My 1989 f350 Crew Cab brakes feel great while driving around with no load but if I put my 24ft travel trailer on back and have to stop very hard I can about put the brake pedel on the floor. Yes the trailer has brakes that work but the truck feels like there is air in the line. I have bleed the brakes and had it done by a shop which did not help. Any ideas out there???

 

Try your brake booster or master cylinder.

 

Thanks Threefiftyone,,
I have put in a new master cylinder but I am not sure how to tell if the brake booster is good or not? The brakes feel fine unless I have to step on the brakes hard such as when towing.
Matt

 

Have you checked the adjustment of your trailers brakes? If they are working but out of adjustment your back to the truck doing the majority of the stopping and will require more effort on the pedal that can make it feel spongey.

 

Even with the truck empty I would be hard pressed (no pun intended) to lock up the brakes. If I push hard on the pedel even when stopped the pedel gets spongy like a bad MC but I already replaced that. Unless you are doing a hard stop the brakes feel normal.

 

Hey Matt did you ever get your answer to your question, I'm having the same problem, I'm thinking i may have drop a spacer from the power brake unit, into the bottom, after i replaced the master cylinder, but am unsure so far.... but my truck is acting the same way, I only have brakes from half of the pedal.

 

No PoolBoy I still haven't figured it out. I went to one of the local Les Schwab tire shops and spoke with one of their guys. We went out to his truck and his did the same thing. (spongy pedel that you could push to the floor). So we are not alone and SOMEONE must know the answer.
Matt

 

Hey Matt,
I found out the problem with my truck was a small rubber spacer which fell to the bottom of my power brake unit, and i had to fish it out to put it in it's correct spot, My guess would be the unit itself, Do you build up pressure in your pedal while the engine is off?

 

I am not sure what you mean by do you build up pressure with the engine off but with the engine off the power brakes go away and the pedel becomes hard to push. With the engine running they feel normal unless I get on them hard.

 

If you engine is running and you remove the vacuum line to the booster and plug the vacuum line, your pedal should be stiff, as if reverting back to having manual brakes, if your brakes engage (granted it will be harder to push your pedal down to stop) then it tells you its a bad booster. But be careful in doing that. My money is on a bad power brake unit.

 

My 94 F-250 does this also. I've replaced the Master cylinder, vacuum booster, rabs valve/selnoid, rebuilt the front calipers, replaced the rear flexible brake line and the brakes have been bleed numerous times. I've lighten my wallet but my brakes have not improved.

I did see somewhere a technical bulletin for heavy duty GM trucks or Dodges don't remember which. It had stated something along the lines of if the front pads are wearing out 4-6 sets to a set of rear brake shoes then a larger brake wheel cylinder was suppost to installed. Also was some mention of trucks which were routinely running at 75% or more of their rated capacity should have this done. I tried to refind the article but have not located it since. Does anyone else recall seeing something along these lines??

 

I am a little late on this thread - my 2000 Excursion has the same problem. I bought it 2 months ago and the brakes were spongy - no grab and you could not get much additional response by pressing harder on the pedal. Basically, it felt like you were towing a couple of thousand pounds all the time. Jam two feet on the brake pedal and it still took its time to stop. Not confidence-inspiring at the least.

I blamed it on the brake pads/rotors. Installed new ones (Ford rotors, best performance friction pads I could get), broke them in properly - and - marginally better.

I towed my 31ft travel trailer (8,000 lbs) this weekend, testing out the new truck. Braking was poor at best, with the trailer brakes properly set up, etc. It is, in my mind, unsafe with this level of braking. My old Dodge Ram 1/2-ton out-braked this thing by a long shot. This doesn't seem right.

Front calipers replaced 20K ago, master cylinder assembly 30K ago (this was done by Ford dealer prior to me as owner).

MattF350, did you get anywhere since your last post? I am searching for answers.

Any insight is appreciated.

Thanks - Norm

 

Although I did not refind the TSB for the GM vehicles I searched the internet and read alot of articles on brakes. There was some very good information on one site which was addressing setting up hot rods and older vehicles which were modified.(Sorry but I did not mark the page or save as a favorite)

The article gave a number of ways to correct braking problems and how the system needs to be balanced between front and rear brakes. I believed this was my problem since the front seemed to brake harder than the rear but the pads and shoes were matched (same compound) and in good shape. I took the plunge and bought larger rear brake cylinders which were a direct bolt in on my truck. Went from a 1 inch bore to a 1 1/8 inch bore. I could not believe the difference. A very positive difference!!

FWIW - My truck is a 94 HD 3/4 Ton 4X4 supercab longbox with a 7.5 L engine. I was always a little hestiant when pulling our 24 foot travel trailer (~6000 lbs) with our four dirt bikes (~900 lbs) in the bed of the truck. I felt like you - it took too dam long to stop even with the trailer brakes set correctly. I also noticed the poor braking when I would be pulling our snowmachine trailer (no brakes on it) the truck just wasn't doing what I expected it to do. When the truck was empty I can not say that I was ever concerned about stopping, but in reality I did not realize the braking was as poor as it was until I changed the brake cylinders. It was also the very cheapest thing that I did to the brakes - go figure. (~$35 for the set at Auto Zone and 45 minutes per side to install)

Hopefully this fix may work for you or others.

P.S. I was a little concerned that my ABS (rear only type) may not work with the larger brake cylinders so I checked it out as best I could be braking hard on asphalt and a dirt road. The ABS seemed to be working on asphalt but I could not tell if it was working correctly on the dirt road. The front and rear wheels would both lock up at about the same time on dirt. My understanding is that the RABs system on my truck is really for a unloaded truck which mine was during this test.

 

OK guys, this is not Ford related but our new 2003 Honda Oddessy had a slow sinking brake pedel and under warranty Honda replaced both the master cylinder and the anti lock brake unit (both I have replaced on my truck) it made the Honda stop like it should. I am not sure were to turn with my truck but it is going down to one of the local brake shops and I am not going to bring it home untill it is fixed because it just ain't right. I will post what I find.

Matt

 

Just an update on the spongy brakes on my truck. It turns out that the NAPA master cylinder I put in was bad so it got replaced with a new F450 master cylinder (bigger cylinder to move more fluid). The brake peddle is a little stiffer but the thing will stop now and that is what I was after.
Thanks for everyones input.

Matt