1970 vibration issue help
 

i was at breakfast today and a friend told me his vette is giving him a tisy fit? i'm not sure if he is telling it correctly but here is the story and maybe someone here can tell me what he may be experiencing? his car is a 70 vette 4 speed. 350 cid.

he says this is what he is having. at 1800 to 2300 rpm's he gets a vibration in the steering wheel. and he says at the same time it sounds like the engine is. misfiring.

he has had the tires balanced took off the valve covers to make sure the rockers looked to be all moving the same, just in case the cam was failing. and that is about all i could get from him for troubleshooting. he has asked tons of questions to the car guys around the area and on one of the vette stores in fl.

this is what i told him have the tires balanced on the car to see if any component besides the tires and rims are at fault.

rev the engine using the idle speed adjustment to 1800 rpms and when the engine vibration occurs start to close the choke to see if it is lean misfiring.

put the car on the lift and try to move the suspension parts with a bar to see if any move around the mating parts for loose rubber parts.

change the plugs and or wires to take that out of the equation.

he said he has what i interpreted as a pertronix ignition. in the distributor so i told him to see about installing the points back in it to take that out of the picture.

and if he could locate another known good carb just to change that out for testing to see if that fixes the issue. if choking it fails to eliminate the problem then the intermediate fuel circuit may be plugged and failing to give the engine enough gas to run at the desired mixture.

so can anyone add to this testing procedure for me to give him for testing and eliminate. that is all i can think of. beside i told him the car is like 45 years old and things are going to start happening. he kind of thinks it should run like a 20018 car? thanks for any ideas you may help with. thanks bp.

It sounds like you pretty much covered everything I could think of. It's always hard to troubleshoot something second hand like that. Could you tell if he was getting the vibration in the steering wheel at those RPMs while the car was sitting still or going down the highway?

shark like you i got this second hand. i will be getting to take it out for a test ride this week and also some troubleshooting this week also. the only thing i got for others sofar from what i covered was harmonic balancer and or the flywheel. also tires with a flat spot that do not get round as they are driven like the old nylon tires used to do when they sat. but those tires warmed up and the flat spot went away.

in order to eliminate that he has to find tires that fit the car and tru-y them. i may be able to take my corvair wheels off and put them on his car for a trial so he can eliminate that one. can't do much about the harmonic balancer outside of just replacing it as a process of elimination. you parts? and the flywheel of course but he does not feel like pulling the engine. i have a feeling i will wind up doing that . the engine he said was rebuilt so after reading up on the possible problems that may cause that he could have the wrong flywheel wrong crank even broken piston skirts, but broken skirts to me would not be a vibration that shows at 1800 to 2300 rpm when most of the people complaining are leaning to carb distributor or harmonic balancer that failed.

my corvair had that issue and it caused timing issues. and he is telling me he had to take the vacuum off and set the advance to a number and leaves it there so i'm leaning to a harmonic balancer that has failed and tossed the timing marks off. i will be looking at that this week real hard.

thanks bp.

Wouldn't the harmonic balancer failure be noted by deteriorating rubber and the ring getting loose?

Wouldn't the harmonic balancer failure be noted by deteriorating rubber and the ring getting loose?
Edit: still curious to know if this vibration is occurring at rest or under way.

i can't tell you yet i have not test drove it. and maybe on the balancer. my corvair failed and the only way i found out was the matching marks the mfg. put on it for witness marks so you could see if they were not aligned then it was off.. i did not get any vibration as the flat engine don't viberate as bad. i had timeing issues with pinging and i had to advance it so far i could not see any timing marks so i checked the balancer and found the witness marks out of align.

Sorry, I just thought maybe the other person had told you whether he was driving it when the vibration occurred or if it was just sitting in the driveway. That's sort of critical since if it's just doing it sitting in the driveway, that eliminates a lot of possibilities.

don't be sorry. all answers are very welcome and spur other ideas we may have not even thought of. keep them coming. bp.