3.73 gear = vibration....why?

85_SS_302_Coupe

it sucks (I know) to be on the receiving end

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#1

• Nov 9, 2005

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My buddies car got a 3.73 swap about a year ago and has recently developed a vibration. We're guessing it has something to do with the gear, but what would cause a vibration to start a whole year after they were put in?

 

8

87'GTstang

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#2

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How are the U joints on the driveshaft? Also just for the heck of it notice how much freeplay (aka backlash) is in the rear when you are rocking the pinion back and forth during the assessment of the U joints.

 

HISSIN50

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#3

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DS's can bend without a whole lot of effort too. Checking it for run out (after U-joints) is a decent idea.

Good luck to your bud.

 

85_SS_302_Coupe

it sucks (I know) to be on the receiving end

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We're gonna throw my aluminum DS on just to see what effect it has. Any chance this could be related to the gears? I don't see how the back lash could cause the car to shake like it does. The shake is really bad in the shifter, like it's in the drive train.

 

S

speedytang

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Nov 10, 2005

#5

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I have the same problem but mine is after a transmission install. I am posting to see if the Alumi Shaft helps.

 

timewarped1972

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#6

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not to sound silly but, in addition to checking that other stuff don't forget to check the tires. a bad belt in the tire, a thrown weight, even flat spots from skidding or a sudden stop can do really nasty things....what speeds does it seem to vibrate at??

 

HISSIN50

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85_SS_302_Coupe said:

Any chance this could be related to the gears? I don't see how the back lash could cause the car to shake like it does.

Click to expand...

Like others indicated, and you suggested in the opening post, if the gears were the issue, they should have reared their head a long time back.

The other possibility (if it wasnt mentioned) is the clutch went south and is imbalanced. Is the vibration any different with the car in gear vs coasting in neutral vs coasting with the clutch disengaged?

It does not have any vibes at any RPM while stationary, right (ruling out the balancer)? I am sure you were all over that, but it was worth mentioning.

Good luck.

 

85_SS_302_Coupe

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HISSIN50 said:

Like others indicated, and you suggested in the opening post, if the gears were the issue, they should have reared their head a long time back.

The other possibility (if it wasnt mentioned) is the clutch went south and is imbalanced. Is the vibration any different with the car in gear vs coasting in neutral vs coasting with the clutch disengaged?

It does not have any vibes at any RPM while stationary, right (ruling out the balancer)? I am sure you were all over that, but it was worth mentioning.

Good luck.

Click to expand...

Ok you've got my gears turning...i didnt think of the clutch because it's not slipping...if the clutch were going out and wasnt balanced wouldnt it slip? The trany has been changed but the clutch was reused. Also, the tires/wheels were actually just swapped with mine (traded wheels) so that wasn't it either. As far as vibrating while stationary, it's only at 3k+ RPM while driving...usually 65+mph.

 

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87'GTstang

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85_SS_302_Coupe said:

I don't see how the back lash could cause the car to shake like it does.

Click to expand...

What I meant was to just basically see see if everything was nice and tight so as to nothing loosened up.

Good point about wheel weights, but if it were them it could only be the rear wheels if it were if just the shifter shakes that bad.

Well if it is just 65 mph and above (make sure it isn't rpm related in any way), then you can isolate from the output shaft of the tranny back. From there forward, including the clutch assembly, all rotates at engine RPM. Still try to rule out a worn-out U-joint and/or unbalaced driveshaft first.

 

F

fox_bodies_rule

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Nov 12, 2005

#10

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A thought. You said the transmission was replaced, so did the driveshaft get put back in clocked to the same positon it came out? Seeing as how it comes on at about 3k, I'm with hissin 50- I think it is driveshaft related, been there and done that one, ended up high speed balancing my DS (U joints were good but replaced them anyway) and life is good. One other thing, if you get it up to 65 and get the vibration going, put the transmission in neutral, does it still vibrate as the engine rpms go to idle? If it does, DS related for sure IMHO, unless we are talking about bent axles, bad axle bearings and other really off the wall failures that would manifest themselves in many more obvious ways.

 

slow5poh

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Nov 13, 2005

#11

• Nov 13, 2005

• #11

alright i was too lazy to read all the replies so if someone already said it im sorry. But i have heard alot of guys have that problem when they install numericly higher gears. And alot of people say the aluminum driveshaft solves the problem. Maybe like dampens it more than steel.

my 02.

 

HISSIN50

"How long does it take to get help in here?

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#12

• Nov 13, 2005

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slow5poh said:

And alot of people say the aluminum driveshaft solves the problem. Maybe like dampens it more than steel.

Click to expand...

It is the lesser weight and arguably better intrinsic balance that helps.

 

slow5poh

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#13

• Nov 13, 2005

• #13

i dont' know exactly what that means but ok sounds good