Clunk when shifting into gear

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Oct 4, 2025 | 12:19 PM

skookumchuck

Thread Starter

Intermediate

Joined: Jan 2020

Posts: 31

Likes: 7

Clunk when shifting into gear

Hi knowledgable ones,

I have a '76 with the 350 and TH350 transmission. It runs very well, but recently there has been a noticeable clunk when shifting into gear, either reverse or drive. Could this be a transmission issue, driveline, U-joints or rear end? I went for a short cruise yesterday, and I did not notice any shifting problems under normal driving even when I jumped on the freeway and opened it up a bit. Any insights will be greatly appreciated. I'm mechanically challenged, so please be gentle.

Oct 4, 2025 | 12:29 PM

barkingrats

1967 Pedal Car Champion

Joined: Mar 2020

Posts: 9,137

Likes: 4,248

From: US-PNW

My '72 TH400 has done this as long as I've had it. How hard it engages seems dependent on idle speed, but even at low idle it seems to thunk and squat at times. In the last 5 years, I've had the trans rebuilt, installed new driveshaft u-joints and new differential snubber cushions. Still does it. I've not rebuilt the differential or changed axle u-joints, but I'd think if there was that much backlash and slop it would reveal itself with other problems, which there aren't. @GTR1999 Gary?

Oct 4, 2025 | 12:33 PM

Bikespace

Race Director

Joined: Mar 2017

Posts: 11,953

Likes: 4,510

From: Virginia

Quote:

Originally Posted by barkingrats

For the OP, I'd do the snubber bushing first.

For you, I'd check your idle speed, vacuum connection to the trans, and the vacuum modulator (unit, and adjustment).

Oct 4, 2025 | 12:59 PM

Laughing Coyote

Racer

Joined: Nov 2023

Posts: 296

Likes: 502

From: Vail, AZ

Quote:

Originally Posted by Bikespace

For the OP, I'd do the snubber bushing first.

For you, I'd check your idle speed, vacuum connection to the trans, and the vacuum modulator (unit, and adjustment).

I agree on the differential front snubber bushings. Mine were just about gone and I had a clunk when putting it in gear, but drove and shifted fine. After changing it out, no more clunk.

Oct 4, 2025 | 01:05 PM

barkingrats

1967 Pedal Car Champion

Joined: Mar 2020

Posts: 9,137

Likes: 4,248

From: US-PNW

Quote:

Originally Posted by Bikespace

For you, I'd check your idle speed, vacuum connection to the trans, and the vacuum modulator (unit, and adjustment).

Idle speed in D is ~600, trans shop checked the modulator and said it's fine, 2nd and 3rd shifts feel smooth and uneventful. I can certainly check vacuum to it and play with adjustment.

Oct 4, 2025 | 01:28 PM

skookumchuck

Thread Starter

Intermediate

Joined: Jan 2020

Posts: 31

Likes: 7

Quote:

Originally Posted by Laughing Coyote

I agree on the differential front snubber bushings. Mine were just about gone and I had a clunk when putting it in gear, but drove and shifted fine. After changing it out, no more clunk.

Thank you for your insights. Is replacing the snubber bushings in the differential an expensive fix? I know that's relative; what's expensive? I have no experience inside a transmission or differential, nor do I possess a lift, so I would have to take the car to a transmission shop. Any ball park guesses on the cost of this replacement? Sounds like the rubber bushing kit is the way to go. Fast forward: after doing a little research, I discovered the bushing kit is only $20. or $30., and maybe a hundred bucks for a shop to put it in. Thanks again.