trini

BLEEDING BRAKES

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:) 1928 Dodge Brothers Senior  4 door sedan. I work alone, no help. I tried using a tube with the end in a can with brake fluid and the other end stuck to the bleeder screw, I  push the pedal once to give the flow a start. There was little flow .I did the 4 wheels the same way one at a time  and the pedal came up a little. The pedal is spongy at best and this system of bleeding does not seem to work on this particular model master cylinder. I have no choice but to get some one to pump the pedal for me. THE QUESTION IS WHY. Can some one explain, please ?

Thank you.

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If the system was bone dry it can be hard to get all the air out of the system because air bubbles get mixed in with the fluid. You have to wait a few days for the bubbles to rise to the top then bleed the brakes again, slowly, to get the last bit of air out.

 

I find a vacuum pump on the bleeders works best, or a pressure bleeder. Pumping the brakes works if you have an assistant, but you must be careful not to pump the reservoir dry, and to work slowly and not mix any air bubbles into the fluid.

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I do mine on my own. Make sure the bleed line into the can goes UP from the bleed nipple, otherwise fluid can drain from the tube and air can get into the wheel cylinder. This way, any drainback into the cylinder is fluid. I can do three full pedal depressions before refilling the master cylinder. So I do the slow pedal presses and returns, shut the bleed nipple then carefully fill the master cylinder, trying very hard not to spill brake fluid on everything. I actually use a syringe to fill the cylinder, with a short length of tube on the syringe. This method works; I have a good pedal and very good brakes for a 1930 car.

 

I work on each wheel until clean bubble free fluid is coming into the jar.

 

Of course, you will have adjusted the brakes before bleeding them.

Edited by Spinneyhill (see edit history)
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It's spongy because when you let up the pedal it causes suction throughout the system. Brake fluid is much more resistant to flowing  than air, and air can far more quickly  move through very tiny space, such as the clearance that all threaded parts need to not bind.

 

So, with the bleeder screw open, lifting the brake pedal  sucks some air back into the wheel cylinder through the bleeder screw threads. That's why when bleeding with two people,  you always have to make sure to close the bleeder screw BEFORE the pedal pusher lets the pedal up.

 

That's also why pressure bleeding is the best way and why commercial shops use pressure bleeders. The hand vacuum systems can do the same - suck air through the bleeder screw threads. Only then you waste fluid thinking there's still air in the system when it may not be. I have  a brake hand vac but only use it for priming and testing fuel  systems.

 

I have adapters to fit master cylinder reservoir caps and I use shop air pressure - turned way down through pressure regulators. Or I use a spring-loaded "brake man's helper". Looks like a storm door closing piston, but works in the opposite direction. It's length is adjusted then the tip pushed against the brake pedal and  it's compressed against the spring inside. Then the padded butt end is put against the front seat. The spring keeps pressure on the brake pedal while the bleeder screw is then opened and closed just as the fluid  stops flowing through the drain tube.

 

Plus, trying to bleed the system by gravity won't work. There isn't enough flow force/velocity  through the system to dislodge all the air bubbles and push them through and out the bleeder screw. 

 

Paul  

Edited by PFitz (see edit history)
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trini,

 

With bleed screw closed and hose from bleed screw into glass jar with some brake fluid below tip of hose,

Starting with the wheel farthest from the master cylinder, and continuing with the next most distant until all are finished, 

1. Have helper pump brake pedal until resistance is felt in pedal - and have helper hold pedal all the way down..

2. Open bleed screw to allow fluid and air into jar.

3. Immediately close bleed screw.

4. After a few times, be certain that there is still sufficient fluid in the master cylinder

5. Repeat steps 1 through 3 until upon opening bleed screw, there are no more air bubbles exiting hose into fluid in jar.

6, Repeat this process for all wheels in greatest distance sequence until all are done.

 Do Not Re-use brake fluid

Also, it is a good idea to use Dot-4 where Dot-3 was the original since, despite being a bit more expensive, it is less hygroscopic, less tendancy to retain water condensation causing rust - especially in our collectibles which are less frequently used than every day drivers. It can be mixed with Dot-3 without problems, but do not mix Dot-5 (silicone fluid) with the others.

 

I've been doing it this way since helping my Dad in the mid-1940s, and my wife now helps me with the process when needed.

If switching to Dot-5, it is recommended to change all rubber parts, and to flush the entire system with alcahol, and to let it air-dry, so as to not introduce water or condensation into the system - worked well years ago for our '58 Bel-air and '63 Impala.

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Don't know if this was mentioned, but be certain the brake shoes are ADJUSTED properly or you will never get a firm pedal.

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Had an old Dodge truck and couldn't get a pedal with proper adjustment and continued bleeding. On eyeballing the situation with another pushing the pedal I found the drums had been turned so thin that they were deflecting! Some previous owner must have owned a lathe.

Edited by JFranklin (see edit history)

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When I replaced all the wheel cylinders, hoses and master cylinder on my '31 Chrysler, I used a harbor freight brake bleeding suction gun.

Did it all by myself.

Started at the farthest wheel RR, then LR then RF and then LF.

Filled master cylinder twice per wheel 'cause it does not hold much.

Went back and repeated the sequence a second time just to check for air = there was none.

Rock solid pedal now.

 

Mike in Colorado

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I use a Mighty - Vac all the time to bleed brakes. I have also used the pop bottle (soda bottle) and rubber hose method (aka one man bleeder) with good results.👍

 

How you say? When the bleed screw threads are loose in the cylinder/caliper, I put PTFE tape on them. And it is more common today than in years past. Most every new bleeder screw is undersized threads ( or cylinder/caliper is oversized). 

 

I know there are anti-PTFE tape people out there, of course due to seeing botched PTFE tape applications over the years, but it works for me. Just apply to the threads, keeping clear of the hole through the side of the bleed screw. One does not want to induce PTFE bits into the hydraulic parts of the brake system!

 

PTFE - Teflon (R DuPont)😉

 

Gravity bleeding (the opening of all or one at a time bleed screws at cylinder/caliper with top of maser cylinder removed) only works well if the master cylinder reservoir is above the bleed screws by a foot or so. Frame mounted masters make this difficult! Masters mounted high on the firewall do pretty good. ABS systems, not at all!

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3 hours ago, Frank DuVal said:

I use a Mighty - Vac all the time to bleed brakes. I have also used the pop bottle (soda bottle) and rubber hose method (aka one man bleeder) with good results.👍

 

How you say? When the bleed screw threads are loose in the cylinder/caliper, I put PTFE tape on them. And it is more common today than in years past. Most every new bleeder screw is undersized threads ( or cylinder/caliper is oversized). 

 

I know there are anti-PTFE tape people out there, of course due to seeing botched PTFE tape applications over the years, but it works for me. Just apply to the threads, keeping clear of the hole through the side of the bleed screw. One does not want to induce PTFE bits into the hydraulic parts of the brake system!

 

PTFE - Teflon (R DuPont)😉

 

Gravity bleeding (the opening of all or one at a time bleed screws at cylinder/caliper with top of maser cylinder removed) only works well if the master cylinder reservoir is above the bleed screws by a foot or so. Frame mounted masters make this difficult! Masters mounted high on the firewall do pretty good. ABS systems, not at all!

 

Even a little grease on the threads of the bleed screw will help prevent air getting sucked back in. 

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These are excellent advice. May be I lose patient , but no. I  think Frank Duval hit the nail on the head. The Master cylinder is bolted on to the frame , below the floor board. It is lower than the bleeder screws on the wheel cylinders making gravity  feed near impossible.. These DB wheels are tall and have 14 inch wheel drums. The shoes are well adjusted.. The thing with Teflon tape is there is always a danger pieces breaking and falling into somewhere. The Teflon paste is now available in toothpaste type tube.

Thank you all gentlemen. It is a great session

 

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