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Discussion Starter · #1 ·
ok i am having a few problems with my bronco. i recently got new tires which are the Goodyear MT/Rs 32/11.5/15. after i got the new tires i had massive amounts of shaking when my speed approached 65-70 MPH. not much shaking below that speed. i had some shaking before i got the tire, but not hardly as much as i have now, my doors were vibrating inward and outward it was so bad. the first thing i did was take the truck back to where i got it mounted and balanced and told them to rebalance. they did and i still have shaking. i also needed an alignment as well. so when i took my truck to get aligned, the needed to replace the axle pivot bushings and radius arm bushings just to align it. the bushings were replaced and i still have major shaking. they claim my truck was aligned, but i am going to make them do it again cause my steering wheel is not centered to drive straight. they also checked my ball joints and they are tight as well. i have jacked up my truck and shook the front tire and there is no play in the ball joints.

ok so what else could be causing this shaking? what tire pressures should i be running with these tires on the highway. i had them at 35 psi front and back cold. should i go higher?

the other problem that i am having is that i have a whining sound coming from somewhere under my truck. i can not figure out where it is coming from. it is a medium pitch whining sound that occurs when driving slowing around 15-20 mph with the engine almost idleing. what could be causing this whine? it goes away when i slow down to around 5 mph but comes back when i go a little faster. at higher speeds i dont know if it is there cause i can not hear it, but at lower speeds i can hear it. i have spun all 4 of my wheels by hand listening to see if my wheel bearings are bad, but all 4 wheels do not have any special sounds to them. they all sound the same. what could be causing this sound? could it be the U-joint in the driveshaft? any ideas are apreaciated.

thank you
 

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Trouble shoot the truck and alignment

by taking the wheels and tires out of the equation. Slip on a smaller, closer to stock, wheel/tire combo(known to be balanced) and take a drive. This will tell you whether the tires are at fault (sounds like it).

The whine is probably you drivetrain complaining because it no longer has the 3.55 axle ratio to help it move itself and those honking, heavy tires off the line at slow speeds. Now you've changed things to 2.80 or something (big diffence with a small smallblock).

Read the tire sidewall and air it to the max for highway use. I run my street(on road) 275s at the max and it means better high speed cruising and much better mileage(18 mpg today).

Sixlitre
 

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Road force

Newer balancing machines also check the changes in the amount of force a tire puts on the road as it rotates, because of imperfections in the carcass or tread thickness or belt distribution. These are akin to a blister or separated belt, and have the same effect. Have a BETTER tire shop check them.
 
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Discussion Starter · #4 ·
it is not the tires. it does not shake like how it shakes when tires are umbalanced. the steering wheel does not shake back and forth like when you have an unbalanced tire, more like the entire truck vibrates when it reaches 65-70 mph. also the whine from the drivetrain was there before i got new tires so there is not extra strain on the drivetrain. the stock size tires were 31s and changing to 32s are not going to raise the gear ratio that much--i have not really noticed any difference in power with the old tires verses the new one.

what i am thinking is that my driveshaft might be imbalanced. from searching on this forum, others have a similar problem as me with a very bad vibration only at higher speeds and a whine the gets louder with speed, and the problem was a unbalanced driveshaft. could the whine be my u-joints?

from a little research these two problems might share the same answer.

any ideas?
 

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If it wasn't there before the tires and you did not change the rims or gears then it is the tires. unbalenced tires will not always shake the frontend.

Changing out the gears can cause vibs to show up that were there before but that is because it is spinning the driveline faster.

You are effectivly spinning the driveline slower by increasing your tire size.

There has been folks on this board with vibs after new tires and the original shop said the bal was ok but when they went to another shop they rebalenced them and they were fine.

I can agree with muddy though. the bigger tires may have put a strin on the carrier ball and caused it to go bad and will cause vibs that shake the whole truck
 

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if itt was a dive train problem wouldnt it do it at the same rpm all the time ie keep it in 2nd and run it up to the same rpm just posted this idea in the thread that jucie posted about his front end shaking so some one should tell me if i am wrong
 
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Discussion Starter · #8 ·
Steve83 and Havack are right on track with my experiances, crappy tires or bad bonding of the belts will cause the problem. Been there done that. Go to a good tire/front end shop and have them check the tires after you have heated them up a little. My bet is belts in the tires slipping, one other thing to check is the possibility of water in the tire from the airline used to inflate the tire when installed.
 

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No

By downshifting and revving back up to the same RPM, you're only keeping the engine (& clutch/TC, trans input shaft) at the same speed. The driveline is connected to the tires, so since the tires have slowed, so has the driveline. That means a driveline vibe would disappear when speed changed, but an engine vibe would be back every time you hit the magic RPM.
 
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