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Hot Rods Who's running external clutch slaves

Discussion in 'The Hokey Ass Message Board' started by model A hooligan, Apr 28, 2018.

  1. The pedal feels like it gets firmer at about 3/4 through the stroke, then it hits the firewall. Feels like it's just starting to engage, but the pedal is pretty far up when not depressed.

    (Seems like the pedal wants 30 damn feet of travel) if the pedal could swing from my lap all the way to the headlight it could work it seems. Which I guess would mean it needs a bigger master. I just don't understand why the slave cylinder would recommend the 3/4 that I have if it's not enough
  2. What is pedal ratio? Or, look under to see how much stroke is actually happening at the master.
  3. It says 6 to 1 on their site. It's a Cnc pedal

    I cut 1/4 out but welded the pad on lower so it should be about the same. (Was messing with room to tuck my foot behind the pedal on a long drive)

    I guess it sort of seems like the pedal moves a whole lot vs the slave only half . And like was mentioned before that sort of indicates master is too small. Maybe they listed 3/4 just cause it's easier to find?
  4. Ok, but does it give the master all the stroke it can take?
  5. Very good point, I cannot say yes 100% on that question. I adjusted all the slack out of the rod, and the pedal really can't move any more, BUT maybe their master cylinder has different dimensions than the wilwood that I'm using. Hard to check since it's under the dash and don't want the brake fluid in my car from disconnecting it but may not have a choice.

    It does look like it's pushing the cylinder rod in a lot though
  6. These are all things to know up front. It's in the scope of what 31Vicky is getting at. He get's paid the buck's because he's good at what he does. I just do my own thing for only me. I like making model card board cut out's to see how every thing works together.
  7. Math always works,
    Math depends on calculating the correct things, and human interpretation or elimination of variables.
    I this case variables would be : is the master delivering its full stroke before the pedal hits firewall, is all the air out, is bracket moving, amount of free play/slop.

    This isn't stuff that's very advanced math and calculating. Simple machinery such as levers and bore VS bore / pressure VS volume and calculating volume is covered quite well on YouTube, mostly its 5-8th grade stuff not college Level calculus and statistics.

    Master cylinders are not cheap,
    Calculate the one you need and buy correctly.

    At least post up the specs.
    Everything needed is lined out In earlier posts.

    The manufacturer stating 3/4 " bore is good but do they say the necessary stroke needed? do they give a displaced volume necessary to operate the slave?
  8. I don't like hyd clutch release. The 58 ford trucks had them. the international trucks had them and the 60 thru 62 chevy trucks had them. and they where troublesome. I convert them to mechanical linkage. My OT 86 3/4 ton chev has a hyd clutch. and it gives trouble. I will very soon convert it to mechanical linkage.
  9. Uhm.. okay? If you looked at my post you'd see why I have to to it hydraulic.
    I'll state it again, it's chopped,channeled and I have huge feet. I needed the floor space for my foot where the clutch fork would have been. So it's moved to the passenger side.

    Also, the 60's Chevy truck units worked well from what I've seen. I think of it this way. Aren't we all converting our brakes to juice? Our brakes are a little more important and we rely basically on the same type of function so..
    Last edited: May 11, 2018
  10. It appears my clutch slave moves about the same as the master. The master can not move any more so I'm assuming a more volume larger Mc is needed.
  11. 3/4" master and 7/8" slave is what I run. I originally had the rod lower on the pedal, needed 3 people to push the pedal and wasn't getting the motion from the slave. I moved the master up to the OG hole in the clutch pedal, moved it to the other side of the pedal arm since it was close to the brake master.

    How is the pedal effort? Mine got infinitely better once I moved it to get better leverage. Also greatly improved the motion at the fork.

    I think you are close to nailing it. You may only need another 3/8" at the fork. Try to go higher on the pedal arm if possible. How is the slave mounted? Shoot a picture of that. I mounted my slave and brake master on a common steel plate. The firewall had too much flex to it, another thing to look at.

    Is there any adjustment left at the clutch master rod? If so run that out, but keep track of what you do in case it has to be un-done.
  12. My clutch arm only has one hole at the top. Pedal effort can't really be judged cause it only starts to press the clutch then maxes out it seems. But I'd say it's probably not too hard.

    I have it mounted on some angle iron
  13. The pedal should meet hard resistance with minimum motion; you said you are not meeting resistance until 3/4 of the way down.

    What's happening to the system during that motion?

    Excess pushrod clearance, inability to fully stroke the master (at a 6-1 ratio, the pedal has to move a bout 8-1/2" to move the master thru the full 1.4" stroke), excess TO bearing clearance, looseness in the rod ends, flexing of the pedal or slave mount brackets, trapped air in the master, slave, or lines, rubber hose stretch, stuff like that or maybe a combination of them.

    The way I look at it; (spec wise) your 3/4" Wilwood cyl should move the slave about 1-1/4"; more than enough to disengage the clutch.
  14. chevy went to the HYD release in 1960 when the switched from thru the floor to under the dash firewall pedals. and went to mechanical linkage in 1963. The chevy shared the same master cyl as the brakes. so if you blew a line or had a leak you lost both the clutch and the brakes. My OT 1980,s pk if you let it set for very long you have to bleed the clutch. sounds like you need to convert to a automatic trans. and hyd brakes aint so great on bigger trucks. If the booster goes bad on a 2 ton truck it cost around $400 to replace it. My C65 has air brakes and they always work if you have enough air pressure to release the brakes. If you don't have enough air the brakes remain locked.

  15. You really are not reading the thread..
  16. I would think it should work too. Like I mentioned the slave mount is rock solid. My Heims are solid. The pedal I can push it with my HAND. It's not hard.

    Not sure what it's doing before it reaches the firmer spot at the end of the stroke, looks like it was moving the slave just not much
  17. neilswheels
    Joined: Aug 26, 2006
    Posts: 548

    from England

    Oh boy, i've got all this to look forward to. I based my setup on the Novak stuff, they were very helpfull with slave/master combo, but you never really know till its juiced, which i've not done yet. Lots of useful math in here, which i hope i dont have to use....Keep at it, you'll get there
  18. I'm so frustrated. I've worked night and day for 2 weeks trying to get this car ready for tonight's cruise and I'm going to miss it AGAIN.i used to drive the crap out of this car that's what's killing me. Withdraws I guess. I based a lot of it off the clutch working this way also. Used up every bit of available space to fit my feet in and to hide everything under the dash
  19. I spent 3 weeks working on mine, really complicated compound links at the pedal. Lots of machined and purchased parts too. It was a horror show. Post up some pictures of what you got. Do you have any flex going on where the slave is mounted?
  20. There's a picture posted of the slave. I since made the bracket on the trans out of 1/4 thick plate that has zero flex.

    I'm hearing different things. One end is that it's just air still stuck in the system,the other is that the master cylinder needs to be bigger. I was pushing to drive it. Since I've got 2 weeks I may redo all the lines in the car cause I had metric fittings on hand and I'm really pissed that they are in there. As for actually getting this to work I'm not sure
  21. no55mad
    Joined: Dec 15, 2006
    Posts: 1,765

    from nipomo, ca

    On a Nailhead, the starter is on the drivers side so a longer fork was needed. This was to replace a leaky hydraulic TO bearing. The Hyd TO bearing used a 3/4 master. The replacement slave used was a 7/8 from Speedway. Because the fork was longer, more movement was needed. In talking to Wilwood, a 7/8 master would move a 7/8 slave 1:1; move the master 1 inch of travel, the slave should move 1 inch of travel. More was needed so a 1 inch master was installed. More pedal pressure is definitely required, but it provided plenty of fork movement.

  22. Thank you for your input,this is the type of reply I was hoping for. So with a 1" master and a 7/8 slave was the pedal hard to push?

    Mine may be harder due to a short fork though. But I'm pretty sure that's the ticket is the master. My boss looked and he said it looked like the master was only loving a half inch same as the slave was. So bigger bore should move it more,just not sure of pedal effort
  23. If you have a 6:1 pedal ratio, the foot pad will move 6" and the master will move 1".
    If the master is moving 1/2" then the foot pedal is only moving 3". <<<< if so that is at least one problem. ^^^ the pedal ratio determines a lot here and the ratio is important.

    Now Just For reference purposes for you, let's say a vehicle has 6" pedal travel and the correct throw out bearing movement. In order to keep the T O bearings movements the same with only 3" pedal travel (exactly 1/2) the pedal effort would be exactly doubled. Not only that,,, the distance your foot moves to negotiate the clutch between in and out is 1/2 and the effort is double will make driving it difficult at best. There will be very little feathering distance, feel, or feed back. Oh and if the pedal effort is double, the bracing and mounting would need double as well.

    Distance and force have a direct and definitive relationship here. The constant here, the goal, the thing to look at, the place to start thinking from is the distance the throw out bearing needs to move.
    Last edited: May 12, 2018
  24. For the heck of it, is there any flex where the master is mounted?
  25. It looks like the pedal pad is moving about 5" and the master is about 3/4 to 1" hard to tell up under there.

    I feel some resistance on the pedal but it's not much.
    Last edited: May 12, 2018
  26. Are yo sure the throwout bearing is close enough to the clutch? Sounds like you are moving the throwout bearing through air and then hitting the clutch plate at the very end of the stroke.
    metlmunchr likes this.
  27. I think I already mentioned that I have taken all the free play out
  28. Can you shorten the overall length of your pull slave cylinder ?

    What pedal set are you using ? Pic or a link ?

    It might be tricky to measure, but getting the exact stroke of the master caused by the pedal movement needs to be known. If you have 6 at the pedal pad, and 1/2" at the cylinder that calculates to a 12:1 pedal ratio. Or there's a bunch of slop in there

  29. Like I mentioned it's a Cnc pedal,wilwood MC and Cnc slave. I did shorten the slave already to basically no slack between the fork and pressure plate.

    You are right about a picture I'll have to go out there and get one if my phone will cooperate
  30. I don't think these will help much, but you can see the distance from the pedal to the firewall. I can push it the whole way with my hand. It's about 5 1/2 - 6" away from the firewall at resting position.

    It has some resistance but my hand is strong enough (seems way too easy in my opinion) and only offers little movement at the fork.

    Photo is hard to tell,looks like it's close to the firewall but it's not.

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