short vibration at 25kmh?

I don't know if this is a real issue or not. I've noticed that as I accelerate slowly, as I reach 25kmh I can feel a vibration through the gas pedal for a second. It goes away immediately and does not seem to happen except when first driving. I can't feel it if I doa jackrabbit start. I don't think it's tranny/shift related, I put it in 1str this morning and drove and felt it.

I was under the car the other day and looked at the CV boots on the driveshafts, they look intact, but that doesn't prove anything - Worn CV joint maybe?

Just a guess, but could be an engine mount going bad. The vibration might only be transmitted when the engine is shifting under torque. 1st gear happens to create a lot of torque response.

Yeah, that was the first thing I thought of, but it doesn't happen at a shift, like I said I can keep it in first and hit that speed and it happens. Is thetre a way to check CV joints in the driveway?

If the CV boots are not torn, they should be good. If the boot is bad, grease will leak out to surrounding areas in the engine bay. My original CVs are still holding strong at 225k miles. They really overbuilt them, imo.

A bad CV will "click, click, click" when you are rolling or turning. The CV can also growl when accelerating or decelerating. This would be noticeable at high speeds as well.

Hmmm I just don't know then. I get a little wobble in the steering wheel sometimes too but that feels more like a power steering thing, something I take to be common from reading this forum. Maybe its a tire thing? I'll try to drive at that exact speed and see if it keeps vibrating....

The steering wobble might be a tie rod end thing.

Yeah I know, I know, but if it is tie rod ends experience tells me I can let it get MUCH worse before I fix it ha ha.

After trying to drive around at athat speed it seems like a short jolt - and once it happens it won't happen again until the car is put in park and then driven again. Maybe it is a motor mount "settling" a bit at that level of torque in 1st. I'll try swapping them out once I put my Tahoe back together (doing brakes on it in a peicemeal fashion)

i think i have the same problem here's my post

https://rivperformance.editboard.com/t8302-scratching-my-head-just-can-t-figure-it-out-help-please#129699

first thing to do is get under the car and look at the mounts.

The under-car transmission mounts are nowhere near as robust as the top pass side unit.

Albertj

How do I tell if they are worn to the point where they need to be replaced? The only other time I needed a mount, it was snapped in half, so it was pretty easy to tell.

I took mine to a local mechanic and put it up on a lift. He took a long bar and shifted the engine, showing me the movement and metal/metal contact occurring from the failing rear mount. He also diagnosed a bad ball joint and cradle insulators needing replacement. Well worth the $40 for diagnosis, imo.

its nice to know good honest mechanics

jlaw wrote:

How do I tell if they are worn to the point where they need to be replaced? The only other time I needed a mount, it was snapped in half, so it was pretty easy to tell.

Get the car on jackstands or a lift and look at the mounts.

The trans mounts are basically rubber cubes with a rubber bar molded through surrounding a ferrule. Please do a search, there are pictures on this site. (look for "Filling mounts" or some such)

When you look at the installed mounts, if the rubber is cracking they are weak and it is time to replace. You have some time before they completely fail but during that time they give you all kinds of cr-p when they are weak because the nice high-torque Riv engine whacks against the limits of travel in the mounts. *all* the mounts have to be good for the engine to sit right in the subframe.


Most likely the rear transmission mount is wack. If it has been bad long enough the excess movement will take out the front trans mount.