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Thread: Brake peddle travel - again

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    Brake peddle travel - again

    Here's my situation, I have always thought my brake peddle travel was excessive (just over 3000 miles on the car). I recently discovered a leaking wheel cylinder and after replacing the wheel cylinder, installing new shoes and bleeding the system it seemed the travel had gotten even worse. Currently the rubber pad on the brake pedal is 7 1/4" from the firewall. When I depress the pedal it goes to 3" and the metal arm is about 1/4" from the firewall. And when I pump the pedal there is no change so I don't think I'm compressing air. I've read several old post concerning this problem and the consensus seems to be rear brake adjustment. So, in order to take this out of the equation I have made the adjustment to totally press the shoes against the drums, no adjustment left. No change in the brake pedal travel. The master cylinder was new when installed as well as the brake lines and the hoses. I have not watched the hoses to see if they are expanding but it seems it would take a lot of expansion to allow that much travel. Any suggestions as to what I should do next?

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    Darth Vader
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    Re: Brake peddle travel - again

    DOT 5 fluid?

    I have heard that you can get tiny air bubbles in DOT 5 that are hard to displace. Not sure if pumping in that situation would change anything.

    David

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    Re: Brake peddle travel - again

    DOT 3 Fluid.

    Bob

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    Re: Brake peddle travel - again

    I would go after the brake hoses. There really is not a lot of fluid involved in activating the brakes. One soft hose could cause your problem. This is assuming that you are not still losing brake fluid.
    The brakes on my TR's activate within one to three inches and are full on within another inch but I did not actually measure this. They never go anywhere near the firewall.
    Did you change all "3" hoses? Remember that there is also one just in front of the rear axle.
    Charley
    1962 TR4
    1963 TR4
    1959 TR3A A work in progress.

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    Re: Brake peddle travel - again

    How tight is the joint between the pedal & MC pushrod? Do you have the pedal stop and if so, is it properly adjusted?

    Without measuring, 7-1/4" sounds low to me. I would probably adjust the pushrod (and stop if present) to bring it higher. Only 1/4" remaining travel is not good.

    Get someone to operate the pedal while you watch the front brakes (with the wheel off). If the brake disc is being pushed to one side, you've got a stuck caliper piston.

    Check both runout and thickness variation on the brake rotors.

    Above all, don't assume that a part is good, just because it's new. We've had a lot of stories over the years about defective new components, including MCs that don't work properly and rotors that don't run true.

    If all else fails, I'd have a look at those rear brakes, to make sure the cylinder can move in the backing plate. Or maybe even remove the shoes and use a C-clamp to hold the pistons, to make sure it's not something funny back there.

    Not really relevant, but I once worked on a case where the guide rods for the pads were seized into the caliper body. That car had single-acting calipers, so the body halves had to move relative to each other to apply the brakes. The guide rods would bend under the force, then spread the caliper back out once the pressure was off. Just an example of the kind of weird things that can go wrong. (A bunch of professional mechanics got stumped by that one, and in fact my Dad got the car cheap because no one could fix the brakes!)
    Randall
    56 TR3 TS13571L once and future daily driver
    71 Stag LE1473L waiting engine rebuild
    71-72-73 Stag LE2013LBW waiting OD gearbox rebuild

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    Re: Brake peddle travel - again

    What’s the story on your master cylinder? Rebuild or new?
    John

    1955 TR2

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    Re: Brake peddle travel - again

    MC new from Moss. Calipers rebuilt by Apple Hydraulic. Had to replace one rotor due to warp, other one checked OK, no pedal stops. Push rod could be adjusted about 1/4" before actual contact with MC innards but don't see how that would matter. When I installed new wheel cylinder it could move in the backing plate. Seems to be pointing to bad MC but what indications should I get if that's the case?

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    Re: Brake peddle travel - again

    Quote Originally Posted by BobbyO View Post
    Push rod could be adjusted about 1/4" before actual contact with MC innards but don't see how that would matter.
    I must be misunderstanding something. When you step on the pedal, it has to force the pushrod against the MC piston, and then move the piston a small amount, before the MC even begins to move any fluid towards the brakes. Because of the lever arm involved, that 1/4" at the MC would be something like 1" at the pedal. Since somewhere around 2-3" of travel is normal, that is most of what you are complaining about.

    In addition, lengthening the pushrod should let the pedal move higher, giving you more travel before the pedal hits the floor. Could your pedal be sticking at the top of the travel (so the spring won't pull it higher)? Is the spring even present?

    Furthermore, there should be a retaining plate and circlip in the end of the cylinder that holds the pushrod (and pedal if need be) much closer than that to the piston. Almost sounds like you have the wrong MC entirely ??

    At any rate, 1/4" of freeplay is absolutely not normal anywhere in the system, and should be adjusted properly, _especially_ if the complaint is excessive travel. The spec at the MC pushrod is .030" (about 1/32") for cars with the adjustment. Without the adjustment, it should be set by the retaining plate and circlip I mentioned above (but is still somewhere around .030").
    Randall
    56 TR3 TS13571L once and future daily driver
    71 Stag LE1473L waiting engine rebuild
    71-72-73 Stag LE2013LBW waiting OD gearbox rebuild

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    Re: Brake peddle travel - again

    IMHO...must be a combination of faulty MC or the geometry of the pedal mechanism.

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    Re: Brake peddle travel - again

    Randall, my mistake. That 1/4" is the movement of the brake peddle before the push rod contacts the piston in the MC. The push rod moves only slightly before making contact, could be 0.030". As best I could measure it using a tape measure it's about 1/16". Depressing the brake peddle from 7 1/4" to 3" causes the push rod to move 1". Is this normal? If not, what should the normal movement be?

    Peddle is not sticking at top of travel and spring is present. New spring installed when MC was installed. MC is part no. 581-010 from Moss so I'm pretty sure it's correct for a '61 TS80526L.

    Sorry for the confusion.

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    Re: Brake peddle travel - again

    I would at least try a new different master cylinder

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    Re: Brake peddle travel - again

    Quote Originally Posted by BobbyO View Post
    Randall, my mistake. That 1/4" is the movement of the brake peddle before the push rod contacts the piston in the MC. The push rod moves only slightly before making contact, could be 0.030". As best I could measure it using a tape measure it's about 1/16". Depressing the brake peddle from 7 1/4" to 3" causes the push rod to move 1". Is this normal? If not, what should the normal movement be?
    That all sounds pretty normal.

    So we're down to either that 1" of movement isn't moving much fluid, or the fluid is going someplace. One of those new parts isn't working right, or you still have air in the system.

    Since I really dislike the shotgun approach, I might try blocking off the MC outlet and see what happens. You should be able to only move the piston a very small amount (like 1/16") before it stops solid. I forget the threads offhand, but they are standard SAE fine threads, so you can block the port with a bolt, nut and copper washer. You don't want to damage the conical seat inside, so just tighten the bolt until you feel resistance (with your fingers), then turn the nut down to finish tightening.

    Don't forget, DOT 3 is a very effective paint remover. Be as careful as you can to catch any drips with a rag or paper towel, so they don't mess up your paint. And it will start dripping as soon as you loosen the outlet fitting.

    You can minimize the loss by placing something to hold the brake pedal down slightly. I use a modified bar clamp from HF to hook over the steering wheel and hold the pedal down.
    https://www.harborfreight.com/36-inc...amp-96208.html
    Just drill out the rivet and turn both jaws around to make a spreader instead of a clamp. ISTR I replaced the rivet with a 10-32 bolt and nut.
    Randall
    56 TR3 TS13571L once and future daily driver
    71 Stag LE1473L waiting engine rebuild
    71-72-73 Stag LE2013LBW waiting OD gearbox rebuild

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    Re: Brake peddle travel - again

    Rather than try testing the MC I decided to bleed the system once again although I had not noticed any compression when I pumped the brake. Anyway I did get some additional air from the system and now the pedal starting at 7 1/4" goes down to 4 1/4", a total travel of 3". Randall says normal travel is 2-3" so I appear to be in the ballpark. I guess I'm expecting too much out of a 57 year old brake system. I plan to drive what I have for awhile and see if anything changes.

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    Re: Brake peddle travel - again

    I would not drive the car until the excessive travel of the pedal is sorted.

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