Proper clutch diagnosis?

Discussion in '6.9L IH & 7.3L IDI Diesels' started by chillman88, Dec 4, 2018.

  1. chillman88

    chillman88 Supporting Member Supporting Member

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    Hey all,

    Got in the truck this morning and the wipers weren't even touching the window even though I cleaned the ice off so I was already frustrated...

    Go to leave and it doesn't want to go into gear. Finally shoved a little harder on the clutch and it went into gear. The whole way in you could feel it not completely releasing. I've always had to push it a smidge harder than I thought I should to get it to start.

    I haven't seen any firewall cracks, and the linkage at the master looks fine, but I do sometimes have an odd noise (almost a pop?) from the dash when I push the clutch in.

    Where do I start with this after I check the fluid? I would normally just replace the clutch to find that wasn't the problem anyway but I would like to actually diagnose this for once.

    Clutch has always been firm. I drove another one once and his pedal felt like a car, makes me suspect the clutch....

    How hard is it to get to the linkage under the dash to inspect it?
     
  2. tjsea

    tjsea Full Access Member

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    I would have someone push the clutch in while you watch the firewall. You can't always see the cracks because the two layers separate. If it's separating talk to @freebird01 aka Jason because he makes the firewall kits. If this checks out fine then look up under the dash above the throttle pedal and you will see the clutch push rod. It could be bent or the plastic bushing could be bad. Also make sure the pivot shaft isn't worn through it's bushings and into the aluminum bracket. Check those things and let us know what you find. It is possible it is the clutch, but I like to check everything else first. Also if you are still daul mass they tend to push harder than a single mass setup.
     
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  3. Shadetreemechanic

    Shadetreemechanic Full Access Member

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    what he said. It sounds like it could easily be in the linkage. Pedal feel is not a good diagnostic tool in these trucks generally, because there are so many options for pressure plates and its those springs that dictate feel.
    I have three of these trucks and they all have different clutch feel.
    FWIW I like the feel of my 12 inch smf luk the best.
     
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  4. chillman88

    chillman88 Supporting Member Supporting Member

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    That's actually what I'm wondering given the sounds and behavior. I didn't know how it's actually set up though. How do I get to the pivot shaft? I really couldn't see much under the dash, should I remove the pedal box?

    I thought around 90 they started to reinforce the firewall at the factory?

    It was your brother's truck I drove with the featherlight clutch, that might be why then. His is a solid flywheel right?
     
  5. Thewespaul

    Thewespaul Supporting Vendor Supporting Member

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    The “correct way” is to measure the throw of the clutch pedal and measure the throw of the clutch fork and compare. They won’t ever be 1-1 but the manual has specs for each. I can dig it up if you need them
     
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  6. chillman88

    chillman88 Supporting Member Supporting Member

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    Thanks I'll let you know if I don't find anything obvious.
     
  7. chillman88

    chillman88 Supporting Member Supporting Member

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    Ebay to the rescue. I had no idea how the clutch pivot actually works. Now I understand! At least now I know what I'm looking for.

    s-l400.jpg s-l400 (1).jpg s-l400 (2).jpg
     
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  8. chillman88

    chillman88 Supporting Member Supporting Member

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    Alright so a couple problems here...

    Master cylinder was dry.... Looks like it's leaking into the cab? I pulled off the clutch safety switch.

    IMG_20181204_152508097.jpg

    Does this definitely mean I need a new master cylinder? I topped it off and don't see it leaking anywhere. Seems to be holding its level. I'm thinking maybe it's just been seeping a little at a time?

    There is play in the pedal box, but I think I should start with the obvious first since the master was empty.

    I'm. ASSUMING that leak inside the cab means I need to replace it. How much work is replacing the master and slave together pre bled? Does the transmission need to be pulled back?
     
  9. 79jasper

    79jasper Chickenhawk

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    Easy to swap.
    Not hard to bleed either.

    Sent from my SM-N960U using Tapatalk
     
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  10. Thewespaul

    Thewespaul Supporting Vendor Supporting Member

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    The slave and master shouldn’t ever need topping off, if it does it needs to be replaced. If you use a prebled unit it’s pretty easy. Pop the old slave off, unbolt the master and clutch pedal, bolt the replacement in and once everything is secured cut the strap holding the rod and help it seat in the clutch fork.
     
  11. chillman88

    chillman88 Supporting Member Supporting Member

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  12. Thewespaul

    Thewespaul Supporting Vendor Supporting Member

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    Honestly, for that kind of stuff I buy from the parts store so I know for sure it’s a prebled unit before I buy it
     
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  13. chillman88

    chillman88 Supporting Member Supporting Member

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    I would but the parts store doesn't even list a prebled unit. I will check NAPA but they're usually twice the price.

    Trust me, I had the same thought though.
     
  14. IDIBRONCO

    IDIBRONCO IDIBRONCO

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    I don't cut the plastic strap. I leave it there. It sure makes it a whole lot easier if you even have to pull the engine or transmission. All you do is push the fork back a little bit and hook the strap. It will hold the slave cylinder mostly compressed so that you don't have to worry about breaking it when you put everything back together.
     
  15. chillman88

    chillman88 Supporting Member Supporting Member

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    Thanks. I ordered the one from Rockauto. Next business day shipping was $19. I'll have it Thursday. I'll be pulling the pedal box from the parts truck next halfway warm day to rebush it for this truck.
     

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