96 crew cab 3500 clunking. HELP!!

[Josh20315]

Just put a 350 crate motor in my 96 crew cab srw c3500. 4l80e does have 360k on it but shifts good just have to let off throttle a little. I’m having sum clunking when accelerating up hills. I know absolutely nothing about being a mechanic. Please help. Truck sat about 2 years b4 getting new motor.

 

[Caman96]

I’m having sum clunking when accelerating up hills.

Clunking from where?

 

[Josh20315]

Clunking from where?

I honestly don’t know. I believe it to be trans or rear end

 

[GoToGuy]

At steady speed? When accelerating? When letting off the throttle ? Does noise follow eng rpm or does it follow vehicle speed? Automatic or manual ?
What letting off throttle when shifting? What does that mean?

 

[Josh20315]

im coming up on a big hill… give throttle not too loose speed… start going up hill… clunk. Get up to the top ease up… clunk. Does this at 40, 60. Really any speed. It’s a 4l80e auto. In every gear it’ll rev to about 2500 rpm I’ll ease up and it’ll shift smooth. Is what I mean. She doesn’t just shift trans has 360k gotta ease up on throttle for old girl to shift. But no clunks on shifts

 

[Schurkey]

im coming up on a big hill… give throttle not too loose speed… start going up hill… clunk. Get up to the top ease up… clunk. Does this at 40, 60. Really any speed.

Wild guess with little evidence: Torque converter clutch disengaging/reengaging.

It’s a 4l80e auto.

Generally reliable. Not perfect. 360K miles? How often was the trans fluid changed, and the filter replaced?

In every gear it’ll rev to about 2500 rpm I’ll ease up and it’ll shift smooth. Is what I mean. She doesn’t just shift trans has 360k gotta ease up on throttle for old girl to shift.

Again...what does the fluid look like? Fresh fluid, new filter MIGHT make an improvement.

360K, the thing is likely due for overhaul.

But no clunks on shifts

Yeah, I'm thinking the clunk is the torque converter clutch...but that's just a guess.

 

[Erik the Awful]

To be on the safe side, check all your suspension mounting points and your axle u-bolts.

 

[Drunkcanuk]

Does it clunk when putting it into gear as well? Could be u-joints if so.
But you have a few things above my post to check as well. Give everything a good shake to see if anything is loose. Or it's internal to your trans.

 

[Josh20315]

Fresh trans fluid it was leaking bad had to put new fluid and sum stop leak in it. I’m leaning towards rear end or torque converter but I’ll check suspension and u joints

 

[Josh20315]

Appreciate everyone’s help. Can’t thank you gentlemen enough I’m 20 years old and just bought the truck