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Ask Gm Tech (Cam) Your Own Question
Gm Tech (Cam)
Gm Tech (Cam), GMC Mechanic
Category: GMC
Satisfied Customers: 1693
Experience:  GM Grand Master Technician 2007. 14 year experience.
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I have a 1999 gmc savanna 1500 5.7 with a vibration coming

Customer Question

i have a 1999 gmc savanna 1500 5.7 with a vibration coming from under chasis and took it to gmc dealer 2 days ago and they still cannot find what it is or where its coming from. i took it to them thinking that they would know right away since they are supposed to be the experts
JA: Are you fixing your Savana 1500 yourself? What have you tried so far?
Customer: i had a mechanic replace motor mounts , u-joints ,have the driveshaft checked for balance, re-aligned both front wheels , had all 4 wheels spin balanced , both idler arms replaced but problem still persists
JA: How many miles are on the car? What size is the engine?
Customer: 126,000 miles and its a 5.7 liter ,bought it brand new back then
JA: Anything else you want the mechanic to know before I connect you?
Customer: i also had the harmonic balancer replaced like 5 years ago
Submitted: 1 year ago.
Category: GMC
Expert:  Gm Tech (Cam) replied 1 year ago.

Hi there, I am Cam.
On your van, when does it vibrate? What speeds? what conditions? What gears? Is the vibration fast like when driving over rumble strips or what?

Customer: replied 1 year ago.
it vibrates at speeds between 35 and 40 miles per hour although it will only do it while the van is accelerating. it will also do it at 50and 60mph sometimes .
Expert:  Gm Tech (Cam) replied 1 year ago.

Does changing lanes seem to change it?
IF not then with the difference in speeds I would be thinking there is a problem in the drive shaft or rear diff. First lift the van and support the axle, put the van in gear and watch the drive shaft spin. It should have less than 1/16" wobble. If you find issues, have it repaired by a driveline shop. If not, then the rear diff.

Take the cover off and inspect the gear set, oil and magnet for signs of debris, metal and repair as needed.

If you find nothing in the diff either then your issue is in the transmission and it will need to be rebuilt.

Customer: replied 1 year ago.
my mechanic already lifted the van like you mentioned and put it in gear we looked at the driveshaft and looks fine, no wooble . will have him check out the differential next and then the tranny though transmission was rebuilt like 6 years ago.
Expert:  xsvectOR replied 1 year ago.

what speeds does the vibration occur?