have the gears polished.