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Who wants to guess the solution?

2431 Views 7 Replies 3 Participants Last post by  mt94ss
Ok, so I've been having this problem on the Austin gasser recently, and I finally figured it out today, but it was very unusual, and thought it might be fun to see if anyone here wants to take a guess at what I found that solved it?
Not long ago the car started acting like it had more compression when slowing down, or maybe the brakes were dragging. It mostly happened after I drove at freeway speeds for a few minutes, but more recently it also started happening after driving for 20 min. or so at around town speeds. I'd let off on the gas and it would start slowing down.
Last night I was coming home from the cruise and on the freeway about 55 mph, when the frontend started to get a vibration. I let off the gas and it slowed down even more than usual. Pulled off the freeway, and when I stopped I could smell brake lining that was hot!
Got under the car and spit on the front calipers to see them sizzle!!!! The rear backing plates were only lukewarm, no issue there. After sitting for a few minutes it cooled down, and I headed home the last couple miles on suface streets. Pedal was very hard and high, with little travel!
Today I got in the garage and started checking things on the entire brake system, and discovered the problem. Here's a few details to get you started:
All new lines and braided SS hoses, new calipers, wheel cylinders, brake shoes, master, etc. Basically new everything front to rear. Master cylinder is a late model Subaru with power booster, and I'll tell you right off it wasn't the problem. Disc fronts (GM Metric, drum rear, also GM)
OK, let's see if anyone wants to give it a shot! :) Jeff can't play, he already knows what I found! ;)
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Hedders heating up brake lines causing them to expand the calipers....! just a shot in the dark, that happened to me..
Hedders heating up brake lines causing them to expand the calipers....! just a shot in the dark, that happened to me..
No, not hot fluid. :)

Is there a residual valve? maybe it wasn't letting the brakes retract?

Or was it the brake pedal/arm binding? I have a '78 Chevy truck that does that and I have to pull the pedal back with my toe. I replaced all the brake parts - MC, booster, etc.

Do you know what the problem was?
Yes, I found the problem and fixed it, just thought it might be fun to see what others came up with since I racked my brain with all sorts of possibles when it began to exhibit the problem, and was surprised when I found what it was.

But since you're so close to diagnosing it Mike I'll call it close enough and tell you. No residual valve, but it was due to the master cylinder piston not retracting; just a different reason for that malfunction.
I got under the dashboard with the intent of pulling the master, booster, and brake assembly off. I had decided they just weren't right for this application, and maybe the disc/disc setup on a Subaru wasn't working for my disc/drum vehicle. When I looked up to disconnect the operating rod I noticed the locknut on the adjuster was backed off about 3/8" and when I tried to turn it by hand it was a self locking locknut. That's when the light went on and I realised what had happened. I turned the shaft until the locknut bottomed and cinched it down.
With the rod extened that small amount it was keeping the calipers and wheel cylinders slightly extended when I released the pedal. Not an issue in the rear as the shoes have more clearance than the pads up front, but the slight extra pressure on the pads created heat, which in turn made the metal and the pads expand and that created even more heat and friction. The extra heat and friction of traveling at freeway speeds with the front brakes applied caused the brakes to grab and that was the vibration I felt in the frontend.
After backing the rod off and taking it for a two hour test drive all the issues ceased. I was pretty surprised to find it, and I'm happy I did before I started replacing a lot of other parts for the wrong reason! My wife calls the Austin an "attention whore". Seems like as careful as I am at going over things, it keeps finding these tiny little things to keep me adjusting or tightening things every once in awhile. Neither of the other two Chevy rides do this. They both seem to just run and drive without any extra attention. :)
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Soon the whore will just submit and quit giving you frustrations,,,glad you found the problem, my `33 I built years ago had the issue with one line running to close the the hedder collector, ending with the same result, took me a long time to fiqure out....the only way I did fiqure it out was by chance when I slid under the car to tighten up the hedder collector bolt I burned my hand on the brake line...then the light came on...LOL
Put a lot of miles on it today running around getting parts for the motorcycle I'm selling. It ran around with no complaints, so maybe she's going to start cooperating! ;)
Oh, Ahh! Pat the dash... :p

It was a great day to run around. Got the Impala out and shifted some gears!

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