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Clutch problem

 
marks_85
I love my Chevy Chevette!
Posts: 1
Joined: 09/08
Posted: 09/19/08 09:51 AM

My 85 with 4+3 has a problem in that the clutch does not disengage.  I have watched through the fork access point while the cluch is being depressed and everything appears to be working.  Any ideas?  I am thinking most likely release bearing failure. Frown  

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maxdog0001
I love my Chevy Chevette!
Posts: 1
Joined: 09/08
Posted: 09/21/08 06:41 PM

By the clutch does not disengage , if you mean that gears grind when you try to shift or are unable to shift; then the INPUT shaft to the transmission is still spinning , when it should not be turning. This could be caused if the fit of the tip of the input shaft is TOO TIGHT WHERE IT SITS IN THE BUSHING AT THE VER REAR OF THE CRANKSHAFT. Other things regarding the pressure plate still SQUEEZING  the clutch disc onto the flywheel would turn the input shaft.  

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texex91
I love my Chevy Chevette!
Posts: 2
Joined: 12/10
Posted: 12/16/10 02:31 PM

my 85 with 4+3 has taken me through the ringer!!!!  I am by no means a mechanic..but we have replaced master and slave cyl.  - throw out bearing - push rod - hydrolic line assembly between master and slave.. pressure plate.. Both times it was in the shop, we drove it home and 1/2 day later clutch wasn't working again.. Twice has done the same thing.. any suggestions will help.. I live in NW Georgia and need a mechanic who really knows antique Vettes.. Please Help..  

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waynep7122
I have an SS396 tatoo
Posts: 262
Joined: 08/09
Posted: 12/16/10 07:03 PM

when clutches fail to release...    there are several possible problems....

i have had a lot of trouble with similar clutch masters.. where the top of the bore wears.. this reduces the fluid displacement...   the clutch master and the clutch slave cylinder are matched in displacement...

so a full stroke of the clutch pedal  will move the slave cylinder the proper amount...

there was a hidden problem on other gm models... the fiero... where the clutch pedal would wear.. the opening where the clutch master push rods wears into an OVAL shape instead of being round... this requires the pedal to move farther before you start moving the clutch master piston...

this clutch pedal failure.. and the clutch master failure can be felt in the clutch pedal... as you will notice the pedal has little if any resistance when depressing the clutch until the pedal is part way to the floor...

you may also notice that the pedal is close to the floor...   remember .. the clutch master has to be at the full retracted when your foot is not on the pedal...  try lifting the pedal ... does it come up any????

what happens to the pedal when it fails....   does it stick at the floor.... does it become soft.... like its NOT attached to the clutch...  or does it stay firm... all the way down from the top... so it feels like its really depressing something...

now that you have verified that the pedal is moving through a full stroke...

how long has the clutch been installed for....   there is a fairly good chance.. that the PILOT bearing/ bushing is seizing the input shaft...     this bushing/bearing is pressed into the back of the crank...   it centers the clutch disc when the clutch is depressed by supporting the transmission input shaft...  it not only keeps it on center.. but it allows it to spin separately  when the clutch is depressed...     if you have spent a LOT lof time with your clutch depressed and the engine running..  you might have found the problem...

there is a LOT of discussion upon... to grease or not to grease the pilot bushing...    

i have always greased them lightly...  

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texex91
I love my Chevy Chevette!
Posts: 2
Joined: 12/10
Posted: 12/17/10 08:09 AM

what happens to the pedal when it fails....   does it stick at the floor.... does it become soft.... like its NOT attached to the clutch...  or does it stay firm... all the way down from the top... so it feels like its really depressing something...
...

pedal goes soft.. all of the sudden will not engage clutch to put in gear..pedal stays at the top as normal.. feels like depressing spring only.. no regular clutch pressure  

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waynep7122
I have an SS396 tatoo
Posts: 262
Joined: 08/09
Posted: 12/17/10 07:05 PM

if you are NOT loosing fluid.....

and you do NOT have a centerforce clutch cover...


the clutch master is probably bad.... i know... its been replaced...

i just went through this exact same problem with a saab...   the return spring was off its center.. wore a groove in the master internal seal....    this is how it is lined up in the master...   0----|o)piston { seal  ///////// spring.

so...  i put a kit in the cylinder.. since the replacements were over 150 bucks... kit was 14...  worked great for about a month.. then the spring broke in half...    clutch acted strange again.. took it apart... found the broken clutch master spring...  found a used one from the local saab mechanic..  installed the spring.. and another kit.. worked great...

like i said... i have found that these identical brand units that were used on 90s vintage jeep wranglers.. wore the top of the bore...  work the clutch a few times...   then tip a white paper towel into the fluid.. pull it out quick.. look at it.. do you see any aluminum particles...   if so.. replace the clutch master again...

there is a small chance the system is pushing the diaphragm overcenter..  but then the clutch would be disengaged..


there is also a small chance that the thrust bearing on the crank shaft has failed...    can you start the motor with the hood open....     having the engine running at idle...   you standing in line with the fan belts...  have them work the clutch...   look at the alignment of the crank pulley with the others...   i have seen the clutch push the crank forward almost a quarter inch...  when the clearance is normally 0.020 or so...   the fan belts can actually pull it back to alignment while the engine is running.....   this is one of the weird problems.. that usually only show up in stick shift cars...

you have to really look along the belts to see any forward movement..  

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waynep7122
I have an SS396 tatoo
Posts: 262
Joined: 08/09
Posted: 12/17/10 07:34 PM

here is what the insides of the clutch master kinda look like...

http://contentinfo.autozone.com/znetcs/product-info/en/US/bx3/20171/image/4/
above jeep replacement part...

below the corvette clutch master cylinder kit...

http://contentinfo.autozone.com/znetcs/product-info/en/US/bx3/22268/image/4/

you really might want to remove the clutch master.. and examine the bore...   swap in the new seals from the kit..

but.. checking the crank end play... this is what you could have been chasing for a LONG time...

i replaced the crank in my eX bosses 350 chevy stroker motor. 400 crank turned mains.. turned rods to SJ size.... it had almost 5/16 of an inch of end play.. the crank was so dug out at the thrust surface.. when i showed up at the engine shop to order another to match..  they could not believe it...  and it was an automatic car..   what was funny about that repair.. i built it on a stand as the paint shop had the body.. i wanted to hear it.. as did he.. i tossed on the stubby headers... hooked up the fuel pump... tossed some jumpers on everything and a wire for the hei... turned the engine stand so the open headers were pointing at the car he was asleep in.. and let it rip..   he jumped up so fast.. looking around as that motor rattled the shop...  he thought it was an earthquake.. or some other disaster..  

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