Brake lights are stuck on

[Don Coatney]

Bit of confusion???? Dot 3 is not silicone, Dot 5 is. Post a picture of the brake fluid can you used.

[38plymouth]

Bought 2 bottles at autozone 2 days ago.

[38plymouth]

Oops just noticed it is synthetic, not silicone.

[Don Coatney]

Oops just noticed it is synthetic, not silicone.

That is good news for you. I may be wrong but I believe all DOT 3 is compatible. I am not wrong when I say Dot 5 and Dot 3 are not compatible.

[38plymouth]

I crawled under the car this morning to see if I could adjust the free play at the master cylinder. What a ridiculous design it is absolutely impossible to adjust it while it's in the car. I then cracked the driver side front bleeder and got just a bit of brake fluid out of it. I cracked the passenger front and nothing came out. Nowe my brake lights are off when at rest I'll have to test drive it later to see if that's solved the problem. Thank you all for the ideas.

[T120]

I scanned this page showing a drawing  of the master cylinder  (1937 chrysler Manual).The ports mentioned that must be clear, 1 and 3 are shown in the drawing.Your pedal free play should be 1/4 to 3/8 of an inch before meeting any resistance.

 

Edited August 25, 2016 by Ralph D25cpe

[desoto1939]

Odd experience with the 39 Desoto master cylinder which is the same as in your 36.

My car was driven by the original owner from 1939 to 1965 and had 79000 mile on the odometer.

 

The car was owned a second time but not driven that often and had a rebuilt engine.  I took passion of the car and then started to notice that the brake pedal was not retracting after applying the bake it got harder to push. Let the car sit in the driveway about an hour and then the brake pedal was free.

 

Discivered while doing a major brake job that the ORIGINAl and I say ORIGINAL Master Cylinder to this car was the issue. I took it out of the car after removing the floor boards. This is how you get to the MC that is bolted to the frame member.  I took in out of the car and took the top lid off the body of the MC.

I noticed the two small holes in the bottom of the reserviour and the front one I stuck a thin wire to make sure it was not clogged up and this was open as expected.

 

To my surprise I did the same with the back weep hole but this time the wire would not go all the way throught in the bottom where the piston is located. I tried several times. Then used a stiffer metal rod and still the rod would not go through. I discovered that the machinist never fully taped the weep hole he only started the proess and never finished it. This is the number 3 in the prior picture of the hole that is behind the piston.

 

I then taped the hole and the MC then worked correctly. But remember that this car was driven from 39-65 with this same issue.  Not sure if this your problem but you never know what you might find.

 

Also if your brake light switch needs to be removed put a piece of wood behind the brake pedal and wedge it up againt the floor board. This will prevent the brake pedal from going to the floor when removing the brakelight switch. then all you have to do is  remove and reinstall the new one and connect the wires and no loss of brake fluid. 

 

Rich Hartung

Desoto1939@aol.com

 

Rich HArtung

Edited August 25, 2016 by desoto1939

[BobT-47P15]

One time, several years ago, my brakes seemed to work fine as long as I stopped pretty normally and easy.

Then, one day, I had to jam on the brakes and the rear wheels locked up.   They would return to working if

I opened the bleeder on each side to let a little fluid run out.  The problem turned out to be the rear brake hose

which looked good on the outside, but the inside was collapsing and keeping the fluid from returning to the

master cylinder after a hard stop.  Replacing the hose was what mine needed at that time. 

 

Have you replaced all your hoses, even if they look good?    

 

I believe there is a relief vent atop or near the differential that might bear checking/cleaning also. 

 

See item in the square box at lower right.

 

[1949 Wraith]

A good point about the collapsed rubber brake line. I had that happen on a front line of a 1990 Lincoln Town car. Wheel locked up under normal braking, backed off the pressure through the bleed screw and was able to move again.

[Silverdome]

I have encountered some of the problems mentioned above specifically the relief port in the master cylinder being plugged and the inside of the brake hose being collapsed both of those can cause the brake light to stay on. The hose being collapsed usually will bleed back after a few minutes but the plugged relief port would not. I would venture to guess that it is the relief port.

[38plymouth]

I am pretty sure my problem was caused by an overfilled master cylinder after I released a little pressure from the bleeders it seems to be working fine.

[Don Coatney]

I am pretty sure my problem was caused by an overfilled master cylinder after I released a little pressure from the bleeders it seems to be working fine.

I think not. Your cap should be vented and the master cylinder reservoir should be open to the atmosphere.

[Jerry Roberts]

The tiny vent in your master cylinder cap can be hard to see . The ones that I have found had been on the side ( on one of the flats ) of the cap . If you have an overfilled master cylinder , the only thing that will happen is that when the fluid splashes inside , it probably will spill out of the tiny vent hole . 

[38plymouth]

Interesting, so far it's working fine and the brakes are better than ever. My master cylinder"cap" looks like a pipe plug. If there is a vent I don't see it, I'll pull it out and take a closer look.

[38plymouth]

Here she is ready to roll with new shocks, fenderwelting and powdercoated wheels with new pinstripes.

Edited August 28, 2016 by 38plymouth

[casper50]

looks sharp as heck.

[rb1949]

Nice cruiser.

[38plymouth]

Well I learned something new, the plug does have a tiny hole in it, never noticed it before.

[mopar_earl]

Well I learned something new, the plug does have a tiny hole in it, never noticed it before.

Is that vent clean and open? Very important that the vent functions on that type of master.

Earl

[38plymouth]

So I haven't driven the car much since winter. I fired her up yesterday and pulled her out of the garage and left her running awhile. I turned her off as I cleaned the garage and when I tried to start it back up the battery was dead. I charged the battery and started her up and pulled her back in. I noticed a bit later my brake lights and stuck on again. I drove around all winter with no problem and now the problem is back. 

I guess it's time to dig into it again.

[medium_jon]

I've heard of that happening. Find the brake light switch on that car and you will likely be looking at the source of the problem. 

[Plymouthy Adams]

do not over look the fact that your master could not be returning all the way due to a rust/corrosion ring about the very end stop that is not allowing the fluid to fully return to the reservoir and at the same time the fact the vent hole in the master reservoir itself may be plugged with debris/corrosion  

[38plymouth]

When this problem started last year it was right after doing new wheel cylinders and bleeding the brakes. The problem went away after removing some fluid and I thought it was due to an overfilled master cylinder. It came back yesterday (it has just been sitting many many months no driving) after the car sat overnight all is fine again. I really think it has to do with free play in the brake pedal. I don't have any compared to what I had before I did the wheel cylinders and brake shoe adjustment. Since it is very difficult to get to the master cylinder to adjust the free play there is there any reason why I couldn't back off the minor adjustment on the front shoes to get back some free play? My brake pedal is hard as a rock and the second I touch it I'm on  the brakes and the pedal does not go anywhere near the floor.

Edited August 25, 2017 by 38plymouth

[Merle Coggins]

It sounds like the pressure isn't fully bleeding out when the pedal is released. It could be a pedal free play adjustment, not allowing the piston to fully return. Or it could be a plugged return port in the M/C not allowing the fluid to get back into the reservoir.

[desoto1939]

You have an issue with the MC. Check to make sure that both holes in the MC reserviour section are not blocked with sediment. I had a simalar situation and found that the weep hole was not completely tap and this was a factory installed MC and was orignal to the car.  Overfilli9ng the MC is not your isse. When you let out brake fluid from a clylindar you relived the built up pressure so the pedal will return becasue of the lack of fluid in the line.  Have you done this with different wheel cylinders and not the same one allthe time.  So take out the floor boards then take off the lid to the MC and take a small wire and thry to  puch the wire throught each hole in the bottom of the reserviour. report back if this works.

Rich Hartung   Desoto1939@aol.com.