1946 Plymouth brake fluid problem ?

[dale]

Ive replaced all the brake componets with new ones and put in synthetic brake fluid.  Ive bled the brakes several times according to the manual but still have a spongey pedal.  There are no fluid leaks.  Could this be a brake fluid problem.

[mopar_earl]

No. Does it pump up firm or stay spongy?

Earl

[knuckleharley]

Ive replaced all the brake componets with new ones and put in synthetic brake fluid.  Ive bled the brakes several times according to the manual but still have a spongey pedal.  There are no fluid leaks.  Could this be a brake fluid problem.

I have been told if you switch to synthetic brake fluid that you will need to replace the brake light switch. Don't remember why.

[TodFitch]

I have been told if you switch to synthetic brake fluid that you will need to replace the brake light switch. Don't remember why.

The allegation is that hydraulic switches fail faster with silicone fluid than with conventional fluid. That might be true. Or maybe it is just that modern manufacture hydraulic switches fail quicker than the ones built in the 1930s and 1940s. My current switch has been on the car for about 5 years now, the previous one was, as far as I could tell, the original one from the 1930s and it failed (brake light no longer turned on) after about 15 years of silicone brake fluid use.

 

Silicone fluid is more viscus and entrains air bubbles a lot easier than conventional fluid. This means two things: First you have to be very careful in pouring or otherwise handling the fluid to keep it from getting air bubbles in it. Second, at least for me, it takes a lot longer and many more times around the wheels to get all the air out.

 

In fact, I wasn't able to get a satisfactory pedal on my car with silicone brake fluid until I used a pressure bleeder. I made one using a garden sprayer as described by many on this forum, but I did not use the built in sprayer pump as that introduces air at the bottom which would create air bubbles in the silicone fluid. Instead I mounted a tire stem/valve high on the side of the container and pressurize it with a tire chuck (seems like 15 to 20 psi is about right). 

[mopar_earl]

Silicone and synthetic brakes fluids are two different fluids. Silicone is dot5 while you can get dot4 in conventional or synthetic. Maybe dot3 as well. I've used dot4 synthetic in many vehicles without issue.

I have dot5 in my 52 without issue and a good firm high pedal. Had no issues bleeding the brakes and didn't use a power bleeder.

Earl

[55 Fargo]

I have been told if you switch to synthetic brake fluid that you will need to replace the brake light switch. Don't remember why.

Not true, at least not in my case.

Did the MC get bench bled, how are you bleeding the system?

You are getting air in the system if still spongey, are all connections tight and sealed?

Dot 5 Silicone can be a little harder to bleed, but not a real problem.,...

All is 100% new, and clean, without using Dot 3 brake fluid prior? If it has, flush and bleed the entire system with denatured alcohol or something suitable.....keep us posted, until this is resolved.

[knuckleharley]

Not true, at least not in my case.

Did the MC get bench bled, how are you bleeding the system?

You are getting air in the system if still spongey, are all connections tight and sealed?

Dot 5 Silicone can be a little harder to bleed, but not a real problem.,...

All is 100% new, and clean, without using Dot 3 brake fluid prior? If it has, flush and bleed the entire system with denatured alcohol or something suitable.....keep us posted, until this is resolved.

I'm not. I just wrote that was what I had been told. I still use DOT 3.

[55 Fargo]

I'm not. I just wrote that was what I had been told. I still use DOT 3.

Yes not sure what that is about, could be something I am not aware of, but mine worked okay.

[Dodgeb4ya]

All DOT 3 and 4 and 5.1 fluids are and have been synthetic...polyethylene glycol base.

People today seem to like the word description synthetic being marketed with automotive fluids and will buy it..... IE full synthetic oil.

Todays synthetic DOT 3 and 4 is just the same as the stuff sold in 1980.
 

Edited April 3, 2016 by Dodgeb4ya

[dale]

Im wondering if that once the synthetic get air in it the air is there to stay.  I think Ill start over using the old type if I can still buy it.  Could be I didnt back off the shoe adjusters like I was suppost to.. Ive worked on brakes and one car I didnt even have to bleed the brakes.  Air bubbles just came up thru the fill resevour some and that was it.

[Don Coatney]

Do not mix DOT 3 with DOT 5. They are not compatible.

[Plymouthy Adams]

dale, on 03 Apr 2016 - 1:21 PM, said:

Im wondering if that once the synthetic get air in it the air is there to stay.  I think Ill start over using the old type if I can still buy it.  Could be I didnt back off the shoe adjusters like I was suppost to.. Ive worked on brakes and one car I didnt even have to bleed the brakes.  Air bubbles just came up thru the fill resevour some and that was it.

why would there be a bleeding process if air were in the fluid to stay....seems redundant to make a fluid that is not capable of doing the job...many people ad problems to themselves by pumping the brakes way too soon in the process thus adding air by their own actions.  this pumping action will aerate the fluid but will eventually the air will pool back to itself when idle and allow for further and proper bleeding. 

[TodFitch]

why would there be a bleeding process if air were in the fluid to stay....seems redundant to make a fluid that is not capable of doing the job...many people ad problems to themselves by pumping the brakes way too soon in the process thus adding air by their own actions.  this pumping action will aerate the fluid but will eventually the air will pool back to itself when idle and allow for further and proper bleeding. 

True. . . One issue I have with silicone fluid is that it takes much longer for the bubbles to work their way to the top of where ever they are. Talking seemingly hours rather than minutes or seconds. So if you splash some fluid into the master, entraining some air bubbles in your careless haste, you will probably need to let everything sit for a long time before you pump them into the tubes while trying to bleed the brakes. If you just go ahead and start your bleeding process with all the little bubbles in the master all it will do is move those bubbles into the brake lines.

[greg g]

Is your brake adjustment correct?  You can not effect a proper system bleed if the brakes are improperly adjusted.

Edited April 4, 2016 by greg g

[mopar_earl]

A mighty vac works great for bleeding brakes as well as other uses.

Earl

[dale]

Im thinking my problem is the shoe adjustments.

[mopar_earl]

If you can pump the pedal up to a firm high pedal, it's an adjustment/travel issue, NOT air. If it stays spongy it's air.

Earl

[Plymouthy Adams]

it has been a long time since I have messed with Dot 5  the original formula would stain the transparent reservoirs quickly and the effect is a false sense of fluid being sufficient level at casual glance.  Not sure if this dye problem has ever been fixed but that was the reason I never considered a third use of the stuff....most things get but one chance with me...

[dale]

The fluid I used is Valvoline synthetic that says  " DOT3 or 4 " on the label.. Fittings are tight as there are no leaks.  Pedal is quite spongy but doesnt go on down to the floor.  Stops the car.  Im wondering if air could be trapped in the cylinders.

[Dodgeb4ya]

New brake shoe lining radius that does not match/fit the drum and incorrect shoe adjustment will cause a spongy pedal too.

[ptwothree]

The fluid I used is Valvoline synthetic that says  " DOT3 or 4 " on the label.. Fittings are tight as there are no leaks.  Pedal is quite spongy but doesnt go on down to the floor.  Stops the car.  Im wondering if air could be trapped in the cylinders.

Did you change hoses or wheel cylinders?  There are 3 copper washers used to seal the hoses.  One for each front hose and 1 for the rear.  If any are missing or damaged, you'll never get all the air out of the system.  I've been there in a moment of brain fade....chased that air for a long time before I realized the front hoses didn't have the washers installed!

[dale]

Ill check the washers and like I said there are no fluid leaks.  Ill bleed the system once again this time being carefull about pouring the fluid and move the pedal slowely.  This time around Ill adjusting the brakes back   first.  Its been a few weeks since Ive bled them so any air should have seperated from the fluid by now.  Ill report.

[Captain Neon]

I don't know how many times I have to "explain" to people that "synthetic" DOT 3 will "blend" without problem with the DOT 3 brake fluid already in their systems.  Then there are the people that come in wanting headlight bulbs and "just need a standard bulb; don't need fancy halogen or anything like that."  I just get them what is on the shelf and don't try to explain that DOT 3 brake fluid has always been synthetic and now standard replacement headlight bulbs have always been halogen since their inception.  It just confuses them.  Good luck even finding a 12v sealed beam unit that isn't also halogen.  Most people don't even know what a sealed beam headlight is any more.

[dale]

Well I checked all the lines and connections.  Id think if there was a connection sucking air it would also have a noticeable leak of fluid by now.  ..  Went around and bled the cylinders again being carefull adding fluid and pumping the pedal and got some air out and the pedal got much better though not all the way there.  Adjusted the shoes back up..  Triied the brakes a few minutes later and they were back to where I started.  Im about at my patience limit.  Never had this problem before on several other cars and one was a 1947 Plymouth.  Must be getting air in but ....

[desoto1939]

Dale HAve you used an AMMCO brake Gage 1750 to check the brake shoes adjustments.

Did you replace any of the wheel cylinder push rods with new push rods. People have been having issue with the new pushrods in the new rebuild kits and they are a little longer then the originals.

Rich HArtung

desoto1939@aol.com