Tight Centre Diff?
 

Hi all,

I've lurked for ages and been very impressed by the friendliness and wealth of information on offer. Now I have a bizarre gearbox problem and i'm hoping someone knows something.

The gearbox in my 1995 UK turbo finally gave up the ghost after 177,000 miles. I hunted around and eventually found a low mileage box out of a 2002 bugeye which seemed a direct replacement. Checked all the final drive ratios and they should match, i.e.

old gearbox TY752VN3BA front diff 3.9, transfer gear 1.1, rear diff 3.545
new gearbox TY754VN2AA same as above.

Having fitted the new gearbox it mostly drives fine, nice and quiet and doesn't seem to be dragging or anything. Except, on full steering lock I can feel the transmission badly winding up, and the inner rear wheel hops just like a car with a really tight LSD.

According to the charts, the front diffs are open on these cars, so i reckon either..

a) the new gearbox isn't what it says it is, i.e. it's something other than a 3.9 front diff. But if this were the case i'd expect it to wind up in a straight line as well as on full lock
b) the centre diff is somehow tight or locked.

Has anyone come across anything like this before?

Yours,
confused of Devon. :wonder:

sounds like 'a'

okay thanks. I guess that is the more likely. Is there any way to find out what ratio the front diff is, without takin the flippin gearbox out again....

perhaps take the drain plug out and count the teeth on ya diff obviously you would mark first tooth

You're a star. Many thanks.

If that does not work I would call David at Welcome to the API website for some advice.

You could try researching the transmission number too; or posting it here. That way youll know whats inside it.


Simon

Thanks for all your advice - it is REALLY appreciated. I am as confused as hell at the moment.

Simon - Transmission numbers are as follows:

old gearbox TY752VN3BA, which according to my research is consistent with it being a 1995 UK car. The subaru manual says that it has.
Front diff: 3.9:1 (39teeth:10teeth)
Centre transfer gear: 1.1:1 (11teeth:10teeth)
Rear diff: 3.545 (39teeth:11teeth).

I have verified this by:
- counting teeth thru drain plug hole (thanks to 34SRM for top tip) and it's 39.
- taking the end plate off the tail of the gearbox and watching the transfer gears go round - 11 turns to 10.
- putting chalk marks on rear driveshafts and counting revolutions - prop shaft does 7-and-a-bit turns to 2 turns of the driveshafts, so it's 3.545.

The new gearbox is TY754VN2AA, and again the research confirms this is what you'd find in a 2002 bugeye (standard UK variety), which is apparently what it came out of. Again looking at a subaru manual, the ratios ought to be:
front diff 3.9:1 - i've counted the teeth and it's definitely 39.
centre transfer 1.1:1 - i will admit i haven't actually checked this yet.

So it ought to be a direct replacement for mine. Some time ago I read a posting on this BB from David at API which suggested the same - i.e. provided that both gearboxes have VN in the code then they should be interchangeable.

I've had a suggestion that i should source a rear diff from a 2002 UK car which would then be a match to my gearbox. I'd happily do this if I knew it would solve the problem, but my current thinking is that it will be exactly the same ratio as the one i've already got.

All in all it's a bit of a quandry right now. I hate burdening other people with my problems, but i think it's time to give API a call!

Spoken to API.

They agree with me that this gearbox ought to be right for the car, so there must be a fault within it.....