Help identifying clunking sound

[67sport]

What are the symptoms of old t-case mounts?

I'm trying to find a clunking sound, that occasionally comes and goes from the rotating mass of my 67. Sounds like heavy metal object against heavy metal object.knock, knock.......knock....knock......,,,very irregular. And not always present at all.

'67 with 302, original 3.03 with husrt floor shifter, original d20.

What I know;
It's not connected to the rolling assembly, it does it sometimes when stopped at idle, so can't be driveline.
It has done it through 2 exhaust systems, this one has good clearance, nothing contacts it,
It has done it with the original 289, and does it with the current 302, new motor mounts installed,
I don't believe it's in the motor, it has done it through 2 motors.
I have a new TW driveshaft and new rear end, so it could be in the t-case, but can't be slop in the rear driveline.
I have never pulled or separated the trans/t-case and have what I believe are original bushings. I salvaged the truck 25 years ago, I don't believe they've been replaced ever. They both shift well though.

What it might be;
Loose motor mounts - I have tried to pry the motor, mounts are new-ish, I need to check the torque, but I don't think so, they don't move with a pry bar.
20 year old Duffy headers against starter - very little clearance, but should move in phase with each other, I don't think so. Headers are in good shape.
Clutch/flywheel assembly - possible, but over the years, if something was loose, it should have let go. Also, 2 different motors and clutches, so unlikely.
Internal trans or t-case issue - maybe? Any input here? They both work well.
Old rubber t-case bushings - I hope so? Seems most likely, but I don't want to throw parts at an undiagnosed problem. When I pry at the t-case, I can hear the rubber bushings squeak and see it move, but the whole assembly looks really good.

If its the t-case bushings, should it go away idling with the clutch in? The internals are disconnected at that point, but arent the engine/trans/t-case still vibrating together?

Anyone have ideas on where to look/diagnose, or how to test the rear supports?

Thanks for the input. It's done it for 25 years. It shows how far the truck has progressed, now that this is the problem I'm trying to fix! The truck is finally working great!

Sent from my SM-T560NU using Tapatalk

 

[Rustytruck]

check the doughnuts at the frame connection for the front arms. the doughnuts can look intact but the material insulating the arms from the brackets can be worn through on the inside.

 

[bax]

Check the z bar / clutch linkage. The pivot ball in the block could be worn out. The z bar could be worn out or even boinking up against the frame mount or the header.

 

[67sport]

Thanks for the suggestions. I'll check those additional spots as well.

 

[67sport]

I just wanted to close this thread out.

I finally had the time to replace the t-case mounts, and I've now had it out in the woods on two trips that should have produced the intermittant clunking that used to come and go. It seems I have cured it!

The mounts I took out were pretty wallowed out as well, and had clean shiny metal from where they had been rubbing the crossmember, indicating movement at the mounts. I assume they were stock, but I was surprised that the rubber mount was bonded to a metal washer against the crossmember. Seems like a design that would lead to noise. New ones are from energy suspension, and seem designed well enough.

I think this one is dealt with. Thanks all for the input.

Sent from my SM-T560NU using Tapatalk

 

[bax]

Well at least we didn't help much.

 

[ngsd]

Glad you found it. I have a clunk that is happening when I take off from a dead stop that feels like it's coming from the xfer case that I can't figure out too.

 

[DirtDonk]

Is it just a mild clunking (sound only in other words) or does it also feel like it's settling/squatting down slightly in the rear when it happens?

Paul

 

[67sport]

Glad you found it. I have a clunk that is happening when I take off from a dead stop that feels like it's coming from the xfer case that I can't figure out too.

Do you know if the t-case mounts have been changed? Mine looked pretty good till I took them out. I was surprised that the original mounts look to be rubber bonded to metal washers, so there is metal on metal by design. Any slop is going to translate to a knock as the driveline loads and unloads, by my thinking.

I'll try to post pics of my worn mounts once I get out to the shop. There wear marks clearly indicate movement.

Could also be a worn driveshaft or loose u bolts at the rear end maybe.

Sent from my SM-T560NU using Tapatalk

 

[ngsd]

I will check the mounts as I have been meaning to do that. It is really pronounced form a dead stop and start but not through the gears so mostly under take off load. It does not feel like it is settling in the rear. If I put my hand on the shifter I don't feel it but the tcace handles it feels pretty pronounced. It also have a Klune V in the mix.