Brakes sticking on, booster not yet hooked up - is this the cause? - Team Camaro Tech
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post #1 of 3 (permalink) Old Jun 19th, 10, 08:20 AM Thread Starter
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Brakes sticking on, booster not yet hooked up - is this the cause?

Hey folks, had a bit of a setback with the camaro last night, a friend and I have been working on the camaro every night this past week trying to get it ready to get it on the road finally - I got the safety certificate for it last week, just some minor issues left and it's going to my mechanic friend to get everything checked out and the carb tuned next Friday. I got the safety for it in advance with the theory that I could drive it there, as long as I can get everything working properly. We've been working on getting the gauges hooked up as well as chasing some electrical gremlins. Last night we changed the temp sender to finally try to get the Autometer temp gauge working properly. We drove it around the neighborhood to see if it was working - apparently it is not reading very accurately, the car got very, very hot but the gauge only read 150 at it's maximum. We drove around a bit longer than I have before as we were watching the gauge waiting for the engine to warm up, on the final lap around the block I started feeling resistance, as if something were dragging. Then we started to smell burning brakes. The resistance increased greatly the further we went - turned the corner to come back to the house, stopped, got out to check, and the brakes were smoking. Figured we couldn't leave the car there, it was getting dark, had to get it home, it was only a few hundred more feet. I found if I pulled up on the pedal with my foot I could somewhat release the brakes. When we got to the driveway the "temp" light came on, a bit of a surprise as I didn't even think it worked. The gauge only read 150. Got the car in the garage, shut it down, brakes were no longer smoking but very, very hot. The rad was making some hissing, bubbling noises, a bit of steam from the cap, heater core started dripping out the front, apparently a lot of pressure in the cooling system. The repro original style cap did not vent very much if at all, whatever steam came out probably came from around the cap rather than from it, and there was enough pressure to leak from the heater core, probably the hose connections as it's a new core and hasn't shown any signs of a leak before - no leak into the interior, just from the bottom of the cover in the engine compartment.

I'm thinking the overheating could be from an air bubble or something, we had just drained the rad to change the temp sender and re-filled it. The temp sender is located in the head, we vented the block through the fitting on the intake manifold, but maybe there is still a bubble in there. The rad is a used repro big block 4 core, I don't have much money in it so if I have to replace it, it's not the end of the world. The fan is a factory style 5 blade clutch fan. Correct shroud, etc., in place.

My main question is the brakes. The booster vacuum is not yet hooked up, could this cause the master cylinder to not release? As it released when I pulled up on the pedal I'm thinking it's more likely in the way the M/C linkage is connected rather than the M/C being defective itself. I found a post by David Pozzi regarding a similar issue:

Quote:
These are classic symptoms of a master cyl that is not returning fully. Some boosters have a pushrod that is a bit too long preventing master cyl piston return, which prevents fluid from being vented back to the reservoir. The first thing to check is that nothing is preventing full pedal return, check the brake light switch adjustment and any rubber bump stops. Power brakes do not use a rubber bumper for the pedal, the booster pushrod stops the pedal and controls pedal height. The clevis on the brake pedal has a small amount of adjustment available. Next pull the master cyl slightly off the booster, if the booster pushrod to master cyl is a bit too long you should be able to feel it when pressing the MC into position. If you drive the car and the brakes drag, undo the two nuts and pull the master cyl forward a bit and see if this helps. I had to grind the rod a bit on the last booster install I did. .010" is the proper clearance here.

There are two lengths of MC rear holes a deep one and a shallow one, and two booster pushrod lengths to match them. A cross match of them usually prevents rear brake bleeding and you can't get much pedal at all. So I dont' think your problem is a complete mis-match. Probably a length issue.
Also, my brake pedal has always seemed a bit high to me, and quite hard, but as the booster isn't hooked up I assumed that was why it was hard. I'm hoping the master cylinder isn't bad, I've spent an awful lot of money on this car in the past couple of months and I was hoping it was almost over for the time being. I guess some setbacks should be expected.

Mike...

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post #2 of 3 (permalink) Old Jun 19th, 10, 02:54 PM
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Re: Brakes sticking on, booster not yet hooked up - is this the cause?

On the M/C, you can unbolt it from the booster and measure the m/c hole depth from the mounting surface and mesaure the pushrod from the booster mounting surface, and adjust the length accordingly. If the rod in the booster is like OE design, the threads are of the locking style thread and the rod will turn hard, not a problem.

Same goes for the pedal rod, if pulling back on the pedal releases the booster/brakes, then a shorter rod is needed and/or relocate to the upper hole in the pedal. You might be able to shorten the existing rod if needed or add more threads and shorten the rod. Whatever is needed.

On the temp gauge, it appears you may need a thermal resistor, sending unit, of lower resistance to allow the gauge to read closer to actual temperature, lower resistance, higher indication. make sure the sender body is grounded good to the head by the threads, must have a good path for conduction.

A quick kitchen calibration is a pot of water, thermostat suspended in the water, same with the sending unit, suspend the body only in the water, jumper power to the gauge, gauge to the sender, and a return jumper to the battery. The thermostat will prove the gauge plus allow you to see the t/stat open. Once every thing proves out, the sending unit must be the only device into the head/manifold, no adapters as this 'lifts' the s/unit out from the coolant flow and give an incorrect reading.

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post #3 of 3 (permalink) Old Jun 19th, 10, 09:29 PM Thread Starter
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Re: Brakes sticking on, booster not yet hooked up - is this the cause?

Thanks Everett, that is a huge help.

As far as the temp gauge goes, it is a new Autometer 3531, I'm using the sender that came with it (should be calibrated one would assume), it's hooked to the temp gauge wire from the American Autowire harness which appears to also run to the "idiot light" in the dash (I didn't realize that until the idiot light came on - go figure that actually works when nothing else does!). I'm thinking the wire should run directly to the gauge and bypass everything else to get an accurate reading, I will change that. The sender is about a 1/4 NPT, the head probably is 3/4" or 1" NPT, the sender was supplied with a reducing bushing. I do need to check if it's threaded in far enough, perhaps we used too much teflon tape and it's not seated far enough to make proper contact with the coolant. I also have a mechanical temp gauge that I can install in the port in the intake manifold to compare readings.

Mike...

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