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#82494 09/27/14 09:26 PM
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My 40 Chevy/302 GMC/T5/Ford 9" has developed a high frequency vibration around 60 mph, 3000 rpm in 4th and 2000 rpm in 5th. The driveshaft has been balanced, the angles are equal and the rear end play has been checked by professionals but the vibration is still present. The rear motor mounts are under the bell housing and two front mounts are on each side of the engine and all are in good shape.

Has anyone had vibration problems coming from the T5 trans? May be a bearing? This is a high frequency vibration that shakes the shifter as well as the clutch and brake peddles.


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Pressure plates do sometimes move & get out of balance.

MBHD


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I had a tire with a slow leak and when it got to a certain point it would shake at 60 mph and be fine above or below.


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Originally Posted By: radar
My 40 Chevy/302 GMC/T5/Ford 9" has developed a high frequency vibration around 60 mph, 3000 rpm in 4th and 2000 rpm in 5th. The driveshaft has been balanced, the angles are equal and the rear end play has been checked by professionals but the vibration is still present. The rear motor mounts are under the bell housing and two front mounts are on each side of the engine and all are in good shape.

Has anyone had vibration problems coming from the T5 trans? May be a bearing? This is a high frequency vibration that shakes the shifter as well as the clutch and brake peddles.


Make sure that a weight hasn't slung off of the driveshaft. It has been known to happen. The guy may have only tack welded in to the shaft as he was finding the right amount of weight to get it close enough to get it in range, and just never went back and fully welded it on. It can also be a bent mainshaft in your tranny, especially if it came out of a Camaro or Mustang.



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The RPM difference between 4th and 5th is much smaller than 3,000 to 2,000, which is 67% recovery.
If it's the clutch, balancer etc. or a harmonic order it will occur in every gear at the same RPM, and also in neutral.
If it's a tire it will continue when you take it out of gear.

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Originally Posted By: radar
My 40 Chevy/302 GMC/T5/Ford 9" has developed a high frequency vibration around 60 mph, 3000 rpm in 4th and 2000 rpm in 5th.


I vote NO to it being a failure of the T5 input shaft bearing. The input shaft RPMs are identical to the engine RPMs (unless you have the clutch pedal depressed). So the way I see it, if input shaft bearing failure was the problem, it would have the same vibration at the same RPMs in 4th and 5th gear (or any gear for that matter).

Last edited by Lugnutz; 09/29/14 09:48 AM.
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If it is happening at a certain road speed even when trans is in different gears it has to be a rotating part behind the transmission output shaft. I worked on a friends Buick several years ago that had a similar problem and it turned out that he had the wrong u joint in his transmission output yoke allowing the drive shaft to move off center. The caps were the right diameter but the side spacing was wrong allowing the shaft to move off to one side at speed. Installed proper u joint problem went away. I would start at front u joint and check everything to rear tires until I found it.


Been there, Done that, Hope to live long enough to do it again.
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Thanks for the inputs. The car has been tied up at drive line shop for the last week or so. They have balanced the driveshaft and made a 2 degree change in my rear end angle to match the engine angle but it still vibrates. Next test will be to run the engine and transmission with the driveshaft disconnected. The rear of the trans will be plugged with one half of an old universal joint.

I am wondering if I should scrap the rear bell housing mounts and go with to a single rear mount on the T5 near the output shaft. The T5 just hangs out there now even though the bell housing mounts are very solid. Or, I might add the rear trans mount in addition to the existing bell housing mounts? What do you think?


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People argue about whether having bell housing mounts AND T5 tail housing mounts is a good idea or not. To me, the engine torque will cause some movement of the bell. The rubber bell mounts allow for this movement. The T5 case and tail housing must be able to move as a unit with any bell movement. The S10 T5 tail housing bushing has a 2 hole mount and the rubber mounts to the frame with only 1 bolt so it will allow minor rotation caused by torque. As long as the tail housing is NOT more rigid than the bell, then having both should be OK. Just my opinion but necessarily fact.
Jay

Last edited by Lugnutz; 10/02/14 09:47 PM.
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I agree with Lugnutz on the rear mounts. Also if you have the single center front mount you have to retain the wide rear mounts to prevent the engine front rolling over. I don't think the mounts are your problem. If I am understanding you correctly you are noticing this at 60 mph in both 4th and 5th gear which set engine at to different RPMs. This tells me the vibration is being caused by something behind the transmission. What happens if you get you truck up to 70 mph place trans in neutral let engine idle down then let truck slow down through vibration range. If vibration is still there it is in the drive line not engine. The odds of it being in the transmission are slim so that leaves the Ujoints, drive shaft, rear end, or wheels/tires.
Start by making sure that you don't have a bent wheel or a broken belt in a tire, also the balance of the tires. If they are fine then I might consider taking it to a different shop to have the drive shaft/ ujoints checked out. Just my thioughts.


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I got the car back from the driveline shop yesterday. While there, I ran it on a lift to 3000 rpm in neutral and all gears with old universal yoke in place of the drive shaft. The engine/trans ran smoothly except for 5th or overdrive. It has a strong vibration in like what I'm feeling on the road. So I think there is some play in the overdrive portion of the trans.

When I drove it home it seemed smoother than before, so the driveshaft angle correction helped somewhat with vibration at about 65 mph in overdrive. But, I plan to have the trans rebuilt to correct the overdrive vibration.

Thanks for your help.


FranK Hainey

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