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MG MGB Technical - 70MPH vibration
|I have a front end vibration in my 1969 MGB. This vibration occurs at about 70mph. The motion is transmitted mostly through the steering wheel and a little bit into the body. |
Oddly, the car still tracks straight even with the vibration.
I have swapped from wire wheels to disc wheels, changed tire brands, rebalanced the wheels, replaced the steering rack and tie rod ends, brake discs, replaced all of the rubber in the front suspension and all of the brass bushings EXCEPT for the kingpins.
I didn't replace the kingpins because I can't "feel" any movement in them. What are the chances that replacing the kingpins would solve this vibration?
|On the one hand it's the only thing left! On the other my V8 started doing that the first time I changed the tyres, and has done it ever since despite further changes and repeated rebalancing. I'd like to do an on-car balancing but no one seems to do it anymore. With mine if I'm on the straight the vibration will fade in and out once every 2 or 3 secs or so. If I'm on a slight curve one way the rate speeds up, if the other then it slows down. I.e. it is definitely wheel wobble, both wheels are doing it, and they are alternately cancelling each other out and adding to each other. Why it should fade in and out on the straight when the wheels, tyres and pressure is the same is another mystery, as that implies they are rotating at different rates.|
|If it resonates at one speed, 70mph, but fades off higher or lower, then it is out of balance.|
|If you have Rostyle wheels and your shop that does the balancing uses a regular unit that assumes that the hole in the center is concentric with the rim then he is at fault. It requires an addition to his balancer that uses fingers that actually bolt to the mounting holes. With that, then he can properly balance those type wheels.|
Ask him to check the balance his way and when it balances get him to remove the wheel from the machine and then reinstal it. I bet that then it is out of balance once more. This is a common problem with those wheels.
|Thanks for the quick replies.|
The car has aftermarket alloy wheels on it, however I am certain that they were balanced in a hub-centric fashion.
I too have suspected wheels out of balance, but I expected 3 sets of tires and two sets of wheels it may have been corrected. The vibration does seem to go away about 80mph. I will have the wheels rebalanced and see if that helps any.
|Just to be complete, you might check your driveshaft for play (U-joints).|
|Thanks Dan, I actually replaced the U-joints a little over 3k miles ago.|
A driveshaft out of balance has crossed my mind. I just anticipate that vibration to come through my seat rather than my steering wheel.
|I had a similar problem at 55-60. Rebalanced the drive shaft, wheels, replaced the stearing rack, etc to no avail. Finally, replaced one of the front rebuilt shocks (leaking), that fixed the problem.|
|Try a different tyre balancer. I kept going back to the same tyre dealer to try and get my alloys balanced. In the end I gave up with them and went to another garage, they put then on the balancer and they were way out! They rebalnced them...........perfect.|
Goes to show, not only do the operatives vary, but so do the machines used!
Sounds like a balance problem if it is always there at 70 mph but if it comes and goes while at a constant 70 it could very well be a shockabsorber problem as James suggests. Next time you get your wheels balanced ask the guy doing it to set his machine to fine. Most balancers now balance to within 5grams which is ok for average use but they do have a fine setting which balances to within 1gram. I would suggest if your guy's balancer hasn't got this you might be better off finding somewhere that has.
Also don't overlook balancing the rear wheels as well. I know you won't feel rear wheels out of balance through the steering but it is at around this same speed and can make your front balance problem feel more pronounced than it actually is. Cheers Willy.
|Mine comes in at 68 and fades out at 85, and that is with having the wheels balanced on a stud adapter and not the centre hole.|
|Interesting Paul, that is almost exactly the same speed that mine comes in and then fades out. |
I am pretty sure the car will be getting tires this summer, hopefully a re-balance will cure the problem. It is certainly cheaper than a set of kingpins!
Thanks again for the replies,
This thread was discussed between 03/05/2009 and 04/05/2009
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