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Diagnostic conundrum

2003 van, started shuddering about 2 months ago; occurs usually between 35-45 mph, initially intermittent, now more pronounced, feels as if going over speed bumps; new tires and alignment; replaced sway bars and transmission fluid, to no avail; no change if accelerating through 65 mph, or braking; no change when turning; does go away if placed in neutral when this rumble occurs.

Fanatic, Has Anybody Checked The Engine’s Harmonic Balancer ?

CSA

In addition to CSA’s recommendation, engine mounts are a possibility.

How well has the engine been maintained?
If you have the vehicle in park and manually (slowly accelerating) rev the engine, does it begin shaking?

It might be time to have the vehicle scanned at a transmission shop. Offhand, it could be a torque converter or fluid pressure problem or even an oddly worn halfshaft.
With the latter (and if it’s not clicking or knocking) sometimes the only way of knowing is by removal and physical inspection on the bench.

Not yet, mechanics have been stumped by the intermittent nature of the shudder, now more noticeable at lower speeds 30-40 mph.

Engine mounts OK; I’m pretty compulsive about engine maintenance, oil changes including transmission fluid
No shaking in park

I’ve wondered about the transmission, in part because the vibrations stop if I place it in neutral; there was no code when initially scanned by the mechanics, which I thought a bit odd.

Ok i dont know a lot about cars, but I had something similar happen to me awhile back with my van. We found out that the rims weren’t on very tightly and the tire was loose. I know that might not be what is wrong with yours, but its a thought. Because if you have new tires they will generally have to be tightened after driving for awhile. My van didnt do it at 65 either, just 30-45 like yours.

Sounds to me like torque converter clutch (TCC) shudder. I too think it is time to have a good transmission shop put it on a scanner - NOT a chain-type transmission shop. A good, local independent is what you need.

ditto.

Thanks; I’ll try that route; hopefully a code will pop up.

Easy to do; I’ll check it. Thank you to all the folks that gave us some ideas.

Took it to a local tranny shop, recommended by Consumer Checkbook in DC; many codes off; the main problem was the clutch torque converter; rebuilt transmission, now have a warranty of 24 mos or 24 k miles.
Hopefully this is it.
Thank you to all who responded and made suggestions.

If this is a rear wheel drive vehicle I’d change the universal joint.

A Town and Country is a mini-van (OK in the 60’s it was a station wagon)In any case people may wonder about your words of wisdom, please educate us.

Although the alignment shop checks the CV joints, maybe the problem wasn’t obvious. You might want to have them checked again. Wheel bearings and the whole alignment shop stuff may have to be gone over by another shop. Wheel balance jobs have been botched before.

Universal joint.

Really?

In a FWD vehicle?
ZW–Your lack of technical knowledge is simply stunning.

You need new struts or shocks.