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Revisiting the "howling" noise from my 1970 GTO drive train

607 Views 27 Replies 9 Participants Last post by  Bopman
Hopefully you will be able to follow along with my explanation about this noise. I have had the car running and driving since last summer. It is a 4 speed with an M20 "rock crusher" . It doesn't matter if am accelerating and shifting gears, or driving along at a steady speed, I have a "howling sound" that I originally suspected was coming from the transmission. I had the transmission professionally rebuilt, but that did not solve the issue. I had the car on a two post lift, with the motor running, and the sound appeared to be coming from the rear end. Now since the weather has warmed up here in Michigan, I have had the car out several times trying to pin down the noise. What I have discovered is that when I disengage the clutch and coast along, the noise disappears. As soon as I engage the clutch, the noise returns. I can coast along in "neutral", with no noise. It becomes louder the faster I drive, and then with the clutch disengaged, coasting, it goes away. I understand that the M20 transmission has a noise of its own, but I can't believe it would be this noisy. Any ideas???
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BOP axles have the bearing slid over the axle, and up against the hub, then a retention collar is slid onto the axle, and as it approaches the bearing, it needs to be pressed up onto a shoulder.

So, you're partially right... the assembly is held in by the four bolt plate... HOWEVER, that plate is merely clamping the bearing into the axle housing, meaning:

If your bearing fails for any reason, it will rapidly wear down the shoulder on the axle... which of course then renders a press fit useless. So, yes, the four bolt plate will continue to hold the bearing in place, but the axle will slide right out oh the housing, effortlessly.

It goes without saying that the quickest way to test this theory, is to drive a 50-year-old-car, without knowing if or when the bearings were last serviced. In most cases, Gerald Ford was probably still in office.
To sum it up, the four bolts only retain the bearing, not the axle. If the axle wasnt "stuck" in the bearing, there's nothing else to hold it in.

Chevy, OTOH, uses a c lip at the diff, so unless the axle cracks completely in half, it cannot come out by accident.
Heres a good pic... (right to left) Notice the hub, then the four bolt plate, then the bearing, then the press fit collar.

As you can see, the plate merely clamps the bearing into the axle. It doesnt physically hold it in any way.
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Thanks to everyone for your input, I will check for "play" in the ring & pinion by twisting the driveshaft, and check the pinion yoke for any "for and aft" movement. I will post my findings. Phil
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Acting on the suggestion about "twisting" the driveshaft with the trans in neutral, and the parking brakes locked, here is what I discovered: There was no "in/out" play in the yoke, and the driveshaft moved approximately 1/8" when I "twisted" it manually. I don't know if that is significant movement to show wear?
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Acting on the suggestion about "twisting" the driveshaft with the trans in neutral, and the parking brakes locked, here is what I discovered: There was no "in/out" play in the yoke, and the driveshaft moved approximately 1/8" when I "twisted" it manually. I don't know if that is significant movement to show wear?
Really hard to say... how old are the ujoints? Do you know? Are they very rusty or do they have rust around the rubber seals?
Both ujoints front/rear on the driveshaft are new. I will be taking the car into a repair shop specializing in servicing the rear axle. I am leaving the repair to professionals. Way above my pay grade. Phil
Sounds as if it does have some excess backlash in it...but I have seen a lot worse, like an inch of twist !
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