when you push in the clutch pedal, the noise stops? If so, that sounds like the throwout bearing.
Revisiting the "howling" noise from my 1970 GTO drive train
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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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???
Do you have a M20 or M22? You mentioned the term "rock crusher" which applies to the M22 and its straight cut gears. If it's a M22, the howl could well be normal. Try hitting YouTube and check videos of other cars with the same trans. Lots of M22 videos on there demonstrating how it got its name.
Yes the M22's are noisy as I have one in my 70 judge. But the noise is different than a howling rear-end so it could be wear in the ring and pinion...play needs to be checked in ring and pinion.Do you have a M20 or M22? You mentioned the term "rock crusher" which applies to the M22 and its straight cut gears. If it's a M22, the howl could well be normal. Try hitting YouTube and check videos of other cars with the same trans. Lots of M22 videos on there demonstrating how it got its name.
Kind of hard to diagnose based on a written description no?
I have forgot two include that I installed a new "bent finger", pressure plate, clutch disc and throw out bearing initially, then I changed from the "bent finger" pressure plate to a "flat disc" pressure plate, clutch disc and throw out bearing. The noise was still the same. I like the possibility of the wear on the ring and pinion, as I know the original owner and he was an avid street racer and realy beat the GT while he owned it.
OOOPS, forgot to correct the transmission, it is an M21 "close ratio" according to the build sheet. The rear ratio is 3:90.
You can check wear pretty easy by twisting drive shaft back forth while tranny is in neutral and parking brake applied if car is jacked up with rear wheels off the ground/ floor. Should be VERY LITTLE play. You can feel the pinion move and stop while twisting shaft back and forth. Just trying to help !I have forgot two include that I installed a new "bent finger", pressure plate, clutch disc and throw out bearing initially, then I changed from the "bent finger" pressure plate to a "flat disc" pressure plate, clutch disc and throw out bearing. The noise was still the same. I like the possibility of the wear on the ring and pinion, as I know the original owner and he was an avid street racer and realy beat the GT while he owned it.
Well, the M22 is called a rock crusher because of the noise it makes. That would have fit your description to a T, but the M21 is normally quiet and since you had the trans rebuilt we can probably rule the trans out.
The lower the ratio the more prone to noise, and your 3.90 rear would be more inclined. A 2.56 ratio is much more forgiving on setup that yours - but if the rearend was healthy there still wouldn't be noise.
The most common cause would be that the differential was run low on oil sometime in its life and the ring and pinion gears are toast.
As Bopman said above, the next common cause would be improper backlash changing the meshing of the gears. I would only expect to see about a 1/4" of play when twisting.
While you are under there check and make sure that the differential pinion yoke doesn't have any play fore and aft. It should have preload but could have been damaged or even had the pinion nut back off.
The lower the ratio the more prone to noise, and your 3.90 rear would be more inclined. A 2.56 ratio is much more forgiving on setup that yours - but if the rearend was healthy there still wouldn't be noise.
The most common cause would be that the differential was run low on oil sometime in its life and the ring and pinion gears are toast.
As Bopman said above, the next common cause would be improper backlash changing the meshing of the gears. I would only expect to see about a 1/4" of play when twisting.
While you are under there check and make sure that the differential pinion yoke doesn't have any play fore and aft. It should have preload but could have been damaged or even had the pinion nut back off.
I re read your first post and it does sound like a worn ring and pinion, "too much play in it", I have seen yoke/pinion move almost a 1/4 turn on some differentials...badly worn ! 🤣🤣 I had a 61 Ford enconoline pickup that was worn that bad ! 🤷♂️🤣OOOPS, forgot to correct the transmission, it is an M21 "close ratio" according to the build sheet. The rear ratio is 3:90.
I re read your first post and it does sound like a worn ring and pinion, "too much play in it", I have seen yoke/pinion move almost a 1/4 turn on some differentials...badly worn ! 🤣🤣 I had a 61 Ford enconoline pickup that was worn that bad ! 🤷♂️🤣
I re read your first post and it does sound like a worn ring and pinion, "too much play in it", I have seen yoke/pinion move almost a 1/4 turn on some differentials...badly worn ! 🤣🤣 I had a 61 Ford enconoline pickup that was worn that bad ! 🤷♂️🤣
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???
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???
I had the same problem on my 72 GT. Sounded like it had a supercharger on it! LOL! Turned out to be the ring gear/pinion assy. I had rebuilt the M20 the year before and it was very quiet. The reason it may go away while coasting is the lack of thrust you experience under acceleration. 400CID 4BBL M20 3:55
I agree that it's in the gears, but I dont think it's in the gears themselves.
My money is on the pinion bearings and/ or axle bearings.
Both make a horrid howl, and both ALWAYS go bad on 50 year old cars. No one EVER maintained them and they (often) didn't get oil on their own.
More importantly, stop driving the car!
Unlike Chevy, BOP rear axles are held in place by the outer bearings, and once they stick or seize, they'll then wear out the axle, which will slide out of the diff housing and pass you on the freeway.
If you catch it in time, it's a simple repair. Start with the axles, if your howl persists, do the inner and outer pinion bearings. They're a bit more tedious, but easilly doable my a novice, in the driveway.
My money is on the pinion bearings and/ or axle bearings.
Both make a horrid howl, and both ALWAYS go bad on 50 year old cars. No one EVER maintained them and they (often) didn't get oil on their own.
More importantly, stop driving the car!
Unlike Chevy, BOP rear axles are held in place by the outer bearings, and once they stick or seize, they'll then wear out the axle, which will slide out of the diff housing and pass you on the freeway.
If you catch it in time, it's a simple repair. Start with the axles, if your howl persists, do the inner and outer pinion bearings. They're a bit more tedious, but easilly doable my a novice, in the driveway.
BTW, my car had the same issue.
If you have a 50 year old car, the bearings need to be replaced/ serviced/ and maintained. Ive seen even the best mechanics completely neglect the bearings.
If you have a 50 year old car, the bearings need to be replaced/ serviced/ and maintained. Ive seen even the best mechanics completely neglect the bearings.
BTW, if it goes away when you push in the clutch, then it's not the axle bearings, it's the pinion, but I'd still change them all.
I'll fill in tomorrow when I get the time but I just got back from a 2700 mile trip in the '67 and had to have the rear axle bearings replaced in Cortez Colorado. Got back from Mesa Verde and heard squeaking in the hotel parking lot. Jacked it up and oh crap---axle play. (It was fine when I did the pre-trip inspection) I've had that rear end in the car for the past 15 years or so, no idea how old the bearings were. Ordered two new ones from NAPA and the owner of the store hooked me up with his buddy who runs a truck and hot rod shop and he installed them the following morning. No problems on the 900 miles home at 75-85 mph!!! Back to topic....I agree that it's in the gears, but I dont think it's in the gears themselves.
My money is on the pinion bearings and/ or axle bearings.
Both make a horrid howl, and both ALWAYS go bad on 50 year old cars. No one EVER maintained them and they (often) didn't get oil on their own.
More importantly, stop driving the car!
Unlike Chevy, BOP rear axles are held in place by the outer bearings, and once they stick or seize, they'll then wear out the axle, which will slide out of the diff housing and pass you on the freeway.
If you catch it in time, it's a simple repair. Start with the axles, if your howl persists, do the inner and outer pinion bearings. They're a bit more tedious, but easilly doable my a novice, in the driveway.
Shit bro!!!!!! You really lucked out! Glad you had no incident!!!!
When I got my car from my uncle, it howled like crazy! I immediately bought all new bearings, and when I took the axles out, one was all rust and dry as a bone, but still spinning! NAPA gave me the wrong bearings, conical, so that sucked...
What a lot of the GTO guys dont seem to realize is that GTO rear axle bearings are not like a conventional, conical-type race and bearing, like you'd see up front. They use a permanently mounted bearing, like on a skate board wheel, so once it's dried, it's failure is eminent.
Conical bearings, OTOH, can be cleaned and regreased for an eternity, and will never go bad.
When I got my car from my uncle, it howled like crazy! I immediately bought all new bearings, and when I took the axles out, one was all rust and dry as a bone, but still spinning! NAPA gave me the wrong bearings, conical, so that sucked...
What a lot of the GTO guys dont seem to realize is that GTO rear axle bearings are not like a conventional, conical-type race and bearing, like you'd see up front. They use a permanently mounted bearing, like on a skate board wheel, so once it's dried, it's failure is eminent.
Conical bearings, OTOH, can be cleaned and regreased for an eternity, and will never go bad.
FTR:
For those who never had their axles apart, here's a GTO wheel bearing. You can see that it cant be removed and cleaned, or repacked with grease, very easily, if at all.
![Wood Gas Bumper Automotive tire Auto part]()
![Automotive tire Tire Rim Auto part Wheel]()
And here we see the rear diff bearings, which are OFTEN mistakenly sold to GTO owners as "axle bearings", but they wont fit our GTO's! Notice how these are conical race bearings, which can be cleaned and repacked.
![Tire Wheel Automotive tire Product Rim]()
For those who never had their axles apart, here's a GTO wheel bearing. You can see that it cant be removed and cleaned, or repacked with grease, very easily, if at all.
And here we see the rear diff bearings, which are OFTEN mistakenly sold to GTO owners as "axle bearings", but they wont fit our GTO's! Notice how these are conical race bearings, which can be cleaned and repacked.
Caught mine just in time
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Dadspackard 1969 GTO
Hello all, I am new here, I once owned a GTO and regretted selling it. I have been looking at adds lately and my twin found this me Facebook market place. We went out to look at it a few weekends ago and I could not pass on it. Body work and interior has been restored, engine bay could use some...
www.gtoforum.com
I thought it was the Chevy axles with C clips that could turn into a 3-wheel car if you snap an axle.I agree that it's in the gears, but I dont think it's in the gears themselves.
My money is on the pinion bearings and/ or axle bearings.
Both make a horrid howl, and both ALWAYS go bad on 50 year old cars. No one EVER maintained them and they (often) didn't get oil on their own.
More importantly, stop driving the car!
Unlike Chevy, BOP rear axles are held in place by the outer bearings, and once they stick or seize, they'll then wear out the axle, which will slide out of the diff housing and pass you on the freeway.
If you catch it in time, it's a simple repair. Start with the axles, if your howl persists, do the inner and outer pinion bearings. They're a bit more tedious, but easilly doable my a novice, in the driveway.
Don't the BOP 10 bolts have the axles retained by bolts at the ends near the brakes?
I think the bearings are pressed on to the axles but I haven't torn apart a BOP in decades....
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