I was looking at the Cup Diff, but decided against this as quite a few have broken the hats clean off, especially as I would be running it in the Turbo... So it was between the GT or trying to locate a RSR Diff and I managed to find one last week here in UK... I have had it inspected and it was given a clean bill of health, plates were ok, but might just fire some new ones in anyway.

 

Mikymu

I find it amusing you say you can do things with the GT3 that your M3 can do - with its stock M-diff.

You shoud look into getting a real data acquisition unit i.e. Traqmate (not u in front of your tv with a stopwatch lol) and a chase cam and see what lap times you are running and analyze where you can improve and what are your strong points and weak points on a track over a season.

Since you are coming from an E46 m3 that looks prepped, it would be interesting to see what lap times you are running with a GT3RS.

Nice write up

 

Hey Tom, Like I have said before, you must be a great mechanic. I am still trying to take my tires off after 1 hour lol. I love working on my car as much ... or even more than driving on the track. I tend to sip my tea, take couple photos and write some notes for DIY write up before moving to the next bolt. Wife was glad after I finally put the LSD back.

Yes, Matt will build the LSD to your specific need. 90 lbs-ft is pretty aggressive. money saving is the key in rebuilding the OEM LSD since no need to shim - just drop and go!

RSR diff ... wow, 200 lbs-ft preload?

 

I must coment a thing

Becouse you only hade 2 lbs left of preload doesnt say you have a oppen diff, that has nothing to do with the lock up working or not, but you are right there should be the right preload in there

 

lol, you know what I mean ... it's pretty darn close to an open diff. The rebuild LSD has been working great since install. No noise, no issue in wet road and does it's job w/o fuss

 

No it not an open diff anyway, i still locks up but it will not work as it should but the lock is still there the preload has a diffrent job

 

^exactly, that measurement applies to the preload only, not the locking action of the diff under load, which is what the ramps apply

 

Exaktly..

 

Yes and no. As I tried to explain earlier in the thread the preload can be used as an indicator of wear on the LSD but low or high initial preload does have a different function and relationship to how the differential works.

I will try and explain it a little better. The reason that you can use the preload measurement as an indicator of the condition of the LSD is because it gives you an idea of how much wear the friction discs and plain plates have experienced. I'll make an example, though with made up ballpark numbers so that it's a little more clear.

Let's say that a GT3 LSD leaves the factory with a 1.3mm gap between the body and the stack height. If the differential wears .1mm and now has a 1.4mm gap the amount of preload that belleville washer provides is going to go down. That's something you can measure if you take the LSD apart but not something you can calculate while the LSD is in the car other than seeing that the preload number has changed because the stack is looser. Does that make sense? What we are seeing is that the latest variants of factory LSD's lose their ability to provide lock up with as little as .1mm of wear. For comparison, our LSDs generally require .4mm or more of wear before they stop locking.

Furthermore, it is correct to say that just because the preload on an LSD has dropped to zero it's not automatically true that the LSD is worn out. But in the case of these GT3 LSDs we're finding that it's a pretty good indicator. Because of how steep the cutouts are on the newest factory ramps, they just don't allow the crossshaft very much movement at all. Without much movement and the ability to push the ramps apart very far they aren't going to lock very well at all even with the bare minimum of wear.

However the real indicator that I trust more than any breakaway number is what the car owners are telling us. They are telling us they are experiencing wheelspin in corners where it wasn't present previously. They are telling us that their rear ends have gotten loose under hard breaking and on corner entry. It's what the drivers can feel that's a better indicator than any garage test we can come up with.

 

Matt got your email... will get back to you soon... inspecting 2nd gear anyway.

 

Well, since we're showing off...

 

both look a stunning bit of kit

 

Matt

LOL on showing off but your GT1 LSD looks mighty nice. Thanks for taking the time dissecting the question on preload and indication for LSD wear. It was easy to follow your explanation. I just wish I can get back on the track soon. I can only drive around the block so many times pretending I am on the track before I get bore out of my mind lol. Next event at Laguna is not till 2/1

 

I am really impressed with the new billet cup car LSD bodies. They really are gorgeous.

I know you had this apart. Any chance it's still open and you can snap a shot of the ramps? I would also be interested in the number that's stamped into the edge of one of the four "clover" fingers on the ramps. I'm curious if they changed the ramp angles again on the newest ones.

 

You've got it easy. I don't expect High Plains to be clear until well in to April.