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Trying to pin a drive train vibration - Bad Yoke??

October 8 2017 at 10:06 AM
Bob S.  (Login convertable)
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Cobra kit car, very short driveshaft. Had some vibration and noise. U joints seem fine,so while I was under I did the 180 with the shaft at the pinion. Took the car to the HWY and much worse. A week later I have the shaft balance checked, close but they did make a change. Now the vibration is the same either way I mount it. It's a cast yoke, and I'm guessing I need to replace it. (can this be checked in any way?) What would be the truest running yoke for pinion (9-inch)??

 
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javier
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chase

October 8 2017, 12:15 PM 

make sure no loose bushings on the rear differential attachment points,

steel drive shaft?

 
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Bob S.
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Yes, steel shaft. No, slop anywhere and no leaks. n/m

October 8 2017, 12:35 PM 


 
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javier
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Alum driveshaft

October 8 2017, 12:46 PM 

Aluminum absorbs driveline vibrations. is the engine solid mounted? does the vibration continue to become worse with speed?

 
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Bob S.
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Engine is on rubber-

October 8 2017, 2:41 PM 

And the vib. does increase to a point. It's at its worst coasting down from higher speed (like 80 ) even with clutch in..


    
This message has been edited by convertable on Oct 8, 2017 2:43 PM


 
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javier
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what is the pinion angle? n/m

October 8 2017, 3:57 PM 


 
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Bob S.
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always had this, now a little worse after balance of shaft--

October 8 2017, 9:41 PM 

4 Link all solid hiems. 2 deg. down horizontal set by lasers to parallel

 
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Anonymous
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Re: Trying to pin a drive train vibration - Bad Yoke??

October 8 2017, 4:41 PM 

Is this a new thing or been going on since day 1?

Things to check if you haven't already;

-motor mounts
-tranny mount
-rear end bushings
-u joints, be sure to pull off caps and check needle bearings
-driveshaft angles, tremec has a nifty app for that
-with driveshaft off, spin rear end make sure pinion isn't all sloppy
-double check driveshaft length while you're at it.

To answer your question, I don't think a yoke change will solve your problem.

Here's a good read on driveline phasing

http://jniolon.classicpickup.com/drivelinephasing/drivelinephasing.html

 
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john vermeersch
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stupid things,like a bad brg roller.....there

October 8 2017, 5:49 PM 

are 5 brgs / races in the differential/ 22 rollers in each U-joint end, it only takes one galled roller to make noise and vibes, dont forget tires, you can perfectly balance a square tire, just wont ride worth a s@^*....

 
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Bob S.
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New u joints (non-grease) with the balance, -

October 8 2017, 9:54 PM 

Had a different set of tires, no change, wheels are true, I watched when they spun-um..

 
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kleandan
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Bad parts or workmanship.

October 8 2017, 10:26 PM 

Bob, I have spent considerable time searching for issues only to find them right where I thought I had already been.
Driveshafts that are NOT balanced even after taking them to the shop and paying considerable money to have them balanced.
When the shop tech finally says to you, "Look. if I balance that shaft, take it off the machine, put it back on the machine and check it it will read differently because our machine is so accurate."

To which I answered, "That is pretty much the definition of inaccurate."
I took the shaft to a different shop and what do you know? They found the shaft out of balance but when they balanced it the shaft no longer had issues...because their machine IS accurate.

Bad U-joints right out of the box. I will no longer purchase Precision brand U-joints. I pretty much spent a summer chasing a drive line vibration. After checking EVERYTHING I took the U-joints apart to check the accuracy of them.
Sure enough one of them was built out of round and causing a vibration but I never considered the new U-joint would have issues. I replaced a worn out U-joint with a poorly made U-joint but figured the issue was still elsewhere due to replacing U-joints.
I buy nothing but Spicer U-joints now and they are getting harder to source at auto parts stores because all they sell anymore is cheap...gotta be cheap in order to sell rather than quality.

What kit are you working with? ERA, Superformance, FFR, Contemporary, Kirkham? Other?
The driveshafts in these are really short so they are easy to check run out as compared to a regular length shaft.

Don't forget about the tail shaft bushing or the yolk in the trans either. If there is play that can vibrate like a bad U-joint.

 
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