1970 SS396 El Camino. So I bought a complete TKO600 kit and had a local reputable company do the conversion from a Turbo 400. First off, I am very pleased with the product and instal. However I have a driveline vibration I'm having trouble isolating. I get a harmonic vibration in either 4th or 5th above 60 mph. It doesn't occur during accelation (even past 60), but manifests itself when I lift the throttle then slowly goes away as the speed decreases. Its funny, but I can maintain the vibration after I lift by re-applying a little throttle. I put on an Edelbrock adjustable upper control arm, checked angles and have ended up with about 3 degrees down on the transmission, about 3 degrees up on the pinion, then the drive shaft is about 1-1.5 degrees (which makes for 1.5-2 degrees working angles). I thought that would solve it but it didn't. Now I'm starting to think that the bushings on the lower control arm (being 38 years old) are still allowing the rear end to slightly rotate during acceleration and deceleration, and hence allow the vibration. I also didn't change the original bushing on the diff where the upper control arms mount to. Could this be the problem that could be solved with aftermarket lower control arms and all new rubber bushings? I've checked for everything else I could think of: its not the flywheel or clutch, I got a new balanced driveshaft and u-joints with the kit, the rear end was just rebuilt with new 3.73 gears, rebuilt posi, new axles and bearings, I have complete new drum brake assemblies on the back, and I have new tires that are balanced. Help me you experts! Jeff
harmonic driveline vibration after TKO600 install
JeffN
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1970 SS396 El Camino. So I bought a complete TKO600 kit and had a local reputable company do the conversion from a Turbo 400. First off, I am very pleased with the product and instal. However I have a driveline vibration I'm having trouble isolating. I get a harmonic vibration in either 4th or 5th above 60 mph. It doesn't occur during accelation (even past 60), but manifests itself when I lift the throttle then slowly goes away as the speed decreases. Its funny, but I can maintain the vibration after I lift by re-applying a little throttle. I put on an Edelbrock adjustable upper control arm, checked angles and have ended up with about 3 degrees down on the transmission, about 3 degrees up on the pinion, then the drive shaft is about 1-1.5 degrees (which makes for 1.5-2 degrees working angles). I thought that would solve it but it didn't. Now I'm starting to think that the bushings on the lower control arm (being 38 years old) are still allowing the rear end to slightly rotate during acceleration and deceleration, and hence allow the vibration. I also didn't change the original bushing on the diff where the upper control arms mount to. Could this be the problem that could be solved with aftermarket lower control arms and all new rubber bushings? I've checked for everything else I could think of: its not the flywheel or clutch, I got a new balanced driveshaft and u-joints with the kit, the rear end was just rebuilt with new 3.73 gears, rebuilt posi, new axles and bearings, I have complete new drum brake assemblies on the back, and I have new tires that are balanced. Help me you experts! Jeff
My TKO install resulted in the same after substantial suspension work and near perfect driveline geometry. Sold it before I tracked down the cause. I have seen u-joints (even new ones) cause this before. I have also seen “new” driveshafts improperly balanced set up a harmonic vibration at selected speeds.
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Try getting your working angle down to less than 1* but at least .5* difference front and rear angle. Make sure the exhaust does not touch anything metal on the car body or frame. IT will do the same thing and sound like and feel like a drive line vibration.
Jeff
Put a dial indicator on the drive shaft to make sure it's rotating true. If it's ok then it's possible the drive shaft balance is off. Before removing the drive shaft to check balance, try turning it 180* in the yoke and test drive it again. Camaros and Chevelles have a compound angle (there is a left to right angle as well as a up and down angle). Try adjusting the pinion angle down a little at a time (below what the text book says) and test drive it each adjustment. Small adjustments are easier to keep track of to see if things improve.
Put a dial indicator on the drive shaft to make sure it's rotating true. If it's ok then it's possible the drive shaft balance is off. Before removing the drive shaft to check balance, try turning it 180* in the yoke and test drive it again. Camaros and Chevelles have a compound angle (there is a left to right angle as well as a up and down angle). Try adjusting the pinion angle down a little at a time (below what the text book says) and test drive it each adjustment. Small adjustments are easier to keep track of to see if things improve.
Jim. Thanks for the advise on the driveshaft. You really think it's a possibility that it is out of balance? It's brand new and purportedly balanced. I will rotate it 180* and re-torque. Is the driveshaft only supposed to go on one way?? If I recall correctly, I think someone posted one time that the bolts should be torqued to something like 14 ft.lbs., and if higher could cause a problem like this. You ever heard of that?
I planned on boxing the lower control arms anyway, and replacing the bushings on the lower control arms and the differential 'ears' with new rubbers. I'll probably do that to tighten things up, then start adjusting the pinion angle again. Thanks again for your advice, and that of everyone else that replied. I'm going to solve this vib problem yet! Jeff.
I planned on boxing the lower control arms anyway, and replacing the bushings on the lower control arms and the differential 'ears' with new rubbers. I'll probably do that to tighten things up, then start adjusting the pinion angle again. Thanks again for your advice, and that of everyone else that replied. I'm going to solve this vib problem yet! Jeff.
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Jeff
Yes it is possible (not usual) to have a new drive shaft out of balance. Depends on the guy doing the balancing. You describe your vibration as harmonic. Do you mean cyclical? (not constant). A constant vibration can usually be associated with balance or bad run out. Cyclical, or a come and go, as you describe harmonic is usually associated with u joint angles not working together. Hard to describe in writing but U joints don't turn at the same speed throughout their turning circle, unless of course there is a zero angle. As the joint rotates (while at a given angle) it turns quicker as it enters the inside of the angle and slower as it goes around the outside. Both U joints must be at equal opposite angles to counteract each others rotational speed differences. Usually if you are within 1/2* of each other you won't feel any vibration but. it's there. When under load the entire drive line is rigid and will transmit noise and vibration much more efficiently. Lots of guys will put in solid or urethane suspension and body bushings and or engine mounts in an effort to make the car more responsive and solid but one must remember the factory used rubber for a reason. It isolates noise and vibration. The old U joint connector works very well but it does have it's limits. That's why higher end cars use CV (constant velocity) joints as they turn at the same speed the entire circle of travel. More expensive but much better. There are many other factors to consider when trying to find drive line vibrations such as drive shaft diameter, length, wall thickness, material used, critical speed and a few more. Give me a call and I'll try to help you out. If I can't answer your questions I'll put you in touch with our drive line shop.
Jeff I had this same problem and still do to a small degree, my car was lowered when I got it, I did a complete restoration includeing TKO-600 and have battled a vibration at about 60-65 mph. After adjusting pinion angle with pinion up 2 degrees and tranny at what I thought was 2 degrees down, vibration was absolutly unbearable after checking angles again I realized tranny was -4 down not 2 and upper controll arms would not adjust up over 3 degrees. In my case my tranny tunnel needs to be recut so tranny can go up in rear. However in desparation I have tried adjustments in 1 degree increments and have found that with the pinion at 2 degrees down, vibration is almost gone and only noticeable to me passengers dont seem to notice it. Its frustrating for sure.
Jim, I'll try rotating the driveshaft 180 degrees, then retorque the bolts 15 ft.lbs. The vibration is cyclical, so I agree it must be the angles. I'm going to mess with the pinion angle in small increments to try to reduce the vibs to a minimum (hopefully none), then have the bushings replaced with new rubber ones, and have the LCAs boxed. Been wanting to do that anyway. Thanks again to everyone for your advice.
Sid, thanks for the comments. I may shim the back of my tranny to get it up a little and reduce the downward angle from about 3-3.5 degrees down (pointing down toward the rear of the vehicle) to about 1 or 2 degrees down. Then adjust the pinion to match, equal but opposite. I've been doing these pinion adjustments with the car on the ground (no jacks), so it is a little hard to get underneath and get a real close eyeball look at the angle meter. I think I will re-measure and work on it again new years day. Jeff.
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This is a interesting subject as i am doing swap i want to get it right first time jim certainly seems to know his stuff was wondering has someone got a diagram showing side view of complete driveline showing correct angles they can post. Also to set up trans angle / diff angle should car be sitting on road at its ride height or should chassis rails be parallel to road [level surface] but still with load on axels, hope i explained that right?. Hope this post continues its a help to everyone
If people would quit believing these swaps can be done without major floorpan mods,most of these problems would go away. Before you start the install,take a protractor and find the angle of the transmission output shaft,(providing that you have good motor and transmission mounts installed) then install the new tranny and keep cutting and fitting until you have the same angle. Finish the install and drive away.
Mike
Mike
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1,519 Posts
Driveshafts have occasional problem with a vibration at half critical speed...you can up tube size(3" now ? ,go to 3.5"). The gear change and overdrive can make the driveshaft speed increase and cause this problem.I know this means having all new unit built but it might be cheaper than the time chasing unknowns. Talk to your driveshaft guy,maybe he will work with you.Post up center to center length and tube size and I'll tell you critical speed from Spicer chart.
I flipped the drive shaft 180 degrees then re-torqued the bolts on the pinion end to 15 lbs. This seemed to have reduced the vibration. But on the other hand, since I had the lengthen the upper adjustable control arms in order to pivot the rear enough that I could get a socket on the ds bolts, I may have just changed the pinion angle to a more favorable position. Next week I'm having the bushings in the LCAs on the ears changed, as well as boxing the LCAs. Needed to do that anyway, however I'm hoping that will tighten up the rear movement enough that I can find the sweet spot on the pinion angle and eliminate the vibs altogether. It will be about a week and a half before I can do it and report back. Thanks everyone!
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