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Guest Message by DevFuse
 

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are you a good enough mechanic to figure this out?


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15 replies to this topic

#1 nathan

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Posted 05 March 2004 - 04:41 PM

This isn't subaru related, but it is my only non subaru vehicle and I don't want to subcribe to other forums just for this problem, so please humor me, plus I know there are some mechanics here that are much better than me.
I have a chevy truck that has a fairly substantial vibration which only occurs from barely moving to about 15mph. It does not occur when coasting at those speeds, ie. downhill, instead it only occurs under power. It also goes away, or is not noticeable as soon as the truck is above 15 mph. I have taken it to a tranny shop where they changed the ATF and put in all new tranny mounts, no change. I also had the entire driveline rebuilt, all new joints and carrier bearing(it is a 2 piece driveline supported in the middle by a rubber mounted carrier bearing) still no change.
I have been able to see the driveline shaking, like it is out of alignment but I really don't think it is a balance problem because the vehicle is smooth at all other speeds. I have also checked to see if the tranny and transfer case are securely bolted down and that the output shaft is not wobbling at the junction of the transmission tail, as far as I can tell all is good.
Does any body have any ideas where to go next?

#2 Suzam

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Posted 05 March 2004 - 06:20 PM

Have you checked the rear differential?
I had a rear going bad on a Dodge that shook the whole car at low speed. Slowly got worse for about 1,500 miles then started to bind up. Ended up I replace the entire rear end.

#3 eyesore

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Posted 05 March 2004 - 06:21 PM

motor mounts?

#4 calebz

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Posted 05 March 2004 - 06:27 PM

output shaft bearings?

#5 1 Lucky Texan

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Posted 05 March 2004 - 07:18 PM

You could purposely glue a weight to the shaft to see if it produces the same effect. If you happen to be opposite the bad side it may reduce the effect.

I kinda like the diff idea though.

#6 99obw

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Posted 05 March 2004 - 07:38 PM

I have seen tire balance and driveshaft balance problems be speed dependent.

If you want to test the Texan's idea use a hose clamp.

#7 oddcomp

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Posted 05 March 2004 - 07:58 PM

yeah some driveshafts will cause vibration problems at certain speeds
take bolth shafts out and have a driveline shop test them bolth

i saw a recent article on driveline vibrations thats how i know

#8 tcspeer

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Posted 05 March 2004 - 09:54 PM

Have you tried the cheap stuff? Putting the front tires on rear? Just uneven wear pattern on tires can cause the problem you are describing. I dont see in your post where any thing was tried with your tires. Balance problems can also seem fine at different speeds.

#9 Tolerance02

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Posted 06 March 2004 - 03:11 AM

I agree with tcspeer. A tire problem.

#10 camosuba

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Posted 06 March 2004 - 06:54 AM

I concur also, bent wheel maybe ?

#11 Cougar

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Posted 06 March 2004 - 11:57 AM

It sounds to me that your driveline may have a defect. I would try another driveshaft unit to see if that will fix this.

#12 cookie

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Posted 07 March 2004 - 01:53 AM

checked the motor mounts. The driveshaft should be two piece.
Have you ever seperated it? It really has to be aligned correctly or will do just waht you describe.

#13 hatch4x4

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Posted 07 March 2004 - 02:09 AM

I had a ballooned tire (where one area kind of sticks out) and it gave me the same effect you had. Give your tires a good inspection and look from a couple different angles, it's hard to spot.

#14 subyroo

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Posted 08 March 2004 - 06:35 AM

Check both parts of the tail shaft for a missing counter weight, if one is missing you will be able to se where it used to sit.

I agree with "oddcomp" get it re-balanced and ensure it is married up properly, they normally have an alignment mark if not you should have center punch each part to make sure it went back together the same way.

#15 nathan

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Posted 09 March 2004 - 05:58 PM

turns out that subyroo and cookie kind of have it right. I started checking with driveline specialty places and they had the same idea. But somebody suggested the driveline and u joint angles. I hadn't even thought about it. The funny thing is that the vehicle had an engine swap and what happened was the new mounts changed the driveline geometry. The 2 piece shaft was not in a straight line at the center support, it was actually making a slight v shape instead of being linear. I took out the center mount and refabricated a new shorter one out of some thick steel and it actually worked no more vibration, the other advice was to get a driveline protractor so that the angles could be checked and made perfect(supposedly within 3 degrees of each other). Anyhow, thanks for everyones help, I thought I would let everyone know the culprit. BTW, this is supposedly a common problem for drivetrain swaps and in some instances, suspension lifts.

#16 cookie

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Posted 09 March 2004 - 06:14 PM

that would be one of the first things to check.
I found a lot more mismatched two piece shafts in my years of mechanics though.




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