Blowing rear diffs or cv's

Hi all,

Hoping someone may be able to shed some light on my problem

I have a 1998 Legacy VDC and over the past year have blown 4 rear diffs and 5 cv's. The problem strated when i got 2 cheap tyres and put them on the vehicle. On the front i was running 215/50/16 and on the rear had 215/55/16. i drove approx 200km and the rear diff heated up so much it melted the rear diff mounts and set them on fire.

I realised that this was prob due to different profile tyres and after towing the car home; replacing all tryes 205/50/16, replacing the diff 4.44:1 ratio and the rubber mounts i put the car back on the road. About 200 km of open road driving the replacement diff started smoking and eventually wining until i replaced that one. Diff number 3 was from an earlier model of same ratio 4.44:1 but with 4 spider gears so thought it may be stronger, i also had to change the inner cv's to match the diff. After installing this i went to a subaru dealer to get hin to check all was good. He replaced the diff oil and road tested it saying that it all seemed ok. Around town it was good however; after some highway miles, one of the rear cv's started making noises. I thought i may have put it in wrong when i changed them to suit the diff. 4 rear cv's later i thought maybe its the diff/cv combo so purchased 2nd hand another 1998 diff and 2 half shafts from the wreackers and installed them. About 200km later that diff melted the rear rubbers and the car has been in the shed ever since.

It seems that the 98 diff is weaker then the other hence the diff not cv's blow and when i put the stronger diff in, the cv tended to be the weak link and blew.

Can anyone plaese suggest what may be going wrong as i have no idea... The ratio is the same as the diff i replaced and it seems as if the front and rear diffs are working against each other causing a shitload of frition out trhe back leading to overheating and eventually the rubbers melting.

Any advice on how to solve this would be appreciated... I miss driving my Suby

100% sure the ratio is the same?

Yeah, counted crownwheel and pinion teeth on original diff

40 on crownwheel

9 on pinion

my guess would be u have lunched the centre diff while running the different size tyres

 dubbedup said:

100% sure the ratio is the same?

Post up your gearbox code dude so i we can check it

what dubb'd said.. continual lunching of your diffs and cvs would indicate that something thats remaining in the car with repeated changes is not happy.

From your post

1) have you changed your center diff?

2) are you positive your front diff is correct.. like 110% crystal, checked gb codes, and counted teetn in the front and even split your gearbox open to check.??

It would be my bet you change the entire gearbox incl center diff and your car will be happy again.

if

 

it seems as if the front and rear diffs are working against each other causing a ****load of frition out trhe back leading to overheating

It has to be either

1) your center diff is lunched

2) your front diff isn't matched to your rear (however possible). Aren't VDC subbies 4.111.. am i barking up the wrong tree by thinking VDC only came on Autos? autos of that era are 4.111 no, thus putting in 4.444 in the rear will make it fight itself like ****..? Thats what Viv's was like.

I did a quick search in the Gb charts and most GTs', RS's and legacies in general around the 98 era (not incl the GTB's) came with 4.111

Hey Funkytown, thanks for your response you may have something. the VDC is an auto but im positive i counted the teeth right. it was the rear diff that blew, the centre diff wasn't making any noise so didn't think there was a problem there.

i have thought that the only logical thing i can see is mismatched ratios however; im sure i counted right.

the trans code is TV1A4YBAAA, if it shows that the ratio should be 4.11:1 im an ass :-\...

grateful for your assisstance.

Weird. I would have picked mismatched diff ratios to smoke the transfer clutch, not the rear diff.

it was the mismatched front/rear tyres that caused the first diff to smoke itself

Oh and by the way it's a 1998 BH5 VDC Legacy wagon

 boostin said:

Weird. I would have picked mismatched diff ratios to smoke the transfer clutch, not the rear diff.

yeah I would to, the clutch pack to me would seem the weakest link...

thats why i was thinking it already lunched

transfer clutch is pretty strong, and if its fried there will be no rear wheel drive at all

drop the front diff oil and conunt the # of teeth on the front crownwheel to be sure

There will be either 37 or 40 teeth

37 = 4.111

40 = 4.444

I take it that to get to the front diff i'll need to remove the trans? I just remember what a mission it was to change a few years ago :'(

sweet man.. least your getting it sorted now.. (funky ftw!)

to check the teeth you drain the oil out the gb.. you shud see the front duff through the drain hole.. no need to remove it.

(this is assuming the autos are the same as manuals).

count and check the ratios to be sure but based on the gb code.. go get yourself a 4.111 rear and you shud be away laughing

 Whetz said:

I take it that to get to the front diff i'll need to remove the trans? I just remember what a mission it was to change a few years ago :'(

Ahhh the under lying secret -- it not the orginal trans

Just drop the oil and count the teeth thru the drain hole, no need to remove the trans

Yeah its not the original, that blew a few years ago however; i got another with the right numbers, installed it and everything ran well for a couple more years until i mismatched the tyres; thats when all the problems started and thats where i still am :'(

 Whetz said:

Yeah its not the original, that blew a few years ago however; i got another with the right numbers, installed it and everything ran well for a couple more years until i mismatched the tyres; thats when all the problems started and thats where i still am :'(

mismatch of tyre has probably done some damaged then, considering you have replaced CV and diff, possible that the gearbox at fault then?

able to swap to try out?

assuming the rear diff was correct way back then? cud have melted that gearbox as well.

hard to tell with out confirming the teeth on both rear and front diff

Cheers guys,

Is it possible to know what the ratios should be by the codes?

my data for vehicle with VDC is 4.444 so a 40 tooth crownwheel

You are at a stage with this vehicle where you need to go back to basics

so drain the front diff and start counting - tip let it drain for an hour first

Cheers Ichi Ban, will drain it and have a look, hope you can see it with an auto

Yeah easy as. Just make sure you pull the diff plug out, not the auto trans fluid plug.

Hey thanks for that, I probably would have drained the trans fluid, lmao @ myself now ;D

And the moral of the story, never ever missmatch tyres. Ever. Sorry to hear about that Whetz Hope you get it sussed soon.

This is pretty strange as im rather sure your car has a VTD box that allows front rear slip unlike a viscous coupling, so even with a miss matched ratio it would still live for some time. to me it sounds like something has happened in the center diff and its driving the diffs at differnt speeds (if there ratios are matched) put the car on four axel stands and drive it see if theres a miss match in speed. But in saying all that if there was a missmatch or binding you would be able to feel the car lurching at low speeds during tight turns. Id be checking that front diff oil because i think you might find some steel in there