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I have a puzzling and annoying vibration problem in my 70 XR7 vert that I would appreciate people's thoughts on. I've searched on this topic and found some clues, and have tried several things, but most of the problem persists.
About the car: pretty much stock 351 2V windsor (145,000 miles, rebuilt heads, new timing chain, runs strong, only mod is larger 2V Holley carb), FMX trans totally rebuilt last spring including new torque converter, new U joints front and rear, drive shaft seems to spin true (have not checked balancing), 3.00 traction lok rear end (operates properly/no noises), new tires on true rims, tight front end (all new except upper control arms / ball joints that are in very good shape)
About the vibration - that bad, but noticable enough to be annoying when it happens. Definitely coming from the driveline in my opinion - you can feel it in the seat, dash, in the steering wheel. Slight constant vibration under acceleration - this alone I would not care about. At constant speed between about 45 mph (approx. 1800 rpm) and 65 mph (approx. 2500 rpm) there is a vibration that cycles on and off - about 1/2 second on / 1/2 second off. The frequency of the cycling increases if you accelerate between those speeds and it the frequency decreases if you decellerate. If you coast downhill it pretty much goes away. If you shift it into neutral, it completely goes away and coasts smooth as glass. There is no vibration under 45 mph or over 65 mph. What is also interesting is that if you are stopped in neutral and rev the engine, the vibration appears at the same rpm as on the highway - between 1800 and 2500, although it is constant iin neutral - does not cycle on and off.
My mechanic seems to think the engine is fine and is likely not causing this. I've never experienced or heard of an engine issue causing a vibration like this. I took the car back to the transmission shop that rebuilt it. He checked the tranni mounts, tailshaft bearing, rear end, driveshaft... He found the U joits were not great - especially the front one so he replaced both. That seems to have improved the vibration, but not eliminated it. He acknowledged that it could be a bad new torque converter (out of balance...). He said he would remove and replace it under warranty if it fixed the problem, but if the problem persisted, I would have to pay a few hundred $$ for his labor which I can understand.
I'm reluctant to tell him to pull the tranni and swap out the torque converter for a new one until I think I've exhausted other possibilities. Any ideas or suggestions from any of our very knowldgeable members given your experiences...?
Thanks in advance for any comments. John
About the car: pretty much stock 351 2V windsor (145,000 miles, rebuilt heads, new timing chain, runs strong, only mod is larger 2V Holley carb), FMX trans totally rebuilt last spring including new torque converter, new U joints front and rear, drive shaft seems to spin true (have not checked balancing), 3.00 traction lok rear end (operates properly/no noises), new tires on true rims, tight front end (all new except upper control arms / ball joints that are in very good shape)
About the vibration - that bad, but noticable enough to be annoying when it happens. Definitely coming from the driveline in my opinion - you can feel it in the seat, dash, in the steering wheel. Slight constant vibration under acceleration - this alone I would not care about. At constant speed between about 45 mph (approx. 1800 rpm) and 65 mph (approx. 2500 rpm) there is a vibration that cycles on and off - about 1/2 second on / 1/2 second off. The frequency of the cycling increases if you accelerate between those speeds and it the frequency decreases if you decellerate. If you coast downhill it pretty much goes away. If you shift it into neutral, it completely goes away and coasts smooth as glass. There is no vibration under 45 mph or over 65 mph. What is also interesting is that if you are stopped in neutral and rev the engine, the vibration appears at the same rpm as on the highway - between 1800 and 2500, although it is constant iin neutral - does not cycle on and off.
My mechanic seems to think the engine is fine and is likely not causing this. I've never experienced or heard of an engine issue causing a vibration like this. I took the car back to the transmission shop that rebuilt it. He checked the tranni mounts, tailshaft bearing, rear end, driveshaft... He found the U joits were not great - especially the front one so he replaced both. That seems to have improved the vibration, but not eliminated it. He acknowledged that it could be a bad new torque converter (out of balance...). He said he would remove and replace it under warranty if it fixed the problem, but if the problem persisted, I would have to pay a few hundred $$ for his labor which I can understand.
I'm reluctant to tell him to pull the tranni and swap out the torque converter for a new one until I think I've exhausted other possibilities. Any ideas or suggestions from any of our very knowldgeable members given your experiences...?
Thanks in advance for any comments. John