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Apr 6, 2001 | 06:21 AM

78f250

Thread Starter

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Joined: Mar 2001

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master cylinder

Got a 78 F250 camper special. I am losing brake fluid out of the master cylinder from the smaller of the two fluid holders only. I am not sure where it is leaking from but it is all over the master cylinder it's self (both sides, bottom, top etc.) Brakes are great otherwise and pump up nice. Any ideas on what could be going on?

Apr 6, 2001 | 09:53 AM

beartracks

Lead Driver

Joined: Nov 2000

Posts: 6,635

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From: Albuquerque

master cylinder

Are you sure the rubber gasket is properly in place? It covers the top of the cavities completely.

1977 Ford F-100
400m/c6
280,000 miles
Stock on the outside
modified/rebuilt everything

Apr 6, 2001 | 11:16 AM

78f250

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master cylinder

It seems to be in place but I am not sure why I am only losing fluid out of the smaller of the two only. I figured if the gasket was bad, I would be losing fluid from both fluid holders. I am not sure though.

Apr 6, 2001 | 10:10 PM

79f150

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Joined: Nov 1999

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master cylinder

I can help cure your problem. My 79 F-150 does this occasionally ( okay, every couple months ). The leak occurs between the rubber gasket and the top of the master cylinder surface. I take off the lid to the master cylinder and flip it over , the bottom of the rubber gasket ( which should have come off with the lid) will have a kind of scaly rusty build up. Just wipe it off with a little solvent( brake fluid works well) . That's it, no more leak for a couple months. My guess is the scaly build up keeps the lid from sealing well and when you stop and start the brake fluid sloshes out between the brake fluid reservoirs and the rubber seal. I hope this works for you as well as it did for me . I thought my new master cylinder was leaking right through the casting until I tried this. Have a good one, Alan

Apr 7, 2001 | 05:20 PM

rlehman

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Joined: Nov 2000

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master cylinder

My 74/F250 was doing the same thing. I installed a rebuilt master cylinder, same thing now it was comming out of the other resivoir, took that one back, installed one more, problem solved. I think the internal seal was bad in both so pressure was going the wrong way. Brakes worked with both previous ones but much better with thew good one.

So the short ans is, you have a bad mater cylinder.

Bob

Apr 9, 2001 | 06:37 AM

78f250

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master cylinder

Changed out the seal on the lid and that seems to be doing the trick (so far). I'll keep an eye on it. Thanks for you help.

Apr 9, 2001 | 01:08 PM

weldman

Fleet Mechanic

Joined: Feb 2001

Posts: 1,290

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From: Toronto, Canada

master cylinder

Mine is leaking as well, will try a new top seal. Mine is also leaking where it bolts on to the booster. Is there a seal there that can be replaced or does it mean a new master cylinder? I will try tightening the nuts that bolt it onto the booster to see if they are loose as well.

Matt
1978 F250 4x4 - 351M