[batarchangel]

Ok so many of you may be familiar with my issue on my 71 XR7(85-302) (C6). The whole vibration rotation Ive been struggling to figure out. Ive tried numerous things and just got done with a transmission rebuild, consisting of new torque convertor, new clutch plates and new bands. Other than that, the trans was good. So now Im stuck at this point. Im going to the harmonic balancer. I looked at the flex plate and no cracks no broken teeth. My question, I know the plates are weighted different, is it the same deal with the balancers? I now know that the plates for 85 are .50 oz and upon looking online I noticed the balancers are weighted as well. Just wondering whats the correct weight I need to get. Thanks

 

[Bad69cat]

an 85 SBF is 50 oz internal balance so yes, you need the correct flex and balancer. There are aftermarket balancers that have the ability to do both (using a bolt on counterwieght) and also use 3 bolt or 4 bolt pulleys (yours is 4 bolt I think) Kinda handy - but a stock 50 oz will work if you have no need to run anything else/different

 

[Cedar Rapids Ia]

Just curious (as I haven't been watching this thread)... are you "positive" that your universal joints are seated properly? Also, you haven't lost a lead weight from one of your tires either have you?

 

[redcougar]

There are also weights on the drive shaft

 

[Cedar Rapids Ia]

There are also weights on the drive shaft

Good point on the drive shaft...he says it is "rotation vibration" anything that spins is suspect until ruled out.

 

[Bad69cat]

OR - Do you know for a fact that the crank is indeed an '85 one...? If it got swapped in favor of something else - who knows, just another thought to chew on.

 

[wonderwrench]

Question: Do you get this vibration if you rev the engine up in park? I would think if its an engine balance problem you should be able to reproduce the vibration parked. If not it not an engine balance problem and you need to look elsewhere.

Bill

 

[batarchangel]

ok here we go again.
Things Ive checked and/or replaced:
1. Driveshaft- 1st suspect= Brand new driveshaft made my Nashvilles oldest and most reputable driveshaft shop (weighted, balanced and measured)
2. Tires- 2nd= New tires weighed and balanaced
3. Front wheel bearings-3rd= new bearings and packed with new grease
4. Vacuum leaks-4th=checked and no leaks
5. Distributor- 5th= New HEI GM style and timing reset( this helped a lot with the shaking, but shaking has started again(never helped with the rotating vibration)
6. Tune up-6th= No effect what so ever
7. Transmission-7th= Completely gone through and rebuilt(replaced clutch plates, torque convertor, and bands)

Problem still remains.

Car idles fine, put it in gear and holding the brake it shakes badly
At speeds above 45mph a kind of rotating vibration is heard

Any other helpful questions I need to answer to help diagnose please ask

Ive been told from my father the only thing he can think of now would be the harmonic balancer

 

[RayH]

Have you tried checking the balancer with a timong light? If it is slipping it will show up. Also years ago I had an 83 mustang gt that you could feel a vibration in when reving the motor, turned out to be a bad water pump.

 

[Seafoam jcode]

The harmonic balancer outer ring on my '85 mustang slipped and was just rattling around while driving a couple of years back.
Smooth as silk and them BAM, tons of vibration. If yours is the original balancer, I'd consider replacing it with another 5.0L balancer. Did you have your C6 flexplate rebalanced to match the balance characteristics of a 5.0L flex plate? If not, there's your problem.

 

[batarchangel]

Wheres the transmission identification number located on the casting of the C6? Its a 50oz weighed flexplate right? I know before like 81 it was like 28oz

 

[batarchangel]

Also noted the vibration rotation almost seems to come from under the car, hard to tell whether its in the from under me, not in steering wheel

 

[Bad69cat]

Draw a mark across the face of your damper if the ring moves you'll see it......other than that if you don't feel it in the wheel, it may be pointing to something in the rear perhaps? I did see something a while ago that somebody posted about loading the trunk with a bunch of weight and going for a drive to see if it alters anything....just for giggles I'd try it.

 

[batarchangel]

Trunks already weighed down by tons of tools, jack stands, floor jack and more, ha. I just ordered a new harmonic balancer. Guess I'll know soon enough

 

[wonderwrench]

Trunks already weighed down by tons of tools, jack stands, floor jack and more, ha. I just ordered a new harmonic balancer. Guess I'll know soon enough

The added weight changes the u joint angle so in your case you would need to remove the weight then test. From a previous post of yours it sounds like you have the vibration problem standing still. If this is the case the drive shaft, diff, tires etc. are out of the picture. No vibration in park but vibrates in gear. Almost sounds like a motor mount problem or a poorly hung exhaust system transmitting engine vibration to the frame when in gear.

Bill

 

[Seafoam jcode]

Still couldn't tell from your posts what flex plate you're using. Is it the stock, unmodified C6 flex plate?

 

[batarchangel]

ok so heres one for ya. upon pulling the transmission i noticed the driveshaft needed wedging to get out, but didnt when I put it in. When i put the trans back in I literally had to unbolt the rearend the get the drive shaft back in. Also noticed the driveshaft had hit the floor board a few times, by the shinny area right above the end that goes into the transmission. I know the trans mount needs to be replaced but it didnt get here in time to put in when I put the transmission back in. So as soon as it gets here Ill pull the trans crossmember and replace it. The motor mounts are new as well. I just replaced them too.

Big issue with my exhaust, The header on passenger side is very tight, so tight actually right after the collector the pipe sits on the trans fluid pan. I was thinking maybe I could strap a ratcheting pull to a tree and then around the exhaust and pull it out. Maybe this will work.

Going to try emptying the trunk and see what happens.

 

[Bad69cat]

The trans mount was probably your trouble all along......vibration wise at least. Now that you have the shaft out - double check all the joints including the yoke side to side movements on the rear. It's not unusual to have to "massage" the headers to fit. (some might say its required!)

 

[batarchangel]

Not trans mount, just replaced. Issue still remains.

 

[Bad69cat]

HUH? You checked out all the joints including the rear too then? Boy IDK!? How many ways can you reproduce it at a stand still? In neutral/park/rear end on stands......