So im removing the center diff in a 1g awd auto and it got me thinking about the viscous coupling and its importance.

When welding the center diff i see that some leave the vc alone, some cut the vc down, while others remove it completely. How much does each effect the overall strength of the center diff? With as tight a tolerance that the vc fits in there, there has to be some support gained from leaving it in there? Shaft support or relieve some stress on the outer gear?

There isnt much info on this topic in particular out there. Opinions?

I did some research on it when I rebuilt my TSI AWD auto a few years ago. Someone was making a coupler to eliminate the VC at the time and it looked like it wasn't much bigger than the shaft diameter. I have also seen picture of them cut apart and the inside diameters welded together. I came away from it thinking it was just better to leave it alone, but mine is a street car and I never bring it to the track. Your application may be different. The good thing is that if you change your mind its easy enough to get too while its still in the car.

If it was me, I'd just weld the vcu and leave the cd alone on an auto. It's harder to weld, and it doesn't see near the shock loads a 5 speed does. I've been running a welded vcu on my car with a normal diff for some time. I do shim the diff tight to basically lock it though.

bastarddsm said:

If it was me, I'd just weld the vcu and leave the cd alone on an auto. It's harder to weld, and it doesn't see near the shock loads a 5 speed does. I've been running a welded vcu on my car with a normal diff for some time. I do shim the diff tight to basically lock it though.

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I'm sending it out to be done. I dont want to make a jig just to do one diff and i dont feel comfortable with controlling the heat properly with what i have here.

With that being said, and both already being out, would you still weld just the vc? I also should have mentioned that the diff has already experienced thrust washer failure.

Any other opinions on this? Hypothetical even.

It appears to me that the vc would add a considerable amount of strength to both the case and the shaft vs leaving it out. As well as removing some stress from the outer gear. Opinions and suggestions are welcome.

Shep trans told me they use a sleeve with a welded diff to keep the output shaft in place. That also probably locks the two splines and assists the welded joint.

er82 said:

Shep trans told me they use a sleeve with a welded diff to keep the output shaft in place. That also probably locks the two splines and assists the welded joint.

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So basically they run a vce even with a welded center diff? Thats good to know.

Now im speaking on autos specifically, but without the vc it leaves a large amount of the shaft unsupported. Not only that but a complete vc has a few inches of surface area that rides against the case on a bearing race. The tolerance is so tight that it has to add support to the shaft and the case, which in turn should help with stress on the diff as well. Win, win, win it appears. Unless im just looking into this too much.

Imo, a viscous coupler eliminator and 4 spider diff would be a great street/strip option on the cost effective side.

That doesn't make any sense at all. ^

bastarddsm said:

That doesn't make any sense at all. ^

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I should clarify, "without spending money on lsd's"

Then I could be wrong still. I'm by no means a dsm drive train expert, just an idea from what I do know about them

A vce locks the diff. It's the same as welding the diff. No sense spending the money on a 4spider if your just going to lock it up.

gotcha! just shows my limited knowledge of the awd transmission

bastarddsm said:

A vce locks the diff. It's the same as welding the diff. No sense spending the money on a 4spider if your just going to lock it up.

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Actually it does make sense. With VCE, you still sent FWD torque through the spider gears, so they can brake. And this failure is even more likely if you have a worn center diff with excessive play in your gears (very common on used units). Now, they aren't seeing as much load as when you have a working VC, but they can still break.

I was one of the first people to use a VCE, back in the late 90's. And I always used it with Speed Design 4 spider diff. That used to be "the norm" back then.

However, I have also seen a VCE which broke off from a differential, shot out of the tranny and seized the front PS wheel, causing a nasty accident at the track. I would not RACE on VCE if you have a motor making more than 500ft*lbs of torque!

I suggested it because this thread was geared toward automatics, and they don't have the shock loading of a 5 speed. With a 5 speed it doesn't make any sense to spend the money on a 4 spider if your just going to lock it up when it's so easy to weld.

Different strokes for different folks I guess.

backtrack, is the speed design cross shaft still availible? Did those drive off all 4 posts? or just the 2 like stock?

It's still listed on the TMZ Performance website, though it is from Beyond Redline Performance.

http://tmzperformance.com/Mitsubishi Transmission Parts.html

I had been hoping to send one of my spare transmissions to him, but it doesn't appear the website has been updated in a bit and says he still isn't taking more work for now. I may try my own rebuild if I can find the time.

No, that's not the speed design one, that's the beyond redline one. I've been through 2 of them, neither of them survived any abuse at all. A beat up stock 2 spider lasted better.

GRNDSM said:

Actually it does make sense. With VCE, you still sent FWD torque through the spider gears, so they can brake. And this failure is even more likely if you have a worn center diff with excessive play in your gears (very common on used units). Now, they aren't seeing as much load as when you have a working VC, but they can still break.

I was one of the first people to use a VCE, back in the late 90's. And I always used it with Speed Design 4 spider diff. That used to be "the norm" back then.

However, I have also seen a VCE which broke off from a differential, shot out of the tranny and seized the front PS wheel, causing a nasty accident at the track. I would not RACE on VCE if you have a motor making more than 500ft*lbs of torque!

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i think the vce was only created so people with working spider gears could dyno there cars in FWD. welding the center operates the same as using a vce. it is both cheaper and stronger to weld.

I welded many diffs here and just used old taper bearing to hold shafts in place. you have to grind end of bearing to fit in groove nice. first used stainless band clamp to hold the bearing tight in the groove. then a small tack weld on clamp gear so it doesnt back out. later just ground a groove in big end of taper bearing and used a heavy grade of tie wire to hold it in. both methods are super ghetto but never had a problem. bearing is only there so tcase can be pulled off with out shaft coming out with it. had one trans come in here with no retainer bearing. it was quite tricky getting the case off, but can be done.

bastarddsm said:

No, that's not the speed design one, that's the beyond redline one. I've been through 2 of them, neither of them survived any abuse at all. A beat up stock 2 spider lasted better.

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Oops, I didn't realize that. I had remembered that there was one made and the manufacturer had two names. Maybe it was the Shep Racing site that used to list it. I was happy because I thought they (the cross shafts) were still around. Sorry to derail the thread a bit.

94awdcoupe said:

i think the vce was only created so people with working spider gears could dyno there cars in FWD. welding the center operates the same as using a vce. it is both cheaper and stronger to weld.

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This is ancient history now It all started when Extreme Motorsports talked how they were running 10's on a stock center diff (this was back when that was one of the fastest DSMs in the world). Everyone was calling BS on it so they came out and clarified that they were using a welded viscous coupling.

I took a farther look at the VC and realized that there is LOT of extra weight, if you aren't going to use it as a VC. So I machined off EVERYTHING that wasn't needed and welded it together. I called it a "Solid coupling" (as opposed to Viscous Coupling). I sold a few units and then I got a phone call from a guy who said that made them from a billet and he called it a VCE. He was asking my permission to sell them since I started making/selling them first. I think it was a courtesy thing, as I had no patent on this thing. Besides it was Extreme MS original idea anyway. So I said "be my guest".

Anyway, my point is that was originally meant for racing! I would install it for drag racing and then remove it for autox! Naturally, I also used it to dyno my car in FWD mode, as AWD dynos were very rare in the late 90's/early 00's.

I wasn't until mid '00s that I saw a failed VCE that broke off the center diff and destroyed EVERYTHIG in that corner! I stopped recommending it for drag racing after seeing those photos. But this was 700-800hp car, I still think that they should be OK for up to 500-600hp range.

Wow that is interesting info there. Its neat hearing from someone who was on the ground floor of the idea.

GRNDSM said:

I wasn't until mid '00s that I saw a failed VCE that broke off the center diff and destroyed EVERYTHIG in that corner! I stopped recommending it for drag racing after seeing those photos. But this was 700-800hp car, I still think that they should be OK for up to 500-600hp range.

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What are your opinions on the vc's role in supporting the shaft and/or case? And if so, would that support take stress off of the outer gear?

What negatives would there be to running both a welded VC and a welded center diff?

I ask, because i was planning to run a welded VC and welded center diff if for nothing else but the piece of mind.

I do not think that VCE is necessary if you have a welded center diff. Just use one of those sleeves that keeps the ball in place.

If fact, the only way they would work together if you weld one part first (ether diff or VC), install VC on the diff and then weld the other part.

If you try to install a VCE or previously welded VC onto a welded center diff, you have about 1% chance of them fitting together .

Auto center diffs are more susceptible to cracking and breaking than our 5-speed counterparts. I've got cracks in mine from just a 14B/2.4 setup, even my old 2.0/16G setup that trapped in the 90's in the 1/8th, was showing signs of stress. I think you're over-thinking it a wee bit. Weld the center diff, ignore advice from those who have never used, or even like, automatics. No politics, just some advice. There are things on Autos that you do, that wouldn't make sense on a 5-speed, but they work brilliantly.


Edit: Welding my center diff and leaving the VC in solved all the problems. Turning was kind of a PITA, but DSM turn radius suck anyway...just leave it in. Other experienced auto guys[key word AUTO guys] feel free to chime in.

Right, EVERYTHING I said was regarding a 5sp transmissions! Perhaps you will get a more specific automatic advise when you post your question in automatic forum section .

Out of curiosity, what cracks in automatic center diff?

I really think on an auto unless your are going to be launching the balls off it, I'd leave it open. A locked center diff really makes the car suck.

The 5speeds are hard on the cd because of the shock loading. The auto will kill the transfer gears way before you hurt the center diff. Any car will kill the CD if your letting it spin one end excessively.

Well I feel a little less stupid. I was thinking in terms of distributing load evenly through the center diff, but like I said, im no expert an I haven't torn a dsm trans down fully and just know the most basic power transfer theory for them.

Good to hear some back story and actual use tho!