Hi all,

Ive never dabbled into the rear axle of my car yet apart from changing the oil and gasket, so bare that in mind when replying as all this talk of 3.08 gears etc goes straight over my head, at the minute ! lol

So basically, ive just finished swapping in a 5.7 TPI into my car, which orignally had a 5.0 TPI.

Other mods include, hooker headers, full stainless exhaust ( no cat ), Bosch 3 injectors, AFPR set at 42psi, 9th injector delete, ECU has been reprogrammed by Tuned Perfomance as ive deleted my EGR, all other emissions and AC have been removed too.

ive driven the car 3 times now and im getting more confident each time as im very consious lots of things are new and something might need adjusting or whatever, but last night i joined a 60mph stretch of road alongside an Audi, a big 5 door one, im not sure if it was petrol or diesel but he saw the car and must have thought i will have a go, and i thought to myself now is as good a time as any open the car up and see if it moves, and it does...... but just not as much as i thought it would. I was just managing to keep up with the Audi that was infront of me.

I felt a bit disappointed to be honest, i thought my car should be leaving stuff like that for dead.

Now, about the rear end. Ive suspected it to be worn out since i got the car, its got an LSD tag on the cover, but its got drum brakes ? i will have to look at the number stamped on it to see if anyone can say for sure its an LSD, but when i put my foot down usually on the RH side wheel spins.

Browsing over various topics on here ive noticed a few times that some people have said by putting in certain gears in the axle can be like dropping in a new engine in itself, as the engine can lay its power down properly and really get the car moving ?

 

Gear can help acceleration but its not gonna magically make a car faster at a roll speed. Gear usually helps in reducing et at the track with little change in mph

A stock 5.7 tpi car with those mods is a 96-100 mph trap speed car. Thats not fast by todays standards.
If you have 2.77-2.73 gears, goin to a 3.27/3.23 or 3.42 may help get you 1-3 mph more in 1/4 making a 96 mph car a 98 mph car. Mine never gained more than 2 when i did two gear swaps.
Gear will make acceleration quicker so it feels faster, but power is what you need to increase to be faster from a roll race

 

By today's standards stock 5.7 TPIs are kind of turds. They were only about 230 crank horse power back in the day if I'm not mistaken. Depending on what Audi you were playing with I'd be he's got a few ponies on you.

I went from a 2.73 to a 3.42 this spring and its not like dropping a new engine in, the cars not noticeably faster, its just easier to launch.

I don't think changing your rear end is going to yield the results your hoping for.

 

If you have a stock car concerning your rear end than you should have a 3.27 ratio.

Changing to a 3.73 ratio and a new L.S.D. will make a difference off the line but if you go with new parts it will get pricy.

Here's what I did to mine = https://www.thirdgen.org/forums/tran...de-photos.html

 

Ron thats awesome, it sounds like your car really has a get up n go factor now ?
Thats what im after really, better acceleration, im not really wanting to race the car but just be able to take off when i feel like it, and if im being honest, donuts ! my car sucks at doing them in the dry with only one wheel spinning.

Im not sure how much a full rear end rebuild will cost me bearing in mind i will have to get all the bits imported from the US

 

I'm guessing that by having drum brakes you probably have the 10 bolt rear end, but you must be sure before you think about purchasing parts. You don't want to pay shipping for parts for the wrong rear end. Your car could have the 10 bolt GM rear end or the 9 bolt Borg Warner rear end.

 

It is a 10 bolt i know that much. Does that mean its not actually a limited slip diff ? I thought all GTA's had rear discs but apparently some had drums either because of parts shortages or as an option

If i jack the car up and its in neutral if i spin one wheel forward the other spins backwards, there's a bit of play while doing that too

 

It's probably got a worn out Auburn in it. This is very common. The Auburn is just about the worst differential you can use. I recommend replacing it with a new Eaton Posi, Yukon Dura Grip or Eaton Truetrac. You must know what gear ratio you are going to use before you get a new differential.

 

Well ive got no idea on that front, something that lets me spin both wheels nicely, and preferably keeps the RPM's down when im in overdrive if thats possible ?

fuel over here in the UK is stupidly expensive, i havnt calculated my MPG since putting the 5.7 but im pretty sure its gonna be bad

 

You would need to go to at least a 3.23 gear to use one of the after market differentials. They are only available in 3 series, which will not work with gears from 3.08 to 2.14.

 

I think the whole axle needs an overhaul anyway, if i jack the rear up i can move the rear wheels in and out a bit which cant be good ? They aren't falling off though !

so, replacing the actual gears inside the diff, is it a fairly straight forward out with the old and in with the new type of deal ?

where's the best place to buy the new parts to do the whole thing

 

Setting up a ring & pinion set is definitely not a simple bolt in job. You must know how to set the pinion depth, bearing preload and backlash to get the correct contact pattern. You must be able to read the contact pattern to know what adjustments need to be made to the pinion depth. It takes some special tools to do the job correctly.

Tom's Differentials is a good place to get quality parts, much better than Summit or Jeg's.

 

So the car programmes i watch where they seem to just take the cover off, unbolt the gears, swap it for the new one then the car is all done is all just a load of edited crap then ? lol,

hmmm, sounds like quite a job then. I know there is a good place that does American cars by me, they built my stainless exhaust, i might have to ask how much he thinks rebuilding my axle would be. I get the feeling it wont be cheap though :/

 

The guys on those TV shows are idiots and they **** me off. There is no telling how many people have screwed up their cars and trucks because they followed the instructions of those goof ***** on TV.

 

thought id test my theory last night as i havnt done it for a while. Nice quiet country road back to the garage. There is no denying the car is now a tyre shredder, i think if if i hadnt of lifted off the throttle it would of just kept going ! but it only shreds the RH side !



This might be a stupid question but if the axle is rebuilt with a new LSD, both wheels will spin when doing a burnout wont they ? and the back end will want to let go more easily when messing around ?

 

If you have a LSD in there then it's worn out. Doing one wheel burnouts is going to make it worse.

 

This is what i need to check for sure, its a 10 bolt axle with an LSD tag on the cover, but its got drum brakes.

I cant remember if when jacked up and in neutral, if i spin one wheel forward the other spins backward or not

 

When the Auburn wears out it acts just like a standard differential. I'd say that this is exactly what you have. You can check for the G80 code on the RPO sticker, but removing the cover is the only way to be sure.

 

Got no RPO stickers on my car unfortunatley

 

I got under the car tonight, i jacked it up in neutral and both wheels spin the same way when turning.

I also took a picture of the diff with the numbers saying as ive got no RPO stickers on my car at all, im not sure if that tells us what kind of diff it is ?

 

You are going to have to remove the cover to find out what you have.

 

Damn, i guess i will leave until winter when its parked up then