NJTman

Do you guys have issue with your brake fluid cap leaking ?


Bought a NEW master several months ago and it hasn't stopped leaking out the cap, between the seal and the body.

I've:

1. Bent the spring to increase the pressure on the cap
2. replaced the seal with new
3. Contacted the manufacturer:

Manufacturer said.....

1. Check the cap for level....place on a sheet of glass
2. Lower the level to 1/2 " below the body top REALLY ????
3. Ensure surface is level and clean
4. Bend the retaining spring tighter

if the cap is bent replace the cap or the entire unit

Will test the cap for flatness today. and re- re tighten the hold down bailing wire.

For the life of me, I've never ever heard of anyone having to keep the fluid level 1/2" down in this type of master cylinder..... Ever.


Is it possible that the system is experiencing excessive backpressure ?????

The brakes work fantastic, so I don't understand how this would be possible.


TIA



T.

jimbo486

Check the top surface of the body where the cap seals as well. They've been known to be a little smooth and not quite a true flat surface and therefore keeping the rubber seal inside the cap from actually sealing. You could take a somewhat course sandpaper to it to rough it up and give the seal something actually seal against.

j_martin

Who's the manufacturer so we can all avoid him?

Email the link to this page to the mfg. and ask him if you should answer this question.

maybe368

Hey T, I remember someone here used 2 seals. I would imagine that you would have had to remember to keep the old one off the core. I have a couple old mc's laying around, let me know and I can send you one...Mark

BILTIT

Had this same issue with my old chevy forever. Finally upgraded to a newer MC with the plastic rexevoir and aluminum body, fixed the problem.

I am sure there is a newer style master that would retrofit.

bobva

I to say double up its a C2F basically you just want the outer edge.

Yes 1/2 inch low no problem.

Reality some people dont fill reservoir as the as the pad-shoes wheres.
The fluid level tells you were your pad-shoe % is.

thrashingcows

Yup I've had to run two seals. The old one you just cut out the center area and keep a 1/2" or so outer lip to put under the new gasket. PITA to try and close but it will seal.

I remember seeing a couple posts about guys swapping to a new booster and MC from a 2001 Cummins ram. It has the aluminum body and plastic reservoir tank.

NJTman

IMO, it's ridiculous that a new master... not a crapo rebuilt... would leak like this...

I put the cap on a section of glass. The cap is perfectly flat. The housing is perfectly flat, and that's why I asked about excessive backpressure. I remember reading about a guy with a Jeep with a bad prop valve that caused the pressure to back up into the reservoir. My brakes work fine, so I don't see how this is the issue.

The Manufactuer was an A1 Cardone NEW master # M2326 from Napa.

Last one I'll ever buy... Yes, they make New Ones Now

Next step is to find a 2001 in a boneyard, and replace it with that one.... or maybe even a new one from a parts house.

Thanks for all of the ideas. I'm just going to let it pour out until it finds it's own level and stops leaking.

T.

sootnsmoke

T,

Funny thing is I was looking at the same weeping master cylinder cap issue on the 91 we just got. I was doing this just 2 hours ago. I noticed the rear was filled right to the top edge. I mean, right at the edge. I removed some fluid from the back resevoir to about a half inch from the top. I also noticed that the top edge of the resevoir was not heavily pitted but there was some light rust along that top edge. I took a rag and some brake cleaner and wiped it down. I also cleaned the sealing edge area of the rubber seal as well. Hopefully that will do it and I will know for sure over the next few days.

Jklawinsky

My cap will also leak. I run a thin bead of rtv around the rubber and it works good for me. No leaks. I couldn't stand the brake fluid eating my paint.

NJTman

I went back to my local Napa store and told them of my problem.

After they gave me a "new" seal for the cap, and I drove around for a month or so, having it continue to leak outwards @ the cap / seal line, they said they would order me another NEW master, this time directly from the factory. It eventually stopped leaking once it reached the bottom 1/3rd of the reservoir, but I'm not really keen on driving around with just enough fluid in there to cover the ports.

If replacing this doesn't work, I'm ordering a new master for a 2nd gen that is the aluminum body / plastic reservoir on it, with the closed caps . 99% sure that the 2nd gen trucks came with it, and it should bolt right in.

All that work I did, cleaning, de-rusting, priming and painting.... wasted, directly below the master and about a foot rearwards on the frame. All has to be done again once the leak is fixed.

what a PITA....

NJTman

Ok,

Napa replaced my master cylinder again. The cap still leaks

Can someone point into which year the second gen dodge master will fit my truck ?


I appreciate it, as it's a pita driving around with a diaper bungee corded to the master cylinder to prevent it from leaking all over my frame again.

archer39

I have this issue to. I finally was able to fine one that does not leak. After going to all the auto part stores around I relized that there are two different size MC. I came across one where the lid fit on good and tight around the MC body. The reason that it fit tighter was because the body of the MC was .25" longer (from front to back). The lid fits in the MC tight and stays on without the hold down over top of the lid. This MC came on a booster when I got a booster with the MC. The MC was bad when I got but I rebuilt just so I could keep the larger body MC. So far it's not leaking.

NJTman

I'm following your lead..... and buying a different manufacturer and see what happens.

Apparently it's a common problem for these trucks. This DTR member changed it over to a sealed cap type as I asked before. He bought it from Oreilly's autoparts, but he never finished his thread as to what happened after installing it.
https://www.dieseltruckresource.com/...aster+cylinder

Being inquisitive, I took the cap off and had my wife depress the brake pedal. I was in shock as to how much pressure the master is under. Two streams of pressurized brake fluid were shot straight up out of the master and hit the bottom of my hood. With that kind of pressure blowing upwards at each time you hit your brakes, it's no wonder these caps leak. What a stupid design. How difficult would it have been to install a deflector shield in the reservoir ? I mean really. These caps aren't leaking from sloshing around, but leaking due to excessive stream pressure of brake fluid being shot against the underside of the cover constantly.




More of the same issue

https://www.dieseltruckresource.com/...aster+cylinder

https://www.dieseltruckresource.com/...aster+cylinder

https://www.dieseltruckresource.com/...aster+cylinder

https://www.dieseltruckresource.com/...aster+cylinder


EDIT:

After researching this, I found that he had a master cylinder from a mid 1980's dodge truck that had the plastic reservoir and twist caps. That, according to this information below, was for trucks that had the 3500lb axle.

NJTman

Hey Archer.


Looks as though you were correct. It's the product (master cylinder seal) itself. bought a Bendix master cylinder, installed it, and drove it around for about an hour. No drips.


First time in 6 months that my truck master cylinder cap wasn't leaking on my frame. The Bendix master seal was much softer than the other brands. I guess after all that effort, it was something as simple as that.


Don't buy Cardone, otherwise you'll just be dealing with the same that I have been.