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Braking System and Starter on 1972
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Picture of Spud
Over the last few months I replaced most of my coach's braking system. I put in some new hard lines, a new master cylinder, front calipers and pads, pulled the axles and rebuilt the rear drums, new flex hoses, new wheel cylinders, etc. Barth was sitting for a while because I was putting on a new carb, starter, and exhaust manifold.

Yesterday, I got everything together and couldn't get the motor to stay running. I saw that I was only getting 1v to the ignition coil with the key in the on position. I think my new starter might not be the right one and/or I've wired it incorrectly. I broke old solenoid to pieces and am not even sure if it had an "R" and an "S" post in addition to the big lug. Anyway, I've got it running now by wiring the ignition coil directly to the battery, but it's not a permanent solution. I only have two electrical connects on the new solenoid. 5 wires on it, 3 on the big lug, and 2 on the little, one from the ignition (I think) and one to the coil. I've Googled for days and can't seem to figure out the proper solution. I read the mini starter install guide on this site and so on. Unless someone has a clear idea of what the problem is, I'm going to wire in a fuse and "security switch" (this is what I'm calling it so I don't feel like a complete hack) or find a wire that is only hot when the key is in the on position and splice off it .

More importantly. After bleeding and bleeding the brakes, I'm not seeing any bubbles. However, the brakes are hard and hardly working. This is the same problem I was having before I rebuilt the system.

There are a few things I haven't replaced. The two Hydrovac boosters and one of the front flex lines. I went through 3 sets of flex lines trying to find ones that would fit, and I got one for the passenger front, but not for the driver front. I don't know how this happened, it just didn't fit, but in any case, even with that one brake totally out presuming the old flex line is collapsed internally (it's not), I should have more braking power. So, I think my problem must be the boosters. I have vacuum to the first one at least. I don't have a reliable way to measure how much vacuum I'm getting. I've read that Cardone will rebuild these, but I think I found a reman match and will try it first.

Posts: 25 | Location: New York | Member Since: 03-10-2017Reply With QuoteReport This Post
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Picture of Steve VW
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Lots of work! (I commend your efforts at getting the brakes right first, a good priority if you ask me.)

Since you have a separate coil, you must have the old points style ignition...

You may have a problem in the wiring or in the ignition switch itself.

Most of these systems do not run full voltage to the coil except while cranking. When the ignition switch connects the power to the starter solenoid, that line then backfeeds full 12v to the coil. (Actually more like 10-11 while cranking) If the engine starts you must be getting power to the coil while cranking.

When the ignition switch is back in the RUN position, the switch feeds power to the coil through a resistor, which drops voltage to 6v or so. The resistor could be a resistance wire or a ceramic ballast resistor. Either one could fail. With 1v at the coil there is something wrong, too much resistance.

Check for 12v at the igntion switch. Run a bypass wire from ignition switch to coil and see if it stays running. DON'T RUN FULL 12V TOO LONG, THE COIL WILL FRY.

Assuming it then stays running you must have a bad resistor. The ceramic block ballast resistors are cheap. Wire one into your new bypass wire and you're done.

If you don't have 12v at the ignition switch terminal your ignition switch may be bad.

As for brake boost, it sounds like your system work points to the vacuum booster. Not sure what system you have, the newer larger coaches run a Hydroboost hydraulic system powered by the power steering pump.

Your old vacuum style boosters may well have failed. They have a large rubber diaphragm inside, which given the age of your coach, may well have failed. I have not worked on these.

Search the site here for more info, you may be able to find references in the older GM motorhome chassis manuals.

Good luck with your classic coach! Mechanic

"98" Monarch 37
Spartan MM, 6 spd Allison
Cummins 8.3 300 hp
Posts: 3703 | Location: Kalkaska, MI | Member Since: 02-04-2011Reply With QuoteReport This Post
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Thanks Steve. I'm about nine months into this project and the advice and encouragement from Barthmobile is invaluable.
Posts: 25 | Location: New York | Member Since: 03-10-2017Reply With QuoteReport This Post
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    Forums    Tech Talk    Braking System and Starter on 1972

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