hey all,

i have a 700r4 with about 105k miles on it. i am getting an odd thrumming vibration intermittently when driving the thing.. but its most severe when at a set speed (cruise control on the highway) at around 65-75mph or decelerating . its slightly noticeable when accelerating, but very slight. when i pop it into neutral at these speeds, its as smooth and quiet as can be. when decelerating (in gear) it is also quite noticeable all the way to about 30(ish). this isn't an **** retentive just barely noticeable vibration either... it rattles the change in my ashtray.

i know this is fairly general, but what do you think i should do first? i am going to have the fluid flushed and filter changed just to see if there are any pieces or debris in the pan to be concerned about, and i am considering changing the ujoints just as a precaution. if these things don't help, what is my next diagnostic step?

thanks all,

thunder


additional info: this might not be part of the same problem, but there is a 1-2 second lag before my car will shift into drive or reverse. i click the shifter... wait... then it engages.

and yes, i know there are other posts about tranny vibration in a 700r4... but none of them that i have found had all vibration go away upon popping the car into neutral at highway speeds...

maybe its your drive shaft.

if that were the case, wouldn't the vibration stay when i was in neutral at highway speed? the drive shaft is still spinning at the same rpm

i got a used 700r4 and put it in recently because mine went out bad.

It vibrates when i accelerate slow but it is give it a decent about a gas it does not really do it.

Most of the time when it does it during accel i can pop into 3rd and it smooth again.

it does not burn fluid or slip

also if im slowing down and try to gun it again it vibrates


to me its feels like if i was shifting into 5th to early in a 5 speed

like maybe the tranny is going into OD to soon i dunno

i just dont feel like taking it back out lol

yurs doing anything like this?

check the mount

sounds liek u joints if it shakes on deacceleration. Could also be the mount.

U JOINTS

tim91, yes, i do get that... when its cruizing it vibrates, but when i punch it the vibration reduces by about 80%.

i will buy U joints and drop the driveshaft tonight. i need to change the tranny mount and install my ds loop anyhow, perfect excuse. is there a brand recommended?

on an additional side note... if i want to kill my tc lockup without burning a test chip what do i unplug? i am wondering if its a combination of issues with maybe the u joints, bad mount, and shuddering tc lockup clutch

update:

u joints weren't bad, but were old so i replaced them. changed tranny fluid and had no chunks of metal or any debris... just the usual silver sludge stuck to the magnet. i'm putting all high mileage tranny fluid and 1qt of Lucas transmission treatement. the tranny mount was good and fairly new looking, but rubber. i am changing it out with a new urethane bushing (and installing my ds loop). i'm also putting posi treatment into my diff... see if maybe thats vibrating some too.

could a jacked up tc cause these issues?

thats what I wanna know to the TC on my 700 is from a caprice and my 700 is from a truck.....my original 700r4 had to much clutch dust in it after the tranny burned up to save the orig tc