'93 Ford E350 - Master cylinder bore size?

The E-450 has a 14,500 GVWR, while the F-53 GVWR is 17,000 or more pounds, so you DO NOT want to change to a F-53 brake system.

Does your motorhome have rear drums? Someone on Rv.Net wrote in about getting the rear brake pads installed on the wrong sides, so the rear brakes where not working properly.

Spoungy brakes are normally caused by some air in the lines, or a bad flex line on one of the brakes. There normally are flex lines on each front tire, and between the rear axle and the frame, to allow flexibility in bumps, and front tires are longer due to them turning.

I would first have someone purge the brake fluid. Get a quart of Ford motorhome brake fluid. The stuff for the 24,000 GVWR Ford motorhomes has the very highest "wet" boiling point. You want the highest possible wet boiling point, so that if the brakes get warm, and some moisture in the brake fluid boils (it will become really spoungy or the pedal can go all the way to the floor) then you can lose all your brakes - and have to coast to a stop.

You can use a service like Jiffy Lube to flush out the brake fluid. I would supply them with the brake fluid, so that you know it is the highest quality, and highest possible wet boiling point. And it only costs about $15 at Ford to get a quart. Do not use any 'old' brake fluid, that might have been open more than about 3 hours. The brake fluid used at Jiffy Lube is probably been open more than a few hours.

Normally your brakes should be strong enough to stop your RV in about 100 feet.

Good luck!

Fred.

You're right, Ryan, haven't seen you here in literally years. We spoke on the phone. About a miss I think. Bear in mind that 1993 Class C chassis was only E350. The E450 and predecessor called E-Super Duty didn't come out for another half dozen years.
The physics gurus might correct me, but I believe that MORE diameter in a brake cylinder piston will result in LESS output pressure, not More, given that the linkage and booster provide the same pressure to that piston.
...Is a pic of what RockAuto.com shows as the OEM Motorcraft replacement for your master cylinder. E350 from 1990-1996. I look at Rock because they list a wide variety of parts for an application. That's "1-1/8" cast into the side of the cylinder in the picture. Other sources I looked at showed same size in the few cases where Diameter was included in the detail. Rock shows BRMC38 as its Motorcraft replacement part number and F4TZ2140BD as an alternate number.
I don't think Diameter is the issue. If not, what DO I think? What comes to mind:
1. Nature of Beast. Our 2002 E-FOUR-50 (that uses a hydroboost brake, not Vacuum like 1993 E350) has a crummy-feeling brake pedal that stops simply great when driven.
2. Contaminated Brake Fluid. A thorough (perhaps professional) flush, fill, and bleeding might yield some results.
3. Ryan's Beast has rear DRUM brakes. Are they working properly and adjusted up to the drum surface like they oughta be? The way we drive a motor home doesn't lead to enough stop-and-go, backward-forward, maneuvers to let the self-adjusters do their job.
4. The Brake HOSES may have deteriorated to the point where they expand a little under application pressure. If you don't have record of them being replaced, new ones might tighten that pedal feel up. There's a Hose to each front brake and one to the Rear axle. Your question makes me think about something I've noticed. Sometimes when the brake's applied, the hose will "jump" a little. I wonder if that "jump" means the hose is changing size (getting longer) with pressure. Any distortion in the hose is going to show up as softness in the pedal. I've seen this "jump" happen but didn't wonder till now if it ties to softness or loss of pedal.
5. Take the Diameter question to the parts counter at a large FORD dealership. A NAPA store as an alternative. Try to pick a time they're not busy and can spend time with you.

Good to hear from you, Ryan. Hope you've been well, call if I can help. Have a Blessed Christmas!

Hi j-d,

Yea, it's been a while. We have only used the coach once in the past year and a half (had our first grandchild and some other transitions - been a very hectic year, 2 years). Took it out a month ago and noticed the pedal seemed worse, so I have started looking in to it again. A friend and I just 'bled the snot' out of the brakes - RR, LR, ABS valve, RF and LF, in that order. Got some air out of the ABS and the front brakes and I have a better pedal- not GREAT, but better. I have yet to take the coach out and drive it, but I'm going to try and do that tomorrow or Wednesday. We are planning on taking the family home (Oklahoma to Ohio), over Xmas, and so I just wanted to check things out.

I'm thinking its a bad ABS valve - been reading a lot about that causing a soft pedal. I'll try and post back as I go along. The brake lines look, and feel solid, but I know that can be misleading...

Take care - and thanks! Merry Xmas!

Ryan

I have an '85 E350 and my brakes are very soft as well. Takes both feet on the pedal to stop it quickly. I had the entire system replaced...shoes, drums, pads, rotors, master cylinder, booster, new fluid....and still soft. $3000 and no difference :( I have sadly learned to live with it.

I feel your pain, remembering doing all that on our '83 E350. I didn't pay anywhere near that as I bought parts to do the front, booster and hoses myself. A friend helped with the rear. OK I actually helped him... I really thought we had it licked when we found the rear cylinders so stuck that new linings never wore into newly surfaced drums. Installed new shoes, cylinders, hardware kit, and wheel seals. Even then braking was not significantly better, rebuilt MC and Booster and all. Replaced front rotors, calipers and pads...Again. First time I did the front I didn't replace or resurface the rotors. This time...not significantly better.

Back to the later models, 1992 and up. A new (2008 or newer) take-off axle from a 4*4 retrofitter WILL upgrade the braking. I did that project in my driveway with zero assistance till it was time to bleed the brakes. Really not difficult and it's a super upgrade.

Ryan,

I looked at our master cylinder and couldn't see if it had a diameter on it. According to RockAuto's lookup, it's 1-5/16" (shown in some places as 1.3125" same thing). But ours has HydroBoost, not Vacuum Boost, and so does the F53 Class A chassis.

You may find this article interesting. It discusses the relationships between MC diameter, caliper pressure, pedal effort, pedal travel.

RockAuto includes a listing of which vehicles a given part also fits. It showed some E350's, even a 150, and various years. The thing I didn't like was that the "will fit" lists were not the same, meaning that one of the MC's to replace our 2002 with 1-5/16" bore would fit more others than another MC from the same listing. There were also some notes about "with HydroBoost" and I don't believe HB came out till the E-SuperDuty (basically the E450 till Ford decided on how to badge their vehicles) in the late 1990's.

If you look up "Ford, 2002, E450, V10" you'll see where they're closing out a 1-5/16" MC for $30-something. If you want to try it... I think you'd get a higher pedal with less travel but more pedal effort than you'd like.

Article above shows a company called Vanco that offers HydroBoost retrofit kits. Instead of Engine Vacuum, it works off an existing Power Steering Pump.

I'm into a big project right now so I gotta bolt. Call, PM, email me if I can help.

Drum brakes need a larger diameter M/C. Even though kit makes less line pressure than a disc-brake M/C, the drum brakes need the additional volume.

That said... before blaming the M/C entirely, bake sure the rear shoes are adjusted properly. Out of adjustment shoes cause more pedal travel. They are supposed to self-adjust, however that hardware can rust up, and most Motorhome drivers never brake hard enough in reverse to "click" the adjuster anyways.

And X2 on J-Ds recommendation for a new front axle. I did it on my van. in 2009. The older brakes are pretty weak compared to the '08+ axles, and they also come with better suspension bushings, and will take care of likely worn out ball joints.

Yo! Bryan! I found that 2008+ models use a different MC than my 2002, and I wondered how that would work out with the new brakes that came with the 2012 axle. I didn't notice any issue, and now I see that both MC's are same diameter. That suggests that the new brakes don't know they're working with an older MC...

And...Brakes, I got that second rear caliper replaced. And you're right, a brake issue on a vacation trip s___s, but if I can correct it and don't have to be towed, I call it a "W"!

Thanks for all of the replies - no one has yet to comment on my bad ABS hydraulic valve theory. I have found several troubleshooting procedures, but I'm not sure if I should proceed.

I found this link with all kinds of information and a suggested procedure for testing the ABS valve.

Kelsey-Hayes RWAL Antilock

One other thing - if my emergency brake is working fine - and it is - does that indicate that my rear shoes are adjusted properly?

ryan

By all means, test RWAL if you think you can. As a '93 chassis, diagnostics are OBD-1, and I believe there's a limited self-test you can do. We've had two Aerostars, '92 and '97. One was OBD-1 and the other is OBD-2. I haven't had occasion to try and test either, but I did have a Vehicle Speed Sensor (VSS) to bad on the '92. It took out ABS, Speedometer, Cruise, and Overdrive.

I scanned the article and it seems that if RWAL has electronic/electrical failure, it'll report the problem. But hydraulic failure, not so much. Good luck with that.

Does it also have a Proportioning Valve? Our '83 E350 did, and I replaced that too, in search of better braking. But it did not also have any form of ABS... I believe Front Disk/Rear Drum needs a proportioning valve but Four Wheel Disk does not. Belief could be wrong...