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I have a 1983 F250 4X4. It has disk front and drum rear. The master cylinder has a dual reservoir. I noticed the front reservoir was very low on fluid and I refilled it. After driving, I observed fluid dripping from the master cylinder. It was leaking from around the reservoir cap. I replaced the rubber seal on the cap and refilled again. Same problem. After driving, the fluid leaks out at the cap until the fluid level is very low. It only does this in the front reservoir. Any ideas?
Thanks!
My '88 F250 has the plastic resevoir and I guess yours has the steel cap with rubber seal.Years ago I had the same problem with a '74 Lemans.I recall that the rubber seals and caps were very specific to each vehicle.I went through three seals before I found that the cap was warped.Replaced cap and seal and stopped the leak.I even tried putting a spacer between the seal and the cap(a thin piece of sheet metal)which only slowed the leak.
My 83 F-150 is doing this very same thing, except mine is running out the back of the master down the front of the booster. For me it looks like i'm in for a new master/booster combo and with luck my brake woes will come to a conclusion.
I'd see if you couldn't get a different cap for your M/C at either a boneyard or your local parts place to try and stop this leak. Not being able to stop often results in lots of raising experiences.
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Tim 1976 F100 360/c6/3.08's 2wd
1995 F-350 Dually 7.3 CC - Stock
Are you sure it's leaking out the cap? The cap is high up. Theoretically you could run it without the cap if you drove carefully and slowly applied the brakes. The only reason the fluid would want to leak out of the cap is from it sloshing around, and the geyser that forms when you hit the brakes hard and fast.
You should not be filling it up to the top also. If it was leaking out the cap, it should go down to a certain level and stop. Generally speaking, if you are losing lots of fluid it's because of a leak somewhere else. Your smaller front reservoir serves the rear brakes, so I would look back there for fluid or wetness behind the rear tires.
Are you sure it's leaking out the cap? The cap is high up. Theoretically you could run it without the cap if you drove carefully and slowly applied the brakes. The only reason the fluid would want to leak out of the cap is from it sloshing around, and the geyser that forms when you hit the brakes hard and fast.
You should not be filling it up to the top also. If it was leaking out the cap, it should go down to a certain level and stop. Generally speaking, if you are losing lots of fluid it's because of a leak somewhere else. Your smaller front reservoir serves the rear brakes, so I would look back there for fluid or wetness behind the rear tires.
Yes, it is leaking out around the cap. No doubt about that. No other leaks anywhere else. I can fill it up, drive a few miles with normal stops, and when I get to my destination, the master cylinder will be saturated with fluid from the top and running down on the ground. I drove it quite a bit on Friday and fluid is still running out on the ground, even though the front reservoir is almost empty. Of course, it does it worse when the reservoir is full.
Could the master cylinder have an internal fault that would be pressurizing the fluid in the wrong direction? Pushing it into the reservoir instead of toward the wheel cylinders?
have you tried just taking the top off sitting in park and having someone apply the brakes while you look? Watch it and see what's doing just in park. Maybe you will be able to see what it's doing and provide some additional clues.
Seems very odd. You say this is for the resevoir for the rear brakes? If you have jack stands and some wheel chalks...try putting the rear end up in the air and put it in drive....apply the breaks and see if it stops them. This will tell you if you're applying any pressure back there or if it's just forcing it out the top.
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Kevin
82' F100 with 460. Wieand Stealth with Holley 750 and Hooker headers.
The fluid expands as it gets warm, that's why you are not supposed to fill it to the top. You have some sort of weird problem if it's pushing all the fluid out of the top though. I believe I would think about getting a new master cylinder. With all this going on, you can't have very good brakes on the truck correct?
have you tried just taking the top off sitting in park and having someone apply the brakes while you look? Watch it and see what's doing just in park. Maybe you will be able to see what it's doing and provide some additional clues.
Seems very odd. You say this is for the resevoir for the rear brakes? If you have jack stands and some wheel chalks...try putting the rear end up in the air and put it in drive....apply the breaks and see if it stops them. This will tell you if you're applying any pressure back there or if it's just forcing it out the top.
While replacing my rear springs, I checked to see if the rear brakes would stop. I placed it in 4th gear and pressed the throttle. I then moderately applied the brakes and the wheels stopped immediately. I didn't have a helper to apply the brakes while I observed the master cylinder, plus I ran out of time to tinker with it last night.
Everyone I mention this to, says they have never heard of this type problem. I may just replace the master cylinder and see what happens.
I had a similar issue with mine except it was completely around the cap seal. Replaced the seal and still had the problem, so I put a couple of dimes between the metal retainer and where it slots on the cap at each reservoir to make sure it was nice and snug. This stopped the leak, so rather than waste a couple of dimes (it is 20 cents after all) I unclipped the metal retainer and adjusted it somehow to have a tighter fit, just can’t remember what I did to adjust it, but it seemed pretty obvious at the time.
One other thing to keep in mind. Eventhough you were able to stop the real wheels, this proves the brake system is functioning, but don't prove it is funcitoning correctly or efficiently.
How well do the brakes work while under load? When the truck is at speen and you need to come to a stop?
You may be putting enough pressure to stop the wheels with no load but if your master cylinder internal seals are leaking by, you may not be pushing enough pressure for full load braking capability and the fluid may just be blowing by the piston seals.
If this is the case then I would recommend replacing it. They do sell master cylinder rebuild kits but for the hastle I just replace it. To rebuild it you also need to hone the cylinder bore to remove any burrs...not worth it in my opinion
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Kevin
82' F100 with 460. Wieand Stealth with Holley 750 and Hooker headers.
First photo is my 81 F100 the day I got him home, after driving 100 miles. Second photo is three months later. He had been in the garage for most of those three months, and I hadn't put even 100 more miles on the engine. I was worried about all that seepage, and a mechanic was concerned that the bladder inside the booster was a goner, causing the brake pressure to do weird things.
Having suffered a catastrophic brake failure in 1980, in which my '56 Olds 88 plunged underneath the rear of a stopped 18-wheeler while doing about 40 mph, I'm a bit of a fanatic when it comes to brakes. I got a new booster from LMC and a master cylinder from Jeff's Bronco Graveyard, around $200 all in. Better safe than sorry.
Yes, over the weekend I removed the cap and observed the fluid as the brakes were applied. The fluid in the front reservoir spewed upward. Just like a glass of water, if you were to blow into it with a straw while it was submerged. Since I had already replaced the seal on the cap, I decided to shim it to make it tighter. I then refilled the master cylinder and drove down the road and back. The fluid is still leaking around the cap but it is not near as bad as before.
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raising experiences.
