scoobymark66

Hi guys. I am still trying to figure out why my car (my93 JDM WRX) is so slow. The engine runs OK it just seems to rev a lot slower than other Scoobys I have been in.
One idea I have just come up with is the diffs. I know that the gearbox was replaced before I bought the car. The previouse owner said it was fitted with an STI box. If this is the case and the rear diff was left standaed what effect would this have? Would it seem as if the engine was down on power as it is constantly having to slip one of the diffs.
As you can see I am clutching at straws and scratching my head .
Can someone give me part numbers of matching box and diff.
Thank you and have a merry Christmas.
Cheers. Mark.

harvey

iTrader: (48)

Hi Mark : Where are you located ?
Get the car up to 20 miles per hour, in to neutral on a level piece of road, good surface, foot off the clutch and see how freely the car runs and when it comes to a stop does it stop very slowly and gently or as if there was some drag in the transmission.
I think the JDM car has a 4.44 front and rear diff with a 1.0:1 dropper in the rear of the viscuous centre diff coupling. I think the UK car has a 3.545 rear diff with a 1.1:1 dropper. If you have different overall ratios front and rear the transmission will be "tight". I know this first hand because this happened to me courtesy of Scooby God Pete Croney and it took months to find the cause. From my experience it was not enough to make the car slow although it must have had that effect, just that the transmission was a bit tight, especially after 160 mph blasts when the gearbox and centre viscuous were toasted. The other side effect was that it did not like to go round corners like other Subarus did and I spent a lot of time and effort trying to sort the problem before the cause was eventually found.
harveysmith1@btopenworld.com
www.geocities.com/harveysmith3000
Getting somebody to drive your car that is around Subarus regularly might help but it is such an unusual fault not everybody would be alert to it.

scoobymark66

Thank you for the reply Harvey.
I have noticed that the car does freewheel quite easily but I will try this tomorrow.
I am trying to find this problem and am simply stuck. Two of my mates have Scoobys. Same basic mods and spec but theirs are so much quicker than mine. Top end is fine just the pickup seems slow. Also understears like an Astra!!!
Thank you again for your input. Thats twice today for me. I have the alloy header tank fitted now.
Have a good Christmas.
Cheers. Mark.

APIDavid

iTrader: (4)

In my experience, if you fit odd front and rear final drives on a JDM the centre viscous absorbs it for so long then breaks. Generally with a whole load of vibration until after it breaks. Then the car is 2wd.

It is difficult to get to the bottom of this, however you can count the teeth of the crown wheel on both front and rear axles through the drain/ filler plug holes.

Take out the diff filler plug, you'll need to drain the oil; mark a tooth with white paint or tippex, turn a wheel and count the teeth. 37 is 4.1 [ standard WRX ratio ] 39 is 3.9 [some RA's] 40 is 4.4 [STi ] (I haven't counted 3.545 ) Do the same through the drain plug in the gearbox.

On a JDM car front and rear must be the same. On a Uk car the front is 3.9 and the rear is 3.545 because the 4WD step off from the rear of the 5 speeder is 1.1 : 1 like an overdrive, this is to cut down propshaft speed and reduce vibration.

Once you have the ratios figured then we can all advise what to do for the best.

Good Luck David APi Impreza / APi Engines
www.apiengines.com

scoobymark66

Thank you David. That was spot on info I now know what to look at.
Thank you all for your replies.
Cheers. Mark.

harvey

iTrader: (48)

The UK diff is 39 teeth on the crown wheel and an 11 tooth pinion.