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Old 05-18-2004, 09:07 AM
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Low brake pedal

I have been gone for a while but now I'm back!!
Last year I replaced the entire brake system on my 37 Plymouth with a new manual GM setup. I'm using a dual reservoir master cylinder w/o power boost. Front brakes are disk, rears are drum. The brakes are adjusted correctly. I have a 2# check valve on the front brakes and a 10# valve on the back. There are no leaks in the system and I have bled the system several times with no evidence of air. I'm using typical DOT 3 fluid. The master is mounted to the frame and is higher than the wheels but only by a couple inches. The master mount has a slight bit of flexure but I don't think it exceeds 1/8". I have not tried to lock the brakes in a hard stop. My concern is the pedal travel. I have a total of about 8" of travel to the floor and I'm using about 6.5" of it under normal braking. I'm concerned that I don't have enough pedal left in an emergency or if the brakes start to fade. Any suggestions where to look for a problem?

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Old 05-18-2004, 08:52 PM
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Are you absolutely sure you have the correct master cylinder. The wrong one will cause low pedal. Are your residual valves (check valves) mounted on the brake line as close to the master cylinder as possible. This is the correct location. Are you sure the rear shoes are adjusted out as far as they will go without touching the drum? If not that will cause a low pedal. Have someone watch the front pads while someone else pumps the brake pedal to see if there is excessive travel. Hope this give you a few ideas to work with. What about a proportioning valve?
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Old 05-18-2004, 08:55 PM
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Try a longer rod from the brake pedal to the master cylinder, or maybe the angle is wrong.
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Old 05-19-2004, 12:15 PM
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Thanks fpr the feedback. I have checked all brake clearances and they are fine. The proportioning valves are within 4" of the master cylinder. As far as the type of master cylinder, I used a remanufactured master for a 72 Nova. I do not remember if the push rod was modified or not, and that could be the solution. If I was to lengthen the push rod, what kind of guidelines should I follow? How will I know I haven't gone too far? By the way, I forgot to mention that I am using the original pedal arm in case that makes a differance.
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Old 05-19-2004, 07:56 PM
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Quote:
Originally posted by jpd37
By the way, I forgot to mention that I am using the original pedal arm in case that makes a differance.
You might wanna compare the distance between the holes/attachment points where the rod and the pivot point of the pedal arm are, as compared to one from a 72 Nova with manual brakes. If they're closer together on the original (the one you're currently using), it'll have more travel.
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Old 05-20-2004, 06:01 AM
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Thanks Poncho62 and BstMech. I didn't consider that. I'm going to try to get at the master this weekend if I can find the time. Lengthening the push rod sounds like the solution I'm looking for.
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Old 06-15-2004, 11:18 AM
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Just an update to close the query. I added 1/2 inch to the length of the push rod and the travel distance of the pedal is much less. It really made a big differance and all the little quirks like a slightly soft pedal, leakage of fluid past the cover gasket and long travel distance of the pedal are gone. Finally I have brakes I can rely on!

Thanks to every one who responded.
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