OT. Bleed brakes on the old Hot Rod

Jason1Pa

Member
Hey Guys! I think I'm writing this maybe to just blow off some stress but I'm open to any ideas as well. My family has a 1938 Chevy Coupe that needed a new master cylinder(VERY long story) so I got a hold of one that I think was defective outof the box since it wouldnt even bench bleed. I got ticked at dealing with parts from China and go out and buy top of the line one from Wilwood. Anyway after fighting many flares that were leaking I think I got that all taken care of. Now I just cant seem to get any brakes at the front. I think I got the air out but I can still grap the hub with one hand and turn it with the peddle down. Seems like the pistons arnt even beginning to push out of the calipers. Even if there is air in the system dont you think the pistons would still get pushed out and do something?? This project is going to put me in the nut house. It all started when I had to remove the front brake lines to make room for a new power rack and pinion (thats a whole other nightmare in its self) because it wasnt the same size as the old one. I've been working on this thing for 3 and a half moths now pretty much every night.. Im not geting anywhere..
 
Jason,I just went through this on my hot rod,do you have a residual valve for front and rear brakes? Are the fronts disc and the rear drum? If so they take different psi residual valves and you will need a proportioning valve for the rear brakes so you can get the 60-40 pressure difference needed so the fronts will work properly.Speedway has all the parts and you can get the info you need off the internet for proper plumbing.Hope this helps.
 
Google "stuck proportioning valve" It also called a combination valve...

I open the side that works then slam as hard and fast as i can the brake pedal to make the valve center are open to the side that has air in it then bleed the air out. If you do not have bleeder equipment short stroke the pedal to bleed are you will cause the valve to move and block off the side you are trying to bleed... You may have to repeat till you can get out enuff air out so the valve will stay equalized to complete the bleeding...
 
I shouldn't even say it,but it was the puzzler on Car Talk a few times over the years. The answer in the puzzler was that somebody had both front calipers off at the same time and put them back on the wrong sides so the bleeders were at the bottom instead of the top.
 
You think you have it bled, but I'll bet you don't. Installing a new master cylinder can be one of the most frustrating things as it seems you can't ever get it bled. Keep at it. Do you have a power bleeder? The combine has to have the power bleeder running in combination with bleeding it the old way. It is a bugger. The worst one I ever did was 25 years ago on a VW beetle. I still have the car. It will need another some day soon. I may take it somewhere this time.
 
If you can bleed the rears with a good squirt the pressure differential valve may be stuck. Stomping on the pedal may help that as Hobo suggested. Did you measure the pushrod length on the new master cylinder? A lot of the diagnosis depends on whether the rear brakes are working.
 
One way to tell if there is air in the system is to pump up the pedal, then watch the fluid in the reservoir when you release the pedal. If a little fountain of fluid squirts up out of the return port, there is still air. There will be a very short return flow when the air is out but a continued flow indicates air. Also, is the mc fully returning when the pedal is released?

A good homemade pressure bleeder can be made out of a NEW pump type oil can (might want to wash out a new one with non petroleum solvent just to be sure).

Fill the pump with brake fluid, pump the air out, slip a short hose on the nozzle, the other end on the open bleeder, pump fluid backward to the mc until the air bubbles stop.

If there are air trapping bends in the lines, raise one end of the car to get the mc as high as possible.
 
I'll have to test that tomorrow.. As for the oil can trick. I did buy a reverse bleeder tool and that pretty much does what I think your talking about. However I heard on a hot rod forum that sometimes those tools can make you loose the bench bleed in your master cylinder causing you just to chase your tail. i dont see why this would happen,but that is what one person ha a experiance with. Thanks for your reply!!
 
Well here is the thing I'm doing the front first because of a couple tips I got on a hot rod forum. I have a new adjustable propotion valve and some claim to have better results doing the front first. Howevr I think I'll try doing the back first next time Im working on it. What you said makes sence. I've been trying anything and everything. Yes I took my time getting the push rod adjusted to the new MC and feel good that it is ok. Thanks taking time to reply!
 
Yes,this has been difficult to say the least. I do have a reverse bleeder. You attach it to a open bleeder and you pump new fluid from a bottle threw the system back up and threw the master cylinder. I've heard pros and cons about it so today I was just trying the old school way.
 
I can see how that could happen. I didnt have the calipers off so I'm ok there HOWEVER these calipers have the bleeder located on the side. I've read where these things will almost never bleed unless you take them off and use a c-clamp to keep the piston from coming out and hold the caliper so the bleeder is facing up.. Heck of a thing but some will say you got to go threw this or youll never get it out..
 
The car had one of the ol style proportion valves on it and I had a feeling that it got stuck when the master cylider gave out(long story) so I replaced it with a new adjustable proportion valve. Everything in this system now is new except the calipers and wheel cylinders.
 
"If a little fountain of fluid squirts up out of the return port, there is still air."

That is true, but drum brakes that are not set up close enough also cause an extended return of fluid to the master cylinder after the pedal is released and the springs retract the shoes too far away from the drums, and the appearance is the same.

That is especially noticeable with an older, heavier vehicle with 4 large drum brakes.

Right now, I have a heavy 3/4 ton in the shop and we power-bled the snot out of it, and still had the large return of fluid.

Trouble was a stuck adjuster on the 13" drum brakes on the left rear wheel.
 
Yes Mike I have a 10psi valve for the rear that are drums. I dont have one for the front calipers due to the fact the MC sets up on the firewall and everything I have read says you dont need one unless your MC is down on the frame.
I used the diagram off of Speedways catolog to get this system set up. I'm really working with some tight areas. Not much room to move
 
Jason, when you stated that you can turn the wheel or rotor with brakes applied, it sounds like the pistons may be sticking in the bore. I didn't catch if the vehicle had been sitting for some time or not. Of course, this can happen at any time. Although I will admit it is unusual for both sides to develop the same problem at the same time. Just a thought.
 
Thanks for your reply. The car has been sitting for almost 4 months now since I started on this mess of a project. I thought about sticking calipers as well,but I'm like you the idea of both going bad at one time would odd,but there was a lot of rust in the old MC that is why it failed. The car is a 20+ year restoration with only a little over 8,000 miles so it does sit most of the time especially before we bought it so anything is possable
 

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