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| | | | Joined: Dec 2025 Posts: 2 Moderated | | Moderated Joined: Dec 2025 Posts: 2 | I have a 1950 2 ton dump truck with a Bendix Series 42 hydrovac booster that was recently rebuilt. I asked the vendor to rebuild the master cylinder but they said it was too far gone and replaced it. We installed the booster and master and got the brake system bled then used the truck for a handful of material runs.
The master cylinder has leaked varying amounts of fluid into the boot at the push rod since reinstall but the brakes worked fine until they locked up on my last run; it seemed like the check valve may have locked up. Relieving pressure on the line at the booster from the master allowed me to get home. We're re-bleeding the brake system following the Chevy Truck Shop Manual. We continue to get air bubbles during the bleed and fluid leaking out of the boot at the push rod.
Thoughts? Would the leaking fluid indicate a bad seal in the master cylinder? | | | | | Joined: Apr 2005 Posts: 2,097 'Bolter | | 'Bolter Joined: Apr 2005 Posts: 2,097 | Yes, if fluid can get out, air can get in.
Some of the offshore made products have serious quality issues.
Brakes are not something you want to guess about.
Fred
Last edited by rfs56trk; 04/23/2026 10:02 PM.
1956 3100 Pickup/Red/350/3sp OD/PS/Disc Brakes
1957 Bel Air Sport Coupe/Red/355/TH350/PS/Disc Brakes
2017 Silverado LT Single Cab SB/Black/5.3/6 Speed Trans
1947 Willys CJ2A w/F-Head engine
| | | | | Joined: Feb 2016 Posts: 1,987 'Bolter | | 'Bolter Joined: Feb 2016 Posts: 1,987 | Return the new master for a full refund and find a different brand.
1957 Chevrolet 5700 LCF 283 SM420 2 speed rear, 1955 IH 300U T/A, 1978 Corvette 350 auto, 1978 Yamaha DT175, 1999 Harley Davidson Softail Fat Boy
| | | | | Joined: May 2015 Posts: 11,052 Housekeeping (Moderator) Making a Stovebolt Bed & Paint and Body Shop Forums | | Housekeeping (Moderator) Making a Stovebolt Bed & Paint and Body Shop Forums Joined: May 2015 Posts: 11,052 | The brakes locking up may be caused by the pedal pushrod being adjusted incorrectly without adequate end play.
But like the other guys said - send the master cylinder back and replace it. It should NOT leak into the boot area.
Kevin 1951 Chevy 3100 work truckFollow this saga in Project JournalPhotos 1929 Ford pickup restored from the ground up. | 1929 Ford Special Coupe (First car) Busting rust since the mid-60's If you're smart enough to take it apart, you darn well better be smart enough to put it back together. | | | | | Joined: Feb 2004 Posts: 29,780 Kettle Custodian (pot stirrer) | | Kettle Custodian (pot stirrer) Joined: Feb 2004 Posts: 29,780 | The original master cylinder can be sleeved with brass or stainless steel- - - - -I hope it didn't get discarded!
Jerry
"It is better to be silent and be thought a fool than to speak and eliminate all doubt!" - Abraham Lincoln
Cringe and wail in fear, Eloi- - - - -we Morlocks are on the hunt!
There is nothing noble in being superior to your fellow man; true nobility is being superior to your former self. - Ernest Hemingway
Love your enemies and drive 'em nuts!
| | | | | Joined: Dec 2025 Posts: 2 Moderated | | Moderated Joined: Dec 2025 Posts: 2 | Thanks for the feedback! My first inclination was that I did something wrong with the master cylinder. I'm not convinced that the leaking master and the locking brakes are related. But I'm new at all this! | | | | | Joined: Oct 2005 Posts: 4,252 "Hey! I sound like Darth Vader!! | | "Hey! I sound like Darth Vader!! Joined: Oct 2005 Posts: 4,252 | I currently have a leaky master out of one of my projects, at this place near me, for a stainless sleeve. For me it's a one and done. I maintain a '46 International US Marine WWII Maintainer, most all the wheel cylinders and master leaked. 20 years ago, I brought an axle worth of wheel cylinders for sleeving to this place. The thing sits and is maybe operated once a year. Not a drip since. Everything is done minus one of the three axles. I'm sold! Find someone near you that will sleeve your original master, since originals are less junky than late model versions. If you can get your original back!! Karp's Brake Service | | | | | Joined: May 2015 Posts: 11,052 Housekeeping (Moderator) Making a Stovebolt Bed & Paint and Body Shop Forums | | Housekeeping (Moderator) Making a Stovebolt Bed & Paint and Body Shop Forums Joined: May 2015 Posts: 11,052 | The misadjustment of the pedal to master cylinder pushrod will close up the relief hole in the bottom of the brake fluid reservoir. If that happens, fluid can't get back into the reservoir when the pedal is released and will eventually lock up the brakes. It shouldn't cause the master cylinder to leak.
Kevin 1951 Chevy 3100 work truckFollow this saga in Project JournalPhotos 1929 Ford pickup restored from the ground up. | 1929 Ford Special Coupe (First car) Busting rust since the mid-60's If you're smart enough to take it apart, you darn well better be smart enough to put it back together. | | |
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