Clunk from rear end upon launch
 

ok well not really launching the car, but dropping the clutch.. if i start off smooth, no problems..

Few weeks ago i threw in a s4 TII lsd. my subframe is up tight, diff is mounted tight, front diff mount is good, even got a pinion snubber on it. There is a clunk that i cant determine. I dunno if its the diff, seems like if i have the rear in the air and move one wheel there is a slight play til i hear a clunk and the other moves. Otherwise the diff seems to be good, fresh fluids etc.

Could it be the u-joint? anything i should suspect?

maybe you snapped the diff mount mount like that other guy recently did?

It started ever since the S4 LSD swap?

yeah i think so after i swapped the diff, i had a NA welded in there *came with the car*, and that was a harder clunking from what I believed to be breaking *tho i havent cracked that diff open yet, just sitting in on the ground *..

I dont feel like droppin the subframe to look at that front diff mount, ill try putting preload on that snubber against the diff and see what that does.. Im by myself so i cant really have someone engage the drivetrain while lookin at it in the air.

ok im assuming maybe i jus got a bad diff.. theres a lil play from the spline to where it actually engages. is that possible? from my knowledge and the car i got the diff from *car was stock*, i doubt its ever been cracked open and messed with as far as if the gear mesh is off etc..

im Assuming its the diff, can i just pull the driveshaft and hit the spline with a impact gun?

If you want to rule out the diff mount, jack the rear up and have a friend engage the clutch in 1st gear several times while you monitor diff movement.

Did you check the Oil level in the Diff?
Check the axle nuts,to make sure that they are on Tight.also see if the Driveshaft U joints are good.(all can be done,alone).
Are you leaking Fluid at the Front of the Diff?>is it loose there?.If so,the Bearing is Kaput..the bearings are 65 Cdn( I checked Mazda).the oil seal and nut are about 20 bucks CDN.

thanks, seems teh diff mounts are fine. no fluid leakage, and i put fresh gear oil when i put it in about a month ago. *it had this problem when i put it in, but i always thought maybe something was loose so i didnt investigate til now*

What im seeing is i can turn the center driveshaft with my hand and theres a slight few degrees of play b4 it spins the wheels.. While in the air with the car on, i can drop the clutch while leaning out of the car looking in that direction and really cant determine what exactly it is, but im sure its that slop. Compared to this old welded NA diff i have sitting on the ground, theres no play at all when i turn the spline.

Figure it out? Try pushing on the front of the differential when you're under the car. If it moves upwards about an inch or more then your front mount is shot. I have this problem as well.

if your pinion snubber is not preloaded then its probably bouncing off it on a launch.

A pinion snubber is a thick chunk of rubber. Even if the front diff mount was a clean break, I wouldn't expect a clunk from the snubber unless he was launching at 8k with a 4-puck clutch. I think he's right to suspect the internals.

Describe this clunk? Is it a dull sound or a sharp sound?

I suspect excessive gear backlash. Just for example, when you have excessive backlash in the rear end with an automtic transmission and you put the selector into drive, the rear end will clunk as the gear teeth engage each other due to the engine loading up the drivetrain.

it was a bad motor mount.. probably the whole drive line taking a shock.

Swapped the motormounts and it went away.