TAC Tech => Mechanical => Topic started by: Bayou_Flyer on September 23, 2021, 08:08:38 AM
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My Project YardBird 75 Formula post is long gone, but I continue to chip away at the stone...slowly! Backstory, I bought the car after having sat in a field for over a decade...it’s Saginaw trans busted. I had a Muncie (not Rock crusher) sitting in the garage. I put it in along with a zoom clutch setup.
Yesterday, I brought the car to my exhaust guy to get the 2.5” Pypes exhaust installed. Occasionally, when downshifting from 4th, there is a loud grinding/whirring sound. If I put it back in 4th or neutral and let off the clutch, the sound stops. When I stop, everything works fine. Shifts fine. It’s just the downshift.
Is my throw out bearing hanging up? With car idling in neutral, foot off pedal, ai can hear the whirring sound...but I always associated a bad throwout bearing with a chirping sound. Could the bearing be improperly sized for this setup? It’s a 69 P350 to a late 60s Muncie M21
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My Project YardBird 75 Formula post is long gone, but I continue to chip away at the stone...slowly! Backstory, I bought the car after having sat in a field for over a decade...it’s Saginaw trans busted. I had a Muncie (not Rock crusher) sitting in the garage. I put it in along with a zoom clutch setup.
Yesterday, I brought the car to my exhaust guy to get the 2.5” Pypes exhaust installed. Occasionally, when downshifting from 4th, there is a loud grinding/whirring sound. If I put it back in 4th or neutral and let off the clutch, the sound stops. When I stop, everything works fine. Shifts fine. It’s just the downshift.
Is my throw out bearing hanging up? With car idling in neutral, foot off pedal, ai can hear the whirring sound...but I always associated a bad throwout bearing with a chirping sound. Could the bearing be improperly sized for this setup? It’s a 69 P350 to a late 60s Muncie M21
The “idling in neutral, foot off pedal” part makes me thing input shaft bearing possibly. Under those circumstances the TO bearing wouldn’t be in contact with the pressure plate fingers.
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The loud whirring noise happens when pedal depressed and downshifting...and it isn’t all the time either. Mainly after driving for some time. It reminds me of the noise my old TDI VW starter would make as the shaft was slow to retract. But yes, if I put in neutral and let off the pedal, you can hear that faintly come and go as the pedal is depressed
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If you want to eliminate the TOB sound, (statically), you can loosen your clutch linkage pushrod at the fork, and pull the fork/(TOB) away from the fingers, if the adjustment is close to them. That way you'll know for sure the TOB isn't bouncing off them. Of course you'll have to put the adjustment back to normal. When diaphragm clutches wear, the fingers when relaxed aren't always on the same plane, and will sometimes cause them to hit the TOB, (If the adjustment is tight) and make a noise. But like you mentioned, it's usually more of a chirping noise. If the noise is still there when idling, with lots of clearance, then you'll know it's not tranny or clutch related.
If your input shaft bearing is going, it could make a noise when the clutch is released in neutral, and when the car is in any gear.
And when shifting, (up or down) and you get a grinding noise trying to get it into gear, you could have worn syncros. But I wouldn't associate that with a "whirring" sound, but more of a grinding noise.
Have you checked your fluid level yet? Stick your finger in the fill hole, and see if you can feel oil. If you can't and it's low, maybe you'll have an easy fix. Good luck.
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Thanks! I just drove it 20mi back from getting the exhaust installed. I didn't have any of the noise on the way home. I pushed in clutch, put trans in neutral, let idle stabilize then put it in gear. Syncros are fine..trans shifts buttery smooth. One thing with this zoom street clutxh is the pedal movement is MUCH shorter conpared to other 4spd T/A I have owned. I had to do a LOT of adjustment to get where the TOB wasnt rev’ing with the car while driving. I havent put many miles on this setup, but other than the original noise when downshifting, it drives pretty good.
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When you downshift, does the noise only happen from 4-3, or the other gears too? What about upshifting from 2 to 3? There are no different internal components for upshifting, or downshifting, but the load is directional. When upshifting, the gear is loaded on the drive side, and is reversed on the downshift. But the synchronizer works the same, whether you're upshifting or downshifting. Also, when cruising in 3rd, is the noise gone?
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I am a strict fundamentalist, so I would die before I would admit that the throwout bearing is affected by what gear you're in. That's just the way I am. if it's the throwout bearing, it has to behave the same in other gears. Otherwise my world is going to totter.
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I get the impression Joe, when he pushes in the clutch to downshift, it makes a "grinding/whirring" sound, (his description). But as we know, the throwout brg (if bad) will make noises every time you push in the clutch, not just up-or down, but even in neutral.
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No noise upshifting…just down. I’m accustomed to the chirping noise of a bad TOB, this noise is more like the noise when a starter shaft is slow to retract. The trans came from a family friend’s Chevelle…with the Hurst shifter installed. There is no grinding going in/out of gear. Here is the typical situation:
Car shift up and down the gears when cold..zero issue. After some driving, ai am going 35-40mph and approach a RR crossing in 4th…I start slowing, push in clutch, move trans into 3rd, get noise with clutch pedal still in. Move trans to neutral, pedal still depressed, car slows some more…put trans into second and no noise. I have not verified that this is only a 4-3 issue, so I will have to play around with speed vs gear.
There is no chatter from the clutch, no weird noise when taking off from a stop. It all seems to work as intended. I can hear a whirring noise with pedal out in neutral. Start pushing pedal in (still in neitral) and noise goes away.
After clutch was installed, I had to do a LOT of adjusting of the clutch linkage. Pedal would vibrate, lots of slop on the return, and thw TOB would make a ziiiiinnnng noise whenever the RPM increased in each gear. It would also do that in neutral/pedal released. That I was able to eliminate with adjustment. That is why I was originally thinking TOB was causing this noise. Perhaps the trans isnt going fully into gear on the downshift? Like I said, this does not happen if I push pedal in, allow idle to stabilize, THEN downshift.
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I believe someone mentioned the input shaft bearing in the transmission. If in neutral, foot off the clutch pedal, you hear the noise and then depressing the clutch pedal the noise goes away, it is more than likely a bearing issue in the transmission. Input bearing will make more noise in first gear and progressively get more quite as you shift up.
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also.....I have heard that whirring sound in my transmissions in the past. That happens when you are trying to force the next lower gear into position too soon and/or not having enough
PRM to help the synchro's engage that gear.
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also.....I have heard that whirring sound in my transmissions in the past. That happens when you are trying to force the next lower gear into position too soon and/or not having enough
PRM to help the synchro's engage that gear.
Exactly. I know exactly the noise you're talking about. Not sure if this is the noise he's referring to. Would be nice to hear it in a video.