BlueSix

That's my question. After several long months of debate i have decided to keep my GTO. Now i am developing a plan for mods. What i am worried about is the rear. Assuming the driveshaft has been replaced where is the next weak link, and at what point will it typically fail? I first want to eliminate the wheel hop, because i think that's what actually kills the rear. But how much power can the stock diff/CV shafts take? Lets say 5000 rpm clutch slip (no dump, just a controlled fast slip) with 3.90 gears. And let's use 400 rwhp (n/a) as a power level. I'll probably cross post this to LS1gto.com also, but i want to see if we can get a discussion going here.

05_GTO

I would say the rear end should be good for 450-500 IMO. I think BMR trys to make the driveshaft (along with the rest of the rear) seem weaker than it is. Ask around and see how many people have broken their driveshaft. I have over 400RWHP right now with all stock drivetrain and have no problems. I know a few others with 450+RWHP on a stock drivetrain and they take it to the track quite often with BFG DR's on with no problems.

As far as the wheel hop I hear Harrop differential cover and new cradle bushings is a pretty good start. I will probably do this in the future along with some SFC's. Though the sway bars I had added seemed to help with wheel hop some.

gotzaGTO

well, I got 390 going to the rear wheels now and I drive my car hard, really hard, I'll let you know how it holds up!

demonspeed

iTrader: (7)

BMR 3.5" d/s
Kaaz LSD
BMR Half Shafts
BMR Stubs
Harrop Cover + Bushings

Supposedly that's what you need. That is pretty pricey though.

topperge

Yeah, very pricey ($2500 - $3000 range) There is also a company out of Australia (DiffTechnics) that is making a 9" IRS its $2700 though

CSiJason

Personaly, i'd swap the drive shaft and then go with the 9" IRS and some beefy axles and stubs. Weak link would be transmission at that point without a doubt.

Firehawk0220

I agree. However the T-56 is pretty tough even in stock form. Should be ok for most applications I would think.

Qikgoat

Ya,

I would swap all that out as well if money was not the object. I question the need for all the BMR, Kaaz, DiffTechnics drivetrain upgrades for prevention. A good trailer to bring the car home on when it breaks was my first purchase. I will trade up the driveline parts as they go. Nothing broke yet. Clutch is toast though. 407hp/387tq

BlueSix

You guys are just confirming what i already suspected, that the rear is actually a pretty decent piece when setup properly. I really don't mind breaking parts, the car isn't my daily driver. I think i'll probably do the Harrop cover, some 3.91's, and the cradle bushings and see what goes first. I figure as long as i don't "shock" the rear i should be ok (that's why i mentioned clutch slip, not dump).

gagliano7

You better invest in a clutch that will probably be the first thing to go.I have already slipped mine pretty bad at the track with only 5000 miles on the car.

2edybrd

Check BMR's website or go to

OZ LS-1

BMR got reall close to tens, I believe before they started breaking things.

My opinion, if you are getting into serious racing, you might want to switch out the drive shafts first.

Rob

iTrader: (6)

Change the fluid. Its a cheap fix. If that doesn't do it, then buy a new clutch.

We have guys here that are running low 12's-high 11's still on the stock clutch. And that is with 15K+ miles now.

LS7 clutch looks very promising. As well as the Textralia. Those will be the two on my list of choices. Spec, IMHO, is a disaster waiting to happen.

gagliano7

Thanks for the info.I was gonna go with spec but i hear alot of bad things.Maybe i will try the ls7.

BlueSix

Go with the LS7 clutch or the textralia.

I find it really hard to put a lot of stock in what BMR says about the driveline on these cars. It's their business to make and sell the parts that are stronger than OEM, and will hold up to severe abuse. But part of me wonders how much farther they could have taken the OEM parts. The stock diff was still in one piece when they did the 9" IRS wasn't it?

GoatChs

iTrader: (8)

After upgrading to all BMR components (sans DiffTech 9") they ran a 10.23. They bumped the N2O progressive controller up and had a lighter driver to attempt a sub-10 and found the limit of the factory rear diff components. According to their website: "What we found out later was that the outer carrier that houses the spider gears broke and was allowing the drivers axle to rotate independently inside the carrier."

They upgraded to the 9" then sheared the driverside outer axle stub. This is the last weak link in the rear end and is one that is not "affordably" overcome, as BMR outlined in their chronicle...read about it HERE. If BMR's experience is "typical", it appears that once you've upgraded everything else in the driveline, from driveshaft to halfshafts, then you can expect to break the outer axle stubs and its time for a live axle swap, because you're done with the GTO IRS.

05_GTO

Sounds like a good plan. I would also suggest the LS7 clutch. I fear the very first thing to go out on my car would be the trany, and as for yours the clutch.

roccox

Other than the axle bolts backing out, I do not recall seeing many drivetrain failures on ls1gto.com. I think you should be fine, although you may want to have the dealer check out those axle bolts.

xp3nd4bl3

Stick with a tire that won't hook too hard. With ~440rwhp and 17" ET Streets I like to dump the clutch at 5k or so, scratch a little bit, cut a 1.80 short time and the stock drivetrain has no problems with it. I'd be hesitant to push my luck and go with a stickier tire and cut 1.60's.

BlueSix

That's one of the things i am debating over in my head. I'm not sure what wheel/tire combo i want to go with, and i think my final selection will have a large impact on how my driveline reacts. I'm thinking i wannt go with a 15" wheel combo using some Weld wheels, (i know they aren't a perfect fit, but for the little amount of time they are on the car it won't matter) and a BFG drag radial, or an ET street radial. I'm worried that a 15" ET street will be too much hook for the driveline.

I want to go with the 15" wheels to drop some weight, otherwise i'd just run an et street on the stock wheels.

Does anyone know if te 28 spline spool from deff technics will strengthen the rear any? Maybe help reduce wheel hop?

gtodude

nobodys mentioned the adjustable koni sports / yellows for rear wheel hop - its pretty much a sure cure. personally - i got the whiteline shocks and have no wheel hop issues whatsoever.