Strange "knock" or "catch" in my 80 (1 Viewer)

[Blue27kFJ80]

I have a 91 with the 3FE and A440F auto trans. the truck was towed due to electrical problems. the truck now has a strange "knock" or "catch" but only In gear. this has led me to believe torque converter but I am unsure. the TPS needs to be replaced, and it needs a valve adjustment. nothing else mechanically wrong that I know of. I have a video of the symptom but im unsure how to post it here. where should I start looking fir this "knock" or "catch?"

 

[jonheld]

where should I start looking fir this "knock" or "catch?"

Only when moving?
Try looking under the truck at the easy things, like exhaust.
Why would you suspect the TC?

 

[Blue27kFJ80]

Only when moving?
Try looking under the truck at the easy things, like exhaust.
Why would you suspect the TC?

This only occurs in gear, in park and neutral there’s no sign of any issue!

 

[jonheld]

This only occurs in gear, in park and neutral there’s no sign of any issue!

It is impossible to help you with that vague a description.
Have you inspected the exhaust?
What happens when you drive?
Is it a rattle like aluminum cans banging together?
Is it a hard thump-thump-thump that you can feel in your seat?
Give me something to work with.

 

[Blue27kFJ80]

It’s like a catch, hard to describe. When the truck try’s to accelerate it’s like it’s hitting a rev limiter and it drops revs around 200-400 with an awful cracking sound. If I hold the truck in each gear it isn’t prevalent until 3rd / overdrive, where at about 1800 the catch is there, but less dramatic, dropping the revs about 100-200 preventing the truck from accelerating over 45. If I put my foot to the floor it’s like somethings disconnected as the revs jump, but nowhere near as high as they normally would “in gear” however if I manually cycle from D - 3 - 2 then I get a “normal” second gear. When it finally lets out into 4th after third there’s an odd rumble like I’m drive on the rumble strips if they were less noticeable.

 

[jonheld]

Where is the sound coming from? Front? Rear? Center? Top? Bottom?
With the truck in PARK push the center diff lock button on the dash. Then put the truck in gear. Is the noise the same?

 

[Blue27kFJ80]

It sounds like it’s the front or under, I’ll try to pinpoint today, as well as trying the center diff lock

 

[BILT4ME]

Could be stripped drive flanges.

Kinda tough based on your description of things.

Does it knock, bang, ping, thump, ratchet, clang?

A "knock" is a low tone that would indicate something large and heavy hitting something else large and heavy.
A "catch" is something that will suddenly stop a vehicle as if something is jammed in a wheel causing interference that will stop motion.

If you can make a video (with audio) and post it on YouTube, then post a link here, we can all help a lot more.

The fact that you have a 91, eliminates a few issues borne with newer versions.

If it only does it when in gear, it is drive line related. Torque Converters a a fluid coupling and don't clank, bang, or thump. They typically whir or make no noise at all.

 

[Blue27kFJ80]

Could be stripped drive flanges.

Kinda tough based on your description of things.

Does it knock, bang, ping, thump, ratchet, clang?

A "knock" is a low tone that would indicate something large and heavy hitting something else large and heavy.
A "catch" is something that will suddenly stop a vehicle as if something is jammed in a wheel causing interference that will stop motion.

If you can make a video (with audio) and post it on YouTube, then post a link here, we can all help a lot more.

The fact that you have a 91, eliminates a few issues borne with newer versions.

If it only does it when in gear, it is drive line related. Torque Converters a a fluid coupling and don't clank, bang, or thump. They typically whir or make no noise at all.

ill make a YouTube video, but I already tested drive flanges by removing front shaft and locking the center diff. its more of a catch id say since the vehicle loses power. ill post the link here when I get it uploaded.

 

[BILT4ME]

Is it a front brake caliper that lost a bolt and is locking against a wheel?

 

[jonheld]

Is it a front brake caliper that lost a bolt and is locking against a wheel?

I'm finding it really difficult to interpret the OP descriptions. He needs to remember that we are not sitting next to him in the vehicle.