Screeching sound when clutch is pushed in

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GRTfast
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Screeching sound when clutch is pushed in

Post by GRTfast » Sun Feb 25, 2018 8:27 pm

Hello all. I have an Autogear M23 mated to my big block. I’m using a Howe hydraulic throwout bearing and a GM performance Kevlar clutch (11 inch). Yesterday in traffic when I had the clutch pushed in while idling, I heard a couple “chirps”, then when I revved the engine to take off, it made a high pitched screeching sound until I let the clutch out. Car has 12000 miles of street driving in Florida. The rest of the drive home (20 miles or so), it did it once more when I pushed the clutch in and revved the motor, but otherwise it behaves normally and the clutched worked as it should.

I’m pretty sure it’s the throwout bearing, but I’d like to hear what everyone else thinks. I’m pulling it apart tomorrow. I’ll report back.

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Re: Screeching sound when clutch is pushed in

Post by GRTfast » Mon Feb 26, 2018 4:06 pm

Got it apart. The throwout bearing doesn’t feel bad, but the noise was very intermittent so that was somewhat expected. Also found that the clutch was worn out (sipes are almost gone), and the pressure plate and flywheel had some interesting wear. Any idea what causes the pressure plate and flywheel to wear like this (see pics)?

I’m replacing all of it. Got a RAM HTOB, a Hayes 30 lb billet steel flywheel and a McLeod extreme street ceramic 11 inch clutch on the way.

The old flywheel was an 18 lb aluminum unit. Never really liked it for street driving. I’m exciting to get it all together and see how it works with the meatier flywheel.
Attachments
pressure plate 1.JPG
pressure plate 1.JPG (94.59 KiB) Viewed 2049 times
friction 1.JPG
friction 1.JPG (101.43 KiB) Viewed 2049 times
flywheel 2.JPG
flywheel 2.JPG (112.94 KiB) Viewed 2049 times
flywheel 1.JPG
flywheel 1.JPG (105.39 KiB) Viewed 2049 times
pressure plate 2.JPG
pressure plate 2.JPG (113.92 KiB) Viewed 2049 times

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Re: Screeching sound when clutch is pushed in

Post by SupStk » Mon Feb 26, 2018 7:42 pm

The clutch appears to been severly overheated, such as by slipping.
The scretching sound is many times caused by the throw-out bearing locking up and sliding on the pressure plate fingers. Since it felt smooth wonder if the pressure plate fingers were contacting the clutch disc?
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Re: Screeching sound when clutch is pushed in

Post by GRTfast » Mon Feb 26, 2018 8:36 pm

SupStk wrote:
Mon Feb 26, 2018 7:42 pm
The clutch appears to been severly overheated, such as by slipping.
The scretching sound is many times caused by the throw-out bearing locking up and sliding on the pressure plate fingers. Since it felt smooth wonder if the pressure plate fingers were contacting the clutch disc?
The only slipping it’s seen is during some spirited launches, but they weren’t bad. It does look like it got hot though. It doesn’t look like the pressure plate fingers touched the clutch. It must have been the bearing squealing.

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Re: Screeching sound when clutch is pushed in

Post by peejay » Mon Feb 26, 2018 9:38 pm

You'll see a lot of hot spotting like that on aluminum flywheels that see a lot of launching, because the heat of clutch slip doesn't really have anywhere to go. The steel friction plate doesn't really transfer heat to the aluminum and out as well as you'd see in an all-steel or all-iron flywheel. Plus, less mass overall, even after it transfers to the aluminum part, means it gets hotter regardless.

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Re: Screeching sound when clutch is pushed in

Post by GRTfast » Mon Feb 26, 2018 9:51 pm

peejay wrote:
Mon Feb 26, 2018 9:38 pm
You'll see a lot of hot spotting like that on aluminum flywheels that see a lot of launching, because the heat of clutch slip doesn't really have anywhere to go. The steel friction plate doesn't really transfer heat to the aluminum and out as well as you'd see in an all-steel or all-iron flywheel. Plus, less mass overall, even after it transfers to the aluminum part, means it gets hotter regardless.
Yeah that makes sense.

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Re: Screeching sound when clutch is pushed in

Post by FirstEliminator » Wed Feb 28, 2018 8:03 am

Make sure you check the pilot bearing as it is active whenever there is a difference in engine rpm versus input shaft rpm. Like when standing still with the clutch pushed in and the trans in gear.

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Re: Screeching sound when clutch is pushed in

Post by GRTfast » Wed Feb 28, 2018 8:04 am

FirstEliminator wrote:
Wed Feb 28, 2018 8:03 am
Make sure you check the pilot bearing as it is active whenever there is a difference in engine rpm versus input shaft rpm. Like when standing still with the clutch pushed in and the trans in gear.
I'm installing a new one. I'll be working on it tonight. Thanks for the advice.

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Re: Screeching sound when clutch is pushed in

Post by autogear » Wed Feb 28, 2018 9:56 am

Make sure you do a cursory check on bellhousing concentricity and parallelism while you're at it.
I had one customer with a bad pilot bushing; apparently it was slightly oversize for its bore, and it was pounded home. This decreased the ID of the bushing, pinching the tip of the input. Symptoms were hard to engage reverse cleanly, hard shifting and a squealing noise occasionally.
I've also had customers who had aluminum flywheels without sufficient SLR (the 9 - 10:1 rule of thumb for most guys assumes a steel flywheel and a sub-30" tire). Lacking sufficient gear reduction, they were forced to slip the clutch more; which can be very hard on aluminum flywheels.

Not saying all these things are your problem; but these may help someone else in the future.

PS
THANKS for waving the Auto Gear flag!!!!

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Re: Screeching sound when clutch is pushed in

Post by GRTfast » Wed Feb 28, 2018 10:06 am

autogear wrote:
Wed Feb 28, 2018 9:56 am
Make sure you do a cursory check on bellhousing concentricity and parallelism while you're at it.
I had one customer with a bad pilot bushing; apparently it was slightly oversize for its bore, and it was pounded home. This decreased the ID of the bushing, pinching the tip of the input. Symptoms were hard to engage reverse cleanly, hard shifting and a squealing noise occasionally.
I've also had customers who had aluminum flywheels without sufficient SLR (the 9 - 10:1 rule of thumb for most guys assumes a steel flywheel and a sub-30" tire). Lacking sufficient gear reduction, they were forced to slip the clutch more; which can be very hard on aluminum flywheels.

Not saying all these things are your problem; but these may help someone else in the future.

PS
THANKS for waving the Auto Gear flag!!!!
No problem, you guys are awesome. Nathan helped me select my transmission and it has been great!

Regarding the alignment, I checked it on the original install and it was good. If memory serves, it was concentric within 0.005" and parallel within 0.002"

Shifting has always been really smooth, and the input shaft and existing pilot bushing look to be in good shape. I'll check again on this install just to make sure.

I think my issue was a light flywheel (18 lb aluminum, car weighs ~2850 lb with me in it, rear gear is 3.27) and me slipping it a lot during "spirited" launches.

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Re: Screeching sound when clutch is pushed in

Post by autogear » Wed Feb 28, 2018 10:38 am

Thanks for the pat on the back. Im always the one who posts here; unless I have to tap George for a more esoteric or historical answer; I try to remember to put his name on it though. We're really proud of the M23-series of gearboxes; and our happy customers with them. I just had a customer send me a timeslip with 10.68@125.82mph on it (full disclosure, he had Liberty's 'faceplate' it). He said he 'magged' the gears when he replaced the 'plates; everything looked perfect.

Nathan

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Re: Screeching sound when clutch is pushed in

Post by GRTfast » Wed Feb 28, 2018 10:51 pm

Everything went together smoothly, I just have to put in the driveshaft and button the interior back up (trans tunnel is removable, trans comes out inside the car). The Mcleod clutch has a slightly lighter pedal than the old one, that's kinda nice. Can't wait to drive it.

I used the bread trick to get the old pilot bushing out.. worked like a charm.

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Re: Screeching sound when clutch is pushed in

Post by autogear » Thu Mar 01, 2018 1:08 pm

Just a shot in the dark, if you wanted to keep the alum. F/W. I'd want you at a minimum of 11.5:1 SLR, which means a theoretical 3.85 ring n pinion at a minimum, with the 2.99 1st gear (assuming a sub 30" tall tire). I think you're way better off with the corrected fw and clutch

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Re: Screeching sound when clutch is pushed in

Post by GRTfast » Fri Mar 02, 2018 7:02 am

Drove the car to work this morning. Man, the new clutch feels great. Also, the heavier flywheel is much nicer. It makes me wonder if my old one wasn’t balanced correctly, because the engine used to have a pretty noticeable harmonic vibration around 2500-3000 rpm and its 100% gone now. It runs like a sewing machine. Super happy.

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Re: Screeching sound when clutch is pushed in

Post by peejay » Fri Mar 02, 2018 7:08 am

One thing I noted when I switched to an aluminum flywheel on my car was a lot more gear rattle/whine in the trans.

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