Vibrations on 71 Mustang from 45mph-65mph with 5 Speed Tremec - Vintage Mustang Forums
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post #1 of 36 (permalink) Old 08-20-2019, 08:13 PM Thread Starter
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Question Vibrations on 71 Mustang from 45mph-65mph with 5 Speed Tremec

So I finally got my stang back on the road after a bunch of work. Long story short, I am experiencing some vibrations that start at 45mph and continues on through 65mph and beyond. I notice the vibrations more when I am OFF the gas coasting at the speeds mentioned above. Once I give it a little gas, the vibrations die down just a little but they are still there. It doesn't matter what gear I am in, the vibrations seem to be speed related.


I've checked and ruled out these items below:

1. Mounted and balanced my tires twice by two different shops. They told me there was one tire that was out of balance and my rims aren't bent in any way that would cause vibrations.

2. Driveshaft was also balanced twice by two different shops. I had to cut about a half inch off my driveshaft so that's why I had to balance it again.

3. U joints are brand new and don't appear to have any play.

4. Rear end was rebuilt with new bearings.

5. Checked to see if exhaust system was possibly rubbing on any engine parts. Steering box and rear axle clear any parts of the exhausts system.

6. I inflated my tires to about 38psi to rule out the tires (just in case). That didn't make any difference.

7. I don't think its engine vibrations as pushing the clutch in doesn't change the vibrations at the speeds mentioned above.

8. Checked my brakes to see if they might be rubbing. Brakes are all good.

9. Transmission mounts are brand new and rubber is in great condition.

10. Tried rotating the U joints on the pinion yoke



I think I have an idea of what the issue might be, but I want to see if others come to the same conclusion.
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post #2 of 36 (permalink) Old 08-20-2019, 09:20 PM
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Have you checked the transmission and pinion angles?
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post #3 of 36 (permalink) Old 08-20-2019, 09:58 PM Thread Starter
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That's the next culpit. I have a feeling that they may be out of wack. Can I measure with a dial indicator?
How can I correct the angle if it is off? Some sort of shims?
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post #4 of 36 (permalink) Old 08-20-2019, 10:22 PM
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Do you feel a vibration just sitting in neutral between 2500-3500 rpm ?

Cliff
1966 Blue Hardtop. 200 CID with 3 Speed Trans
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post #5 of 36 (permalink) Old 08-20-2019, 10:37 PM
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My eyes aren't what they used to be. I went to home depot and bought a Husky short digital level for 40.00...very accurate and easy to read. The engine and trans were pointing down around 5 degrees and the rear pinion yoke was at 0. I shoved some body shims between the trans cross member and mount, raising it up a 1/4 inch,. Took it for a drive and it was so much better. The a.o.d is up as high as it will go and I think if it was a little higher it would be completely gone. I think I could raise the rear pinion angle shimming the leaf spring perchs and then pulling out the shims at the cross member but for now its hardly noticeable ...More winter project work. So, report back after you try that and tell us if it helped!

https://www.homedepot.com/p/Husky-10...9403/205999357
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post #6 of 36 (permalink) Old 08-20-2019, 10:47 PM
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Quote:
Originally Posted by neurotoxin312 View Post
How can I correct the angle if it is off? Some sort of shims?

You can buy tapered shims that go between the leaf spring and the rear axle perch. They come in different degrees of angle- 1*, 2*, 3* and maybe more.
There are apps that turn your cellphone into an angle finder.
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post #7 of 36 (permalink) Old 08-20-2019, 11:47 PM Thread Starter
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Originally Posted by geicoman58 View Post
My eyes aren't what they used to be. I went to home depot and bought a Husky short digital level for 40.00...very accurate and easy to read. The engine and trans were pointing down around 5 degrees and the rear pinion yoke was at 0. I shoved some body shims between the trans cross member and mount, raising it up a 1/4 inch,. Took it for a drive and it was so much better. The a.o.d is up as high as it will go and I think if it was a little higher it would be completely gone. I think I could raise the rear pinion angle shimming the leaf spring perchs and then pulling out the shims at the cross member but for now its hardly noticeable ...More winter project work. So, report back after you try that and tell us if it helped!

https://www.homedepot.com/p/Husky-10...9403/205999357
'


Wow this is really insightful. Thanks man, I'll take this route.
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post #8 of 36 (permalink) Old 08-20-2019, 11:50 PM Thread Starter
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Great advice here guys. I'll test and then post!
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post #9 of 36 (permalink) Old 08-21-2019, 12:47 AM Thread Starter
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Just so I get thing straight, what kind are angles values should I try to stay near? I would imagine that the Tremec is probably pointing down 4degrees and maybe the diff yoke pointing up 2 degrees. This would in theory create a 2 degree difference (bad). Should I be shimming either the transmission mount and/or spring perchs until I get .5-1 degree difference?
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post #10 of 36 (permalink) Old 08-21-2019, 05:35 AM
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Quote:
Originally Posted by neurotoxin312 View Post
Just so I get thing straight, what kind are angles values should I try to stay near?
It doesn't really matter what the angles are as long as they're in sync. In a conventional set up you have good, close, and consistent distance of your cooling fan blades to your rad both top and bottom and the fan fits in the shroud as it should. You don't want to mess with that and shimming the trans mount would. My RMP adjustable motor mounts and T5z mount resulted in a pinion angle 5 degrees down so when I placed the spring perches on my 8.8 Explorer rear I set them for a pinion angle 5 degrees up. I've had my car over 100mph a few times with no vibration, nice and smooth.
In your case (assuming everything is good up front) I would shim the spring perches for the match.

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post #11 of 36 (permalink) Old 08-21-2019, 07:18 AM
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I think 4ocious's logic is correct, but if you want to just try to shim the trans first it is quick, cheap and easy..and you will know right away if you're on the right path. Then order some shims and longer leaf spring center bolts from summit to place under the leaf springs...which is a lot more work. Get the measurements first and give it a quick try. I also added RonMorris lowering engine mounts and my fan just barely clears the bottom of the shroud. I think they only added .5 of a degree change on the angle...not as much as I was hoping for.
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post #12 of 36 (permalink) Old 08-21-2019, 02:23 PM
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Hi, Bret from Modern Driveline.

The proper engine/transmission angle should be about 3 deg down. The pinion on a lower plain 3 deg up. Both angles being equal but opposite. Or simply put, like rail road tracks that never intersect or separate. This should then give about a 5 deg down angle on the drive shaft.

Check the phase of the U-Joints. They must be 90 deg from front and back and perfectly straight when looking at the caps front to back. Any deviation will cause vibrations.

Next, ensure the drive shaft is going straight to the rear end. No side to side deflection. This is another cause of vibration.

If this all checks out, remove the axles and do a run-out check. We had one issues with new axles where one was bent out of the box.

Hope this helps.
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post #13 of 36 (permalink) Old 08-21-2019, 06:12 PM Thread Starter
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I noticed that my driveshaft does not go straight back to the diff. There is a slight offset unfortunately. Is there anyway to correct this ?

According to the Tremec Toolbox Driveline angle, I have a 7 degree operating angle, but I will double check this against a real meter tomorrow.
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post #14 of 36 (permalink) Old 08-22-2019, 04:27 PM Thread Starter
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So I just took some measurements

I have 3 degrees down from the transmission yoke and about 6 degrees up from the diff. I'll be trying a 2 degree shim on the rear spring perch and use shims on the trans mount to dial in better if needed. I have about .25" of shim clearance to use on the trans before I hit the tunnel.

Does anyone see anything wrong with this ?

Last edited by neurotoxin312; 08-22-2019 at 04:43 PM.
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post #15 of 36 (permalink) Old 08-22-2019, 05:59 PM
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My 69 has a 302 with t5 swap. Had the same issue. The things I did was replace my 2-piece rubber insulated driveshaft with an aluminum driveshaft out of an explorer, install new u joints and slip yoke on the aluminum one and finally, replace the output shaft bushing in the t5. The t5 has an output shaft bushing that the slip yoke rides on and mine was worn out. You could climb under the car and grab the slip yoke and wiggle it around. After replacing the bushing, no more vibrations at all. Give it a look
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