rear pinion angle

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May 15, 2013 | 10:14 AM

SuperDutyScaler

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From: South Jersey

rear pinion angle

i tried to search Google but didnt find my answer. Trying to figure out my rear pinion angle should be. I still have vibration in the truck around 65-70 mph and sometimes around 80mph if i go that fast. I checked my rear axle last night and its at 8.5 degrees on top of the pinion snout is that correct???? And i forgot to measure the rear driveshaft angle but i can do that after work when i get home
truck is a 2004 ext cab short bed 4x4

May 15, 2013 | 10:46 AM

sammie0126

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From: Westfield, Indiana

You need to measure the angle of the transmission output, the pinion ouput and the driveshaft then compare them to know if you have a pinion angle problem. See post #12 of this thread.
Vibration between 70-75mph - Page 2 - Ford Truck Enthusiasts Forums

May 17, 2013 | 02:37 PM

SuperDutyScaler

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thanks to christina's advice i took more measurements. Parked the truck on a level piece of asphalt i think and this is what i have

t-case: 5*
double carbon joint: 7*
driveshaft: 9*
pinion snout: 8.5*

May 17, 2013 | 02:39 PM

SuperDutyScaler

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since the drive shaft is completely rebuilt and balanced and IF the degrees are within spec I'm going to borrow my dads wheels and tires off his 2000 F and put them on my truck and see if i still have this vibration shake thing I'm feeling. Since both my old tires and my new tires have this i think its the truck and not my wheels or tires

May 17, 2013 | 05:28 PM

sammie0126

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From: Westfield, Indiana

Quote:

Originally Posted by SuperDutyScaler

I think you do need to rule out tires first. Does it vibrate all the time at those speeds or just under throttle or coasting? If it is at that speed regardless of throttle or gear, (shift to neutral or turn off the OD to test that) then that points toward tires. If the vibration goes away doing any of those things, then it's likely NOT tires, if keeps up the it likely tires/wheel axle shaft area.

If the tire swap test doesn't narrow it down you need to come back to that angle. This is a copy and paste from an article I have read until my eyes bleed. If you apply this to your numbers and assume you will get a 2 degree axle wrap under load from any leaf sprung vehicle, my math tells me you need to shim that pinion down by about 2 degrees.

RR (aka shim degree needed) = DS 9 - Pinion 8.5 - WA 2(aka expected wrap under load) means your RR is -1.5. 9-8.5-2=-1.5

The equation is RR=DS-PS-WA. Where RR = rotation required (of the pinion at rest), DS - driveshaft slope, PS = pinion slope, and WA is the estimated pinion wrap angle. If the result is (-), we must rotate the pinion down at rest that many degrees, if the result is (+) we must rotate the pinion up that many degrees.
Of course - we would need to make this adjustment (rotate pinion down 3° at rest) and then re-measure and re-calc everything to get to perfect, as the change may effect driveshaft slope.

Here is the link to the full article

 http://www.pirate4x4.com/tech/billav...ft/index2.html
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May 19, 2013 | 11:47 AM

SuperDutyScaler

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it starts right around 66mph and goes away at 70 or 71mph and is fine and then comes back at 79/80mph. It does it while accelerating on the highway or after i get to speed i can go past the speed and let off the gas pedel and aqs the truck slows down it starts to shake. Ive done it with the OD on and off and with the trans in 2nd D and coasting in N all with no fix.

May 19, 2013 | 01:41 PM

sammie0126

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From: Westfield, Indiana

So it does it accelerating at that speed and coasting at those speeds, does it continue to vibrate if you run up to 68 and hold it steady there? That is a critically important fact to narrow down. You say it starts to vib at 66 up to 71 then again at higher speed and you mention when you let off the go pedal it will vibrate as you coast back through that speed range. What I'm missing is (if you hold it steady there what does it do)? The answer tells you if it's a speed sensitive vibration or a torque sensitive vibration.

Sounds like this is speed sensitive not torque sensitive if you coast down through that entire range in N and got the same result. If that's the case then you need to look hard at tires, wheels, axle stubs and the balance and/or runout of all three - as well as your inner and outer wheel bearings.

Your pinion angle can cause you vibrations at low or high speed, but these are torque sensitive meaning if you unload the drive train by coasting and it occurs at those same speeds then it's not your pinion angle. It could still be drive shaft balance though.