Cylinder Brake Master Leak (1 Viewer)

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Hi,

I have a 1974 FJ40 with a cylinder brake master that has a single reservoir. I noticed that lately the master has been leaking on the inside around the seal. Is this an easy fix or do I have to replace the entire master cylinder? Any help is much appreciated.

Thanks.

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pb4ugo

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You'll have to replace or rebuild it. Rebuilding it would be dependant on the condition of the cyldr bore.
 
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Not sure about AUS, but '74 would be dual res with a booster (here in USA). If you have a single reservoir, now would be a good time to upgrade to double.
 

1911

chupacabra
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Fix it soon if you have a vacuum booster; brake fluid in the booster will rust it out and/or make it fail also.

I have rebuilt master cylinders in the past; it works if you have an appropriate cylinder hone and use it carefully. Nowadays I usually just buy a new master cylinder rather than bother with rebuilding the old one.
 

Pighead

Stop calling it an FJ
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It is a fairly easy fix with the correct rebuild kit and a cylinder hone. I was always able to find a good rebuild kit at my friendly local auto parts store. Hope the same is true for you.
 

65swb45

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You won’t actually know if it’s rebuildable until you disassemble, clean and inspect it. If there is pitting on the cylinder wall, the pits will eat up the piston seals; IOW don’t go there.

If it has the large nut on the front that the brake line screws into, you’re better of cracking the nut loose while the cylinder is still installed. The firewall is the best leverage.😉
 
Joined
Aug 24, 2021
Messages
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Location
Sydney
Fix it soon if you have a vacuum booster; brake fluid in the booster will rust it out and/or make it fail also.

I have rebuilt master cylinders in the past; it works if you have an appropriate cylinder hone and use it carefully. Nowadays I usually just buy a new master cylinder rather than bother with rebuilding the old one.
Thanks for your message mate. The booster actually sits after the master cylinder on my 1974 - how can you test if there is fluid in the booster?
 

1911

chupacabra
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Thanks for your message mate. The booster actually sits after the master cylinder on my 1974 - how can you test if there is fluid in the booster?

No worries! The bad thing is, you may not see many signs until the vac booster begins to fill up with brake fluid and then it will leak out between the union, or in the case of U.S. cruisers with the booster on the bulkhead, out the back and down the brake pedal or on the surface of the bulkhead. The best way to detect it early is to keep a close eye on the fluid level in your master cylinder - there is no reason ever for it to go down unless there is a leak somewhere. Cheers and good luck with it in any event.
 

pb4ugo

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Brake fluid will go down as the brake linings wear. It will happen over time.
 

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