Brake overhaul - last step - need your help

[Peter B.]

Hey Guys - 71 Convertible....

I decided to re-do my brakes since I noticed that, by accident I mixed Silicone brake fluid with my Dot3. I ended up replacing the pistons and I already had sleeved calipers. I then took IPA (Isopropyl Alcohol) and ran it through the lines from the master cylinder using a vacuum pump mechanism I bought at the autoparts store. Wow. Lots of particles. I repeated this step with an air-blowing in between until I saw no particles in the IPA. I then put back the rebuilt capipers (new pistons in them) and then with them installed ran more IPA and air. Total was about 2 liters of IPA but I feel good that the lines are clean. I even replaced the front rubber lines (what the heck). I put in brake fluid and I found that priming the lines with the vacuum hand pump was not that great because air was going in through the threads of the bleeder valve due to the higher viscosity of the brake fluid.

Well - here is the question.....I had to do other weekend family activities but the car is somewhat primed with brake fluid. I pumped the brakes a few times to activate the pistons and have the brakes tighten up prior to a proper brake bleeding. However when i pumped the brake pedal a few times it got pretty hard to the point that even after being out of the car, my roters up front do not turn freely.

Is this normal????

I was going to bleed them the old fashion way with one of my kids at the pedal (rear-right, rear-left, front right, front-left). Is that OK?

Lastly, what is the cable that comes out of the proportioning valve for?

Thanks Guys!!!!

[Joe L.]

Re: Brake overhaul - last step - need your help

Hey Guys - 71 Convertible....

I decided to re-do my brakes since I noticed that, by accident I mixed Silicone brake fluid with my Dot3. I ended up replacing the pistons and I already had sleeved calipers. I then took IPA (Isopropyl Alcohol) and ran it through the lines from the master cylinder using a vacuum pump mechanism I bought at the autoparts store. Wow. Lots of particles. I repeated this step with an air-blowing in between until I saw no particles in the IPA. I then put back the rebuilt capipers (new pistons in them) and then with them installed ran more IPA and air. Total was about 2 liters of IPA but I feel good that the lines are clean. I even replaced the front rubber lines (what the heck). I put in brake fluid and I found that priming the lines with the vacuum hand pump was not that great because air was going in through the threads of the bleeder valve due to the higher viscosity of the brake fluid.

Well - here is the question.....I had to do other weekend family activities but the car is somewhat primed with brake fluid. I pumped the brakes a few times to activate the pistons and have the brakes tighten up prior to a proper brake bleeding. However when i pumped the brake pedal a few times it got pretty hard to the point that even after being out of the car, my roters up front do not turn freely.

Is this normal????

I was going to bleed them the old fashion way with one of my kids at the pedal (rear-right, rear-left, front right, front-left). Is that OK?

Lastly, what is the cable that comes out of the proportioning valve for?

Thanks Guys!!!!

Peter------


The disc brakes in a 65-82 Corvette are "constant contact" type. In this system, the springs behind the caliper pistons keep the brake pads pressed against the rotors. It's a light pressure, but it's a constant pressure. So, if you are expecting the discs to "spin" freely with the brake pads installed, they will not. Of course, there could be excessive pressure due to some other problem, but I doubt it. If you have a firm pedal, that should be good enough. However, it does depend somewhat on what exactly you mean by the front rotors not "turning freely".

Manual bleeding using the process you describe is fine. However, you might not have to do it now; you may be done.

There is NO proportioning valve on ANY 1969-77 Corvette. There is, however, a brake fluid distribution block and pressure differential sensing switch on all 1967-77 Corvettes. This is the device that folks often incorrectly refer to as a proportioning valve. If you note in the actual name of the device you will note that it has DUAL functions. One of those functions is pressure differential sensing. If there is an imbalance in the front to rear braking systems (due possibly to a lack of pressure or loss of fluid in one of the independent front and rear braking systems), the pressure differential sensing switch will cause the "brake" light on the dash (the same one that indicates parking brake application) to illuminate. The "cable" is the "vehicle" through which the switch transmits this information to the dash light.

[Chuck S.]

Re: Brake overhaul - last step - need your help

By "priming the lines" with the vacuum hand pump, you have essentially done what some would consider "bleeding the brakes". Given your process, it's not hard to understand why you have a hard pedal.

If it were me, I would probably go on and do the manual process as well to confirm the bleeding...if the brake system is completely free of air, it will be immediately obvious at each wheel.

I also found that there was air leakage around the bleeder threads even with conventional fluid. In my opinion, this makes the vacuum pump bleeding method pretty much useless for anything but the first bulk fill. Even though I own a vacuum pump, I do maintenance bleeding manually. At least until I get around (if ever) to fabricating myself a pressure bleeder using a small garden sprayer.

Pressure bleeding eliminates the bleeder air leakage problem, and is the best way to bleed old Corvette systems. The disadvantage is that you can waste a lot of brake fluid in the bleeder reservoir if you're not careful.

[Patrick H.]

Re: Brake overhaul - last step - need your help

I agree with the others.
I've done the MityVac method, the "assistant-pumps-on-the-brake-pedal" method and the pressure method using a Motive unit. None of them are fun or easy, and each has its down sides.

The MityVac will always suck air at the threads unless you use those special sealed/valved brake bleeder screws which I've never tried. The assistant pump method works OK, but no guarantee of a hard pedal. The Mityvac can give you one heck of a mess as you can't tell when you do - or don't - have enough brake fluid pushed through the system to bring the fluid level down so you don't spill brake fluid all over creation when you remove the pressure cover from the MC. And, even using a large vise + support to hold that cover on (the Hinckley method) you can still have fluid leak out under pressure.

I've been trying to get the brake system on the orange 72 to get a hard pedal. Despite using a couple of different methods and having all new hardware, it's a mediocre pedal at best.

I'd go through the "assistant pedal" method right now if I were you, and if you have a hard pedal just be extremely thankful and move on with life.

Patrick

[Joe L.]

Re: Brake overhaul - last step - need your help

I agree with the others.
I've done the MityVac method, the "assistant-pumps-on-the-brake-pedal" method and the pressure method using a Motive unit. None of them are fun or easy, and each has its down sides.

The MityVac will always suck air at the threads unless you use those special sealed/valved brake bleeder screws which I've never tried. The assistant pump method works OK, but no guarantee of a hard pedal. The Mityvac can give you one heck of a mess as you can't tell when you do - or don't - have enough brake fluid pushed through the system to bring the fluid level down so you don't spill brake fluid all over creation when you remove the pressure cover from the MC. And, even using a large vise + support to hold that cover on (the Hinckley method) you can still have fluid leak out under pressure.

I've been trying to get the brake system on the orange 72 to get a hard pedal. Despite using a couple of different methods and having all new hardware, it's a mediocre pedal at best.

I'd go through the "assistant pedal" method right now if I were you, and if you have a hard pedal just be extremely thankful and move on with life.

Patrick

Patrick-----


You can apply silicone grease to the threads of the bleeder valves and this will usually eliminate the air problem at the threads.

You know, when it gets right down to it I have only a few things to do to finish up the 1969. All I need to do is install the carburetor, install the distributor, install all the fluids, fire up the engine, install the master cylinder, and bleed the brakes. I think the reason I'm having such a hard time getting to the first 5 things on this list is because when those are done I have to get to the last one. That's one of the few jobs on a Corvette that strikes IMMENSE FEAR in me. Really!!!! All kidding aside!!!!!

[Edward J.]

Re: Brake overhaul - last step - need your help

Patrick-----


You can apply silicone grease to the threads of the bleeder valves and this will usually eliminate the air problem at the threads.

You know, when it gets right down to it I have only a few things to do to finish up the 1969. All I need to do is install the carburetor, install the distributor, install all the fluids, fire up the engine, install the master cylinder, and bleed the brakes. I think the reason I'm having such a hard time getting to the first 5 things on this list is because when those are done I have to get to the last one. That's one of the few jobs on a Corvette that strikes IMMENSE FEAR in me. Really!!!! All kidding aside!!!!!

Peter and Joe,

I agree with you corvette brakes will sometimes get the best of you when it comes to bleeding brakes, There is a way that I like to bleed brakes and it can be a one man show, I brought a couple sets of the bleeder that have the one way check valve and they do work great. If you only purchase a set of two then you can move them around as you bleed each caliper. Joe for a completely empty system you should bench bleed the master first and install and then bleed the brakes in the correct sequence. on the rear calipers with two bleeders leave one closed and then open the other and then switch. use a hose about 18" long and direct fluid into a coffee can or bottle.

[Patrick H.]

Re: Brake overhaul - last step - need your help

Patrick-----


You can apply silicone grease to the threads of the bleeder valves and this will usually eliminate the air problem at the threads.

You know, when it gets right down to it I have only a few things to do to finish up the 1969. All I need to do is install the carburetor, install the distributor, install all the fluids, fire up the engine, install the master cylinder, and bleed the brakes. I think the reason I'm having such a hard time getting to the first 5 things on this list is because when those are done I have to get to the last one. That's one of the few jobs on a Corvette that strikes IMMENSE FEAR in me. Really!!!! All kidding aside!!!!!

carb- not tough
distributor - make sure it's at TDC first as it makes it easier
fluids - use water in the cooling system in case of leaks.
fire it up - yeah baby!!!
install MC - gotta bleed the $*&^"@# thing first
bleed the brakes - ya gotta hate it. When I told Ryan tonight that it's the only thing left to do on the orange car, and I need his help, he was trying to do almost anything to get out of it....

[Joe L.]

Re: Brake overhaul - last step - need your help

carb- not tough
distributor - make sure it's at TDC first as it makes it easier
fluids - use water in the cooling system in case of leaks.
fire it up - yeah baby!!!
install MC - gotta bleed the $*&^"@# thing first
bleed the brakes - ya gotta hate it. When I told Ryan tonight that it's the only thing left to do on the orange car, and I need his help, he was trying to do almost anything to get out of it....

Patrick------


There's no doubt that most of the stuff that remains is easy. The problem is that once I do all the easy stuff, then I have to bleed the brakes. So, if I don't do the easy stuff, then I never have to get to bleeding the brakes. This is really deep psychological stuff; I've explored my inner self.

[Terry M.]

Re: Brake overhaul - last step - need your help

Joe, bleed the brakes first -- then the hard stuff is done. BTW: It is not that hard. The trick with an empty system is to get the lines full. After that it is duck soup (I wonder where that expression came from).

[Joe L.]

Re: Brake overhaul - last step - need your help

Joe, bleed the brakes first -- then the hard stuff is done. BTW: It is not that hard. The trick with an empty system is to get the lines full. After that it is duck soup (I wonder where that expression came from).

Terry-----

Yes, but if I did that I might never get to the easy stuff.

Bleeding the brakes in this car has always been one of the most hellish and frustrating experiences of my life. As far as brake bleeding goes, it's the "Corvette From Hell".

[Terry M.]

Re: Brake overhaul - last step - need your help

Your brake system is no different than thousands of other C2 & C3 Corvettes. There can be nothing, unless you changed something, different about your brake system. It is not your car.

[Joe L.]

Re: Brake overhaul - last step - need your help

Your brake system is no different than thousands of other C2 & C3 Corvettes. There can be nothing, unless you changed something, different about your brake system. It is not your car.

Terry------


Actually, there is a difference. 1969 used a one-year-only brake fluid distribution and pressure differential sensing switch. It was never even superceded by later switches; it remained the same until its discontinuation.

I've often wondered if some "foible" related to the above causes the difficulty in bleeding 1969 systems. I have heard from other folks with 1969's that have had similarly difficult experiences bleeding 1969 systems.

[Paul O.]

Re: Brake overhaul - last step - need your help

Terry no one knows for sure where the term Duck Soup came from. This is from http://www.grammarphobia.com/blog/20...duck-soup.htmlThe Random House Historical Dictionary of American Slang

[Patrick H.]

Re: Brake overhaul - last step - need your help

Joe, bleed the brakes first -- then the hard stuff is done. BTW: It is not that hard. The trick with an empty system is to get the lines full. After that it is duck soup (I wonder where that expression came from).

My house is closer than Joe's. I've bled the brakes on this orange car 3 or 4 times, and the pedal is still soft. You're welcome to come over and show me just how easy it is.

I don't know why, but it seems that some Corvettes are a PITA to bleed the brakes. It seems to be a crapshoot whether you're going to have an easy one or a difficult one. I definitely empathize with him.

Patrick

[Terry M.]

Re: Brake overhaul - last step - need your help

There is no reason for one car to be harder than another when you are starting empty lines. The brake lines all run in the same places.

I prefer gravity bleeding. Have you tried that? It will not work on a dry system, but will work if there is not so much air that the lines get air locked.