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Discussion Starter · #1 ·
I have just put my Sprints on last week, and I seem to get these vibrations at certain speeds. I have 255/35/20 on the front and 285/30/20 on the back. Shocks are good, but low end shocks. It kinda seems to have slacked off a little bit, but I wanna know what it might be.

Thanks :confused:
 
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Discussion Starter · #2 ·
i would ahte to think it is from a spring install, but is there any chance that the axel got twisted. vibrations after a bigger lowering usually point to a bad angle for the drive shaft, but after only a 2.5-3" drop, i would hate to think that it affected it that much...

if it starts vibrating, and you take your foot off the gas, does it stop, or let up some...
 
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Discussion Starter · #3 ·
Its mainly noticeable around 55, also 85 on the interstate. I had Eibachs on the car until I changed to Sprints. It slacks off as the speed is decreasing.
 
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Discussion Starter · #5 ·
Get a driveline shop to check your pinion angle. It may have been marginal before the swap, and lowering the car (which will change the pinion angle) threw it out of spec.
 
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Discussion Starter · #7 ·
I seem to have the same problem (for a while now). I thought was the rear wheels/tires, but this sounds more like the problem. How do you correct the pinion angle?
 
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Discussion Starter · #8 ·
How do you correct the pinion angle?
Adjustable rear upper control arms, to change the length of the arms (and thus the pinion angle).

Check the FSM to be sure, but I believe you want to aim for around -2 deg of pinion angle.
 
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Discussion Starter · #9 ·
People have a HUGE misconception of a pinion angle.

There are two angles that need to be measured to insure a good pinion angle.

First you need to measure the angle of the driveline at the transmission. EG -2 degrees for my car. Then you need to measure the angle of the rear pinion itself. EG + 0.5 degrees on my car. The rear pinion will lift - on average - 1 degree positive under acceleration thus a +1.5 degrees under load for my application.

The pinion angle needs to be within 1 degrees of the of the two measured angles.

In stock applications. A -2 degree pinion angle may be right, but when you start messing with lowering springs, extended RCA's, or change to a tranny mount which is taller (PST). Your pinion angle WILL dramatically change. Due to the length of our shafts
. Pinion angle is very critical.

The best way to measure a pinion angle is to have the car on a alignment rack up in the air. You will need a device that will measure a angle in degrees. Harbor Freight has a dial indicator with a magnetic flat base which cost $5.99 that will work great. First turn the transmission yoke until the u joint on the yoke is pointing straight down. Pull out the retainer from the inside of the yoke which hold the u joint in. Now find a socket that fits inside the hole and place it snugly against the u joint cap. Now place your angle finder on the opposite side of the socket and record your findings. Repeat the procedure on the rear pinion yoke.

Remember speed sensitive vibrations are usually driveshaft related.

RPM or load vibrations are pinion angle related.

Your problem may be as simple as shimming the tranny mount.

Basically you need to duplicate (reverse may be a better word) the angle of the driveline (engine/tranny) from angle of the pinion. Try to take the letter Z and place it on it side and pull both ends and you will see the even but opposite angles .


Hope this helps.
 
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