I just got my 1964 chevelle back on the road. Recently put in a 700r4. The driveshaft has been balanced and new yoke/u-joint at the tranny end. I get a bad vibration between 50 and 70 mph, above about 73 mph it is smooth as silk. Same vibration accelerating and decelerating. I tried rotating the tires from front to back with no improvement. :(

What should I do next?

It sounds like a driveshaft vibration, is it like a drown noise?

Dave

Driveshaft balanced, new yoke and u-joint on the tranny. All set up by the driveshaft shop in my area.

It is more of a vibration than a noise.

Shorter drive shaft might have thrown the driveline angle off. Do a search on pinion angle.

I did a similar swap on my el camino. Double check the rear u joint, and rear pinion. This became more evident after I swapped. When vibrating at say 55, does shifing to a lower gear remove the vibration or change it.. Bent drive shaft? Flex plate or T/converter balance. I have had a flex plate break from wobble (dibris behind mounting points). It vibrated. Will it vibrate if you just rev it to 2500-3000rpm in neutral? Take it to the balance shop and have them look.

Vibration is dependent on mph, not rpm. Makes me think the vibration is coming from behind the transmission. :confused:

I checked the pinion angle and it appears OK to me. I dont remember what I measured but did research it when putting the tranny in. I guess it wouldn't hurt to double check it again.

What should I check on the rear pinion? The rear u-joint was part of the assembly that was balanced at the driveshaft shop, I would think it is OK.

Could a "loose" front suspension cause vibration between 50-70 mph? My front suspension is getting close to needing an overhaul.

Can you duplicate this on jack stands. If the vibration is still there then that eliminates the front end. Next remove the wheels, bolt the drums or discs to the hub to eliminate the tires. If you can plug the trans out put, remove the drive shaft to elimitate it. Chances are it is the pinion angle but all this will eliminate components.

I found my pinion bearings were worn. This and a slightly worn u joint caused vibration. I noticed it right away after the swap, because I had been driving a new car for a while during the swap.. I have had out of balance drums, bent wheels, poorly machined axles; all cause vibration. I was able to eliminated the problems.. It takes a methodical approach. Did this car vibrate before the drive line change? If not, it *must* be the components you changed. You can raise the rear axle and support with Jack stands. Run the speed up to 60. THIS IS DANGEROUS. But it will tell you a lot. If the vibration is gone, it was your front wheels etc. I suspect it is not. But, if it still vibrates, you can let it idle in gear and check for bent rims etc. ARE the wheels balanced? Thrown weights?? Driveline is higher frequency than wheel or tire vibration. My 78 elcamino had 1 bent rim, and I ended up buying 2 salvage yard axles, and one brand new axle to eliminate wheel wobble. Old cars...........be careful and good luck.

Vibration was there before swap, but now it is much worse. Before swap it was between about 60-70 mph, now it is about 55-70 mph.

bent axle , bad tire , out of balance drive shaft, out of balance tire , bad shocks , loose lug nuts, but I'd check for a bad U-joint , its possible you don't have one seated correctly in the yoke !! BTDT :p

I had the same problem and had my drive shaft straighten and that it, no vibration. Maybe get you drive shaft checked out again by someone else.

Well, I put the rear on blocks and ran it up to 50 mph. Stopped at this point as the vibration was much worse and started sooner (about 40 mph instead of 50 mph) than when I was driving it.

Now I am confident that the front end is not the culprit.

Rotated the tires and same vibration, I don't think the wheels/tires are the culprit.

I had the driveshaft trued and balanced with a new front yoke (the old one was twisted), I don't think that is the culprit.

That leaves only the rear end, right? Anyone have any other ideas? Where is a good place to look for upgrading the rear end. The original posi unit has bad axles and ring gear, the open unit currently in the car was a junkyard donor out of a cutlass if memory serves right. Also the car seems like it has "slack" in the driveline, was evident both before and after the swap from 4-speed to 700r4.

Should I rebuild or start fresh. Both axles are 10 bolt. Will any year rearend fit 64 or is it a different width than other years?

Anyone?

Depends on your budget. You can overhaul it and still wind up with a somewhat weak 10 bolt. Buy new and you have lots of choices. Personally, when my diffy packs it in I'm buying a Ford 9". Currie has a good website where you can build the rear end and it cost's it out for you. Another good source is Moser.
http://www.currieenterprises.com/
http://www.moserengineering.com/

I had a similar problem with my daily driver Toyota and it turned out to be a bad U-joint.

not a u-joint, replaced rear u-joint (new u-joint in front when driveshaft was balanced) and still have same vibration.

if you jacked the rear up, the pinion angle changed, therefore changing the angle of incidence for the vibration....double check pinion angle

I have been chasing the same type of vibration on a 65 El Camino for 8 years. I have been everywhere with the pinion angle, I have completely changed out the drive train, replaced components etc., etc. Yes I have swapped out transmissions , rear ends, driveshafts ( I'm real hard headed)..... I have reached the conclusion that an after market 4:11 gear set will produce a buzz. The more you tighten up the suspension such as polyurethane bushings and frame bracing, the more you will transfer the buzz up to the passenger compartment.

Update.

After taking a few months off from working on the chevelle I decided to take it to an "old school" mechanic and let him try and fix it. One week later its fixed, he put in another driveshaft. Now its smooth past 100 mph.

Looks like I will not be using the driveshaft shop ever again.