ok, i'm trying to figure this one out and need some input. car is an 85 GS with an SE engine and trans but GS suspension and brakes. within the last couple of weeks i have installed new front and rear oem wheel bearings and seals, swapped the driveshaft and differential (not complete rear axle) and have royal purple in the diff. at highway speeds above 75mph the car vibrates and sounds as if there's a bad bearing somewhere. if i'm at 80mph (which i the test i was just doing a few mins ago) and i put the trans in neutral and let the clutch pedal up, the vibration seems to get worse. the tires are new. the trans bearings are a bit noisey. the u-joints feel ok..but no change when swapping driveshafts. i hear a clunk in between shifts from first to second and second to third. when i let off the gas at low speeds i hear a clunk and when i apply the gas i hear a clunk again. same clunking before swapping driveshafts and differentials. perhaps i swapped in another poor diff? the clunking is coming from the rear end. if you lay on your back under the car, trans in neutral and grab the driveshaft at the rear and spin it slightly one way and then quickly back the other way, you hear the clunk. same when driveshaft is not installed and you are grabbing and spinning the pinion flange. i need some input on this one. this is new to me. backlash problems?

 

I just went through a similar situation. My trans mount and 1 engine mount was completely torn. Replaced it and 90% of the vibration is gone. My vibration also got worse when I had the car running down the highway in neutral. That was my expeirence.

as far as the driveshaft goes; I had a clunk too. The front u joints were smooth and rotated fine, but the rear u joint did not rotate smooth and would have like a hiccup when I moved it around. I chaned my driveshaft and the noise went away.

 

the motor mounts should be good..but maybe cracked due to age..not sure but felt fine when i put the engine in a few months back. the trans mount on the other hand...i think that looked pretty ratty..

 

Checked tire balance?

 

no, but it doesnt feel like an out of balance tire. its more of a harsh vibration and makes noise..

 

+1 transmount
maybe a motor mount is spongy.

 

It was hard to tell from just looking at it so I put the 7 on a lift and got a screwjack to lift the trans. That's when I saw the tear on the trans mount. I started rocking the trans from side to side and then saw my motor mount torn as well.

 

i ordered a new mount from the dealer this morning and it will be in on monday. engine mounts check ok when rocking.

 

here is a video of the car i took tonight for further synopsis.. not great quality as i was driving and operating the camera:

 

envious of your engine its so much smoother than mine haha. plus you probably have more than my 60hp. hoping the transmount fixes it. how much did you get it for?

 

the trans mount, car or engine?

 

I vote for the trans mount as well. You seem to be very thourough with your cars Dave I'm surprised you didn't change motor and trans mounts while you had the engine out....

 

i must have missed the trans mount as i had a friend help me install the engine and it may have been one part that i thought he checked and perhaps he though i checked..usually why i do all of my own work... and now i pay for not checking the mount properly or at least double checking as i always do. this is frustraing. but at least i'll have a lot of new reliable parts

 

how much was the trans mount?

 

ordered form the dealer and will be in on monday for a cost of $34. i have the part number if you would like it.

 

I've gotten several from Rock auto. About $18 +shipping. Don't get the one for the GSLSE. They list a 2nd gen mount.

 

i vote that the drive shaft you replaced it with is out of balance.


what i meant to say was sometimes they break and you need to take the batteries out. youll have to call the manufacturer for a replacement. but all of my past girlfriends will just buy a new one, there only like 20$


p.s. any update on that windshield?

 

One fb I used to have (a few back) had the same symptoms you descibed and I finally narrowed it down to one of my trailing arms going to the rear. Where it mounted to the body, there was only the bolt, and not the bushing inside were it should've been, so the previous owner just tightened up that bolt real tight to try to take out the slop...Just something else to check if you are still having the vibration.

 

well, i'll check teh trailing arms when i put the mount in. still waiting on the dealer to call me to confirm that the mount is in. i do plan on ordering another new driveshaft here within a month or so.. i just want the car to be reliable and i want new parts to ensure reliability.

 

replaced the trans mount today and took the car for a drive. better but not great. got the car on a lift and ran it. i really need to replace the trans as the bearings are pretty noisy. i have another trans..here's hoping its good. i also was able to see play in the rear u-joint and feel it as well. little bit of noise from the diff..not sure what route i'm going to take with it.

 

Thought that would have been the problem; as it was for me. You're sure that both motor mounts are good right? They need some good force to move since the weight of the motor is sitting on them. I thought my engine mounts were good till I I lifted the trans up from the bottom and saw the seperation.
Possible your driveshaft needs rebalancing. Did you see if the balancing weights were still on the driveshaft?
Hope you figure it out because it was really annoying.

Just notice all your 7' in your sig. Why not try swapping the driveshaft to the 7 with issues?

 

the trans mount was toast. so i'm glad that i replaced it. otor mounts are fine as i checked those. i'm not ruling out a driveshaft at this point. i may pick up a used one to save some cash. the weights are still on it but there is play in the rear u-joint. seems like the differential has way too much backlash...

 

I had to change my driveshaft too. The rear u joint was really stiff and didn't rotate all that great. I kept hearing a distinctive CLUNK noise when shifting gears. Got a different one and the clunk went away.


Looks like you have alot of 7's maybe swap a driveshaft from one of them?

 

thought about that but the one in my 85 S isnt any better, there isnt one in my other 85 GS (wrecked) and the one from my 80 LS will not fit. i sold all of my good driveshafts. wishing now that i hadnt done that, lol. i get the clunk when i shift gears. all signs point to u-joints there. but the vibration is awful..

 

I hated the vibration. That's all I worked on the whole week, before work, during work, and after. Hope you get it squared away.