Need a little help, I have a vibtation in my truck at 40 MPH. It is a small vibration, only the driver can feel it thru the steering wheel. It seems to be harmonic vibration, only there at a certain RPM. It is not the driveshaft, it was built with all new parts and then checked by a different company. It is not the harmonic balancer, changed it twice. Drive shaft angle at the tranny and at the rear end is within tolerances. Could it be the torgue convertor? Rotating assembly was not balanced when engine was built, could this be it? Could the vibration come from the engine thru the motor mounts then thru the pipe motor mount kit to the frame, thru the short distance thru the frame to the original steering box then up to me holding on to the steering wheel? Others have told me to just drive it and not worry about it, maybe thats is ok. I am interested in everyones opinion. Thanks, Gerald in Florida
Tires balanced, or are they older? Have your tires balanced, with a shop that has a Hunter GSP9700 balancer. http://www.gsp9700.com/
Steering Wheel Vibration For a quick test , swap the wheels front to back ~ if the vibration goes away or changes , it's the tires or wheels.... You may have a hard spot in one tire's treads or whatnot , first you have to chase down the location .
Tires I forgot to mention that it is not the tires. Bridgestones that took very little weight to balance. The vibration is much faster than a tire at 40 MPH, the engine is turning 4.11 for every revolution of the tires. Thanks for answering my post. Gerald
Does the vibration occur at 40 if you put the tranny in neutral and let the engine idle? Does the vibration occur at 40 if you put the rear axle on jackstands just tall enough to get both rear wheel an inch or so off the ground? Make sure you have open area in front of the truck before trying this, just in case.
40mph At 40, when put in neutral, the vibration stops. Sitting still, reving the engine to the same RPMs the vibration is there. Like I said, it is a minor vibration, only the driver can feel it or a passenger holding the steering column. Maybe the type of motor mounts I used do not completely dampen the engine vibrations. The rubber isn't very thick on them. You can see them in our hosts catalog. For a while I thought it might be the cam I used but it smooths out below the RPMs required to feel the vibration. Maybe I should just ignore it and just enjoy the truck and drive it. Again, thanks for the comments. Gerald
Harmonic Vibrations Well ; When you said the driver feels it through the steering wheel , this indicates a wheel / tire problem . Now you're saying it's engine RPM related ~ that's a whole 'nother deal . After doing the most involved tune up you can , if you don't find anything wrong (low compression etc.) I'd maybe be worried about loose flywheel or rod cap bolts , might be a bent crank shaft too.....
Oh My Never thought about a bent crank, the crank came from a machine shop, you would think they would have noticed anything wrong with it, but it wouldn't be the first time a machine shop messed something up. The engine has over 5,000 miles on it and the vibrarion has not got any worse, the is no noise when it first starts, oil pressure is great. I am beginning to think it is just a natural vibtation and a balancing of the rotating assembly would have taken it out. Engine runs good at all RPMs, has an abundance of power. In the future a different tranny is in the works, a 700R with overdrive to help with the milage, maybe that will cure the problem. I suppose if this is the worst thing I have to worry about, then I am lucky. I do appreciate all the responces. You can't beat all the experience available on this forum.
engine belt Running without the belt made no difference, nice try though.It only has one v-belt. Runs the water pump and the alternator. Thanks
engine It is out of a 1975 Impala, was a low horsepower 350 V8 with a 2 barrel. The lower pulley has 3 grooves, originally it had power steering, air conditioning, alternator belts. It no longer has AC or power steering. The engine now has lots of horses, breathes thru a 750 Edelbrock. Headers and dual exhaust. Several upgrades in the engine and it is now a 355 cu inch. I am not a speed demon but it is nice to know the power is there if I want it. Old guy in Florida Gerald
Always Remember : There is no replacement for cubic displacement ! . I assume this one is an automatic tranny , maybe the flex plate is loosening up or developing a crack ? . I keep thinking about this vibration issue as I hate harmonic vibrations .
flex plate This weekend the oil and filter gets changed, while under the truck, I will inspect the flex plate and check the torque convertor bolts. The tranny is a 350 turbo that was rebuilt before installing it in the truck. At that time I used a stall convertor but did not like it and replaced it with a stock convertor. There was a vibration at that time but I believed it was from the driveshaft. I replaced the u-joints, no help. Replaced the tailshaft bushing in the tranny even though it had been replaced before, no help. Had the driveshaft checked for straightness, it had a slight bow to it, had new one built with all new parts, it reduced the vibration some. The driveshaft angle at the rear end was too small, added wedges to the springs, no help. Vibration is there when in park and the engine is at about 2000 rpms, it is there while driving at the same rpms. At higher rpms the vibration is gone and thats why I call it a harmonic vibration. 2100 rpms is a speed of 40 mph and that is the speed limit of a lot of roads I drive on. It might vibrate at double the rpms but I never driven it 80. And the fun continues. Gerald
Harmonic Vibrations A visibly bowed driveshaft will vibrate but only when moving . If you see no issues in the TC & flex plate , I'd next index both then remove all the bolts and rotate it 180 degrees then re insert the bolts , if the vibration lessens or gets worse , you've found it . Keep us posted .
torque convertor Thats a great idea, I certainly will try that soon. I will let you know how it works out. Gerald in Florida
Time Spent If you work on old problematic junk no one else wants to hassle with long enough , you'll learn a thing or two . Me , I relish the chanllenge because I'm too stupid to quit . YOU are going to find some thing amiss eventually and I'll learn from you .
?? Well ?? We're waiting.......... . The occasional chassis vibration in my big brother's old Mercedes turned out to be the bad tire I told him to ditch last year..... It went flat right after we exited the freeway Monday , coulda been really bad had it blown @ 85 MPH instead if 25 . All's well that ends well .
today If nothing goes wrong today I will rotate the torque convertor in the hopes of solving this problem. Plans are to change the oil filter and oil and while I am under there move the flex plate. I will post the results later. I am crossing my fingers, arms, legs and eyes for luck but it makes it harder to use wrenches. Gerald in Florida
no change 350 turbos have 3 bolts, rotated flex plate 120 degrees, took it for a test drive, no change. Certainly looks like it is in the engine and transmitted thru the after market motor mounts, which have a thin rubber pad, to the frame and up the steering shaft to the steering wheel. I will just have to live with it. Thanks everyone for all the great suggestions. Gerald in Florida
