Mitsubishi 3000GT & Dodge Stealth Forum banner

41 - 60 of 69 Posts
Joined
·
17,575 Posts
I don't rebuild transmissions for a living, but I find the 90% claim to be highly inflated.

I've had 3 getrags apart and the vcu was good in all of them. 2 18 splines and a six speed.

The VCU only seems to die if the car is towed improperly or otherwise mistreated.
 

·
Registered
Joined
·
1,298 Posts
Discussion Starter · #42 ·
Viscous Coupling - HowStuffWorks explains how a VCU works.

The teeth on that shaft look pretty bad. If you want to go the rebuild route, I would look take a look at all of the gears and just buy ones that are missing chunks like that plus a new shaft (I believe that gear is part of the intermediate shaft...) Clean up the case, put in all new bearings in it, (I would suggest) rebuild the synchros, and if the crack is only in the bell housing get a non-cracked one.

It's tough to tell but my guess is those "rabbit pellets" are from the chipping in the gears.

Transmissions can take a surprising amount of abuse. It wouldn't surprise me if that trans worked without any noises even if you fixed it without replacing any gears or the shaft.
Thank you helping. Sounds like good advice. Any suggestions where to buy bearings and syncros? I found a couple places that want about 800.00 for a complete rebuild kit, gaskets, syncros, and bearings. Also going to post a video of my gears with the mid-case off. I still cannot see any damage. Probably need to tear them down farther. BTW, the bellhousing has already been welded by someone else.
 

·
No more VR4!
Joined
·
798 Posts
Well, you can come by my house for the parts that I still have. Bellhousing, intermediate shaft, and others. :)

But if the test of a good VCU is that it can't be turned by hand, then I suppose mine isn't good, either. That said, I never noticed the car to feel FWD at all in its behavior, and routinely would get all the tires spinning around corners with a definite hint of oversteer with the old transmission, and no understeer. Put it in snow with bad tires and both rear wheels would spin, one front wheel would. So, I'm not sure if I buy that the VCU needs to be at that 75 ft-lb spec to actually be sending power to the rear wheels.
 

·
Registered
Joined
·
1,298 Posts
Discussion Starter · #44 · (Edited)
Not sure what our VCU looks like on the inside, but I did find a shaky video from a guy rebuilding one for a Honda. My guess is ours is similar except for the outer c-clip business.

 

·
Slowly rebuilding...
Joined
·
702 Posts
I'm not sure who said it but getting a long table, taking your time and documenting things as you go is a HUGE help. The last thing you want once you put it all back together is say "Where did this shim come from?"

800 sounds about right but if you have the time you might be able to save some money searching for similar bearings. No auto parts store carried a bearing for the vehicle so I took some measurements and looked. Took a few days to find it, but the difference was 20 bucks versus 120 from the dealer for one bearing.

As for the bell housing, I'd try to find one that wasn't re-welded. Do you have a picture? Level of concern about it weighs heavily on location.

Only the cars with blown VCUs are 100% fwd. The VCU works similarly to a conventional center differential where all 4 wheels provide the driving force. The difference is that there's no solid connection (like toothed gears) connecting the front and rear so it allows for a little slip between the front and rear. The input side of the VCU is rotated by the transmission which will spin the goo inside. The goo inside is thick and will resist moving. This resistance (think friction and Newton...) spins the output side to drive the rear wheels to minimize the difference in rotation speeds between the front and rear wheels. It's a lot to visualize... A simple model would be to take an egg and spin it on the counter. Grab the egg briefly to stop the egg from spinning then let go. It will continue to spin because the yolk still rotates a little after you stopped the egg.

/novel...
 

·
No more VR4!
Joined
·
798 Posts
So this poses a question to me of what constitutes "blown" vs "weak"? Like I said, my old trans definitely did not have the 75 ft/lbs, but it also definitely did have power going to the rear wheels. There must be some middle ground.
 

·
Registered
Joined
·
1,298 Posts
Discussion Starter · #47 ·
So this poses a question to me of what constitutes "blown" vs "weak"? Like I said, my old trans definitely did not have the 75 ft/lbs, but it also definitely did have power going to the rear wheels. There must be some middle ground.
I would imagine that even if a small amount of silicone is left in the vcu it would be thrown to the outside of the coupling when running the car and allow some functionality when slipping occurs between the front and the back. During a test the fluid is probably more free to spread out and possibly not bridge the gap between the plates as much.
 
Joined
·
17,575 Posts
Its really simple to see if a vcu works in a car that's driving. Do a decent launch. Do the back tires spin? If so or you just dead hook everytime its okay. If the fronts spin excessively and the rears don't its junk.
 

·
Registered
Joined
·
1,298 Posts
Discussion Starter · #49 · (Edited)
Its really simple to see if a vcu works in a car that's driving. Do a decent launch. Do the back tires spin? If so or you just dead hook everytime its okay. If the fronts spin excessively and the rears don't its junk.
I agree but I found this video of a test. I believe all of the other wheels are on the ground,so all of the rotation is forced into the VCU. Nice thing about this is the time to drop the jug could be measured and compared to others.

https://www.youtube.com/watch?v=huvPUNzhUFA
 

·
Registered
Joined
·
1,298 Posts
Discussion Starter · #50 ·
Found a reference that says the stock vcu only requires 10ft-lbs of torque and that most of them can be turned by hand. Also SCE came up with an alternative to the VCU. It is pricey but sounds really cool.

Supercar Engineering
 
Joined
·
17,575 Posts
personally I wouldn't rebuild that trans you had. pay for a better one, get a better core, or eat the core charge from jacks transmissions.
 

·
Registered
Joined
·
3,346 Posts
It takes a lot to blow the vcu goo into your trans.
I have owned like 10 of these and never had one puke it's vcu.
It's usually a low or no fluid condition that cooks them and makes them puke.

That 90% figure everyone claims as having bad vcu's is a myth.

You toasted that thing.
Prob be cheaper and more reliable to find a good used one.

Stop touching it though. You don't seem to be very well versed on trans disassembly so thinking u are gonna rebuild the thing and have it function properly is a bit of a pipe dream.

Send it out or buy a new one.
 

·
Slowly rebuilding...
Joined
·
702 Posts
The teeth on the gears in DSC 0309 and 0312 are done. Can't tell if 0309 is part of the shaft but 0312 is. The other gears look fine to me. Replace those two parts, buy new bearings, seals and VCU. You don't HAVE to rebuild the synchros if you want to save some money but you are already in there....

If you do go the route of rebuilding it, be sure to clean everything and clean out any oil galleys. You don't want the possibility of any metal blocking any oil flow.
 

·
Registered
Joined
·
1,298 Posts
Discussion Starter · #55 ·
The teeth on the gears in DSC 0309 and 0312 are done. Can't tell if 0309 is part of the shaft but 0312 is. The other gears look fine to me. Replace those two parts, buy new bearings, seals and VCU. You don't HAVE to rebuild the synchros if you want to save some money but you are already in there....

If you do go the route of rebuilding it, be sure to clean everything and clean out any oil galleys. You don't want the possibility of any metal blocking any oil flow.
Thanks again! Both bad gears are part of a shaft. Forest said something about them being made that way from the factory. I think it is due to the way the splines are rolled. I am going to compare those to a friends spare transmission to see if his are better.

Yes there is still a bunch of silicone crap everywhere. I cleaned the outside of the vcu with a brass wire wheel. That is the only thing that worked well.
 

·
Registered
Joined
·
1,298 Posts
Discussion Starter · #56 ·
It takes a lot to blow the vcu goo into your trans.
I have owned like 10 of these and never had one puke it's vcu.
It's usually a low or no fluid condition that cooks them and makes them puke.

That 90% figure everyone claims as having bad vcu's is a myth.

You toasted that thing.
Prob be cheaper and more reliable to find a good used one.

Stop touching it though. You don't seem to be very well versed on trans disassembly so thinking u are gonna rebuild the thing and have it function properly is a bit of a pipe dream.

Send it out or buy a new one.
Been looking for a good jdm used one. The transmission was likely ran dry because I did not find a drop of oil in it when i opened it up. There was a drain plug leak.

I agree with you about not being experienced, but It seems to be a lot easier than I thought. I guess ignorance is bliss. I may continue unless I get a good deal on a used one.
 

·
No more VR4!
Joined
·
798 Posts

·
Registered
Joined
·
1,298 Posts
Discussion Starter · #58 · (Edited)
I agree if you mean fill the VCU with gorilla glue. Thought about just drilling a hole in the case and filling it up. Instantly locked VCU!

Not sure if I am thinking about this correctly but If your tires never slip, the power never get's to the rear end. To activate the viscous coupling there needs to be a significant difference in rpm between the front and the back. If all the tires are traveling straight forward then they all rotate at the same rate. If you are going around corners at a decent rate without slipping your rear end should be tracking the front end.

So, the VCU only sends power to the rear end when the following occurs:

Driving in the snow
Driving in Mud
Pushing your car to the limit so hard around a corner that you lose traction at the front or back.
Bad launch causing a tires to slip.
In a parking lot, cutting the wheel so hard that your rear tires navigate a smaller radius than your front tires.

I guess it is no wonder that 9/10 of our vcu's are not working properly and nobody seems to notice until they see the goo.
Ok I think I figured out that the center diff, does distribute the power when the VCU is working. The outside of the planetary gear system is driven and the rotation of the planet gears is tied to the front wheels and the inner gear is tied to the rear wheels. The rear and the front are loosely coupled with the VCU. So power just goes to whichever wheel set is turning slower. If they are all turning at the same rate power is split.

http://www.stealth316.com/2-awd3.htm#cdvcu
 

·
Registered
Joined
·
1,298 Posts
Discussion Starter · #59 · (Edited)
Finally got all of the gear clusters off of the bell housing. All the gears look great. I am thinking that whenever the outer housing was cracked they shredded the output shaft. They replaced the output shaft but did not fully clean out the transmission. Found a guy on ebay that rebuilds VCU's. He said about 9/10 of the ones he gets cannot be rebuilt due to the inner plates being damaged where they attach to the i.d.

Spent a while cleaning the housings up at the car wash.

Here is a picture of the transmission weld.
DSC_0324.jpg

Mostly clean housing.
DSC_0325.jpg

Lastly, Here is a link to a cool animation of a planetary gear similar to our center diff. Main difference is there is an extra set of planetary gears that allow the planets and the sun to rotate in the same direction. Make sure you click on the options to hold different parts of the gear to see what happens.

http://www.mekanizmalar.com/transmission.html
 
41 - 60 of 69 Posts
Top