update still got the bounce
- Thread starter bobby6319
- Start date
one finger john
Active Member
Do you have to hit a bump @70 mph to induce the hop or does it just start to hop as you approach 70? Have you put a dial indicator on the front rims? Have you checked the run out of the front TIRES? Were the tires balanced on the car? Could the brake discs be out of balance?
bobby6319
Member
it starts as you get up to 70 on smooth road. the tire were balanced off the car. can't find anyone who does it on the car around here. the tires appear round when balanced but have not turned them slow with any type of gauge I know i can jack it up and use aboard or something as a gauge.
Are your tires round? Are your wheels round? Are your wheel bearing properly adjusted? Are your wheels round around the center of your spindles? Balancing can tell the balancing machine you're in control of weight offset, but the tires and wheels for that matter, can be out of round or off center.
I know this will sound anal*, but there are things like (I hate that word - like. Every high school kid tries to put several in most every incomplete sentence they utter).....things like self generating resonances that can built to serious shaking and destructive problems. Sure, I can tell you where it happens in helicopters, but I don't know that it does or doesn't happen in cars.
* I guess I enjoy seeing me in print
I know this will sound anal*, but there are things like (I hate that word - like. Every high school kid tries to put several in most every incomplete sentence they utter).....things like self generating resonances that can built to serious shaking and destructive problems. Sure, I can tell you where it happens in helicopters, but I don't know that it does or doesn't happen in cars.
* I guess I enjoy seeing me in print
"The Bat" out of hell
Member
Do the check as stated. But also try Tire front PSI could also be to high and add to prob. Drop psi tell you see some small side wall bend,than try driving carefuly to check if bonce is gone
one finger john
Active Member
Drive @ 65 mph to a tire dealer that does on-car tire balancing. Mark the wheel position on the hub so that when (not if) you remove the front rims/tires they will be put back in the same position. Also mark left/right wheel position. Heck, while your at it, mark the rears and balance them too. Since I don't know where you are, I can't tell you where to take your rod to have the tires balanced. Are you near a big city? Maybe a truck stop? A telephone to call around the area? A computer that is connected to the internet? It shouldn't be that hard to find a shop that does on-car balancing.
John
P.S. Are these tires/rims new? Is the front end solid? Are the spindles tight? Just throwin' out possibilities.
coops
Member
I have had the exact issue several times on different vehicles all sharing a common item.Try dropping the rear tire pressure say from 28 to 15 then take it out for a test drive and see how it changes.Do not change the front until after testing on the rear and adjusting rear to max press below vibration point,then when satisfied with rear feel turn attention to the front if needed.This is for reasons as Dave mentions but helps for those of us that don't wish to continue to trade tire sets till finding that good set.
Ted Brown
Member
I was re-reading all of this, and I do not see anywhere if it is the fronts or rear tires that are the problem... If you have a locker type rear gear, tire truing is/can be very important... I tried to run a set of Mickey's rear tires once, for a week, they kept a flat spot on them, even if I sat in water and then burned them down, they never did get round, almost shook the radiator off the frame, one would hit then the other!! they gave me the tires I have now...
Six-Shooter
Member
I just went through a similar thing only my wobble began at only around 45 mph. Both tires in harmonic wobble! Real scary too! Both front wheels were way out of balance (spin balanced off vehicle). I also replaced both front bearings and tightened steering (vega gear box). So far things are running good without wobble. However, understand that I have a vintage 36 Ford front axle, tie rod, arms, spindles, and drag link. Also, I have old school drum brakes on all fours and no emergency brake or anchor to toss out so I don't get too crazy on the gas pedal.
Neshkoro
Well-Known Member
The thing that still bothers me is that cars have been built for more than 100 years and we still don't know the root cause to the problem. My car has had the same problem, off and on, for 25 years. I've tried more tire pressure, less tire pressure, front and back, had the tires re-balanced, toe in, toe out adjustments, new king pins and bushings, etc. It is mostly gone but, when it happens, it will scare the hell out of you. The only way to stop it is to stop the car and then continue on. I'm thinking about buying a new set of front wheels and tires before I kill myself.
Gerry
Well-Known Member
I needed to know the 'grow' on MTs to think about rear fenders so called them and ask the question?
How much will a 18.5X29X15 grow at 85mph. The answer was 5/8 inch (at the center of the tread). While i was talking to them I also asked about pressure for a 1900lbs T. 15-18 psi is what they said. I know I run 5-7 on my Topolion race car and the 2 psi make a bunch of difference.
Dont know if this helps.
Gerry
I run 13 to 15 PSI in the Hoosiers in the rear and 23 to 25 PSI in the 165 fronts. It seems to work out best for me. Any higher on the front, I get some bounce.
It's Friday evening, I'm on my second glass of a very nice Chardonnay and I had a great week ! !
OK, by now I know I must sound conspiratorial or maybe troglative....... but what about the ratio of unsprung weight to car weight?
Do you have heavy wheels and tires? Heavy front axle? Can you try a pal's wheels and tires that might be lighter? Much lighter?
You know that self generating resonances thing I mentioined? Have you seen the rear axle assembly in a Ford Explorer? There is a five (about) pound weight bolted to the rear end. At first blush I thought it might have been a problem with interference of natural frequencies. I really don't know why but there are several hundred thousand people hauling around five extra pounds of weight and we all know it's not for gas mileage. It's one of those design mysteries that's better addressed with the lowest cost fix.
OK, by now I know I must sound conspiratorial or maybe troglative....... but what about the ratio of unsprung weight to car weight?
Do you have heavy wheels and tires? Heavy front axle? Can you try a pal's wheels and tires that might be lighter? Much lighter?
You know that self generating resonances thing I mentioined? Have you seen the rear axle assembly in a Ford Explorer? There is a five (about) pound weight bolted to the rear end. At first blush I thought it might have been a problem with interference of natural frequencies. I really don't know why but there are several hundred thousand people hauling around five extra pounds of weight and we all know it's not for gas mileage. It's one of those design mysteries that's better addressed with the lowest cost fix.
Similar threads
