Diff/Gearbox Ratio confusion

[Klaus]

Hi all, im a bit stuck and need to pick some brains.

Background, ive had my BG5 GTB for about 6 months. I bought it knowing it had a suspect rear diff.

Firstly it whines on deaccleration. Secondly, floor it and once you hit second turbo, the back end gets the mad vibrations.

I did some research and put it down to probably being a cv/axle issue. Its fine thru the first turbo, and seeing as i only hit second when im on the open road ive just put up with it.

Now, my gearbox is a TY752VBCAA, confirmed by both the chassis tag and the sticker on the bellhousing. 4.44 Correct? so i purchase a 4.4 diff (40.9 on crownwheel).

Pulled old diff out today, low and behold its got 37.9 on the crownwheel 4.1

Im not an idiot, but i must be missing somthing here?? Surely it would have been more evident if i had mismatched ratios? the diff i removed from the car has white wrecker writing on it, so its been changed before. Apart from above mentioned problems, car drives fine.

The logical thing to do would be to just stick the 4.4 diff in and hope for the best, but just thought id ask!!

Any help would be much appreciated ;D

[rex-leggy]

unless the front diff also been changed? stranger things have happened.

im unsure on the effect of incorrect ratios but that could be your whining on decel

[lachlan]

noone would change a front diff ratio . unless they changed box

i suspect mis matched diffs is the problem with your car, symptoms would get worse with more speed and load to some extend

. and your centre diff is probably fucked now

[Klaus]

Thanks for your quick responses guys. I had wondered if someone might of messed with the gearbox too.

From what i have read i thought it would be a lot more noticeable if the ratios were up to shit, bucking and binding and the like.

Think ill stick the 4.4 in and hope for the best, ill let yas know what happens!

[lachlan]

its not a huge ratio difference and the centre diff would soak it up but get hot eventually . its the same as driving in a circle for every km you drive

you can work out exactly what ratio your front one is by spinning the front wheels and counting output shaft rotation

[Klaus]

Well im a happy chappy ;D

Stuck it in and went for a drive, and wow what a difference, its a whole new car on 2nd turbo. No whining, vibrations or funny noises, sweet!

It was probably a no brainer, but as i say, just thought id ask

[lachlan]

yeah i imagine itd be like a whole new car . how many kays you recon its done in its previous state ? i wouldnt be surprised if the centre diff was past its used by date . well the diff will still drive fine but the viscous lsd part of it will be rooted

[Guest]

Ive got a centre diff upgrade if you need it. centre/rear housing/shafts/diff etc. $80+shipping complete.

[Klaus]

Well ive put about 8000ks on it since ive had it, who knows before that?? probably well and truely toast.

Oh sweet, by upgrade you mean its better than standard? sounds like a good price man. Ill hold off while its driving ok, but it will need doing so ill keep it in mind!

[Kiwi_Fozze]

yeah, that center diff\'ll be f**ked....

[Guest]

Phase 1 so is an upgrade for any phase 2 box and comes with everything to be a bolt in upgrade and yea very cheap considering the diff alone are 1250 new.