Sm 465 clutch engagement issues

[Lsc]

First of all I wanted to say that I found a post that sounded like it might be the same problem I'm having, but it wouldn't let me post on that thread so I've started this one as it didn't seem to be resolved. If anybody knows anything, thanks in advance. The truck has been in service since 1990 and has over 500k miles on it. A lot of these miles I put on it myself, the rest were the old man. I am very familiar with the idiosyncrasies of the sm465 and it's a rare day when I make the slightest grind going into L or R. I'm making two points: that this is a high milage transmission (although in my opinion the sm465 is capable of many more miles than this if driven properly) and that this is not operator error. Sometimes she shifts like she just rolled out of the factory, sometimes like there's no clutch at all.
It'll go something like this: I'm parked, and cold start it. With the clutch fully depressed and proper resistance from the pedal it will just grind when I try to engage anything. I have tried to put it in 3rd and 4th while at a standstill, just to see if they would engage. They just grind too. Then I FORCE her into reverse, and she shifts perfectly for a while until she arbitrarily doesn't again. Always seems to disengage properly but sometimes just won't go into 4th after coming out of 3rd when the rpm is near matched anyway. And then sometimes when it happens the clutch pedal goes soft. It'll shift poorly for a moment, and then like it's brand new again.
I even broke down and took the damn thing to a mechanic, which never happens. It shifted perfectly for the whole test drive.
The master and slave cylinders are both less than a year old. The clutch is about 18 months old. I bled the line yesterday, thinking there might be an air pocket. No such luck, or if it is its still in there somewhere. Any insight would be appreciated.
George
1990 C3500 454 sm465

 

[Joe In Montana]

I fought something like this once on a 454 5 speed and it was a bad thrust bearing in the engine.

It took three other mechanics who kept faulting the transmission and/or the clutch and a lot of "defective parts" sent back to the suppliers with no actual repairs made before it fell into my bay door.

I just knew that three other guys and multiples of new, rebuilt and otherwise parts couldn't all be bad so I went through a different door, mechanically that is.

The #5 main bearing had lost rear the thrust side, gone metal to metal and the crankshaft was floating back and forth making compensation at the slave and master cylinder impossible.........sometimes.

Check your end play on the engine and see if it's more than normal first.

If so then try this next trick...... it's pretty much instantly definitive of the problem if the clutch us not the actual cause.

Park slightly nose downhill.... not enough to actually roll, but almost.....

Clutch pedal IN - make sure it's not dragging!
Transmission in lowest gear forward
Transfer case in 4Hi
Parking brake OFF
Start engine

Does it want to start rolling? (PS - I like to jack up the tire pressure for this test too. It helps)

If so, I'll suspect the pilot bearing. I'm actually pretty sure it's the pilot bearing after re-reading your post for the third time. Without having your truck here and me instead burning up a lot of Internet bandwidth, that's my guess anyway.

 

[dyeager535]

Everything sounds good up until the pedal randomly going soft bit. Hooked up properly, with resistance from the clutch assembly, the pedal effort should never change. The only way pedal effort should change is if the slave or master is leaking internally. No question external factors could affect this, but it would seem very odd that it would randomly happen.

If you could replicate it, with someone watching the clutch fork/slave, that might be beneficial.

Mine doesn't want to shift when cold, but only takes a few seconds of driving before it shifts ok. Your problem appears different.

 

[diesel4me]

How are the floors and cab mounts ?..

I have seen a few trucks with mechanical clutch linkage that had rotted cabs and body mounts,and depressing the clutch would make the cab raise up before actually moving the clutch fork!...and it caused all kinds of weird shifting issues..

Also saw one truck that had all 4 transmission to bellhousing bolts loose,allowing the transmission to "hang" instead of being bolted up tight..

 

[Joe In Montana]

One more thought......

Since this is a hydraulic clutch....I don't suspect cab mounts should be a problem, but I remember the Ford F450s having firewall problems where the pressure of pushing down on very worn pressure plates - which require more foot pressure to disengage - caused the firewall to crack.

This resulted in very vague clutch feelings and especially made clutch adjustments appear to be inconsistent.

Ford made a repair kit for the firewall which was nasty to install but if done then made the truck serviceable again.

I always took those Borg&Beck style clutches out and replaced them with diaphragm type units. They were so much easier on the whole driveline. Remember over-center springs?

Either type can cause much higher operational force if they're worn badly enough though. It may not slip yet... but by all this time and mileage it just might be used up.

OK: although I have never seen this same firewall cracking problem on a GM truck.... with the many miles.... 500K?.... on it, I guess anything is possible.

Clutches take a lot of pressure to operate when the friction material gets thinner because the contact point of the T/O to the 3 finger (Long-Style/Borg&Beck) or the diaphragm contact points cause a loss of mechanical advantage. The resulting mechanical disadvantage puts much higher load on the whole system.

Like grey hair, this process may take years and many miles to arise... and the driver will not recognize this problem until "something's wrong".

I'm very interested in the answer and resolution of this problem. ... keep posting.

 

[Lsc]

I'll keep you guys posted. More or less took yesterday off to see what the Internet would say. My uncle thinks this might be more simple than I am making it. I was under the truck working the bleed valve on the slave while a friend worked the clutch yesterday. I figured doing this a few dozen times would effectively bleed the line, but I am told that this may not be the case. In the interest of cheapest and easiest first I'm gonna go buy a bleeder kit. I can say for sure that it's not a firewall problem, the firewall is rock solid.
If that doesn't do it I will be pursuing the pilot bearing. Holy crap I hope it's not the thrust bearing. The block has been rebuilt once, but it was a long time ago. To answer the question in Joe's first post, when the problem is at its most severe there is definitely a little bit of torque making it to the rear end when it's started in gear.
Special thanks to joe.

 

[Joe In Montana]

.....Then with your last statement, I'm going for the pilot bearing.

 

[diesel4me]

A friend had a 77 Chevy Monza Spyder with a 305 & a 4 speed Saginaw--he claimed the clutch "blew",so we spent a whole weekend installing a Hayes clutch into it..it worked fine,for about a day..next day the free play at the pedal had vanished,and you could smell the clutch slipping..we re-adjusted it (after learning there was a adjustment in the bell housing for the fork ball),but it did the same thing again soon after..it couldn't "hold" a clutch adjustment..

It had a cable operated clutch,I thought maybe it was stretching and getting ready to snap...

It wasn't until I happened to be standing next to the car while he pushed the clutch pedal down,watching the cable,that I noticed the clutch cable where it seated against the firewall,was moving in & out!--closer inspection revealed the firewall had some severe cracking going on,the cable was about ready to pull right through the firewall!..

A few minutes with his arc welder and a hunk of metal plate fixed it once and for all...we had wondered why the old clutch disc and pressure plate looked fine!....all that work and 200+ bucks for nothing..

I agree those old borg & beck 3 finger pressure plates sucked--the pedal effort is about equal to lifting 200 lbs on a universal gym with just your left foot--and those are the ones that were in the rotted trucks I saw with the cab moving ..

I went through 3 of those pressure plates ,rebuilts by Borg-Warner,in my '72 K5..forst one failed at a red light with the truck in first gear and clutch pedal down,and it lurched forward and I bumped a mint 79 Corvette that was in front of me--thought the guy was going to kill me.....other two "dragged" and failed to release fully,and chattered badly --they all failed in a month or two,so I decided to drop down from a 12" to a 11" diaphram type clutch--first time I pushed the clutch pedal down I think I dented the floor,it was SO easy,I thought something was wrong!..

 

[Joe In Montana]

On that 77 Monza......

Was this "adjustment on the bellhousing" an Allen type that moved the throwout fork fulcrum?

If so. ... that's not an adjustment and it has to be torqued home, hard.

 

[diesel4me]

Yeah,we learned that the hard way too !--luckily we were able to tighten it back down with everything bolted up with an allen wrench..
We both vowed that was THE last clutch job we'd do on a Monza too..

 

[Joe In Montana]

Yeah,we learned that the hard way too !--luckily we were able to tighten it back down with everything bolted up with an allen wrench..
We both vowed that was THE last clutch job we'd do on a Monza too..

I disliked working on those horrible vehicles too.

As you work on these things, you cannot help form opinions as to whether you'd own one or make sure your enemy did.

Same thing with an Audi 100. Gawd! what a piece of junk!

 

[diesel4me]

It took us like 2 hours just to put 8 new spark plugs in that Monza--it had headers too,to make it twice as miserable !..had to jack it up,take off both front wheels,remove the steering shaft,etc..what a piss poor design !..

Another car Gm made to frustrate mechanics was the Chevette/Pontiac T1000..one day a friend asked me if I could put a new starter in his wife's 70's Chevette--he was a disabled Vet and it was about 20 degrees out,snow on the ground,and he had only a small shed,with a wood stove,that the car couldn't fit in..

I went to his house,dressed like an eskimo,and jacked the car up--after crawling under it,I discovered you had to remove the steering shaft,and maybe the power brake booster,and some braces,to allow the starter to be removed and installed..

After a half hour of wresting with the bolts,some which were rusted and had to be torched off,I decided to go in his shed,where he had the wood stove roaring,to warm up for awhile..

We then heard a "crash" outside,and saw that the car had slipped off the jack,a floor jack,that had its wheels sink into the thick ice,and let the car slide sideways off the jack stand --and the jack's lift plate landed squarely on the oil pan,and cracked it,it was oozing oil--the steering rack hoses got squashed flat too..that was "it"..

He decided to call a tow truck and had it towed to another friends shop,who had a lift and a hot air furnace..it took him like 3 days of a few hours each to get the oil pan welded up,the starter back in,and get it to run again,then the P/S hoses had to still be fixed..the owner was so disgusted with it by then he sold the car for 500 bucks a few days after it was driveable again..

We should start a new thread for "The worst friggin cars to work on" or "The worst job you ever had to do on a particular vehicle"..

 

[Joe In Montana]

It took us like 2 hours just to put 8 new spark plugs in that Monza--it had headers too,to make it twice as miserable !..had to jack it up,take off both front wheels,remove the steering shaft,etc..what a piss poor design !..

Another car Gm made to frustrate mechanics was the Chevette/Pontiac T1000..one day a friend asked me if I could put a new starter in his wife's 70's Chevette--he was a disabled Vet and it was about 20 degrees out,snow on the ground,and he had only a small shed,with a wood stove,that the car couldn't fit in..

I went to his house,dressed like an eskimo,and jacked the car up--after crawling under it,I discovered you had to remove the steering shaft,and maybe the power brake booster,and some braces,to allow the starter to be removed and installed..

After a half hour of wresting with the bolts,some which were rusted and had to be torched off,I decided to go in his shed,where he had the wood stove roaring,to warm up for awhile..

We then heard a "crash" outside,and saw that the car had slipped off the jack,a floor jack,that had its wheels sink into the thick ice,and let the car slide sideways off the jack stand --and the jack's lift plate landed squarely on the oil pan,and cracked it,it was oozing oil--the steering rack hoses got squashed flat too..that was "it"..

He decided to call a tow truck and had it towed to another friends shop,who had a lift and a hot air furnace..it took him like 3 days of a few hours each to get the oil pan welded up,the starter back in,and get it to run again,then the P/S hoses had to still be fixed..the owner was so disgusted with it by then he sold the car for 500 bucks a few days after it was driveable again..

We should start a new thread for "The worst friggin cars to work on" or "The worst job you ever had to do on a particular vehicle"..

Too late for you now on that Chevette, but I had a slug of them in for starters as that car was running around in those days and i was an Automobile Club/AAA Shop and they got towed into me all the time.

The easiest way to get a starter out and in again was to disassemble the starter where it was mounted on the engine and reassemble the new one in place....on the engine.

That's a good idea for a "Rotten Repair Job" post though. I kinda like it if it won't bring back the nightmares again.

 

[Lsc]

Seems to have been a hydraulic issue. Makes sense, could've sworn i changed the pilot when I did the clutch last. Moral of the story: a bleeder seems to be required to do the clutch line on these old Chevys properly. Guy at the parts store said he has had the same problem, bled it by hand, still had the problem; then he bought a bleeder and that took care of it. Go figure.

 

[campfire]

Seems to have been a hydraulic issue. Makes sense, could've sworn i changed the pilot when I did the clutch last. Moral of the story: a bleeder seems to be required to do the clutch line on these old Chevys properly. Guy at the parts store said he has had the same problem, bled it by hand, still had the problem; then he bought a bleeder and that took care of it. Go figure.

Makes sense to me.