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Dear friends

As part of restoration to a 73 coupe, put Yukon new ring gear (8.5") and pinion (1.375"), raising ratio from 3.1 to 4.1, and also installed a Eaton Detroit Truetrac new differential.

Car has a T5 transmission, rubbers are 17", and has a Dana 44 differential axle.

Also changed bearings and seals to axles and differential.

 

Before above changes I drove the car up to 140 km/h and as far I remember vibrations were normal, were not a problem.

After above changes, car started vibrating at 80 km/h, specialy when decelerating or pressing down the clutch.

Measured the angles at the yoke and pinion finding yoke was pointing down and pinion was pointing up. So placed 4º wedges over the leaf springs to get a paralel situation. Vibrations decreased but not disappeared. My mechanic insisted in balancing the driveshaft, what I did. While driveshaft was in the workshop we changed the speedometer drive gear, the yoke and the rear sleeve of the T5 box because we found original yoke had wear and was rather loose. My mechanic did this without taking down and away the T5 transmission because was needed to take away all exhaust dual tubing he said.

After balancing and reinstalling the drive shaft, vibrations increased again!!!

Always same pattern, vibrations happened when decelerating.

Checked again angles and found angles needed an extra correction so placed 6º wedges.

Result was again some lower vibrations but still not normal. Now I feel vibrations are also coming from below the shifter lever and that frequency is higher than initially.

Beg your comments and recommendations.

Thanks!!

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Check that the yoke runs true and the main shaft in the transmission is not bent. The worn tail shaft bushing may be an indicator. Also check for dings in the aluminum right at the end of the transmission indicating that it may have been dropped. I've seen this several times. Even runout of .008 can cause a vibe above 80mph.

 

Here is a video of me after fixing that problem on a friends Tremec 3550 transmission.

Mike

__________________________________

Black 1985 GT

Yellow 1973 Mustang Mach 1

Black 2012 5.0 GT, 6-speed, Brembo brakes, 3.73's

Wimbledon White 1966 F-100 Shortbed Styleside, 390ci, Tremec 3550, FiTech EFI

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Did your car always have a manual transmission? Does the vibration change when you dis-engage the clutch? How's the pilot bearing in the end of the crankshaft? What kind of bellhousing are you using? Is the bellhousing concentric to the crankshaft?

 

You and your mechanic are going to have to play detective...

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Thanks Mike and MJLan, note that the problema started after replacing differential and gear/pinion.

Before this it was running good, so seems to me there is no reeason to look inside the T5.

The vibration appears when I dis-engage the clutch or reléase the gas pedal, and goes away when accelerating. This means according other people opinions that pinion needs to be moved up, to get in line with the yoke angle within 1º, that is what I did,

Now planning new angle measurements and making some serious vibration analysis and play some detective work.

Regards

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Changing the differential would not have changed the relative angle of the parts. If it didn't vibrate before, then it is more likely something in the new differential such as a bad bearing or improper set up. The first place to look is the U joints for any possible damage. It probably isn't the problem, but it would be the easiest fix. Did the caps on the U joints ever come off? Could you have lost a needle bearing out of one, or overtightened a U-bolt and distorted a cap?

http://www.7173mustangs.com/gallery/1_01_07_15_8_53_18.png

 

"I love my Hookers!" and "Get some Strange" probably have a different connotation to non automotive enthusiasts!

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Changing the differential would not have changed the relative angle of the parts. If it didn't vibrate before, then it is more likely something in the new differential such as a bad bearing or improper set up. The first place to look is the U joints for any possible damage. It probably isn't the problem, but it would be the easiest fix. Did the caps on the U joints ever come off? Could you have lost a needle bearing out of one, or overtightened a U-bolt and distorted a cap?

Also, some Ford rear ends ran a different size u-joint cup in the yoke then the driveshaft. Sometimes this goes unnoticed and cranking down on the smaller cups to get them tight in a larger yoke can make them out-of-round.

Stang1.jpg
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