G25MX-R center differential options

[thered56]

I may be wrong, but AFAIK the viscous center diff (BPT G25MX-R) is basically giving the front wheels all the torque until there is slipping at the wheels. Are there any options to distribute the torque to the rear wheels in normal driving conditions. Might it even be possible to lock the center diff to basically get a permanent 50/50 torque distribution front/rear if the same front/rear gear ratios are used. I'm not sure if that would be desirable though.

[thered56]

Well I've pulled up some info on this type of thing:

http://www.dsmtuners.com/forums/articles-drivetrain/173481-welding-center-diff-how-why.html

http://www.uk-ssgti.com/t760-welded-viscous-coupling-on-the-road

Sounds good to me.

[theredrocket]

I thought the factory torque spilt was 43% front/57% rear for the GTX/GTR center diffs.

[jay]

It is, the centerdiff always sends torque to the back.

[nerd racing]

I've spun the rear once pulling out from a gravel driveway onto blacktop. Also did some 360's in the same gravel

[theredrocket]

A 43% front/57% rear is a perfect split. The car naturally will have more traction in the back when the car "launches" and the weights shifts to the back when the front lifts up and the back hunkers down. So sending more power to the back and less to the front is genius. Thumbs up to Mazda! It's just too bad they made everything a little on the fragile side.

[thered56]

Okay, well that's pretty sweet then. Maybe that's the case with the non-viscous center diff then. Now, what is the deciding factor with the torque split? I read somewhere that the diff ratios determine it. Not quite sure how that works though. 57% to the rear does sound like a pretty nice setup.

And BTW, hey Nerd, nice to come across another ff.com member.

[nerd racing]

hmm what's your screen name over there? I have a viscous center diff in my protege, BG GTX trans that is. I can't wait till I get the swap done in my festiva. that will be pretty quick... and have traction!

[thered56]

Same screen name. Right now I'm gathering the pieces for my B6T swap (Rustiva). Then I'm looking to go AWD with BPT (Raltiva). Just doin some research on it in the meantime. I'll have to pull up your build thread over at ff. There's an AWD Protege near me for $1000 I'd love to snatch up, but all my cash is goin into my current projects.

[Rocketman]

The front & rear ratios are not the same so locking the diff full time is NOT good for the drivetrain, both BF gtx & BG gtx transmissions

[nerd racing]

the ratios are the same, 3.909 final drive and 3.909 rear diff ratio. if they were not the same the diff would fail. that is why you must run all 4 tires the same size on all wheel drive/4wd vehicles.

[Rocketman]

This page says differently: http://www.protegefaq.net/transmission.html#G25MX-R

http://www.protegefaq.net/transmission.html#G5MX-R

BF front FDR: 4.388:1
BF rear FDR: 3.909:1

BG GTX front FDR: 4.214:1
BG GTX rear FDR: 3.909:1

Is this info incorrect?

[theredrocket]

My GTR service manual says front is 4.214, and rear is 3.909. Which I don't understand fully. The car has the same size tires, but different ratios for the front a rear axles. Would one set of wheels not constantly be slipping then...? I don't have anough experience with AWD yet.

[Rocketman]

The front will spin faster than the rear. The center diff, being open or viscously coupled, will slowly rotate to make up the difference.

It'd be like going around a turn in a FWD car, the spiders in the diff will rotate slowly due to the different rotational rates

[DuRWooD]

If the car was in the air, the rear would spin faster, that's where the torque bias comes from. The center diff doesn't actually "send" more torque to the rear.