Tranny Noise Question

[Spline64]

Hello,

Hoping somebody can point me in the right direction here.

I have a TH400 tranny in my 1973 GMC C2500. Just recently I have noticed a noise that is coming from it that I can barely hear but is starting to get louder over the last few weeks. I noticed it first when decelerating below 30 mph but now I can barely hear it when accelerating as well. It sounds like a squeaking or somebody quietly ringing a very small bell under the truck. If I place it in neutral while this is happening and coast it goes away immediately and comes back when I put it back in drive. Braking has no effect on the sound.

Ideas?

Thanks,
Pat

[geezer#99]

Could be a u-joint, steady bearing or tranny cover.
You got a one or two piece driveshaft?

[Spline64]

Two piece, and all the u-joints have been replaced with the exception of the one closest to the tranny. I tried to move the drive shaft but couldn't get it to budge.
Just curious why the noise stops when the transmission is switched into neutral while moving, drive shaft is still moving at that point.
Cover is plastic, but I'll look at that as well.

Thanks!
Pat

[GRADYS Performance]

Could be loose converter bolts or cracked flex plate. Or possibly a bad torque converter if the noise goes away in neutral.

[RoughKuntry]

It could also be the fact of the Pilot Bearing going out, Almost Dealing with the same thing, Only I have the Bulldog SM465 transmission.

[geezer#99]

He has a t-400,
No pilot bearing needed.

[RoughKuntry]

Well that's different then. Now if he had the SM465 then you should be concerned

[geezer#99]

No concern even if he had a pilot bearing. They usually don't wear out.

[RoughKuntry]

Wanna make a bet? with the old Bulldog SM465 Transmission for 10/11/1972 they do if they don't get replaced. Wanna know how I know that talk to my dad, ASE Certified Alison Transmission Re builder. I have a T30 in my 73 1 ton 4x4, from all the photo's and video's that I do send my dad. I'm not saying that they always wear out, but me driving one of the first version of the Square bodies that hasn't been taken care of and treated like a complete mess, take it into consideration that I am restoring something that has had enough problems in the past with the fact of this same transmission putting up problems. maybe one of these days Geezer you will understand that I have not only turned away from the old body style but also did a complete rebuild of everything except the running gear from a 1973 Early Model Super Custom. 73/89 front clip, Updated Wire Harness + 77 Cab, with 73 Original Flat Bed.

[geezer#99]

Sure they might wear a bit and need replacing, but 90% of the time the pilot bearing is rotating at the same speed as the input shaft.