vr4 rs 3.9 ratio into ggsr (quick Q)

[mattrat]

ohk im buzzed by all this aswell, i see that the only thing that would truble a vr4 box being used for FWD is just that the transfer case output shaft would stll spin.. now i know it wouldnt be good to have but in a vr4 you could drop the tailshaft and just run it in fwd couldnt you and let the transfer spin still? why does all this welding have to happen when its a mere shaft spinning which may use 1/5 of a hp to spin?

sorry for the noobness but i am by far a gearbox technician..

 

[GVR40]

the shaft itself may only take a little bit of power to spin, but because they have a viscous centre diff, it wants to send 50% of the power to the arse end of the car, which isn't there, thats the way the gearboxes are set to work

 

[MDK87]

I think the way a diff. works Matt, it won't allow that to happen. If the output shaft is spinning, all of the torque is put through to this freespinning shaft, and virtually none to the other loaded outputs???
I think.........well thats a dodgy explanation, look on howstuffworks to understand it a bit better, its pretty good.

Btw, on my gearbox which was already converted, the output shaft didn't exist. It was plugged up with a welsh plug siliconed in.

EDIT: Oops, GVR40's already explained it properly, hehe

 

[mattrat]

ahh i get it, same as a non lsd fwd ith one wheel touching the ground and the other in the air.. all power to that free wheel.. forgot about the torque spread..

 

[rob323]

I think the way a diff. works Matt, it won't allow that to happen. If the output shaft is spinning, all of the torque is put through to this freespinning shaft, and virtually none to the other loaded outputs???
I think.........well thats a dodgy explanation, look on howstuffworks to understand it a bit better, its pretty good.

Btw, on my gearbox which was already converted, the output shaft didn't exist. It was plugged up with a welsh plug siliconed in.

EDIT: Oops, GVR40's already explained it properly, hehe

That's got me thinking more about why your centre diff crapped itself.

Just thinking about the centre diff and what happens if the viscous is welded or you are using a viscous coupling eliminator (and if someone with more knowledge could pipe in, it would be appreciated).

This is my take on what happens (If I'm wrong, please let me know, I'm far from experienced in this side of things).

The drive comes through the input shaft, down through what ever gear you are in and finds it's way to the centre diff. The centre diff then sends power to the front and to the rear.

The drive going to the front goes to the front diff of course and then out to the wheels which assuming they both have traction, load up both planetary gears in the diff and therefore they don't rotate.

The drive going to the rear then goes through the viscous coupling (which is welded or eliminated) then to the right angle drive/ drive shaft etc. Now because the viscous is "locked" equal power gets sent to both the front and the rear, but, all that power still has to be transferred through the plantary gears in the centre diff.

To answer your question, I reckon my initial thoughts about the centre diff not taking any load are wrong. I say get the centre diff welded as that will take alot of the load of the planetary gears and use the diff housing to help them.

Does Mr Gears still get on here at all?

 

[GVR40]

i would have thought that the viscous coupling comes before the centre diff tim, to give equal power to the front and back, the centre diff then seperates the power to the front and back wheels equally...

 

[MDK87]

That's got me thinking more about why your centre diff crapped itself.

Just thinking about the centre diff and what happens if the viscous is welded or you are using a viscous coupling eliminator (and if someone with more knowledge could pipe in, it would be appreciated).

This is my take on what happens (If I'm wrong, please let me know, I'm far from experienced in this side of things).

The drive comes through the input shaft, down through what ever gear you are in and finds it's way to the centre diff. The centre diff then sends power to the front and to the rear.

The drive going to the front goes to the front diff of course and then out to the wheels which assuming they both have traction, load up both planetary gears in the diff and therefore they don't rotate.

The drive going to the rear then goes through the viscous coupling (which is welded or eliminated) then to the right angle drive/ drive shaft etc. Now because the viscous is "locked" equal power gets sent to both the front and the rear, but, all that power still has to be transferred through the plantary gears in the centre diff.

To answer your question, I reckon my initial thoughts about the centre diff not taking any load are wrong. I say get the centre diff welded as that will take alot of the load of the planetary gears and use the diff housing to help them.

Does Mr Gears still get on here at all?

Lol, I don't even know what the planetary gears are, its time I delve into the depths of that documentation you sent me Rob.
About Mr Gears, yeah I tried to attract his attention before, but I don't think he gets on here much anymore??
I sent him a very detailed email and I spoke to him on the phone not long ago about it, but he was rattling out words that I couldn't even comprehend!
So unfortunately, I didn't come out any the wiser.

i would have thought that the viscous coupling comes before the centre diff tim, to give equal power to the front and back, the centre diff then seperates the power to the front and back wheels equally...

Lol haha, I saw it Craig!

 

[blackvr]

Guys, I have done a lot of these boxes. You are on the right track re the centre diff. Think of the viscous coupling as an external LSD to the centre diff. Its external because there simply isnt room to put it in the smallish centre diff housing. The VCE is the easy way of locking the box for front wheel only drive ( or rear wheel drift action in a VR4 if the front driveshafts are eliminated. However, the planetary/side gears of the centre diff are still loaded every time torque is put thru the gearbox. Thats why a few of you guys smash the planetary gears on hard launching/ gearshifts.

This is even more pronounced in turbo cars. So in reality, if the side gear of the bottom of the centre diff is welded, the viscous coupling and its associated hollow input shafts can be done away with. The centre diff is still supported by both tapered bearings ( upper and lower). Obviously it takes a fair bit more work to pull the box apart, but it ends up being lighter.

After having customers continously wreck centre diffs with only VCE's being fitted, I now will only modify centre diffs and not bother with VCE's.

Cheers Mike

 

[rob323]

Thank you, that's a lot more reassuring coming from someone with experience on these matters.

 

[MDK87]

Hey guys, look what I found!

http://www.geocities.com/spencerhut/talon/center_differential_repair.htm

http://www.ecanfix.com/~mdhamilton/centerdiff.html

Man those spider gears look just like mine!

So as I see it, there are three options, either weld the centre diff.
Get a centre diff. with four spider gears.
Or machine out the original diff. to allow the fitment of four spider gears.

I guess the second and third options would be most preferable, but the first would be the most affordable/easiest. The only downside to welding it would be that (in a FWD situation) the driveshafts would be locked together, putting alot of strain on the gearbox (not sure what exactly) when performing tight turns etc. and a less important problem would be tyre wear. (although low profiles ain't cheap aye! haha )

I'm not sure if there'd be anywhere that'd wanna machine the diff. out, not to mention where they would get the dimensions etc. from, but yeah, it really boils down to either welding the diff. or buying a complete new centre diff. with 4 spider gears in it from teamrip etc.

So my next question is, if a new diff. with four spiders were used, what exactly "locks" the transmission to FWD? You'd still have to use a VCE, or welded viscous coupling hey?

Maybe I should just get the diff. welded and chuck out the two spiders + viscous coupling? What exactly will be affected if this method is used?
The guy who done the writeup in the link above says, when doing tight turns, the original gearbox would be strong enough to handle this strain, but the drivetrain would have dramas. - What drivetrain? It's FWD, theres only the CV shafts hey?
I'm seriously contemplating just welding the diff. up.
I'd like to know your thoughts guys. Thanks heaps for your input so far.

P.S - Sorry Matt, I'd have started another thread, but there's already so much info in the above posts, and it seems like you already got the answers you were looking for. I hope you don't mind champ?

 

[rob323]

So as I see it, there are three options, either weld the centre diff.
Get a centre diff. with four spider gears.
Or machine out the original diff. to allow the fitment of four spider gears.

I guess the second and third options would be most preferable, but the first would be the most affordable/easiest. The only downside to welding it would be that (in a FWD situation) the driveshafts would be locked together, putting alot of strain on the gearbox (not sure what exactly) when performing tight turns etc.

You are only locking the centre diff, the front diff is still open, the above only applies to all wheel drives so don't worry about it.

So my next question is, if a new diff. with four spiders were used, what exactly "locks" the transmission to FWD? You'd still have to use a VCE, or welded viscous coupling hey?

Yes.

Maybe I should just get the diff. welded and chuck out the two spiders + viscous coupling? What exactly will be affected if this method is used?
The guy who done the writeup in the link above says, when doing tight turns, the original gearbox would be strong enough to handle this strain, but the drivetrain would have dramas. - What drivetrain? It's FWD, theres only the CV shafts hey?

Again, he's referring to all wheel drives.

Now you just need a front lsd as well 8) .

 

[GVR40]

something like this rob?

http://www.slowboyracing.com/estore/product.php?productid=1241&cat=4776&page=1

also a VCE

http://www.slowboyracing.com/estore/product.php?productid=1969&cat=4776&page=1

 

[rob323]

No, a real lsd, like the one I have in a gearbox at home which I might sell for an insane amount if a suitably insane offer was made for it :wink: .

Theoretically, if the centre diff is fully welded up, I don't think you would need a VCE, like Blackvr said, ditch it all totally.

 

[MDK87]

Yeah Rob, I'd think that the VCE (or welded viscous coupling), the two spider gears+cross shaft could be removed from the gearbox if the centre diff. is welded.??


P.S - I just dropped my diff. at the engineering joint to be welded.
Do the two shims need to remain? Seeing as the spiders aren't going back in, there's not really any need for the shims hey?
I'll try to post some pics up later to explain this better.

 

[blackvr]

You only need to weld one side gear ie the one that splines onto the diff pinion shaft. All other shims ,spider gears and viscous coupling hardware can be done away with. The trick is not to heat the side gear too much when welding....

Remember..... metal tends to shrink once it becomes very hot and subsequently cools. Sometimes the centre diff side gear internal spline can become VERY tight to push onto the output shaft ( diff pinion). If thats the case.... get a heat gun and get the side gear shaft very hot and quickly push it on when reassembling. Alternatively, find a semi worn side gear .... if you have a choice (!) .... and when it shrinks , it will be a perfect fit !

MIke

 

[MDK87]

Hi guys, here are the pics as promised.

So do I need to keep the shims in place when welding the gears to the housing?

Oh crap! Thanks for the input blackvr. Does that mean that welding these gears is not needed? I'm not sure what you mean by "side gear" is that the big sucker welded to the bottom of the centre diff.? I'll try to get another pic up to illustrate what I mean a bit better.

Cheers

EDIT: Oops, sorry about the size of those pics.
blackvr, is this what you mean by side gear? If so, what exactly are we welding? The gear itself is already welded to the housing from factory.
I'm not exactly sure what you mean?

(haha, yeah dodgy sketch I know, but I done it on a laptop/touchpad )

Thanks heaps mate!


EDIT#2:
Just in case there was any confusion where I am getting the engineer to weld, the bits in yellow is where the gears will be welded to the housing.

 

[MDK87]

Oh, ok, maybe all is not lost. I just read on howstuffworks that the proper technical term for what I described earlier as "gear/shaft's" is "side gear". So in the pics above with the yellow, they are the right places for the welds hey blackvr?
Well that's what I am hoping.....
Should I ask the engineer to weld the two splined shafts together also? I guess as safe measure, and extra strength?

 

[blackvr]

No problems. The item circled in yellow is the side gear, not the gear on the outside of the centre diff. That is the "constant" that transfers torque from the gearset to the front differential. Only the side gear deep in the centre diff housing has to be welded to the centre diff housing. The side gear thats in the "lid" can be chucked away, along with planetary gears and cross piece.

Cheers Mike

 

[MDK87]

Thanks heaps Mike!