Wierd brake issue

[1 Patriot-of-many]

Adjusting brakes may not work. The supplier of wheel cylinders for this vehicle chose to use plain-ended springs on the wheel cylinder assembly. Springs without cup expanders. When not used for a time, the cups will leak as there is little tension to prevent weeping.

This manifests as either leaking wheel cylinders if the boots leak OR an initial soft pedal if the leaked fluid is trapped in the boots.

Overhauling the cylinders with proper expander-ended springs will solve this problem.

Where would I begin to find the proper ended springs? I've never rebuilt a wheel cylinder before but if that's the problem I'll certainly learn.

 

[Keith_J]

The wheel cylinders are all the same, 1-3/8" bore. IIRC, NAPA carries them although I don't know a part number. Would like to know since I have another two wheels to service tomorrow and have only one Star-branded overhaul kit.

Since these use DOT 5, there is almost NEVER any corrosion. And it takes 30 seconds with a hone to make them LIKE NEW. Parts pop in, just wet with DOT 5, then assemble. Bolt in, leaving the bleeder open for gravity bleed as you are packing the bearings.

Alternate/OEM Part Number(s): 111624R91, 3004802, 393321C91, 5461612, 592258C91, 66964, 681093, 827223, WCK13644

Possibly NAPA UP-176

 

[Keith_J]

YES!!! Our three days of labor paid off. Perfect brakes over 50 miles of in-town and semi-rural driving in the local Operation Homefront food drive for service members in the San Antonio area. The M35 is mkcoen's, I am the designated mechanic and driver. And I won't drive 20,000 pounds without proper brakes.

Had this problem, soft brake pedal with proper air pressure and DOT 5 level. Replaced one cylinder and overhauled another. Repacked five sets of bearings, sealed all up. Rotating seals were fine.

Next issue to fix is the class 1 fuel leak on the tube from the strainer to primaries. Forklift damage partially crimped the fuel line. There was a class 2 intermittent leak in the cooling system but level didn't drop nor were operating temperatures above 180 F.

 

[1 Patriot-of-many]

How did you determine which wheel cylinders were bad? I see no leaks externally. Do I need to pull all of the hubs?

 

[Keith_J]

Safely? Not possible. IF you can operate the vehicle, power braking until the drums are warm, then working on the cold drums.


Reality? ALL of them. All have wheel cylinders with inferior springs. These are the cylinder springs (wet with brake fluid) with plain ends. Proper springs have ends which expand the cups. These are cones which expand the cups, assuring sealing. NAPA UP-176 should have the correct springs.

The contractors supplying the wheel cylinders used plain-ended springs. Change them along with the boots. 10$ per wheel.

 

[x-ray]

Safely? Not possible. IF you can operate the vehicle, power braking until the drums are warm, then working on the cold drums.


Reality? ALL of them. All have wheel cylinders with inferior springs. These are the cylinder springs (wet with brake fluid) with plain ends. Proper springs have ends which expand the cups. These are cones which expand the cups, assuring sealing. NAPA UP-176 should have the correct springs.

The contractors supplying the wheel cylinders used plain-ended springs. Change them along with the boots. 10$ per wheel.

I replaced did all my wheel cylinders this spring with new OD Iron kits or complete cylinders and perhaps I had the wrong springs - Do we have a pic of the correct spring shape versus wrong? Just my luck - but an easy fix at least.

 

[CobraCDR]

Good information here, thank you everyone for your input.

 

[Keith_J]

I replaced did all my wheel cylinders this spring with new OD Iron kits or complete cylinders and perhaps I had the wrong springs - Do we have a pic of the correct spring shape versus wrong? Just my luck - but an easy fix at least.

OD Iron has the Star brand overhaul kits. The expander springs have cone ends.

The springs causing the problems are just 1" in diameter, about 3" long and a plain cylinder.

The attached image is from NAPA UP-176 is the part and the spring has cone ends

 

[Heavysteven]

Pic of it in the bag

 

[Coal Cracker]

So I'm having the same issue with one of my trucks, pedal goes to about 3 inches from the floor its firm and stops the truck, then as i pump it the pedal stays at the right heigth and is firm but the harder i push on it I hear air coming out of the vent in the engine bay.

I'm thinking air pac rebuild or bleed,, the brakes are all adjusted, and the cyl;s are the correct ones .

 

[doghead]

Airpack rebuild and brake adjustment.

 

[BadMastard]

Can I throw a monkey wrench in? You've got a A3 don't you Patriot? so, you have two brake systems, and I remember something about an adjustment for the two master reservoirs that balances them out. Might just be that.