Author Topic: Clutch Grind when shifting to "reverse"  (Read 235 times)

camaroman1969

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Clutch Grind when shifting to "reverse"
« on: May 01, 2016, 05:36:11 PM »
Hello everyone!!  I have a question for you Camaro Gurus.  I own a 1969 Camaro SS/RS with a 396/375 engine.  Just totally rebuilt tranny (M-22)  Newer clutch assembly also.  Centerforce dual friction clutch set-up.   Problem I have is that when car is shifted into reverse, I get a little grinding on gears.  When car is cold, this doesn't happen.  Seems to be more noticeable when car is at running temp.  We adjusted the free-play out of clutch and it still tends to grind now and then.  When I put 4-speed in first before going into reverse, this seems to help.  But still, its not right.  Any clutch experts out there, any info you can shed on this issue would be greatly appreciated.  Thanks for listening.......

bcmiller

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Re: Clutch Grind when shifting to "reverse"
« Reply #1 on: May 01, 2016, 06:49:58 PM »
Since the transmission is freshly rebuilt, the first thing I would check is the shifter linkage.  Make sure the shifter is adjusted correctly.
1968 Camaro SS 396 - now 468 BBC, M21, 12 bolt.
Looking for 68 Camaro with body number NOR 181016

Mike S

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Re: Clutch Grind when shifting to "reverse"
« Reply #2 on: May 01, 2016, 07:12:23 PM »
 Reverse is not synchronized so the input shaft has to be completely stopped before shifting. Make sure the throw-out bearing is adjusted right as well as pedal travel.  How did the reverse gear look in regards to teeth? Were they well defined or slightly topped off.
 And here is something else to consider if the clutch is adjusted properly and there are not other mechanical issues causing it, and that is the bell-housing to crankshaft alignment. If it is out of specs (I believe it is .005" max) then my theory is that due to friction cause by too far of misalignment, that the input shaft doesn't stop completely due to that friction. The friction can be due to the input shaft nose being too snug in the pilot bushing (from out of alignment) and the heat just aggravates it. 

Mike
« Last Edit: May 01, 2016, 08:57:59 PM by Mike S »
67 LOS SS/RS L35 Hardtop - Original w/UOIT
67 NOR SS/RS L35 Convertible - Under restoration

ko-lek-tor

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Re: Clutch Grind when shifting to "reverse"
« Reply #3 on: May 01, 2016, 08:30:27 PM »
Mike: "Make sure the throw-out bearing is adjusted right as well as pedal travel."
What I was thinking exactly. If there is no free play in the linkage, the disc is is still touching the cover or flywheel. Several things that I encountered switching from diaphram to borg&beck and Long style is that the ball height of the pivot fork and the thickness of the T.O. Bearing can be changed to achieve the correct geometry. Lot of factors to consider as well as what oil is being used, hopefully not synthetic.
Putting you First...Keeps me First. Talent on loan from God. Helping the hobbyist and exposing the fraud
1969 SS/RS 396 coupe Hugger Orange X22 712 bought in 79
1969 SS 350 coupe LeMans Blue 713 bought in 79
1969 307 4spd. coupe Daytona Yellow 711 bought in 85

Stingr69

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Re: Clutch Grind when shifting to "reverse"
« Reply #4 on: May 01, 2016, 09:57:17 PM »

The shifter linkage adjustment is frequently mentioned, but seldom the cause.  Worth a check.
The clutch is adjusted properly with 1" of free play measured with a tape measure at the pedal pad against light finger pressure.  Make sure there is no lost motion in the clutch linkage. If you still get grinding with the right clutch adjustment, the clutch is not fully releasing.  That causes the gears to continue to rotate and clash going into reverse. Try going into a forward gear first to stop the rotation and then try to go into reverse. Might help, but not solve the problem.

If the installer hung the weight of the transmission on the disk while trying to install the transmission, you could have bent the disk. disk can't release fully and it grinds going into reverse.

Usually this is the cause - pressure plate can be warped and cause this grinding symptom. Defective pressure plate or heat related damage from clutch linkage adjustment being too tight. Tight clutch adjustment allows clutch slippage, which causes heat, which then warps the pressure plate, and the disk can't release anymore - you get grinding.

Replace clutch with a stock replacement LUK brand and be done with it.

vtfb68

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Re: Clutch Grind when shifting to "reverse"
« Reply #5 on: May 02, 2016, 09:29:08 PM »
   Camaroman,
I was taught at a young age to go into third before going into reverse, if it gets tight before it pops into reverse back off the clutch a hair and it will fall into reverse.
   It's been working for me for well over thirty years. May I ask why you decided to go with the straight cut gears?
    Victor
05C LA RS/SS U2 712 L34 M21 BR
08E LA RS Y2 749 L30 M35
"In the pursuit of accuracy"

bcmiller

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Re: Clutch Grind when shifting to "reverse"
« Reply #6 on: May 02, 2016, 11:10:25 PM »
M22 gears are not straight cut.  Less of an angle than M20/M21, but not straight cut.

Check the easy stuff first.  In other words, the shifter.  If that doesn't solve the problem, then start looking at the clutch/throw out bearing/bellhousing alignment
1968 Camaro SS 396 - now 468 BBC, M21, 12 bolt.
Looking for 68 Camaro with body number NOR 181016

camaroman1969

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Re: Clutch Grind when shifting to "reverse"
« Reply #7 on: May 03, 2016, 12:22:50 AM »

The shifter linkage adjustment is frequently mentioned, but seldom the cause.  Worth a check.
The clutch is adjusted properly with 1" of free play measured with a tape measure at the pedal pad against light finger pressure.  Make sure there is no lost motion in the clutch linkage. If you still get grinding with the right clutch adjustment, the clutch is not fully releasing.  That causes the gears to continue to rotate and clash going into reverse. Try going into a forward gear first to stop the rotation and then try to go into reverse. Might help, but not solve the problem.

If the installer hung the weight of the transmission on the disk while trying to install the transmission, you could have bent the disk. disk can't release fully and it grinds going into reverse.

Usually this is the cause - pressure plate can be warped and cause this grinding symptom. Defective pressure plate or heat related damage from clutch linkage adjustment being too tight. Tight clutch adjustment allows clutch slippage, which causes heat, which then warps the pressure plate, and the disk can't release anymore - you get grinding.

Replace clutch with a stock replacement LUK brand and be done with it.
Stinger...I've never heard of a "LUK" replacement brand clutch...

camaroman1969

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Re: Clutch Grind when shifting to "reverse"
« Reply #8 on: May 03, 2016, 12:23:56 AM »
M22 gears are not straight cut.  Less of an angle than M20/M21, but not straight cut.

Check the easy stuff first.  In other words, the shifter.  If that doesn't solve the problem, then start looking at the clutch/throw out bearing/bellhousing alignment
Byron, Thanks for the info.....

camaroman1969

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Re: Clutch Grind when shifting to "reverse"
« Reply #9 on: May 03, 2016, 12:26:23 AM »
Mike: "Make sure the throw-out bearing is adjusted right as well as pedal travel."
What I was thinking exactly. If there is no free play in the linkage, the disc is is still touching the cover or flywheel. Several things that I encountered switching from diaphram to borg&beck and Long style is that the ball height of the pivot fork and the thickness of the T.O. Bearing can be changed to achieve the correct geometry. Lot of factors to consider as well as what oil is being used, hopefully not synthetic.
Fresh new oil (90W) gear lube was put in tranny.

camaroman1969

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Re: Clutch Grind when shifting to "reverse"
« Reply #10 on: May 03, 2016, 12:30:04 AM »
Thanks guys for all the valuable info on my clutch issue.  Anybody else that has some tips or past experience, feel free to chime in and voice your opinion.  Again, thanks everyone for your rapid response.

Stingr69

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Re: Clutch Grind when shifting to "reverse"
« Reply #11 on: May 03, 2016, 01:18:20 PM »
I once personally removed and replaced my entire clutch/transmission assembly THREE TIMES in one day dealing with this exact problem. Hard to find the source of the issue.  All the individual pieces looked fine when examined on a bench while all the parts were loosely laid out. On my third trip to the speed shop, they assembled the clutch pieces on the bench for me and we found the pressure plate fingers were obviously warped once the bolts were all torqued down (not a symmetrical cone anymore). This warpage was causing the clutch to not fully release so it was dragging the disk (not stopping the rotation) and the gears would clash as they were trying to mesh. Only showed up when going into reverse because it is the only gear set that does not have a synchronizer to assist the gear meshing. 

Replaced the pressure plate and all was well again.

Mike S

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Re: Clutch Grind when shifting to "reverse"
« Reply #12 on: May 03, 2016, 02:33:15 PM »
 When I had first read this article I took it with a grain of salt. http://www.camaros.org/bellhousings.shtml
Being I had the motor out of the car during its recent restoration I decided to buy a go/no-go fixture like mentioned in the above article (found one on eBay) and put it on the crank and bolted on the bell housing and I was surprised the test ring jammed solid when trying to go into the transmission opening. I thought maybe the fixture was defective so I bought a magnetic stick on electronic dial indicator from Harbor Freight. Boy was I surprised how out of alignment the bell housing was in respect to the crank. It measured .011" total run-out and the limit was .005". The deck squareness was also out at the 7 o'clock position by a few thousands. So now I had two test tools that indicated I indeed had an alignment problem.
   I was able to reduce the run-out down to .002" max by using Lakewood offset dowel pins in place of the factory pins. After determining which direction to shift the bell housing, I finally was able to dial-in the pin positions before locking them down. Afterwards I had to place a flat shim between the bell housing and the block by the lowest left side bell housing bolt to get deck squareness to 0.0" . After all the alignments were done and re-checked with the dial indicator and the go/no-go ring slid through the transmission opening smoothly, and a new pilot busing installed, the transmissions slid into place with absolutely no effort (after aligning the splines of course). Before I always had to jiggle the transmission around a lot to finally get it to seat into the bell housing opening. I don't know if the cause of misalignment were due to factory tolerances or block core shift from age or a factor of both.
  In the past I was always going through bronze (real bronze) pilot bushing and even a needle bearing pilot bushing, and once an input shaft bearing on an otherwise rebuilt transmission, in such a short time of driving. And it always would grind slightly when going into reverse. I had to use the forward then reverse shift trick first. I could never figure it out until I read about bell housing alignments here at CRG. I found articles and how-to's on You Tube to check and adjust the alignment and it is really easy once you  understand how it's done.
  This is why I will now always suspect if the transmission is grinding in reverse and it is not attributed to other obvious mechanical issues, that the cause can be due to interference friction drag on the input shaft machined nose being wedged against the pilot bushing wall due to bell housing to crank misalignment and not allowing the shaft to completely stop rotating when depressing the clutch.

Mike
67 LOS SS/RS L35 Hardtop - Original w/UOIT
67 NOR SS/RS L35 Convertible - Under restoration