Brake Question

[Mike Sweet]

I've inherited my father's 1941 plymouth. One of the problems I have is with the brake system. We put new master and wheel cylinders on the vehicle and my dad used a silicon based brake fluid. We"ve had trouble since then with the brakes not building enough pressure to work very well. Someone talk me that the o rings in the system are made to use with regular brake fluid and that's why the brakes don't work right. My questions are, is this information correct and how is the best way to get the old fluid out of the system. I not going to  drive it until I get this problem taken care of. Thanks for any help.

[TodFitch]

Silicon brake fluid can easily get bubbles in it if not handled properly. Simply being rough when pouring can get small bubbles into it. Once in, they are very hard to get out. That might be an issue for you.

 

Another that can result in very poor braking is if the shoes haven’t been arced to fit the drums. This will result in only a small portion of each shoe making contact with the drum so you will have little braking regardless of the pedal pressure.

 

Any way, if you are going to change type of brake fluid, you will need to get all the old out. To do that you will need to disassemble everything. Some recommend using alcohol to flush the system but I have read that the alcohol can damage things.

 

In my case I also replaced all the hoses and tubing. You may get by with blowing them out with compressed air. 

If I were you, I would verify that the shoes are arced properly and get a pressure bleeding tool and rebleed using DOT5 being very careful to avoid getting tiny air bubbles in the fluid.

[desoto1939]

Mike: since you put on new cylinder and master cylinder, the big question is did the car originally have Silicone Dot 5 did you just put DOT5 into the master cylinder after building with new parts.

 

If the car had the old Dot 3,4 or even 5.1 you CAN NOT mix Dot 5 with any of the other fluids. You wud have to flush the entire system with denatured alcohol and then rebuild all the rubber hoses and rubber parts in the Master and each wheel cylinder.

 

So that is my first question.

 

I have a 39 Desoto and have used Dot 5 for over 30+ years.  Do not shake the bottle let it sit to make sur no bubble.  I fill my master cylinder with a small mouth syringe a little at a time.

 

You have the same MC as I do under the floor board. Swith the fill nut so the lid and the nut is at the front of the MC. Suck up dot 5 and slowly fill the MC until it is full.

As todd also stated what are the lining conditions. If the shoes are not indidudally set to the proper specs you will get a soft pedal. Contact me at

 

Also look at my recent post on the comparison of Dot 3, Dot4, Dot 5 and Dot5.1 brake fluid it is still available to view and is a current posting,

Desoto1939@aol.com. i will explain in more detail

 

Rich Hartung

Edited March 10, 2024 by desoto1939

[Plymouthy Adams]

unless you have new cylinders to install, or new kits on hand for install, you may be able to take each cylinder apart and clean the seals and components well and reassemble with the Dot 3 fluid but I would for peace of mind NOT reuse the seals once subjected to the Dot 5, I highly recommend new kits as a minimum.  Unless there is the constant task of pulling a load behind you taxing the brakes or consistent driving on long curvy down hill grades, odds are you are not going to need a higher temp fluid than dot 3 but dot 4 will bring you minimum of 401 degrees by manufactures specs.  you will need to also flush your lines and flex hoses well also...

 

Good luck, take your time and get all cleaned well.  

Edited March 10, 2024 by Plymouthy Adams

[Veemoney]

1 hour ago, Mike Sweet said:

Someone talk me that the o rings in the system are made to use with regular brake fluid and that's why the brakes don't work right. My questions are, is this information correct and how is the best way to get the old fluid out of the system.

Mike,

To answer the question you had concerning O-rings and I will include the seals used in the brake system on your car as well. They should work fine with the DOT 5 fluid, and I do not believe they are the cause of your problem. If they were leaking though, you would see the oil at the bottom of the master cylinder or on one or more of the wheels and you should confirm those areas are dry.

 

1 hour ago, Mike Sweet said:

We"ve had trouble since then with the brakes not building enough pressure to work very well

The brake major and minor adjustment at each wheel could be your issue if they were not correctly adjusted after the replacement of the master and wheel cylinders if not set correctly. You mentioned you put new master and wheel cylinders on but no mention of new brake pads so I will assume they are used and worn to the drum radius if not the arch could factor i to stopping performance but not the pedal pressure issue. There is plenty of information on this site in the technical area for correctly adjusting the pads and that is where I would start after confirming no brake fluid leakage. I like to adjust each wheel with a slight drag, I use the DOT 5 fluid and my truck can lock the brakes up if needed.