MY99TAWS6

iTrader: (3)

Since have a 4l80 had to got to off the trans torque arm setup.First had spohn tunnel mount but ground clearance was awful so went to crossmember mount setup. Ground clearance is great but think got some more vibrations coming thru. The setup does of course run a poly torque arm bushing and can transmit vibrations directly into the floor thru the crossmember.

So few ideas going to try. First figured should try some rubber sheet stock under the trans crossmember bolts. Figure this might help some,maybe a lot.
Might change out trans output to front yoke angles and already have shims in there to fix that but guess just see depends on how much the rubber compresses and how thick would need to see any noticeable vibration reduction.

Other idea is not sure can make a stock torque arm bushing work in there. The bmr torque arm has the round end on it. The stock has the two part
slotted bushing. Or can maybe make a new bushing out of piece of solid rubber??

I don't think anybody currently makes a rubber round hole torque arm bushing????

So what you think guys..

Also I may stil have my angle wrong and hearing few ideas on that. I watched bmr video and think its different from their instructions..Have to recheck the instructions. Also someone said to put it in fourth hole from bottom and set angle to negative 5. SAid that helped a lot.

MikeG

iTrader: (33)

I've thought about the rubber between the crossmember and the floor too. Anybody tried this?

jimmyblue

iTrader: (11)

I did, but it helped very little. I ended up giving the
crossmember to a local buddy and going back to
tail mounted. You'd have to have rubber above and
below the crossmember, and not fully compressed.
I got up to 1/4 above and below and it still rattled
everything in the console.

MikeG

iTrader: (33)

Jimmyblue, you and alot of guys with the relocation crossmember talk about the rattling alot. I don't get any of that. I get alot of clunks instead though, and that's what annoys me about this setup.

slow67

iTrader: (2)

I don't have any clunks or rattles. I don't really have a choice tho, with a 4L80E.

MY99TAWS6

iTrader: (3)

I have no choice either . Had spohn tunnel mount and ground clearance was really bad on the one I had. It had big dip to clear the exhaust and it hit everything.drive ons, bumps in the road..horrible. So tunnel mount or crossmember mount as 4l80 dont' have tailshaft provision and might break back of trans with my power levels.

I don't understand why some rubber if thick enough or right type of rubber wouldn't absorb vibration if put between crossmember and floor. It has to transmit thru there.
I am going to try a few different thicknesses and see what happens for myself.

I am still going to do my three part plan also. Carbon fiber driveshaft..fluidampr balancer and likely put stock rubber motor mounts in the car again with torque strap.
If still have vibes after all that stuff guess just have to live with them.

I do think it might be nice if someone would make us a torque arm bushing in rubber instead of poly for the round torque arms like my bmr. I would think can just buy a block of rubber and make one up but still nice to have more options . Poly just seems to not be worth a crap at absorbing vibrations.

I know am picky. Want a super streetable super high hp car . But hey guy can try right..LOL

Also keep in mind other things can cause vibrations..driveshaft pinion angle is pretty darn important. unbalanced driveshaft..my new strange was out of balance quite a bit when had it checked.

dlandsvZ28

Don't know about any of the cars above or your car but I fought vibrations too with the tunnel mount crosssmember - a Yank.

After putting the car on a special drive-on lift we were able to run the car up through the gears to about 70 mph. What we discovered is that all of the vibration was from the driveshaft yoke at the rear of the transmission. Raising the tranny a half inch higher off of the crossmember solved most of the vibration. I can't raise it anymore because the bolt isn't long enough to put the nut back on that attaches to the crossmember.

Apparently some crossmembers lower the transmission creating creating bind between the front and rear u -joints. Just one or two degrees from -2 on the rear would cause severe vibration when the transmission was bolted directly to the crossmember. But when we raised the transmission a 1/2 inch off of the crossmember with a spacer most of the vibration on the front u joint would go away.

In fact - there was so much bind the driveshaft would squeak as I turned it with my hands.

Note: New PST driveshaft with new joints front and rear. Moser 12 bolt with complete rebuild gears and bearings.

Summary:

Try raising the transmission up and off of the crossmember using shims to eliminate driveshaft vibration.

Use a special lift where you can road test on the lift and visually see and hear the vibration of the driveshaft on the lift rather than having to road test each time for changes as you adjust the pinion angle.

Shim the front before adjusting pinion at the rear. After shimming my ds was + 2 with pinion angle at -2.

I noticed that driveshaft vibration causes some whine too.

My vibration sounded like a loose bucket of rocks under the car - it was all from u joint vibration due to the angle of the transmission on the crossmember.

The Fugitive

iTrader: (6)

okay I am going to try to post a video of my vibration tomorrow and see if it is the same as any of you when I take it back to the shop. How did you fix this if you did?

MY99TAWS6

iTrader: (3)

I need to drive my car a bit more in spring to see how its doing now. My unbalanced strange driveshaft wasn't helping things. My trans has been shimmed up at crossmember. I think pinion angle is now set correctly to about negative 1.

I will see how things are in spring. My three part plan if still noticeable is to get a carbon fiber driveshaft ,fluidampr and go back to rubber engine mounts with torque strap type of setup. Also will try maybe thicker rubber shims under crossmember.
Hopefully some of all of the above will fix things up.

Like said us 4l80 guys currently have no choice ,have to run either tunnel mount or crossember torque arm relocation. 4l80 have no torque arm provision.

The Fugitive

iTrader: (6)

I am going to remove the tires and rotors to make sure it isn't anything with them maybe being unbalanced then I am going to take the driveshaft off and run it to see if it is the yoke, u-joint or the driveshaft. I have my driveline/pinion angle set at a -2. Weird thing is that the vibration is so bad I think it is setting off my rear knock sensor.

dlandsvZ28

Review posts #19 and #20.

https://ls1tech.com/forums/general-m...l#post12668181

I'll bet the incorrect height/thickness of your poly mount is causing the issue. After shimming the poly-mount you have to reset the pinion angle because the angle of the front u-joint causes a change in the angle of the rear u-joint.

HTH

The Fugitive

iTrader: (6)

oh I am not running a poly mount I have the stock rubber mount that I picked up from autozone

dlandsvZ28

Yes - but is it the correct part number and the same height at the stock one? Mine was not.

The Fugitive

iTrader: (6)

hmm good question am I looking for the stock height for the 4L60 or the 4L80? I got my L80 from a 2002 chevy van

JGA

Does your crosmember have the adjustment holes for the position of the poly bushing like the BMR unit? If yes, check the holes you are using. If the front of the torqure arm goes into the bushing hole at level (no angle), it will reduce the vibration. I had mine set as high as possible without hitting in the tunnel. This put the front of the torque arm going into the bushing at an angle. I lowered the bushing 1 set of holes on the crossmember and it made a big difference in ride quality. No change in performance.

Make sure you get the pinion angle right, or major problems. BMR instructions are correct. If auto pinion should be -1. If M6 pinion should be -2. I would think -5 would destroy your rearend. Take it to a local shop if needed.

MY99TAWS6

iTrader: (3)

Yes adjustment holes at front of torque arm. I think moved it one down from middle currently to gain some tunnel clearance. I think have things set at negative 1 pinion angle.
I won't be messing on the car again till about april 1 ,car is away for winter till about then.