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Discussion Starter · #1 ·
After installing 4" lift and 33 X 12.5 X 15 tires on my 78 R/C, I now have this amazing vibration only between 1800 and 2200 RPM. Worst when driving city streets at 35 M.P.H

It has a 360 with 3:55 gears.

I don't believe it's the tires. Could the engine be improperly, externally balanced and for some reason I feel it more now? or is the gearing to low for the larger tires?

Any info is appreciated.
 

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no expert here, but what about your driveline angles?
 

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You've probably got a drive line problem 35 is to low to feel a tire out of balance(unless it realy badly out) As far as engine problems causing this I think you would have felt the vibration before the lift. So its suspension or drive line. Some times you'll get a vibration because of a worn slip yolk atfer lifting a truck
 

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Support truck on jackstands. Put in drive, and run up to problematic rpm (CAREFULLY!!) If the vibration is still present the problem is in the tires, tranny, or driveline. If it goes away the problem is in the bearings or axles.

-SM
 

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If you had an undersized spare on the rear wheel, it could cause a very bad vibration, right? (My truck I just bought had a bad vibration cause they guy had a blowout before he put it up for sale and only had an undersized spare, not a 33" spare. When I test drove it, they guy said it was because of the undersized tire in the rear. Made sence at the time. I sure hope I don't have something more serious.
 

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Discussion Starter · #7 ·
Thanks for the feedback.

The entire driveline was checked, yoke, u-joints, etc. while installing lift. No sign of bearing wear either. No vibration during rev-up in neutral.

As this was the first time changing the leaf springs, which were quite flat, could a 4" lift and 33" tires change the angles that much to cause this vibration?

If it's the tranny, any ideas what that might be?
 

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I had a similar problem running my 33's -but only while accellerating .i adjusted my throttle linkage to increase the rpms before shifting,now it is not as bad.try shifting it manually at a higher rpm and see if it helps.
 

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Discussion Starter · #9 ·
I'll try the manual shifting since I know the kickdown linkage is not set properly. It changes gears at 2700 rpm, regardless.

How do you set the kickdown linkage properly?
 

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If you still have your old (smaller) tires, put those back on and see what you get.
Or you could remove one driveshaft to see if it stops. I would start with the rear driveshaft first.
Also, see if you still have the weights welded onto your driveshafts.

I had my u-joints checked by a mechanic after I had a vibration. He said that they were good but the vibration stoped after I changed them.

Gonzo
 

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Keep looking at the drivetrain/tires like these guys are tellin ya. That's where the problem is. If you developed a prob after doing a brake job, ya wouln't replace the radio would you?
I vote for d-shaft U joint angles, as already mentioned,
Mike
 

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Discussion Starter · #13 ·
Alignment was done when lift and larger tires were installed.

Truck was fine before lift and larger tires were added.

New front driveshaft was installed also.

*** When I put the tranny in HI-Lock, the vibration almost completely goes away ***

????
 

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Seems like plum crazy might have your solution.
 
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