Hi All,
Very old subject I'm sure but I've searched lots and not got an answer.
I have a type 9 4x4 box in my project car build which runs the gearbox the wrong way around so I get too much torque to the lighter front wheels (engine in back). I plan to remove the centre VC and weld up the planet gears to make it 50/50 torque split and then increase the lock torque in the viscous by uprating the fluid.

I can't see why it shouldn't work as the viscous would still allow enough slip front to rear to stop it locking the drivetrain up, I would still get wheel spin at the lighter front end from standing start but then the viscous should lock to transfer the power to the rear where the weight is. All I'd be doing is removing the 'torque' split feature of the centre planetary gears.

Thoughts?

 

Which Gears?
If you weld the gears in the centre diff then it locked so 50/50 split with not differential effect so no slip at all

 

I had a Scooby with a binding centre diff and the front wheels would skip when turning. It soon shagged the wheel bearings.

 

But it still has the viscous coupling in the same unit so I would presume there would be sufficient slip in that to stop the skip at slow speeds?
Ideally 50/50 planet gears would be the way to go but .... Hen's Teeth.

 

BTW, car is for tarmac hillclimbs. some wheelspin off the line should lock the viscous but after that it should cool down again and allow some differential?
Front/rear diff are same ratio, tyres all same size.

 

I'm not even sure it will be a 50/50 split if you weld the planet gears. But even if it would, the front and rear propshaft cannot turn at a different rate anymore because you welded that part. The viscous is normally slowing the difference between the turning rates, but if it's welded the viscous doesn't do anything anymore. With the front and rear propshafts only being able to turn at the same rate the car will only go straight.

 

As I understood it the input to the 'complete unit', initially runs through the planetary gears to give the torque split, transferring the 'turns' from the input shaft to the outer case. The outer case is toothed to the plates of the viscous and the other plates are toothed to the output shaft.
I theorise that I am only welding the torque split part of the unit leaving the engagement part of the viscous to still rotate. it would only completely 'lock' to permanent 50/50 when the viscous fluid got hot enough.

 

Bara put an uprated Viscous in my Mt75 Oppliger box, It has 60nm written on it in his blue pen, he said it improves the car handling anyway.

 

That would lock the viscous earlier which in your case would transfer more power to the front where the weight is when the rear wheels slip. Would help mine too but I'm getting too much initial spin as my bias is reversed to 67% front which unloads more with the weight transfer. May have even fried my VC with so much spin.

 

Thanks for the explanation...makes sense. The wheels did / do spin first at the rear and when it pushed power forward I did occasionally get a big tug of torque steer which was scary in the wet (it has Quaife up front) but I am hoping the new suspension setup will help to cure that as my compression struts were aparently in an odd mounting position before.

 

You need to do some research into your problem as welding it and making it 50/50 will not be good .
i run a skyline gtr R32 gearbox witch I can make 50/50 on demand I only use it when putting the car on a trailer as the car jumps all over the place when turning . I've used it on track and the car just pushes on in the corner,s

 

Get what you are saying, but I currently have a 67/37 split so I get a heck more push on than yours at 50/50 and mine wouldn't be 'locked' as it still passes drive through the viscous coupling. In my case 50/50 would be better than what I have I think.

 

 

the planet gears do the torque split front rear, the viscous coupling does the locking

so what you need to do is fit a solid centre viscous, it's the big cylinder thing and it's easy enough to get to, but welding it up is going to be much harder as they are made of aliminum i think

you could just get the fluid pumped up or drill a hole into it to let the fluid out and then fill it up with other stuff

 

 

Now this was a big step to help my understanding!
I always thought the viscous part was the link to the front prop, not at the rear prop. Of course it's not looking at the pics (my box is the wrong way round to confuse things).

Does this mean that when the viscous locks, the drive split remains the same, just more 'drive' is sent to the front or does it lock the reduction gear?

Edit:
Answered it myself, no it just transmits the drive but with the same torque split. I need to get a centre diff made to give me 50/50.

 

Still brings me back to:
If I weld up the planetary gears to eliminate the torque split I get 50/50. The viscous will then be redundant as propshaft speed difference will not be possible. I will get some driveline wind up and tyre jump in the paddock but under power when there is tyre slip anyway it shouldn't present a problem. Yes?

 

On a rwd vehicle when the rear wheels are locked together (welded diff) the car jumps a bit on tight corners. But if the centre diff on a 4x4 is locked I believe you will get very serious understeer, as in that it doesn't even want to turn in at normal road speeds.

 

Yeah but I get that now because I have a 70/30 split to the front.

 

Well you can always try of course. If it's not a success you can revert back (although you will need a replacement centre diff). The best option would be still be to find a 50/50 split centre diff, as was available for motorsport.

 

Anyone have one kicking around they can let me buy?

 

 

 

Yeah but that's a whole bunch of work again. Might go that way if I decided to start from scratch again but a bit late now. Would be ideal though to give better control. Mind you, the 6R4 was always a pig to drive, so at least mines authentic in it's character. First hillclimb I did got over-boost issues and under-steered straight off into the tyre wall !!

 

 

But would it be any better? Gearbox is still the wrong way around so whereas it would normally be RWD with control to the front it would give the opposite for mine unless you can run it as 100% RWD OR 100% FWD?
Mines the Type 9 too, not the MT75?

 

 

Had the box rebuilt at 1stMotion trans, should be able to cope with 280bhp but he has had people run more in the cossie days with standard boxes. Mitsu engine is 285.

911 turbo set-up would work but not a cheap option I would guess

 

An open centre diff would probably be better than what you're proposing ?

If you only need the drivetrain to handle 280hp....surely Porsche stuff would be plentiful and cheap ? It's only really the turbo boxes and the like that carry high premiums.

Although their transaxle format would of course be very different than what you're currently using

 

Have you read the above Steve?

Porsche would be no good after thinking about it, transaxle would be too far forward as the engine is rear of the driveshaft line in the Porsche, no good for a short wheel base Metro

 

You could run it as open diff as Steve says though. Do you have slippy diffs in the front and rear?

 

Are you pulling my leg now?
Open diff is giving me 67% torque split to the front which was the reason for the post in the first place. Open diffs front and rear. A LCD in the front would make the understeer worse, not really needed in the back as that's where the weight is.
I'm going to weld up the centre diff and give it a try, it's not like it's a road car and there are people running welded rear diffs without problems.

 

I thought yours had a viscous coupling which set the torque split? I was thinking that if you put an LSD in the front AFTER the diff was fully open in the centre it may help you gain lost traction.

I do not have a clue how the centre diff works, especially not in reverse LOL.

 

The centre diff has 2 parts. Epicyclic gearing to give the split and the viscous coupling to transfer drive when the is a speed difference front to rear. I could get a stiffer viscous but that won't change the torque split and would likely burn out as I get so much slip/ speed difference.
I could put an LCD in the front to stop the one wheel spinning but likely would get both spinning instead as there's no weight on the front, giving more understeer.

 

Gotcha

I have Quaife ATB in the front of my Pug Cos (engine in front) and then Supra LSD in the rear and it drives pretty well although doing a 3 point turn feels like the handbrake is on. I just wonder if the slip could be reduced with an LSD but it might need to be set quite loose...as you say it is light on the front. It seems like one of those age old modified car compromises / frustrations, I have experimented with so much on my car and people thought I was daft as every time it was nearly finished I took it all apart again but I am confident I will get close in the end and I enjoy the journey (sometimes)