Gunat

Hi Guys

new to the forum...although i have a very specific question which i'm hoping one of the experienced/technical gurus can help with.

Have a 1999 STI V- 30,000kms on the clock. Car was used sparingly, although driven hard on Hill Climb Events only.

I recently started experiencing the rear wheel "scrabble" and "clunking" associated with a failing Centre diff. (Agents diagnosis, confirmed with other online forum threads).

Having done the search with the Subaru Parts catalogue and the STI parts catalogue, i settled for the STI part with the hope that its more set up for high performance.

Subaru Part number: 38913AA101
STI Part Number: ST3891355000

What confuses me though, is that there is a disclaimer on the STI parts catalogue saying that the STI part cannot be installed on an ABS equipped car (which my car is). There doesn't seem to be any other part for an ABS car.

I realize its as simple as deactivating the ABS fuse before installing the new part....but i want to know what kind of diff actually exists as stock in the car .

Hoping someone can shed some light on this one.

Many Thanks

Fat Boy

StiV 4 door saloon has a viscous 50:50 split centre diff and 1:1 transfer gears,
StiV Type r (2 door)/ Type RA (4 door) has a dccd adjustbale centre diff (35:65 fully open, 50:50 fully locked).

The type R and Type Ra don't have ABS, but the standard StiV does. So it depends which model you have.

For what it's worth, I have a P1 ( Uk model that's basically an STiV/Vi in a 2 door body) which came with a standard 50:50 viscous centre diff and ABS, but I've replaced the centre diff with a dccd diff and the ABS still seems to work.

Gunat

Thanks for the response- i've got a standard STI V, no DCCD.

Replacing the factory installed viscous C-D with an STI unit- thats when i found this disclaimer. Ideally, the Agents should know the difference, but thats not the case here. Either way, i'm disabling the ABS when installing...

Fat Boy

I assume it's a new Sti viscous diff with a higher resistance than the original as sold for the group N rally cars etc. If so I can't see why it would compromise the ABS. Why not try it with the ABS with a few emergency stops on a private road to see what happens? If you're not happy then pull the ABS fuse.

Like I say my P1 is effectively an STiV, and now it has a Dccd box it is probably/possibly more likely to cause an issue with the ABS than an uprated centre viscous diff and I've had no problems.

PeeVee

iTrader: (1)

Your ABS will still work, but if you were ever in a situation where you were on a slippery road with the diff not set in the open position and had to make an emergency stop whilst taking avoiding action, you could find yourself in a world of trouble.



I'm not sure what diff you had as std but if you give me your Vin No: I can look it up for you on the Japanese parts system.

As for the diff you have bought, this does not come up on my system, but, if the part number starts ST then this means that it is uprated.

I have the part numbers for 2 updated diffs, a 12kg and a 20kg diff and you have neither of these, but either way, as above, you could get into trouble under certain circumstances if you leave your ABS connected with an uprated diff fitted.

Phil

Fat Boy

Phil

Would you care to elaborate on that? I assume that whatever effect you are suggesting would happen would be assuming the diff is fully locked versus slightly up from open, but is there some form of electronic brake force distribution on a P1/ classic scooby that would contribute to what you are suggesting would happen?

I know that RA's etc came without ABS, but then they're homologation models for rally cars where the dccd diffs could well be used in fully locked mode and where ABS would be the first things thrown in the bin during prep anyway. Could it be just International Motors/Subaru justifying why it didn't put dccd's in the P1? All things need to be built down to a budget after all.

I know you know your stuff about gearboxes and the like - in fact you've rebuilt my gearbox (pre dccd) in the past - but I'm trying to understand what sort of effects you are talking about and, being reasonably intelligent, I could probably cope with a more detailed description than I would be in a "world of trouble"... I sent you an email off line on this but you haven't responded so forgive me for asking this question publically.

Cheers

FB

PeeVee

iTrader: (1)

FB

Yea the tighter the diff setting the probability of a problem increases.

IIRC a car that has both the elec diff & abs, would disengage the diff if abs was triggered, but if this is not the case then the ABS Ecu and the gearbox Ecu would be programmed to work together and there would be a degree of talking between them.

In the case where cntr diffs have been uprated or a different type installed, I don't think (but wouldn't bet my life on it) you would have a big problem if all four wheels had the same level of grip whilst in an emergency situation, weather it was on wet grass, dry grass, wet or dry tarmac etc, but If there were differing levels of grip on certain wheels I could see a situation where the ABS is trying to control wheel speed/grip and the cntr diff (having partially locked front & rear drive shafts together) would interfere with this control and it would prevent the abs from independently adjusting (which it does many times a second) the amount of retardation to each wheel. This is fundamental when trying to keep a car under control whilst swerving under an emergency situation. If this is not done to perfection then you could loose the control that the system is fighting to give you & if that happened I for one would not want to be in the car as it could be more unpredictable than a car that didnt have ABS in the first place.

Phil

Fat Boy

Phil thanks very much for replying.

So you see the issue as being the effect of the electronic ABS assuming a certain level of lock/release being required for such an emergency situation based on the rotation (or not!) of the wheels/abs rings, but it would be basing it's level of intervention based on it's expectation that you have a 50:50 viscous diff ?

So, for the avoidance of doubt, you are not saying that the diff and the abs "talk" electronically it's just the differing resistance levels that cause the issue i.e. There isn't an electronic link between the two systems?

I'm still struggling to understand why an open 35F/65R diff is seen as being less of a risk (compared to the original 50F/50R viscous diff) than a partially locked dccd at say 45F/ 55R.

Anyway, the answer seems to be leave the diff unlocked at all times or pull the ABS fuse until I can set up a test on a private road with differing grip levels for individual wheels to try out your theory.

Cheers

John

Welloilbeefhooked

iTrader: (3)

You have got me thinking about the ABS too, although my DCCD controller is an auto version.

I would imagaine that if the DCCD is locked then all 4 wheels have to turn at the same speed. This would then remove the ability for one front wheel to be locked by the brakes with the other turning. If one did lock, the other would have to turn faster than the rears to allow for the effect of the DCCD locking the central axle.

Does this make sense?

Wayne.

PeeVee

iTrader: (1)

I wouldn't worry too much, your abs and cntr diff are both factory fitted & std, so they are designed to work together under all conditions.

You should not be running your diff in or near the locked position on the road as this could damage your transmission. The only time you should be using this facility is in very slipery conditions, i.e. wet grass, mud or snow.

Phil

Welloilbeefhooked

iTrader: (3)

Mine isn't all factory fitted, and there lays the problem.

Gunat

Gentleman- sorry for the late reply; been busy days here.

Phil- Many thanks for your experienced insight and warnings. As you have mentioned, the uprated Diff is not to be used with ABS. I replaced the (Viscous) Centre diff with the STI unit i purchased directly in Japan- same part number i have mentioned earlier, 20kg unit.
I had the ABS fuse removed in the installation process.

I used Subaru FAST to get the part numbers mentioned earlier; and referred to the STI parts catalogue online to determine the equivalent STI part.
It took a little bit of investigative/thorough researching to ensure i was getting the right part. As a JDM car, it wasn't made easy to find the right information.

I don't use the car in competition, and only occasionally drive hard on tarmac roads. Do you see any issues, apart from the safety factor of the ABS being dis-engaged?

PeeVee

iTrader: (1)

No, None at all.

You would obviously lock your wheels if the brake pedal is pressed hard enough, but there are no other side effects of removing the fuse. the brake system will work in exacly the same manner as a non ABS system.

Phil

Gunat

Thanks Phil.

I hope you won't mind imparting some advice later on- when i look into getting a rear diff. I've read that the rear diff is particularly weak on the GC models...so trying to understand what is the correct unit.
Reading extracts of R160, R180 but not quite sure what is relevant.

Cheers

PeeVee

iTrader: (1)

No problem.

The R180 is the larger stronger diff, but you would need different drive shafts etc.

Will discuss it when you are closer to changing it.

Phil

swisstonihasher

Also R180 with suretrac drives alot better with bigger power figures than R160...take my word for that (and a cyclist that once say a scooby going sideways lock to lock on R160 - was fun though).