M38A1 clutch linkage problem?

1952 - 1968, M38A1, M170, questions, discussions, regarding anything related to the M38a1 series.
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willystexas
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M38A1 clutch linkage problem?

Post by willystexas » Sat Dec 19, 2015 4:00 pm

My gut tells me that I have something wrong with my clutch or clutch linkage. I'm just not sure what.

I had a mechanic replace my clutch disk, fork, throw-out bearing and machine the pressure plate a few months back. My jeep hasn't shifted quite right since. Not bad, but not right.

Last weekend, I was no longer able to full-disengage the clutch with pedal on the floor. So, I tightened up the clutch linkage. I went slow, and made several adjustments, but I had to adjust the linkage as far as it would go. I can now get the clutch to fully disengage, but there is no free play (at all) in the clutch petal before it begins to disengage. However, I still have to press the clutch petal all the way to the floor to get it to fully disengage.

In short, it works, but is it right? Without the 1 1/4" of free play, am I wearing out my throw-out bearing or something else? This just doesn't seem right. Am I missing an adjustment? Could something have been installed wrong? Suggestions?

Thx,
mw
1954 M38A1 MD 74751


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Re: M38A1 clutch linkage problem?

Post by artificer » Sat Dec 19, 2015 9:41 pm

Start from scratch not from your current out of adjustment.
That requires removal both the cable & rod from the clutch bell crank.
The clutch bell crank arms when correct should be nearly in a vertical position.
This crank & it's 2 arms can be reversed, so make sure they are right.
Reversed gives lighter pedal feel & provided you do what follows, it really doesn't matter.

You need to maintain the correct bell crank positioning & adjust the rod & cable to hold that position.

The cable link to the throwout fork should be adjusted when the arm/s are near vertical to give the throwout bearing no more than a hacksaw blade width away from the pressure plate fingers.
Then the pedal rod should be adjusted to a position that the pedal is right up as far as it will go. Dust seals on the pedal being too thick can alter things a little, but one can overcome that issue.
With the rod & the cable re-inserted in the clutch bell crank's vertical position when you rev the engine the throwout bearing mustn't rotate & when you depress the clutch pedal it [the pedal] should move about 0.5 to 0.75" before the throwout bearing engages the pressure plate fingers & the throwout bearing starts to rotate....that is what is called free travel.
John GIBBINS Member Institute of Automotive Mechanical Engineers [Ret], ASE Master Medium/Heavy Truck & Auto Technician USA -2002 Licensed Motor Mech NSW MVIC 49593 Current 2015
TO DIAGNOSE, TROUBLESHOOT OR FAULT FIND ANY AUTO SYSTEM....
Understand how system parts interact with one another. GOOD parts can then be established & the NOT GOOD problem/s part/s isolated for repair or replacement.

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Re: M38A1 clutch linkage problem?

Post by Joe Gopan » Sun Dec 20, 2015 11:16 am

Did he change the clutch linkage or the fulcrum ball on the fork? There are several different length clutch rods for Jeep.
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Re: M38A1 clutch linkage problem?

Post by willystexas » Sun Dec 20, 2015 5:10 pm

Mr. Gibbins, I greatly appreciate your write-up and instructions! Very well done! I will take a closer look at this over the next week or two. I will be getting some time off from my "day job", and I would like to get this worked out.

Mr Dover, The fork was changed, but not the fulcrum ball.

mw
1954 M38A1 MD 74751

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Re: M38A1 clutch linkage problem?

Post by 4X4M38 » Mon Dec 28, 2015 5:53 pm

Sure hope he didn't put the plate in backwards.

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Re: M38A1 clutch linkage problem?

Post by artificer » Mon Dec 28, 2015 7:28 pm

Sounds like experience?
Symptoms don't sound quite like that BUT he can check easily....without the engine running of course the OP should be able to feel the raised/stepped side of the clutch plate is to the rear & if he can feel the smooth side of the plate it is in wrong way round.
John GIBBINS Member Institute of Automotive Mechanical Engineers [Ret], ASE Master Medium/Heavy Truck & Auto Technician USA -2002 Licensed Motor Mech NSW MVIC 49593 Current 2015
TO DIAGNOSE, TROUBLESHOOT OR FAULT FIND ANY AUTO SYSTEM....
Understand how system parts interact with one another. GOOD parts can then be established & the NOT GOOD problem/s part/s isolated for repair or replacement.

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Re: M38A1 clutch linkage problem?

Post by Joe Gopan » Tue Dec 29, 2015 3:42 am

If the Clutch Rod is not correct dimension it will create clutch operation problems. The Correct Clutch Rod for M-38A1 is Willys Part No. 640123 and is 10-15/32" center to center at the bends.
Should the mechanic install the A-499 Clutch Control Rod for the MB/GPW, it will be shorter, the A-499 Rod is 9-1/8" center to center of each bend.
2011 MVPA PIONEER AWARD - MVPA #1064
HONOR GRAD-WHEELED VEHICLE MECHANIC SCHOOL 1960 - US ARMY ORDNANCE SCHOOL(MACHINIST) ABERDEEN PG 1962 - O-1 BIRD DOG CREWCHIEF - 300,000+TROUBLE FREE M-38A1 MILES
LIFE MEMBER AM LEGION-40/8-DAV
7 MIL SPEC MAINTAINED MV'S
COL. BRUNO BROOKS (ARMY MOTORS) IS MY HERO

willystexas
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Re: M38A1 clutch linkage problem?

Post by willystexas » Fri Jan 01, 2016 9:13 am

Working through the clutch system, nothing jumped out as really wrong. So, I began to suspect the "new" replacement parts. I keep my old parts. So, I was able to make some visual comparisons. I immediately noticed the clutch bell crank (z-tube) was different. My old tube had arms at each end, and they were different lengths. My new tube had arms that were the same length.
z-tubes.jpg
Compare tubes
z-tubes.jpg (72.88 KiB) Viewed 1238 times
z-tube.jpg
Different arm lengths
z-tube.jpg (85.57 KiB) Viewed 1238 times
It seemed reasonable that the new part would limit the amount of "throw" between the clutch pedal and the clutch mechanism. I ordered the new tube (shown above) from another supplier. So, I called our friends at G503.com, and they were able to confirm that their reproduction part would match my old part.
z-tube-g503.jpg
Arms the right length
z-tube-g503.jpg (61.52 KiB) Viewed 1238 times
I installed the new tube. The clutch immediately worked. Good free play with the clutch pedal relaxed, and the clutch fully disengaged when the pedal was fully depressed.

Thanks for all the help.
1954 M38A1 MD 74751

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Re: M38A1 clutch linkage problem?

Post by dcartledge » Thu Jan 21, 2016 4:06 am

Thank you all for this post - I will certainly keep it in my files for future use,
d
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