Grinding sound... Ugh

[67chevy_hotrod]

1969 longhorn sb350/th400 eaton HO52 rearend. So if I accelerate hard I get a really bad grinding sound. (Sorta like a stuck starter). It runs fine and shifts fine when I drive normal. Last time it happened the shift linkage actually fell apart and I was stuck in low 1 after fartin with it. It's pretty terrifying to hear ha! Please anyone with ideas let me know! Thanks in advance.

[Coley]

I would get underneath the truck and check every connection between your transmission and your differential Including:
All U-joints thoroughly
The hanger bearing....thoroughly
The transaction mount....thoroughly
Make sure your differential is fully and correctly in place ....no broken mounts or shackles etc
(...also check your engine mounts while you are at it)
This would allow you to use the very proven method of process of elimination in isolating the problem
Start there
All good
Coley

[swamp rat]

Is the fan blade hitting the radiator??? bad engine mount and transmission mounts.....

See if it just makes the noise driving under load or if it happens at a stop with revving the engine. Also pop the hood and rev the engine to see if the engine is rocking to one side to check the engine mounts. I think this would account for your linkage mishap.

While your at it jack up the rear of the truck and rotate a wheel and listen for any grinding in the diff, drop one wheel and check again.

Lots of good advice above but i think his "transaction mount" meant "transmission mount" with the damn auto correct syndrome

[snipescastle2]

Motor mounts, man I broke a few in my day, and ate a few radiators too! Brought back some memories from high school (sorry,didn't mean to hijack your thread) carrier bearings/throw out bearings might be a cause also.
Ben

[67chevy_hotrod]

It's not fan hittin radiator.. It definitely sounds like a transmission problem.. I will look into the rearend as well. I recently replaced the pinion seal.. It shifts fine and sounds fine at idle and at higher rpm. Under load or when I give it the gas a little aggresive is when it does it. This is irritating ha

[67chevy_hotrod]

Ok so all mounts are secure and intact. There is no evidence of exterior grinding on any drivetrain components( no fresh metal no scoring marks). The fan is definitely not hitting the radiator. I have not spun the rearend yet because I have had no time will do tommorow. Not sure what the next step would be if I can't decipher what is creating the beautiful sound ha

[70STOVEBOLT]

You've checked to make sure there is not a muffler or e shahs the pipe vibrating against the frame or a suspension component or axle?

[slikside]

Originally Posted by 67chevy_hotrod

It's not fan hittin radiator.. It definitely sounds like a transmission problem.. I will look into the rearend as well. I recently replaced the pinion seal.. It shifts fine and sounds fine at idle and at higher rpm. Under load or when I give it the gas a little aggresive is when it does it. This is irritating ha

Did the noise begin right then, or shortly thereafter? Always consider recent changes, especially when they "sound like" they could definitely be related to your problem.

I've never replaced a pinion seal myself, but I know that when it all goes back together you need a new crush sleeve, and it has to torqued just right...

I'm not saying it wasn't done right, just that it (or something related) could be the cause, since it was recently changed...

[midniteblues]

Just a few thoughts here. Perhaps it's the dust/inspection cover for the flex plate/torque-verter rubbing.

You could try duplicating the noise by setting e brake and pushing on the brake while giving it some throttle.
That might eliminate the road noise for better pin pointing where it's coming from.

[67chevy_hotrod]

Lol brakes went bad today so that's been my immediate issue