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Rear differential, excessive play and horrible noises.

gtluke

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Car clunks bad under acceleration from pass side.
I've never seen or heard of this happening on our cars, but I think my rear diff is shot. I can turn the driver side rear wheel between 1/8th and 1/4 turn before the pass side even engages, and when it does it sounds pretty crappy. If I turn the driveshaft, same thing. WAAY to much turning to engage the wheels. I thought my ring and pinion was all out of whack or falling out so I took the cover off and repeated. All the slack is in the actual differential. The ring gear still has the normal spec play in it from when I set it up a few years ago. I took the diff out, but I'm not even sure what I'm looking for. How the hell does the LSD work in our cars?
Either I'm crazy confused or I have an open 4 bolt rear end.
The housing in my car is the original 1990 3 bolt housing out of Nate's yellow race car. The ring/pinion and diff are out of an EVO 1, the 4 bolt axles are out of some piece of crap automatic that Nate junked like a decade ago.
I find it hard to believe that an evo 1 has an open rear, or that it had enough miles on it to do this. I know the rear was from an evo1 because it's got the 3.909 gears and 2g style splined axles.
Opinions?
I think I have another rear diff somewhere, I hope.
 

gtluke

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1163969818_DqCrY-XL.jpg

1163970471_zHpzR-XL.jpg
 

CSMShaun

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If you were using the Evo rear diff what transmission were you using?

The LSD is comprised of plates that press against the spider gears inside the differential.

Have the bolts that hold the ring gear to the differential come loose?
 

If both rear wheels are off the ground and you turn one wheel and the other spins opposite direction, its an open diff. Otherwise its some form of lsd.
 

3rdstrikedsm

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That's a viscous lsd and it almost looks as if the viscous fluid has come out of the vc sealed unit?

My evo 1 had a mechanical lsd in it as has all of the other ones I have worked on over the years however I am pretty sure Ralliart offered a viscous unit that was a rare factory option if memory serves me correctly.
 

gtluke

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Quoting CSMShaun:
If you were using the Evo rear diff what transmission were you using?

The LSD is comprised of plates that press against the spider gears inside the differential.

Have the bolts that hold the ring gear to the differential come loose?



I have the WQNK EVO/RS trans
The bolts were all tight,
 

gtluke

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Quoting 3rdstrikedsm:
That's a viscous lsd and it almost looks as if the viscous fluid has come out of the vc sealed unit?

My evo 1 had a mechanical lsd in it as has all of the other ones I have worked on over the years however I am pretty sure Ralliart offered a viscous unit that was a rare factory option if memory serves me correctly.



Hmm, I'll have to clean up that one side spider gear, I could swear I couldn't figure out a way that thing would "slip" but it's definitely big enough to contain the VCU
What makes you think it leaked?
 

3rdstrikedsm

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It almost looks like there is a film of black viscous goo coating your internals however it's hard to really tell from the pic either that or you have some seriously dirty gear oil /ubbthreads/images/graemlins/smile.gif
 

gtluke

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Probably had about 25k on it. I'll take a closer look at the oil tomorrow
 

3rdstrikedsm

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That viscous fluid feels like a real thick grease almost and usually won't just wipe off with a cloth rag either so it should be easy to tell it apart from the gear oil.
 

gtluke

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Well the spider gears had like .1" of play in the feeler gauge spot, it's supposed to be .03"
I also took this time to tighten up the backlash, I had about .012 and I had enough random shims from other rears that I got it dead nuts on .008

I've never seen a mitsu rear end wear out the diff like that, I don't even think I recall anyone here ever having any sort of issue. Weird.
Well there you go ladies, a clunk noise from your rear could very well be your spider gears about to eject themselves from the carrier.
I actually had that happen once on my mustang like 10 years ago, WAY too much abuse on the stock diff that I rigged up with extra clutch disks that the spider gears shot out on the highway and momentarily locked up the rear. I almost sh*t my pants. Oddly enough everything moved out of the way enough that it free'd up and I drove it home with a constant clanking. Pinion had a huge chunk taken out of it so it used to tick when I drove after that /ubbthreads/images/graemlins/wink.gif
I would be really annoyed to try and find another 3.909 ring and pinion. I should really have a spare set.
 

DynastyLCD

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this is very interesting. i dont often hear of people having these problems with their rear ends, or even re-shimming them as such. my 4 bolt LSD rear makes a slight speed related whine, im 90% sure its coming from either the rear end itself, or possibly a rear wheel bearing. 100% speed related, only heard while coasting in neutral. however, the cars too loud to see if it gets louder with RPMs as well.

time for a write-up on differential shimming?

good read and interesting post! /ubbthreads/images/graemlins/applause.gif
 

gtluke

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Shimming the gears to the housing is the same on all rears, there are a million writeups on the internet. The basic premise is that you want the correct tooth engagement, and since the ring and pinion are angled, that engagement can be changed by moving the pinion in and out and the diff left and right. Checking pinion depth is a pain in the balls and an even bigger pain in the balls to adjust, so I ignore it /ubbthreads/images/graemlins/wink.gif
Setting backlash is easy, you just measure the play between the gears as you rock the pinion gear back and forth, it has a very slight play between teeth. You measure that play with a dial indicator mounted on the rear. If it's too loose, you need to move the ring gear towards the pass side. There are shims on either side of the bearing cups. Both of mine were .103 size so swapping t hem would do nothing. Another rear I had had a .114 and a .094 so I used that with the thicker one on the driver side. It increased the overall thickness by .002 but that's nothing. You can shim the diff in there tighter to the bearings by increasing the width of both sides, but I don't even know how to measure that. I just know that it's a huge pain in the ass to get the diff in there as is, so I'm not going any tighter /ubbthreads/images/graemlins/wink.gif

Maybe I'll try and find some shims to shim up the spider gears and do a writeup on that one day. But mine is so loose that the gears themselves must be shot. I do have a 3rd 3 bolt diff, they probably use the same spider gears, but the side gears are different.
 

496of2000

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I've been using 3.909 diff. since around 2002 never had problems with it. I brought it to a local shop called progear to shim it and set the backlash.
 

gtluke

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Awesome, I didn't recall anyone else using the 3.909 besides a hillclimb galant I saw in the rally classifieds once.
I don't anticipate having a problem with the 3.909's other than I set them up myself and didn't set the pinion depth. I'm hoping that the mitsu gears are like the ford gears, in that their tolerances are so high on these parts that you basically don't need to do it. I know that if you use aftermarket gears like Richmond's in a ford, their tolerances aren't as good and don't match and you absolutely need to check pinion depth.
 
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