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Vibration after 2-piece driveshaft

4K views 10 replies 7 participants last post by  llafro 
#1 ·
I had ta shop pull the transmission and rebuild it due to a whining noise it was making. While I was at it, I also replaced the rear main seal, clutch (Monster LT1-S), shifter (GTOG8TA.com), and driveshaft (2-piece from DSS).

I have a vibration that feels like a very low frequency bass rumble from underneath the car. This is something you more feel than hear. It's most pronounced at low RPM in second, third or fourth. It's less obvious if I drive the car harder. With the new shifter, I feel less vibration than I did with the stock shifter. Any guesses where to look for the source of this?

I still have the stock trans and motor mounts. I had the poly trans and engine mounts in the trunk and forgot to tell the shop to put those on as well. So, replacement of the mounts is next, but I am wondering what I should look at as well.

The clutch and shifter feel good. The pedal is much lighter than with the LS7 clutch I had in there before. I won't know about holding power until I get it reasonably broken in. The shifter feels really nice by comparison to the stock one. It's much easier to snick off the shifts as needed. It does take some getting used to, though, since it is notchy and doesn't center like the stock unit.
 
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#2 ·
Low RPM, high load?
Did the shop install a bronze shifter cup bushing?
 
#4 ·
(1) Verify the rear seat belt bolts have trimmed to the nuts.
(2) Verify the carrier bearing is bolted down
(3) Inspect the Transmission and diff mounts
(4) Disconnect The driveshaft from the 3 finger flange and move one finger over...due to harmonics one position maybe better then the other
 
#5 ·
My trans mount was shot, that was the cause with my 2 piece. I window welded my stocker but eventually it all broke loose again. Got a Hinson mount and never looked back. I have also DSS told me that if you move the center carrier bearing a little to the side so the shaft isn't perfectly straight that helps too.
 
#6 ·
I got a chance to slide under it, but it was late and I wasn't going to change anything at that hour. Everything appears to be tight and in place. I used a bar to pry against the tailshaft of the transmission, and the mount doesn't appear to be loose or split. The transmission only moves slightly as it should.

At the carrier bearing, the shaft appears to be located more to the driver side than the passenger side. The spacing is obviously different.

The seatbelt bolts weren't trimmed by the shop like I asked them to do. But, they obviously clear and I can stick a finger between them and the driveshaft. There are no marks that would indicate the bolts have hit the driveshaft in any way. I will still get some washers to improve the clearance.

The next step may be to reinstall the stock shaft and see what that does. The problem is that the rubber isolators on the stock shaft are kind of shot (hence the new driveshaft).
 
#7 ·
Well there's your problem:



The driver side engine mount was so torn that I could extend it by almost an inch just pulling with my fingers. It was only held together with the internal metal. The vibration is improved, although not gone. I installed Whiteline Poly mounts and a Hinson poly trans mount. The stock trans mount was partially collapsed and sagging. I know the poly mounts are transmitting some vibration into the cabin now.

I think the remaining vibration may be coming from the rear end. There seemed to be a lot of play in the rear end. We held the driveshaft firm and turned the wheels and got a good clunk back and forth. There appears to be at least a couple inches of rotation on the tires forward to backward with the driveshaft not moving.

More worrying was the play in the driver side axle where it goes into the pumpkin. There is a noticeable movement in the axle up and down on the driver side, where there is no motion in the passenger side axle. I basically grabbed and shook various parts to check that things weren't loose.

So, how much slop should there be in the rear end?
 
#8 ·
Glad to hear you found the mount issues. I tried new mounts after replacing my carrier bearing and guibos on the stock shaft only to find the vibration even more apparent. Cant decide if i should get the stock shaft rebalanced now ($150 + what i already spent in the guibos/cb) or just go dss. No one local seems to have one theyd let me borrow
 
#9 ·
Over the weekend, we put in a rebuilt rear end with a Truetrac, GForce inner stubs, anti-hop axles, and a Harrop diff cover. That really got rid of the vibrations. Even after the new mounts, I still had vibrations that would change under throttle or coasting. There was enough vibration that you could feel it through the seats. Moderate throttle in second gear would cause a good vibration. I figured it was in the rear end somehow, and it was.

If you have to disassemble a stock rear end, just air hammer the side adjusters. Nothing else worked. I had the billet side adjusters from GForce, so no biggie. What a dumb idea to put aluminum parts in a cast-iron housing!

 
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#10 ·
Same symptoms with a 1 piece aluminum shaft. I had hoped the motor mounts were my problem, at 85k miles they were still 1 piece only the fluid was gone. New mounts raise the engine about 1/4”. I then had hoped it was the 1/8” diametral play at the trans output shaft bushing. Fixed that and it still vibrates and has harmonics under load and when off throttle coasting. I’m now down to taking the halfshafts off and getting into the rear end.

So the damage on the side adjusters is from getting them off? Is that where the play is from?
 
#11 ·
I bought a junk yard rear end to rebuild so we could take our time. The side adjusters on that rear end were siezed in the housing. The only way they would move was with an air hammer. The damage is from that process. The guy that took it apart for me tried welding up some tools, but they all broke. He did get to take out his frustration with the air hammer, though.

I couldn't really tell on the original rear end if there was an obvious problem. The axles don't seem to have any crazy amount of play in them. I don't really know what exactly fixed the problem. It was shotgun approach. Do it all while I was at it...
 
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