A/C causing vibration in 5th gear
Thread Starter
Safety Car
Joined: Jun 2004
Posts: 4,023
Likes: 1,181
From: La Mesa CA
A/C causing vibration in 5th gear
Went for a drive in my 90 6 speed.
On the freeway, when in 5th gear, when I turned on the A/C, it caused a very strange vibration.
It felt like it was going though the entire drivetrain, with even the shifter rattling.
What was even weirder was that the vibration would come on for about 5 seconds, then go off for 5 seconds, then on again for 5 seconds, and off for 5 seconds.
If I shifted into 6th it would go away.
Any ideas? Is this the compressor starting to go?
On the freeway, when in 5th gear, when I turned on the A/C, it caused a very strange vibration.
It felt like it was going though the entire drivetrain, with even the shifter rattling.
What was even weirder was that the vibration would come on for about 5 seconds, then go off for 5 seconds, then on again for 5 seconds, and off for 5 seconds.
If I shifted into 6th it would go away.
Any ideas? Is this the compressor starting to go?
Team Owner
Joined: Aug 2000
Posts: 40,156
Likes: 45
From: San Pedro CA
huh? that is strange.
All I can figure is that the compressor is either loose or failing. but the entire 5th gear thing has me baffled.
Try this... run in 4th gear at the same RPM as you do in 5th.
All I can figure is that the compressor is either loose or failing. but the entire 5th gear thing has me baffled.
Try this... run in 4th gear at the same RPM as you do in 5th.
Burning Brakes
Joined: May 1999
Posts: 1,189
Likes: 0
From: Lewisville Texas
Cruise-In II Veteran
When I run my AC it vibrates also. I'm not sure about the 5th gear thing though. Mine vibrates in every gear. I believe it's normal. You might want to check all your brackets to make sure they are tight.
Le Mans Master
Joined: Dec 2000
Posts: 7,839
Likes: 22
From: San Diego, Ca
Assuming the brackets are tight, it may be the compressor. For your '90, make sure the support bracket from the rear of the compressor to the middle header bolt is in place and secure, and if the water pump has been swapped out, check the front bracket bolts. Make sure that the air gap between the outer hub and pulley is .020. Turn the compressor shaft by hand - outer hub. Should spin freely with light resistance, engine cold. Any odors? A worn a/c clutch assembly or if one of the c-clips that holds the pulley and coil have broken, it will usually have a burning rubber smell. Check for a/c oil on the hood above the compressor which would indicate a shaft seal leak.
Thread Starter
Safety Car
Joined: Jun 2004
Posts: 4,023
Likes: 1,181
From: La Mesa CA
It turns out the vibration is rpm dependent.
If I am stopped and in neutral, if I get the rpms up to about 2500 to 3000, it does what I described above.
Why it was doing it in 5th and not 6th was that it dropped the rpm down enough to make the vibration not as severe.
The weird thing is that the compressor isnt making any weird noises and is making a lot of cold air.
I will check above recomendations and report back tomorrow.
Thanks for the advice.
Glenn
If I am stopped and in neutral, if I get the rpms up to about 2500 to 3000, it does what I described above.
Why it was doing it in 5th and not 6th was that it dropped the rpm down enough to make the vibration not as severe.
The weird thing is that the compressor isnt making any weird noises and is making a lot of cold air.
I will check above recomendations and report back tomorrow.
Thanks for the advice.
Glenn
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Le Mans Master
Joined: Dec 2000
Posts: 7,839
Likes: 22
From: San Diego, Ca
A circular disc in front of the water pump pulley, approx. 8 to 10 ins. in diameter. It takes the place of idler pulley and was added to balance out the harmonics created by the length of the belt and the load of the compressor. Some remove it to increase performance which can set up the vibration issue you describe.
Drifting
Joined: Nov 2002
Posts: 1,593
Likes: 0
From: Mobile AL
St. Jude Donor '05
I had a similar vibration in my '96 and it turned out to be the power steering pulley - it was slightly bent and would cause vibration at certain RPMs. Don't remember what engine speed, but take a look across the front of the engine with it running and have someone rev it until it vibrates while you watch.