Well, it's been about a year since my brakes started self-applying! Yep, the outcome of using a j/y hydro unit. I finally got around to pulling it. I planned on rebuilding it, but after spending untold hours rebuilding/dialing in a Quardrajet carb, and after losing the instructions on how to rebuild the son-of-a-gun, I decided to just buy a rebuilt unit. Lessons learned, you know. Happy to pay $140 for a rebuilt, instead of spending a planned day (meaning three) on figuring out how to rebuild it myself.

Gees, now maybe, if my brakes aren't self applying, maybe I can figure out my mpg???

 

Yes self applying brakes would be a problem lol

Do you happen to have a link or larger version of the picture of the engine that is your Display picture?

 

Joe--

Here is a photo of my engine when it was new, and the ones following are my all time favorites of the 300, from mild to wild.

 

Very nice, very nice indeed sir.

What carburetor is that?

 

I really dig the supercharger!

 

Autolite 4100, 1.08" venturi.

I just spent all weekend replacing the hydroboost unit in an effort to solve the issue of my self applying brakes. $140 later, and the problem persists!!!!!!!!!!!!!!!!!!!! So now I can see the problem has to be from the p/s fluid in the brakes when I first installed it back when.

 

Do you think some of the rubber lines might have been damaged from the wrong fluid and went spongy and collapsed inside?

Maybe a professional grade system flush is in order?

That sucks, but at least you know your hydroboost unit is good to go.

 

Hey AB. Yes, that has to be the problem. I just never heard of it working fine for 5 months and then something swelling. When it happened I replaced the master and all new front lines and rebuilt f.calipers. I didn't think it was in system long enough to get to rears, but evidently I am mistaken. Dang.

I have Wed. and Thur. off, and will try to activate the problem, then jack up the truck with it running to determine which wheels are affected. The part that hurts is that all the lines and hoses and calipers are new. I wonder if I need to replace the residual valve and the proportional v. too? Double dang.

Or maybe it is those troublesome Caddy calipers I have on the rear. I'll find out.

 

I wonder, any PS fluid puddling up in the system somewhere? Some residual fluid might be stuck to the metal lines. Maybe try a power bleeder and run some sort of solvent through the hard lines.

I wonder, if your old hydro unit was shot, could it seep PS fluid into the system too?

Good luck man!

Sam

 

Hey sam--

It is a tough one. Hydro is so new few know how to trouble shoot it. Forum info is all over the board, and then throw in the variable of the p/s fluid, and it's a crap shoot.

With a hb the p/s fluid is isolated to the unit, and triggers a plunger to push a rod into the master. The fluids can't mix, but thanks anyway for taking the time to try.

I will do a test to see if all the wheels are affected, raising the rears and front while the prob is occuring. That will tell me if it is a caliper or master. I really don't want to replace everything again.

 

It it was a conventional system I'd say it was the master cylinder, but with the hydro-boost I'm not sure.. My dad would know he was an ASE certified mechanic when they came out on the GMs.

 

It is a strange one for sure! And I know the feeling, I've just put $2,500 into a rebuild on my 390 and spent $2,000 since then to get it to run right, two intakes two carbs, had to re-seal the intake twice now and the thing still doesn't run right. Not a happy camper. Should have gone with the 6!

Anyway, do you still have the old vacuum booster and master? If you've still got them, it might be worth it to stick them back on and see if it happens. Might help isolate the problem, but your wheel idea sounds like a good one.

Sam

 

All you have to do to test if it releasing is with engine running, to loosen the mounting nuts of the master to the HB unit. It will push the master out further when loosening if still actuated and release the calipers.
That brings up another point, check to make sure the master rod is not too long.

BTW, you can rebuild floating calipers very easily, parts are less than 5 bucks apiece. If multipiston about triple that.

 

I know the cal. rebuild kits are inexpensive. It is the cost of the hoses, the p.valve, and possibly the master that concern me...not to mention the time and labor to do it. Hopefully it will be an isolated problem.

Regarding a sticking/too long p.rod/hydro unit: The pedal has free play for first 10 min. each morning, and the wheels move w/o drag. Then the problem arises. I'll start on it Wed.

Thanks for your know-how, guys.