Hi! I have an '89 full size and I have an issue with the drive line. Every time I start out in first gear (700r4), the tranny knocks on the floor boards a few times and then it's fine until I come to a complete stop and then start out again. If I ease in to the throttle, it's fine, but under moderate+ acceleration is when it happens. I've already replaced the tranny mount twice, fluid is new and level, and I made sure that every bolt was tightened up, so now I'm stumped. Any ideas? Thanks a lot!!!

 

Check your engine mounts. Bad engine mounts can cause premature failure of the transmission mount.

 

Motor mounts seem fine, or else I would feel more vibration coming from the engine bay, no? I'll double check that when I get home from work, but any other ideas? Thanks!

P.S.
BTW, wouldn't the engine make a similar noise or vibration in park while revving the motor if the motor mounts were bad? IDK, I could be wrong, I'm still a bit of an amateur at this.

 

Poly trans mount?

It really sounds like the transmission/transfer case are moving around on you. Have you checked the clearance to the body on the trans, transfer case, exhaust, driveshafts, etc?

Will it do it if you rev the engine while holding the brakes? If so, you could chock your wheels and have someone who trusts you crawl underneath to see if they can see exactly what is happening (or find someone you trust and crawl under yourself - lol).

 

Well, it wouldn't surprise me in the least if it were moving around considering the hack job that was done on it by the previous owner. I've had the truck for a week and they just changed the tranny before I got it. The vibration is coming from directly beneath the center console. I also should mention that the truck has a 4" lift as well, maybe the driveline angles are off causing them to bind? If so, how do I check to make sure the angles are correct?

I'll try applying the brakes and revving it to see if that points me in the right direction....

Also, I've noticed a metallic chatter from underneath when I"m slowing down from highway speeds. Ideas? Thanks again!