Trouble shooting "squishy brakes"

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Active member
Jul 25, 2019
1993 F53 Super duty Ford chassis. Brakes went limp on my last voyage and I am worried about a leak or something. Brake fluid is within normal levels in the reservoir. Brake pads and rotors were replaced 2 years ago with only minimal RV usage since then.

What other steps can I do to troubleshoot this issue?
How old is the brake fluid? Did the brakes get soft after a lot of using them? Older brake fluids were prone to absorbing water and when that happens if the brakes are used heavily it can heat up the fluid, causing the water to change into steam and make bubbles in the fluid, thus less/poor braking and in extreme cases, no brakes. Are you talking about the previously mentioned F53 chassis? Ford 460 engine?
I have been working on cars since about 1970 and in the past never gave any thought to fully flushing a brake system. After acquiring my 2003 RAM 2500 in 2018 I realized the brake fluid was dark and probably needing flushing. Only recently did I finally purchase a decent pressure bleeder system and adapters to assist me in doing a good job.

I did my 2004 car for practice and then the RAM knowing it needed brakes and I didn't want to contaminate new calipers and hoses with old fluid.

The first flush of the RAM was some really nasty fluid. The brakes worked noticeably better after that, and of course really good after installing new calipers, pads, rotors and hoses and doing a second flush and bleed.

It appears that the '93 F53 chassis was equipped with a Hydroboost power booster rather than a vacuum booster. Hydroboosters rarely fail but you want to keep fresh, clean power steering fluid in the system also, and the booster or power steering system could also be giving trouble.

Given the age of the motor home, I would consider all new hoses (old ones can balloon under pressure, causing weak brakes) and a complete flush of the system.

There are basically two ways brakes get Soft. but with modern disc brake systems one of them should not be possible.. The advice above is excelent (Flush the fluid)

Brake fluid is "Hydroscopic" if I spelled it right (Absorbs water) and when it gets hot water turns to water vapor which is highly compressable so the brakes get "Soft"

(The other method. my original towed, a 1992 Chevy Lumina APV, had old fashion drum brakes on the rear. Drums were WAY WAY out of spec.. Dealer with "Factory trained" brake man could not figure it out.. I however have the advantage of having worked on brakes and different training.. Finally mentally visualizing the system figured it out. Went to Tire store and gave them one special request "mic The Drums" that fixed it.
Just to add to Johns post, a 1993 F53 might have rear drum brakes, I am not sure, I know that vintage Chevy had both rear drums and rear disc brakes as an option. As a general rule RV brake fluid should be fully flushed every 3 years, keep in mind that RV's tend to sit for long period of time. I also second replacing all the rubber brake hoses if that has not been done in the last decade.

p.s. If you put pressure on the brake pedal and keep applying pressure it steadily sinks down, then you have a problem with the seals inside the master cylinder.
Squishy brakes is a hydraulic problem. Typically either moisture or air in the lines, but any contamination would likely do it. I'd start with a flush & new fluid, which of course also "bleeds" the brake lines. If that works, great, but watch for the problem to slowly return if there is leakage somewhere in the system.
1993 F53. has four wheel disc brakes.
Power brake boost comes from power steering pump, anyway it did on our 1992 F53. ( which by the way went 25 years on the same brake fluid without any problems.)
I’d suggest you investigate the power brake system..
I would start with a brake fluid flush. Then if no improvement, replace the couple of rubber brake hoses. Both things are maintenance items, especially at that year, so no money wasted.
Another problem may be the rubber brake lines to the calipers or wheel cylinders. After time they, they become soft and swell under pressure.
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