Still shakin'

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Tuckerjr

Tuckerjr

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OK, I'm still chasing what I believe to be a driveline vibration. I added some pinion shims and it seems to change when the vibration occurs and the severity. Let me see if I can explain where I am so far.

I have a 360 with a 904 transmission in a 74 dart sport, 8 3/4 rear 742 chunk. I was told the car was a 318 when I purchased it, and shortly after doing so I replaced the motor mounts with 318 mounts, not realizing I had a 360.

Been doing some reading and found that I could use a 318 mount but it would require shimming on the drivers side, which I didn't do when I installed them. Maybe the engine is not fully seated into the mount? That will be the first thing I will check.

Secondly, I checked transmission and pinion angles with it on the lift last weekend and it looks like the transmission was 6 degrees down, the pinion was at 0 degrees. I recently installed an Energy Suspension transmission mount bushing and really like it, but when installing it I had to pry the rear of the tranny over about 3/8 of an inch to get the mount in. Could this misalignment be caused by the motor mounts or is it normal? I put in a 4 degree shim to raise the pinion on the rear and it only got worse. The 6 degrees down seems excessive, so I may shim it up some after making sure the engine is in the mounts correctly.

This car originally had an 8 1/4 rear, which had the same issue. I swapped to another set of rims and tires with no improvement. I have a new driveshaft and ujoints, new harmonic balancer for a 360, and what I believe is a 360 torque converter. Or at least it looks like one, it has weights on either side of the drain plug. Just recently it broke a flex plate, which I replaced. I have some shaking at idle but I am not sure if its just cam (which I don't know what the specs are), or if there is something else wrong.

Its a harmonic type vibration at around 55-60 mph, and it seems better without the shim vs 4 or so degrees up. Maybe I went too much. I'll try to get it back on the lift this weekend and verify all my angles.

I think I would like for it to be 3 degrees down on the transmission, and roughly 3 up on the pinion under load.

Also, Is there a way to verify what torque converter I have?

I'll post my findings after I get to work on it tomorrow, hopefully.

-Russell
 
Harmonic vibration is almost always caused by one or all having wrong torque converter - flex plate - - harmonic balancer.318 is internal balance 360 is external balance
 
I am chasing the same thing. Mine starts at about 70 mph, gets heavy at 85 or so, horrendous at 100 and is practically undriveable at 110. I had it with my 318 and don't remember if it was a problem with the stock rear end. I had a terrible vibration the first time I drove it and knew it was the converter. I changed the converter and installed a Dana 60 at the same time. It was much better, but it came at speed now. I changed wheels and tires for fitment, and that didn't change it. I was driving the car to the shop to install the 408 and the fan broke two blades off. I thought "aha! The damn fan was unbalanced from the cracking!" I put in the 408 and 200R4 tranny. Vibration slightly better but still there. I installed an aluminum radiator and electric fans, still there. As soon as the snow melts I am going to check my pinion angle as well, but I know it was good on install. Worth checking again. I am leaning towards a slightly bent axle. I jack it up and let the wheels spin and I can see a slight bounce on the driver's side. I will keep in touch with what I find fixes mine, and I am subscribed to this post.
 
X3 on the drive shaft balance. I had mine cut for length, then new a end welded on. It had a vibration at 50 MPH. I took it to another machine shop and the index was off. They redid it and rebalanced it and no more problems. Check the index!!!
 
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