904 Downshift Squall or Howl

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nm9stheham

nm9stheham

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My son's '65 'Cuda has an occasional but subdued howling or squalling sound when it downshifts when slowing to a stop. This occurs are both the 3-2 and 2-1 downshifts. The tone is kind of like the low pitched squalling sound that an 18 wheeler's tire makes when it locks up, but much less loud or harsh and lasts for < 1 second.

The car has a 8.75 rear axle and 3.55 Sure Grip. But I don't think that would squall when stopping in a straight line. We have looked for rubbing of the driveshaft but see nothing like that.

So is there anything in the 904 like a band adjustment or rear overrunning clutch problem that could sound like this?

It also has a Gear Vendors OD unit, but I'll call them directly and ask about that. I want to ping the Torqueflite experts here on any possible 904 issues or anomolies.
 
Has the pan been dropped yet to see if there's tell tale stuff in it?
I have heard that before in transmissions that the clutches were worn and pressures to them are low due to wear.

I kind doubt it's the OD unit since it isn't doing anything during these downshifts.
I guess it's possible though.
 
I've run into something like that on a few/several higher mileage 904s, which I attributed to the planetaries. I ran them like that for years,and years. Your results may vary. It was more of a whine tho than a howl.And the pitch and the volume changed with each downshift and with the driveshaft speed.
My GV is dead silent, under all circumstances. I cannot even tell it's there.
 
OK, I did not think of the planetaries; they would be putting power back into the engine to spin it up on the downshifts. Trans was supposedly rebuilt by a shop good with Torqueflites maybe 2 years ago and < 1k miles ago, but I am not sure how often anyone would look hard at the planetaries. But the howl does not change pitch at all, so maybe not.
 
With no change in pitch or volume,Ima thinking it might not be in the gear-train, cuz every thing in there is moving at ever-changing speeds.
Unless it was hydraulics related.But I cannot imagine a scenario like that either, cuz at closed throttle and decelerating, the Throttle pressure is at a minimum,while both the Governor pressure and the Line pressure are dropping, so whatever noise they might be making(under unknown reasons) I would expect a change in pitch and/or volume.

So I'll mention this in passing; If you are running a proportioning valve, the rear hydraulic pressure will be much reduced, and the wheel cylinder pistons will not be extending very far. If the shoes were to be in just the right place to excite the drum, but not actually be doing much braking, those rear drums could be singing This singing might not change much in pitch, but it would most likely change in volume..Just a thought.
 
At this point, just about any idea is a good idea. We have been adjusting the rear prop valve out as we improve the brakes; it may be all out by now as we put in higher CoF front pads and adjusted more prop valve reduction back out of the rears; my goals is to get trid of that thing. But it does indeed sounds sorta like old school bus brakes LOL!
 
Ok well then easy enough to tighten up the rear star-adjusters some.
I gutted my P valve years ago, so running full line pressure back there.I set the proportioning with wheel cylinder size and 295 tires.Car stops hard, and straight
 
Well, it looks like we finally figured this out....indirectly. The PO had arranged the belts so that the water pump was being driven from the slack side of the crank, not the tension side. (That same belt drove the Sanden AC compressor over on the driver's side.) That poor arrangement resulted in belt squeaks and squawks at start up and over 3000 RPM.

We put in an underdrive crank pulley and got the water pump and alternator belt set up as normal. Now, not only have the other belt squeaks and squawks stopped, but this downshift howl is all gone. It seems the sudden engine speed increases on downshifts was squawking the water pump belt.... man, it's always sumpthin'!
 
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