| fordmerc | -- 07-08-2010 @ 9:45 AM |
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my '39 brake shoes (R front only) are positioned asymmetrically: the forward shoe is so far forward that the drum binds; the trailing shoe is far from the drum; if I push/pull the rear shoe back, the front will follow, because the cylinder pistons seem to move well, but when I release the rear shoe, both again move forward. What did I do wrong? (new linings, "new" wheel cylinder) All other wheels OK after same restoration.
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| supereal | -- 07-08-2010 @ 10:10 AM |
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Did you correctly mount the wheel cylinders so the large end faces forward? The long lining goes toward the front, the short one to the rear. The anchor pins at the bottom of the backing plates are also eccentric adjusters. They are marked to show the high point of the eccentric. To properly adjust them, loosen the lock nut and turn the studs until the dots face each other. While applying about 30 pounds pressure to the brake pedal, turn the studs, left one clockwise, and right one counter clockwise, until the linings contact the drum. Release the pedal and adjust the brakes by the cams on the upper part of the plates until no rubbing can be felt.
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| fordmerc | -- 07-08-2010 @ 12:54 PM |
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Cylinder is in correct position. All eccentric cams in proper position. I have removed the shoes and reinstalled them. The wheel barely turns without any pressure on the brake pedal. The instructions as you provided were followed for all other wheels with success. I did open the bleeder valve just enough to let a couple of drops of fluid out, with no change in status. I considered a defect in the wheel cylinder, but I cannot conceive of one since the two cylinder ends move in tandem when I manually push them from either end when the shoes are removed or, as when I move the assembled shoes back and forth. I'm missing something, but I don't know what! This message was edited by fordmerc on 7-8-10 @ 12:55 PM
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| Johns46coupe | -- 07-08-2010 @ 2:24 PM |
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This is a real shot in the dark but is it possible the spring in the wheel cylinder is installed backward or is hung on a burr or something? John
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| fordmerc | -- 07-08-2010 @ 5:19 PM |
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The answer is: of course, any of those things could have happened. Interestingly enough, when I ordered all 4 wheel cylinders, the right front (problem) was not supplied and I had to go back to get the correct cylinder. If there is no easier answer, I will tear into the cylinder (but I don't really want to do that since a can of worms is worse than one!)
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| Johns46coupe | -- 07-08-2010 @ 6:51 PM |
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Sorry to be a PITA but disassembling and reassembling a wheel cylinder is a fairly easy job especially new and clean. Since you've looked at everything else it seems like the place to go. Here is a link with a picture. You don't even have to remove it from the car. http://www.vanpeltsales.com/FH_web/FH_images/FH_brakes-pics/Flathead_Brakes_wheelcylinder_1939to46.jpg John
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| 39 Ken | -- 07-09-2010 @ 3:59 AM |
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"when I ordered all 4 wheel cylinders, the right front (problem) was not supplied and I had to go back to get the correct cylinder". This could be the problem. There are two types of wheel cylinders sold today. Cheap made in China or wherever, and more expensive, USA made. To be sure, the USA made are far superior to the off-shore units. My bet is you have gotten at least one if not all of the off-shore units. A friend got one that actually jammed in the actuated position. Check it out as Johns46 said. If you have the cheaper units, do yourself a favor and replace them with USA units before more problems occur. JMO. Ken
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| TomO | -- 07-09-2010 @ 7:38 AM |
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Fordmerc, is the rear shoe under the clip or is the clip missing? Tom
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| supereal | -- 07-09-2010 @ 9:48 AM |
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When brakes fail to fully release, and the pistons in the wheel cylinders are not stuck in the bore, It is likely that the master cylinder is at fault. When an old brake system is opened for repair, and is bled to remove entrapped air, often the residue in the master cylinder reservoir is stirred up, and the relief orifice is fully or partially blocked. A sure sign is that more than one, or all, wheel cylinders are affected. There is also a "residual" valve in the master which maintains some pressure when the brake pedal is released. This may also be trapping system pressure.
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| fordmerc | -- 07-10-2010 @ 4:22 AM |
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The rear shoe is under the clip and appears appropriately placed The master cylinder is a "new" repro unit (mine was too far gone to use). I can remove the shoes and easily move the cylinder pistons in tandem. With the shoes in place, if I pull back on the rear shoe, the forward shoe will move back, but when I release the rear shoe, all returns to a resting position where the forward shoe is too far forward. Seems weird! I can't see any reason why a cylinder would choose a resting position that is asymmetric, so the problem must be elsewhere. Is there a difference in the shoes other than the lining? I am 99 44/100% certain that the front and rear shoes are where they were when I took them off for relining, but...
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| trjford8 | -- 07-10-2010 @ 7:11 AM |
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Sounds to me like you may have a weak return spring on one side. Did you replace the return springs? Is one spring possibly longer than the other?
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| TomO | -- 07-10-2010 @ 7:37 AM |
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fordmerc, with the bleeder screw open, the shoes should rest against the adjustment cams. The spring (only 1 TRJ) should compress the cylinder pistons. If you do not have this situation, you should disassemble the wheel cylinder to see what is keeping the spring from compressing the cylinder pistons to their innermost positions. Tom
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| supereal | -- 07-10-2010 @ 9:48 AM |
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I'd still suspect the master. The repro quality is often a problem. Even USA parts are infected. At our shop, we have to return many each week. Same goes for wheel cylinders. If the system pressure isn't properly released, the larger side of the wheel cylinder will push the shoe in that direction. As Tom suggests, open the bleed screw and see if the situation is corrected. In the case of only one wheel on the front being affected, I'd suspect the brake hose to that cylinder. If both rears are at fault, the hose on the torque tube may have collapsed internally. We always replace all hoses when doing a brake rebuild. In the single type master, a burst hose can cause a disaster, and replacement is very good insurance.
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| 40fordor | -- 07-14-2010 @ 7:58 AM |
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Super, I think you have identified a problem with my 40. I rebuilt my wheel cylinders, master, new linings and brake hoses and the left front and rear wheels are very tight when the car sits for a length of time. When I drive only short distances they do not drag at least not that I can tell. Bleeding has not improved the situation. I am not sure where the holes in the master cylinder are located therefore I will give everything a good cleaning and see what happens. Don
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| supereal | -- 07-14-2010 @ 8:28 AM |
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Don: The holes are located on the bottom of the master cylinder reservoir. When I bought my '47 about 15 years ago, three of the four brakes were tight against the drums. I leafed thru the stack of receipts the former owner gave me and, sure enough, there was a bill for replacement of the master cylinder. When I examined the cylinder in the car, I don't know what kind of fluid, if any, had been used when the job was done. It was full of dirt, etc. If it was replaced. the part must have come from a junkyard. Two of the wheel cylinders were stuck in the bore, and the clips on the rear shoes were missing. It didn't take long to figure out why we had to drag the car onto the trailer with the wheels stuck. Using denatured alcohol, we flushed the system before replacing most of the parts, and to this day, it is like new.
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| Stroker | -- 07-14-2010 @ 3:16 PM |
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Brake hoses and fuel hoses share some common traits. Most consist of an inner rubber liner which is surrounded by a woven fabric reinforcing layer, and then covered with another rubber outer cover. The problems come when the inner liner de-laminates from the woven pressure-resistant middle layer. Sometimes this can result in a hose that acts like a "check valve", allowing flow in one direction, but not the other. All hoses are "suspect"!
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