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Clutch Slip (I think)
#1384961 Tue Nov 17 2020 04:17 PM
Joined: Nov 2019
Posts: 86
H
HFfarms Offline OP
'Bolter
'64 C60 with 292, SM420, and 15k two speed rear end. Engine and trans are freshly rebuilt. During rebuild I installed a new clutch kit with the old throw out bearing (new and old had different overall lengths). The truck seems to have a bad slipping clutch now. Noticed it a bit during the last heavy load but "clutch slip" never came up in my mind. It was a soft almost shudder after upshifting and beginning acceleration in the new gear. Most noticeable on the 1lo - 2lo shift. Two weeks ago just moving dirt around the farm, she got really bad. From stop and in 1 lo, she would just barely groan into movement regardless of RPM. Stopped next to even just a small 2" mount at the rear tires, she flat wouldn't move. Only 2-4k lbs of dirt on the bed at the time. Once dumped she would move, but slip bad. Road speed tops at ~20mph.

Before the rebuild, the trans whined. After the rebuild the 420 still whined. Never though twice about it. Now wondering if its been something else whining. She whined in reverse a lot more lately which made me start to dig but nothing found. Trans shifts fine, fluid looks good, etc etc. I am chocking up some of the wine to the brass pilot bushing which I will swap to a bearing style.

The 292 is 100% fresh and runs like a top. Cork gaskets so she seeps, but no true leak of oil to warrant adding any. There is a small amount of motor oil on the trans, but no real indication that the rear main would be bad and oil soaking the clutch. Rear main was really bad prior to rebuild and I never had oil soaking issues on the old clutch. The PTO weeps out trans gear oil, but again, not enough to warrant topping the oil off. Maybe the front main of the trans wasn't installed proper?

Research shows that the clutch fork could be at fault due to excessive wear which this truck definingly had prior to rebuild. Maybe its a combo of everything; worn fork, incorrect throw-out, flywheel needing machined, etc. Maybe I got a lemon clutch? Pulled inspection cover and nothing seems out of place or oily on the flywheel or clutch. Clutch adjustment seems well within specs. To date, I have not noticed any burning clutch smell, and no smoke from the clutch at all. That alone makes me wonder if its a problem with the rear end, but that doesn't seem logical to me. Regardless, I am prepping to drop the trans again this week for inspect closely. Any ideas on what to look for?

Re: Clutch Slip (I think)
HFfarms #1384963 Tue Nov 17 2020 04:35 PM
Joined: May 2017
Posts: 349
S
'Bolter
The wrong throw out bearing in a kit would wave a large red flag at me. You may have the wrong clutch altogether. Whoever put the kit together likely knew which bearing went with which clutch but of course that is not guaranteed.

Hopefully you still have the old clutch to compare closely to be sure it is identical in every way. The fingers should be the same height from the flywheel surface to end of the fingers where the throw out bearing contacts them if the same bearing is used with both.

The 3 lever style with coil springs uses different throw out compared to the single diaphragm spring type. There are 3 different throw out lengths to my knowledge and they need to match the clutch that gets installed.

You don't mention which bearing was longer but if the old bearing that you installed is longer than the new one that came with the kit, it could bind at the back of the transmission bearing retainer and never let the clutch engage all the way, no mater how the pedal is adjusted. It could behave as if you had your foot pushing on the pedal all the time.


Mac :{)

1962 K10 short step side, much modified for rally
1969 T50 fire truck, almost nos, needs a few things
Re: Clutch Slip (I think)
sweepleader #1384965 Tue Nov 17 2020 04:48 PM
Joined: Nov 2019
Posts: 86
H
HFfarms Offline OP
'Bolter
Originally Posted by sweepleader
The wrong throw out bearing in a kit would wave a large red flag at me. You may have the wrong clutch altogether. Whoever put the kit together likely knew which bearing went with which clutch but of course that is not guaranteed.

Hopefully you still have the old clutch to compare closely to be sure it is identical in every way. The fingers should be the same height from the flywheel surface to end of the fingers where the throw out bearing contacts them if the same bearing is used with both.

The 3 lever style with coil springs uses different throw out compared to the single diaphragm spring type. There are 3 different throw out lengths to my knowledge and they need to match the clutch that gets installed.

You don't mention which bearing was longer but if the old bearing that you installed is longer than the new one that came with the kit, it could bind at the back of the transmission bearing retainer and never let the clutch engage all the way, no mater how the pedal is adjusted. It could behave as if you had your foot pushing on the pedal all the time.

This right here is what I was afraid of. Original bearing was longer, new one was shorter by a full 1/3. Original clutch was three finder coil spring and I am pretty sure new was single diaphragm. I was naïve to much of this and didn't realize the difference in clutchs until after the fact. Ill accept the consequences of my oversight there. Original clutch and pressure plate are in the other barn and ill inspect side by side. The new clutch kit was the LUK HD L04902 which cross referencing numbers matched up for this truck/engine/trans.

If the throw out is the fault and never let the clutch fully seat, it could explain some of the whine and gradual (yet rapid) fade out to full slip without actually "burning" the clutch up with smoke and smell. Since its down ill inspect everything though. What is the determining factor on if a clutch fork is too worn out?

Last edited by HFfarms; Tue Nov 17 2020 04:50 PM.
Re: Clutch Slip (I think)
HFfarms #1384969 Tue Nov 17 2020 05:45 PM
Joined: May 2015
Posts: 4,172
Housekeeping (Moderator) Making a Stovebolt Bed & Paint and Body Shop Forums
Normally, a clutch will start slipping in the higher gears. Lower gears require much less torque transmitted thru the clutch to get things going. Not saying you don't have an issue with the throwout bearing, but a worn fork will normally cause the clutch NOT to release completely while shifting gears or actually make it impossible to get into gear, especially the lower ratio gears like 1st and reverse.
Slipping in lower gears and not in the higher gears would be very unusual.


Kevin
First car '29 Ford Special Coupe
#2 - '29 Ford pickup restored from the ground up.
Newest Project - 51 Chevy 3100 work truck. Photos [flickr.com]
Busting rust since the mid-60's
Re: Clutch Slip (I think)
HFfarms #1384970 Tue Nov 17 2020 05:51 PM
Joined: Jun 2004
Posts: 8,420
W
'Bolter
Often the old style clutch is replaced with the newer style diaphragm type clutch. It is a smoother clutch with lighter pedal pressure. The to brg. must match the clutch type.
Luk is a good brand of clutch. The brass bushing is better then the roller brg. pilot brg. If the fork is worn down where it contacts the TO brg. It should be replaced or if you are a good welder like you say, you can build it up & grind it smooth.
George


They say money can't buy happiness. It can buy old Chevy trucks though. Same thing.

1972 Chevy c10 Cheyenne Super
Re: Clutch Slip (I think)
klhansen #1385075 Wed Nov 18 2020 04:19 PM
Joined: Nov 2019
Posts: 86
H
HFfarms Offline OP
'Bolter
Originally Posted by klhansen
Normally, a clutch will start slipping in the higher gears. Lower gears require much less torque transmitted thru the clutch to get things going. Slipping in lower gears and not in the higher gears would be very unusual.

That makes sense. Road speed is like ~20 at the moment so I cant even get to the higher gears, so that lines up I suppose. I suppose when I say its most noticeable in the 1-2 shift, its because I cant even get up to speed in 3 or 4 without darn near 100% slip. The 100% slip I was experiencing in 1lo and Rlo was with a couple thousand pounds on the bed. Empty, she doesn't seem to slip until shifting into 2.

Originally Posted by klhansen
Not saying you don't have an issue with the throw-out bearing, but a worn fork will normally cause the clutch NOT to release completely while shifting gears or actually make it impossible to get into gear, especially the lower ratio gears like 1st and reverse.
Originally Posted by Wrenchbender Ret.
If the fork is worn down where it contacts the TO brg. It should be replaced or if you are a good welder like you say, you can build it up & grind it smooth.
George

There is zero issue shifting between gears and she drops into gears beautifully. I assume that means fork is still operating properly and not worn out of spec?


Originally Posted by Wrenchbender Ret.
The brass bushing is better then the roller brg. pilot brg.

Good to know. I assume less moving parts and no needle bearings means a stronger unit? It also begs the question, (which is a common one, but searches yield little to nothing for trucks in this weight class) is it better to stick with a B&B lever clutch for these big girls that still haul heavy? I fully understand the differences between regarding pedal pressure etc etc, but longevity wise especially for trucks grunting off-road thru windrows and fields, is it an advantage?

Last edited by HFfarms; Wed Nov 18 2020 04:20 PM.
Re: Clutch Slip (I think)
HFfarms #1385087 Wed Nov 18 2020 06:12 PM
Joined: Sep 2013
Posts: 11
5
New Guy
Is your clutch hydraulic operated? Brake fluid from a master cylinder? I assume it may be as my 1963 C60 with a 327 engine is hydraulic.

Are you familiar with the term free play? Where the clutch pedal should push easy for a bit before the throwout bearing starts pushing against the pressure plate. If you have no free play the clutch will slip. Probably not your problem but I thought I would mention it.

Re: Clutch Slip (I think)
58n63 #1386563 Mon Nov 30 2020 03:26 PM
Joined: Nov 2019
Posts: 86
H
HFfarms Offline OP
'Bolter
Originally Posted by 58n63
Is your clutch hydraulic operated?

Are you familiar with the term free play?

Nope, manual clutch. And yup, the clutch was properly adjusted with acceptable free play.

Finally got the other trucks taken care of and was able to break this girl down again yesterday. Sure enough, the clutch was 100% slipping. The TO bearing was too long and never let the clutch fully seat even when released. Lots of wear present on the fingers. Problem number 1. Problem number two, the clutch fork (not pictured below) was worn out pretty significantly with a lot of play on the TO bearing. Problem 3, during the rebuild with everything else happening, I overlooked the flywheel and didn't get it resurfaced. Totally forgot to even check it. It needed surfaced.

I wont even bother with this stock flywheel. It is so badly burned the hard spots will never get removed and the depth of the grooves will have it out of spec just to get it smooth, so to the junk pile it goes. All led to the photos below. Lesson learned the hard way on my part. New clutch fork and flywheel on the way and a new level clutch with proper TO awaiting the flywheel for install.

This means the clutch has slipped from day 1 of the rebuild, so once its reassembled, I am excited to see how much more umfph this girl will have off the line, because she was already a beast.

Attached Files
20201129_121226.jpg (198.49 KB, 52 downloads)
20201129_121240.jpg (176.24 KB, 52 downloads)
20201129_121221(0).jpg (205.14 KB, 52 downloads)

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