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Thread: '46 CJ2A Parts Runner

  1. #61
    Super Moderator gmwillys's Avatar
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    The double pump of the brake pedal is common on these old school brake systems, especially when the reservoir is on the same elevation as the wheel cylinders. The issue stems from the fluid draining back into the master cylinder between brake applications. There is a fix for this, and will be purchasing the fittings and documenting the results. The residual pressure valve retains 10 PSI of brake fluid within the wheel cylinder/line to #1 keep the wheel cylinder piston boots expanded to prevent leakage, and #2 to retain fluid within the line for more positive braking when the pedal is applied once. The 10 PSI is for drum brakes, while disk brakes require only 2 PSI fittings. The disks are much more efficient, so less pressure is required to keep primed, (so to speak).

    https://www.wilwood.com/PDF/DataSheets/new_rpv.pdf

    I moved the Heep around this weekend, and it appeared to be braking alright, but the test will be going down the road and testing again. A stuck wheel cylinder piston would be the most logical diagnosis for this issue, and the fix would be to dump the Crown wheel cylinders and scrounge around to find some Wagner USA made cylinders, but everyone is out of stock on them currently.

  2. #62
    Super Moderator bmorgil's Avatar
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    Interesting on the Wilwood part. Check valves are used in all the O.E drum brake systems and should be present in your Master Cylinder. If that isn't "checking" that would explain it for sure. I wonder if you have a bum check valve? I have all KW parts in my system. It is rock solid and a good pedal no matter how long it sets. That said it does not "stop on a dime"! The more payload the more the dimes go by. I am sooo spoiled by modern assisted 4 wheel disc brakes, with wide tires.

  3. #63
    Super Moderator gmwillys's Avatar
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    The master and wheel cylinders all came from KW, along with the brake lines clips and hoses. I've gotten used to driving well seasoned vehicles, it was habit to double pump everything. I vacuum bled it, and have checked have gone through them every year during the annual service, and it doesn't improve. Since the Willys is a single pot reservoir, and one outlet, a single check valve malfunction will cause the whole works to be compromised.

    I am quite satisfied with most everything that I have purchased through KW. They don't have control of the quality of the Crown stuff, and there are little other options out there anymore. Wagner does offer an American made item, but every time I check they are out of stock.

  4. #64
    Super Moderator bmorgil's Avatar
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    My parts are fairly recent. I am not sure what the brand was. Usually I check that. I probably just can't remember what it was. After your warning on the Crown parts I was looking for them. I do not have a "pump up" issue. Its a good pedal, just not a lot of stopping power!

    I am very satisfied with KW also. I am sure they wouldn't give you any trouble on a replacement. If it was dragging a shoe from a stuck cylinder I would think it would dive when you hit it hard. Hmmm on the master cylinder, I wonder if you have a bad one. It shouldn't pump unless it is loosing a little fluid and getting a little air some where. That should make a mess in the brake drum, not to mention a spongy pedal.

  5. #65
    Super Moderator gmwillys's Avatar
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    The pedal has always been rock hard on the second pump, with no fade. The heep will stop within a reasonable distance, and wants real hard to lock up the rear wheels through the weight transfer. I've had to perform several panic stops when driving around town due to some of the idiot driver's we have in this college town. The current configuration has been installed for around six years. It doesn't matter if it is the first application or the fifteenth stop, you always have to double pump. This isn't the first Jeep that the master cylinder I had to change out. They did the same as well, I think the first one received a Wagner, but the rest have been Crown. I'm going to have to research this more, because it is a common problem on anything with a frame mounted master. Common enough that there are several manufacturers who make the residual pressure valves. Ponderous.

  6. #66
    Super Moderator bmorgil's Avatar
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    No doubt your on to something gm. In all the older vehicles that used a frame mounted master or a master down low, the check valve was imperative. The symptoms were a firm pedal that had to be "long or double stroked". It was used on all drum brakes as far as I know. A little junk in the reservoir and the valve gets plugged. Trying to fill the reservoir without getting dirt in it, while pouring fluid through the floorboard, right! I bet that a lot of aftermarket valves go into vehicles with plugged open check valves.

    I bet you have a bad one gm.

  7. #67
    Super Moderator LarrBeard's Avatar
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    Check Valve

    I don't think I have ever heard of a master cylinder check valve - in fact I know I haven't. Very informative discussion.

    Too soon I get old, too late I get smart

  8. #68
    Super Moderator bmorgil's Avatar
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    It's important for me to keep learning because I forgot everything!

  9. #69
    Super Moderator gmwillys's Avatar
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    I looked up the break down of the parts for the rebuild kit, and there is not a check valve within the master cylinder. I didn't want to argue until I had something to back up my thinking, but I didn't remember there being anything between the reservoir and the banjo bolt. You can run a wire through the passage in the casting to remove any rust or sludge when rebuilding after running through the parts washer. At the banjo fitting, the fluid Ys off to the rear and front axles. The residual pressure fittings would then be installed in line, close as possible to the master cylinder to retain the line pressure enough to give you good pedal at the first application. The later master cylinders would have the check valve installed, this was true with our wagon where it had a later firewall mounted single pot manual master run with the later Wagoneer hanging pedals. It had good pedal all the time without the double pump. I've spent a lot of time setting up brake systems on all my old junk, to include using feeler gauges to adjust the shoes for the tightest tolerance possible for the most stopping power. Everything that I've dealt with that had a low mounted master has ended with a double pump on the application, regardless of vehicle make, and style of master cylinder. When researching the issue, I came across the residual pressure valves through a hot rod forum of like minded people who wanted to improve their braking performance. If the valve works, then I will document and post the results. If it doesn't work, then I will need to go back through the whole system and find out where there might be an introduction of air to the system. I don't think that air is the issue, but it is a possibility.

    https://www.kaiserwillys.com/brake-m...llys-jeep-5543

  10. #70
    Super Moderator bmorgil's Avatar
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    I remember these discussions on that check valve from the Chassis Classes we held way back in time. I remembered something from the ASE studies. I attached a quick guide they have posted on it. https://www.freeasestudyguides.com/r...eck-valve.html

    It is interesting what may be here. It looks like if the master does not have a check valve, then it must have cup expanders on the wheel cylinders. I remember rebuilding a few 50's era Chevy pick ups and there were check valves in the master. I bounced around a few of the classic pages and there is discussion about the older Master Cylinders using check valves and the "newer" replacement Master cylinders did not have them installed. In the cases where there was no check valve the expanders were needed to prevent the double stroke. Since you know there is no check valve it leads me to wonder do your wheel cylinders have the cup expanders? The cup expander is just a spring that sets between the cups, pushing the cups back out. If that spring is not in the wheel cylinders that could be it. Since you know there is no check valve, it definitely wouldn't hurt to put one in. If there was air the pedal would be soft. It doesn't seem like you have air in it. I can tell you mine does not exhibit that issue, but I did not look for the valve or the spring.

    Now what you said about feeler gauges. I have never been able to get the shoes to spec. I cannot get enough adjustment from the lower cams to make contact. I have all new parts in there. I can get the tops to adjust out barley to touch, but not the bottoms. It almost seems like the shoes don't have enough material on them. I bet if I could get a good adjustment my stopping power would go up. Any ideas on that?
    Last edited by bmorgil; 09-29-2020 at 06:36 PM.

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