Mazdax605

iTrader: (5)

Hey guys,

While the weather here sucks I did get out in the car a few days ago after finding the coolant leak I was battling since my engine rebuild. What I noticed again was a strange vibration from the car at one certain RPM. Regardless of the gear I am in I get this vibration at around 2250,and it is gone at 2500. With the car in neutral,or with the clutch in I don't get the vibration,so this tells me it is transmission/driveline related. Revving the engine without moving doesn't produce the vibration either.

The car is a mostly stock 78 GS with a factory 5-speed,and Racing Beat dual exhaust with the system firmly bolted to the trans just after the header,and then on rubber isolators from there. Stock belt driven fan as well.

Any help would be appreciated.

mazdaverx713b

iTrader: (91)

have you inspected the engine mount and the transmission mount? i would first inspect those with thoughts leaning toward the trans mount.

Mazdax605

iTrader: (5)

Engine mounts are fine,as I inspected them when I had the engine out. I will have to look at the trans mount. Thanks for the input.

mazdaverx713b

iTrader: (91)

just an fyi on the trans mount, i bought one last year from the dealer and it was only $30 give or take a few bucks. not a bad deal and a nice quality part.

rotarydude

iTrader: (2)

check the driveshaft I had one that sat for awhile and the lube in the u-joints dried up and caused a u-joint to go bad I would. Not that I wouldn't check the T-mount as well. The other thing is if you replaced u-joints not that long ago check the driveshaft bolts it happened once that the bolts were a little loose and she did the same thing.

Mazdax605

iTrader: (5)

I don't know how to check the driveshaft. Can you tell me how? I also didn't know that the u-joints are replaceable on these driveshafts.

A few years ago when I had the lightweight steel flywheel on the car I would get a vibration around the same spot,but it was much more pronounced. I removed the lightweight flywheel,and the vibration went away for the most part,but now I am noticing it more,but at a different RPM.

rotarydude

iTrader: (2)

the easiest and best way for you to check the driveshaft would be to take it to a reputable shop that can put it up on a lift and look at it.