WTR388

Well, the Ls1/T56 combo is a blast... And I'm afraid to really get on it.
If I get on to it hard (near full throttle, quick shifts at higher RPM or if I'm lugging it in a higher gear going up hill but using a bunch of throttle) I hear a noise in the rear, and honestly it sounds like gear teeth "meshing" together. I can replicate it whenever I produce similar scenarios.
I do have a bit of vibration cruising at highway speeds, but I know there is a bit of slop in my front wheel bearings.

I'm wondering if I'm stressing the 10-bolt and it's on the verge of destruction or if it could be something as simple as a U-joint?
Car is originally an 87 T/A with the 305 and T-5.

A buddy and I tried to pin point what it could be... The clutch works great, I used an LS7 set up, brand new. The trans needs a rebuild which is coming soon (can't shift in to 4th).
I'd like to feel comfortable doing some mild launches with this thing (tires aren't super sticky) and to feel ok banging up through the gears... A new rear is in the plans but not the budget at the moment.

//<86TA>\\

iTrader: (14)

Did the rear make noise before the swap?
Are you sure the noise is not from the trans?

If you have vibrations at crusing speed, you may need to correct the driveline angle and this may also be causeing some noise.

Did you do any other suspension work since the swap?

cosmick

Enough 75W90 in there?

WTR388

Didn't change anything on the suspension so the angles are still good.
The rear end used to make a bit of whine before the swap, noticed when coasting off the gas at speed, and still does it. It's hardly noticeable. This new noise never happened before... However I'm now running over twice the power with a clutch that isn't slipping.
I plan on getting the car on a hoist this week so I can do an inspection, and will check the fluid level... I have a bottle of oil in the truck in case I'm low.

I just hear how weak these rears are, so I'm afraid to really get on it and sort of affects enjoyment of the swap!

//<86TA>\\

iTrader: (14)

The rear is not the strongest thing out there but at the same time is not as weak as people say it is. Co sidering the same axle came behind the ls1 car your drivetrain came from chwnces are it will be fine unless u start running drag radials or slicks.

The trans does not sit at the same height as the stock trans so the driveline angle has changed which could make this noise worse.

You have 2 options, fix the rear or buy a new one. Nothing else will help these issue if they are axle related

cosmick

The ring gear is the weakest link, and 3.23:1 is theoretically the strongest ratio that'd work with the 2.66:1 first gear in the '98-'02 Z28 T56. Sure, the teeth are smaller, but there's 2 of them engaged at all times.
I haven't gotten around to finishing my 8.8 axle swap, but it's not my first, it's not difficult, and it's not that costly. Mostly it's just a few days laying on the ground, sweating and cursing.
Not many attempt it, but the 8.5" from a '71-'81 F-car is the same u-joint, same width, same lug pattern, probably the cheapest and easiest upgrade if you can do the fabrication for the suspension brackets. It can be upgraded to survive 900 HP on drag slicks in a full-weight street car.
If you do break what you have, the upgrade is about the same cost as fixing what you have, unless you just grab a salvage yard ring gear. Really, you should keep its pinion with it, but if you don't change ratio and the pattern looks good with backlash set to spec...that risk is your decision. Others have gotten away with it. But it only works if you stick with genuine GM gears, and no mixing a 7.50" ring with your pinion from a 7.625" set.

WTR388

I forgot, the best analogy for the noise is like the sound of a diesel engine, not the exhaust note but the engine itself... Happens at all temps, I've checked and it isn't my motor as there is no excess noise once it's warmed up (some piston slap when cold). The motor was out of an 02 T/A with 140,000km on it (84,000 M) and came out of a car that was traded in to our version of "cash for clunkers" and as such couldn't be re-sold.
The trans was a 94 converted over, the reason it came out of the car was the owner bought the 94 and put a big block in it and took the T56 out so he could put his Auto in it as it's a drag car... But now I'm beginning to think he drove that car with this trans in it, until he bent the shift fork or messed up the syncro being behind that motor. But, it is being rebuilt in the next month or so. I'll be throwing in a new u-joint when I do it. The rear seal is dripping slightly so I have to do it now instead of in the fall like I planned.

An 8.8 is what I want to do, I just have no clue how to go about doing it. By the time I get to doing that swap I will have the skill set to do it. The goal with the car is to do some autox and lap days.
If this rear breaks on me I won't be fixing it, and I don't want to put money in to it since I'm planning on a better rear anywys.

I'll be lowering the car, will that help with the driveline angle? It appears I'm going with weight jackers, founders tubular adjustable stuff in the rear.

Thanks for the help guys, this is my first project car so I'm learning a lot.