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Old 04-18-2006, 07:08 AM
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transmission question

i believe i have narrowed this down to the transmission. tell me what you guys think: driving at 55 or above i get a vibration until i hit 65, then it appears to go away. however, if i throw the car in neutral it stops vibrating. if i bring the engine rpms up (while in neutral) it does not vobrate. going back into gear, it begins vibrating again until i get below 55.

since coasting in neutral, all the drive shafts are turning, so it can't be anything there, and if the engine is brought up to the same RPM's (as going 55 mph) there is no vibration.

this leaves me with the transmission. it's a t350. i'd like to get a general idea what it could be before some shop wants to rip me off. i disconnected the torque converter wires and drove the car...no change, so i think i have eliminated the TC.

the vibration is worse upon accelleration. meaning, if i'm at 55 and give it gas, it can be felt even more.

any suggestions? am i correct in thinking it's the transmission? if it matters, this is a 1981 corvette.

any help would be appreciated!!!!

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Old 04-18-2006, 08:25 AM
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if the car has a 305, i would check the harmonic balancer, if its got a 350, id check the flexplate, it should have a weight on it... and check the balancer as well anyway while ur at it...
as far as unhooking the plugin for the converter, all u did was keep it from getting the clutch in the converter from applying... it still doesnt overrule that the converter may have an internal problem...if it by chance broke a fin on the inside, it could throw it out balance and cause a vibration.
also, check u-joints and the amount of play on the yoke where it goes into the back of the trans.
these r common areas to help find a vibration, also, that car has a live axle diff, so u also have 4 more u-joints to consider there..

also, check here., http://www.inliners.org/cgi-bin/ulti...c;f=1;t=002664 i know its a different car and engine, but read the post here, this guy had almost same problem, and he wound up finding an engine problem that was causing his vibration... gl
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Old 04-18-2006, 08:32 AM
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1. i changed all 6 u-joints...twice. lol

2. there is some play at the end of the tranny, but how much is acceptable? i can grab the yoke and drive shaft a wiggle it slightly....

3. it has a 350. but, if it was anything engine related, would i not feel the vobration when i bring the RPM's up while standing still? i have also put the car i neutral while driving and brought the RPM's up (about 2200 is 55mph) and no vibration. i'll visually look at the balancer anyways.

4. thanks for listening to my problem,. this has been driving me nuts and no one has been able to pin point it. it's become a challenge, but it also took the joy out of driving it.

hey...i read that link you gave. man, that guy went thru everything!!! it was hard to believe a head was causing it. however, i haven't changed anything in the engine...it's a stock 350.

Last edited by diabolical; 04-18-2006 at 08:40 AM.
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Old 04-18-2006, 10:52 PM
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well, how well do u know transmissions??? if u know what ur doing, and want to get into the trans, the next things i would check would be the converter, input shaft and output shaft, and the shell... they can be checked for true(except the converter, which id just replace anyways if ur gonna pull it apart anyways) in a lathe (if available). that would be where id look next, IF u can overrule everything else.
1 last thought comes to mind, simple driveline harmonics. i really cant explain, but my dad had a 70 jeep wagoneer that we basically built from the ground up... 327 chevy (i built) dad built the trans (owned a trans shop from 1965-2004, had fulll machine shop as well) rebuilt or new everything, and always had a vibration from 57-63 mph... no matter what, it was there. so, we either drove it in town (40 mph ave.) or on the freeway where we could drive 65+, and it would be smooth as glass.
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Old 04-18-2006, 11:21 PM
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transmission question

Try checking out the transmission mount. Sometimes when they are failing they can cause a vibration.
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Old 04-18-2006, 11:34 PM
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Diabolical,

This is a driveshaft problem. Check the rear U-joint because when you give the engine the gas the rear end will torque up and cause the rear U-joint to wearout. When the vibration comes in at one speed then goes away at another it is drive-line.

Good Luck
Scholman
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Old 04-19-2006, 01:53 AM
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I can't say that is the problem here as this carrier doesn't move under acceleration or decelleration because it being solidly mounted.

Is there any damage to any of the three driveshafts?
Was there a balancing weight originally attached to the main driveshaft that is now not there?
Did this suddenly come about, or was it gradual and get worse over time?
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Old 04-19-2006, 04:28 AM
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Quote:
Originally Posted by M&M CUSTOM
I can't say that is the problem here as this carrier doesn't move under acceleration or decelleration because it being solidly mounted.

Is there any damage to any of the three driveshafts?
Was there a balancing weight originally attached to the main driveshaft that is now not there?
Did this suddenly come about, or was it gradual and get worse over time?
no damage to the any of the drive shafts, and no weights appear to be missing.

the vibration has been there for a couple of years.

but, while coasting in neutral, all drive shafts are still turning. if it was a u-joint, would not the problem still be felt?

i really appreciate the brainstorming on this!!
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Old 04-19-2006, 06:34 AM
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i was thinking about something...(uh oh)...if my cruise control switch is out of alignment with the brake pedal, would this have any effect on the TCC ?
the car does throw a code 24 sometimes (this is the VSS vehicle speed control) but i just assumed the sensor was dusty (it's located behind the speedometer)

so...if the brake switch for the cruise control isn't adjusted properly, and since the TCC is also wired to this, could this be effecting how the converter reacts? the car seems to "shudder" upon acceleration but only at 55 or above.

i can't recall exactly when this problem started because it's been like....3 years now.
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Old 04-19-2006, 07:03 AM
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Quote:
Originally Posted by diabolical
i was thinking about something...(uh oh)...if my cruise control switch is out of alignment with the brake pedal, would this have any effect on the TCC ?
the car does throw a code 24 sometimes (this is the VSS vehicle speed control) but i just assumed the sensor was dusty (it's located behind the speedometer)

so...if the brake switch for the cruise control isn't adjusted properly, and since the TCC is also wired to this, could this be effecting how the converter reacts? the car seems to "shudder" upon acceleration but only at 55 or above.

i can't recall exactly when this problem started because it's been like....3 years now.
You need to start with the most likely and move through to least likely.
Speed related vibration where you can drive through a vibration is nearly always rear tires. Have the rear tires balanced. Second, If you are quite sure you didn't screw up the u-joints, check the drive shaft for mis alignment. Some Ford Mustangs for example will develop a driveline vibration if you don't install the drive shaft back exactly as it was. It is a balanced assembly.
Check to see if the drive shaft balance weight is gone.
If you added an aftermarket cruise control, sometimes the magnet you added can unbalance the driveshaft.
With the transmission in neutral and the wheels off the ground shake the u-joints by hand to see if there is any slack in the joints or the transmission tail shaft bearing or pinion bearing.
I would bet it would be one of these things.

Last edited by Choctaw Bob; 04-19-2006 at 07:04 AM. Reason: another idea
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Old 04-19-2006, 07:50 AM
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well, bob, i jacked the car up and threw it on jack stands. with the rear wheels up, i started it and put it in drive and brought the speed up to 55. i could feel the vibration.

(the wheels have been balanced on a hunter wheel balancer including road force testing. they were perfect according to the computer)

if it is the u-joints, wouldn't the vibration also be felt when i threw the car in neutral at 55 mph since the drive shafts would still be turning? this is what throws me off. at 55 or above, i can feel it, especially when accelerating. but, if i go, say, 65 mph, and put the car in neutral, it runs as smooth as a caddy. so, with that situation, i eliminated the u-joints. ( in theory)

but, are you saying the u-joints could still be a problem anyways and only show up under load?
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Old 04-19-2006, 09:36 AM
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ok...update. i decided to stop being stubborn and go back to where i began. so, i jacked the car up, put jack stands uner the rear and started it. i brought it up to 55-65 mph and i could feel the vibration.

shut it down.

i then removed the rear half shafts, checked the u-joints (appeared to be OK) then started it back up and brought it up to speed again....no vibration.

so, i have a problem with the half shafts or the yokes.....sheesh.

but, why not show up while coasting in neutral? would the vibration still be there but not felt in the shifter because i was in neutral?
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Old 04-19-2006, 10:11 AM
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Quote:
Originally Posted by diabolical
ok...update. i decided to stop being stubborn and go back to where i began. so, i jacked the car up, put jack stands uner the rear and started it. i brought it up to 55-65 mph and i could feel the vibration.

shut it down.

i then removed the rear half shafts, checked the u-joints (appeared to be OK) then started it back up and brought it up to speed again....no vibration.

so, i have a problem with the half shafts or the yokes.....sheesh.

but, why not show up while coasting in neutral? would the vibration still be there but not felt in the shifter because i was in neutral?
It could still be the tires U-Joints usually vibrate under load but the vibration normally doesn't go away above a speed threshold. This usually indicates a rear tire balance problem.
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Old 04-19-2006, 10:18 AM
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Also could be a tire with a blister or loose spot in the tread. This is a Corvette? it could be a wheel bearing, while you have it up on stands, take hold of the wheel top and bottom and shake it. Same thing side to side. Rock the wheel back and forth while looking at the u-joints, yokes, pinion, transmission tailshaft. There is some slack in there somewhere. Persistance will find it.
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Old 04-19-2006, 12:09 PM
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Quote:
Originally Posted by Choctaw Bob
Also could be a tire with a blister or loose spot in the tread. This is a Corvette? it could be a wheel bearing, while you have it up on stands, take hold of the wheel top and bottom and shake it. Same thing side to side. Rock the wheel back and forth while looking at the u-joints, yokes, pinion, transmission tailshaft. There is some slack in there somewhere. Persistance will find it.

wheel bearings were done a couple of years ago (doesn't every corvette need that?) but, i did check...wheels are tight...no play.

as i stated before, tires were balanced on a hunter gs9700..supposedly top of the line.... at a ford dealer.

when i was removing the half shafts, some of the u-joint straps were kinda loose..i could remove them with my fingers...sheesh. and, i found one u-joint that was tight in the trunion. it was hard to move back and forth. so, i replaced that one and it swivels smoothly now.

so...this is what i'm figuring: (lol) since a couple straps were loose while the wheels were hanging,(this puts pressure on the u-joint). when the wheel has weight on it, the straps maybe gave enough for the u-joint to be loose. keep in mind that the half-shaft is also part of the wheel travel assembly, so, when the car is jacked up, the rear wheels kick in at a gross angle. this puts pressure on the u-joints, so it might appear that they are tight, but once on the ground, they might be loose.

f$@$#@# corvettes!!!!

anyways, when i feel ambitious, i'll put it back together later and see what happens. if the vibration is still there, i'll burn the car. lol

hey...i appreciate the help....this has been a big downer for a long time.
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