The what- 1994 E350 7.5L RV

On our last trip I noticed the brakes were a bit spongy. Didn't happen overnight just getting to the point where it's time to do something.

I pull the rear wheels and drums and notice the cylinders are leaking. Put on new cylinders and shoes and bleed the system, back to front.

With the engine off I can get a fairly firm pedal. Once I start the engine the pedal goes to the floor. Still have good pedal with the key on but the engine not started.

Also the ABS light has been on since last brake job 2 years ago.

Master cylinder, booster or ABS gremlins?

thanks

 

Are your brakes of the hydro-boost type?

Leaking wheel cylinders could very well introduce air into the system so bleeding it more than once at all 4 wheels can't hurt.

Engine off and pushing the brake pedal is a meaningless test on a power-assist brake system. This includes key on---without engine running no way you get an accurate feel for what the brake system is really doing.

 

I don't know if they are Hydro-boost. How could I find out?

Is there a bleeder on the RABS unit? I didn't see one.

 

Bleed screws will be located on the individual wheel cylinders or calipers.

Here's a photo of the hydro-boost type unit:



And the typical normal engine vacuum type:



Those are representative photos only, not of your exact vehicle. It will be one type or the other, typically ambulances had hydro-boost.

 

Thanks JWA. Mine looks like the 2nd one (I think). There's and electrical board in the way for a clear view that deals with the battery charging systems. Just checked and it does have the big 12" diameter by 5" drum.

Could a vacuum leak cause an issue here? I get an annoying noise like a foghorn usually at idle after the AC is used. I think it comes from a diverter valve, part# DV-47. I can't find a replacement anywhere.

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Check the back of the Drums for wet spots.....if not wet bleed the system starting from the back....then the front....if it still is spongy it could be the Booster.....OR you have an Internal leak in the Master ( which means you need a new Master ) ...to check that , disconnect the Booster Vaccuum line and plug it ...If pedal is still hard like you know what, then it is the booster....

 

I should have performed your test blageurt. After replacing the master cylinder it appears it is the booster, probably both needed changing. It was obvious after the new cylinder was installed. Removing it was a challenge as will be the installation of its replacement. There just isn't any room under the hood of a van.

It was late so I didn't do a through examination but I did notice the boot was disintegrating. I'm wondering why- brake fluid? age?

thanks for the replies- C

 

Age and use most likely. The more of either and the quicker they wear out.

 

You do know you need to flush every 2 years or so ....regardless of mileage right ? Chitty fluid corrodes the system ..especially the rear wheel cylinders and the Master ( Internally)....

 

......You are lucky you have a 460...try doing ANYTHING on my engine.....I have to remove the Intake just to change the Fuel Filter....remove the Alternator to replace the Glow Plug Relay ....etc...etc....I Have 2 Batteries and alot of other Chit you don't want to know about.......Replacing Injectors is like doing the Brown Acid at WoodStock....You get LOST for a few days ......Trust me ....Don't get me wrong ...I love Diesel...extremeley hard to grenade .....I Still have a 460 ...The last engine I blew was a 460 Van ....I feel you .....Glad you figured it out....

 

Something I learned about bleeding brakes on my e350 the hard way. If your assistant bottoms out the pedal it might distort one of the springs inside the master cylinder causing it to scrape the inside wall of the master and possibly cause drag. The older the vehicle the more likely there are contaminants or rust inside the master that get pushed to the back and hang out only to nick the gasket when bleeding the system because the pedal is pressed farther than when just braking. Once its nicked it allows the fluid to bypass the gasket and the pedal sinks to the floor. The first way to test for this is if the pedal sinks to the floor when depressing it slowly but does not sink to the floor if you press hard and fast then it often means the gaskets in the master are bad. I was not able to find a rebuild kit so I replaced it. I purchased a pressure bleeder set up from summit racing for about $70 so I don't have to deal with that again. I wish I bought the pressure bleeder years ago.