Hello, I have a tough question. I have a 1990 fox, 5sp, 3.73 rear gear'd, that is ran on the track regular. I will try and explain this the best I can. It got a vibration in it last year and thought I could find it. First we took apart the rear end, check the bearings, axles, and wheels. Swaped wheel, and driveshafts. Still there. It vibrates at 80mph. Rpm doesnt seem to matter, just mph's. We took off the brake drums, wheels and it still did it. Now, this weekend it comes in at 60mph, and have done nothing to the car since the last race. I drive it to and from the track.
Any ideas on this would be great. Hope I didnt forget any details. If so I will post when I remember them. Thanks for any ideas. [8D]

 

Sounds like you swapped everything that may be the fault of your vibration but 3.73's is tough on driveshafts.
Especially at 80mph.

Have you tried an aluminum driveshaft?

 

mine happen to be U joints were bad. i had same symptons as you. get down and grap the drive shaft and shake it. any play in it?? there should be none.

also check drive shaft bolts, mine cam loose once. check for any damage to drive shaft. do you have an other problems or noises?

 

I swapped driveshafts from another 5.0. Same issue. Have not tryed aluminum shaft yet.

 

Could the pinion be bent?

 

Have you checked ball joints, tie-rods, bearings? Motor and tranny mounts. Doe's your shifter vibrate?

 

Yep, when it is vibrating the shifter is so bad, you dont want to hold onto it. Have checked the motor mounts and trans mount, all fine.

 

That is the way my old fox used to do, it hurt to hold shifter. I wound up doing two things at the same time, so i am not sure what fixed it, but it drove great after. I changed my inner tie rods, actually the whole rack and pinion because it was leaking. I realized my tie-rods were bad when i grabbed my tires and 9 and 3 and pushed and pulled, there was way to much play. I had also recently did a gear change, that had about 300 miles on it. I grabbed my driveshaft in the back near the pinion gear and it had play. I had not crushed my sleeve properly. So i tightened my pinion bolt and replaced my inner tie rods and all was well.