my brakes seem weak !!!! - Ford Forums - Mustang Forum, Ford Trucks, Ford Focus and Ford Cars

351w · 09-15-2003, 19:52

ok guys here is my problem, some of you know i have an 86 F-150 that eats other trucks (89's especially) and quit a few cars for breakfast.
but for the last yr or so i have been thinking my brakes have been a little weak.
so now in an attempt to remedy this i have replaced the front calipers with reman calipers and also replaced the rear wheel cylinders to find no difference so i broke down and bought a reman booster and master cylinder also and still the brakes seem weak, so now after replacing all the components and all the fluid in the system the only thing left is the proportioning valve. is there any way that this valve could be restricting my pressure to the calipers. when the fronts are bled i have no problem drawing fluid out.
more specifically i can lock up the back tires if i jam the brakes on so i know they are getting plenty of pressure and about 3 yrs ago i had jammed on the brakes and locked up the fronts as well.
i have no spongy pedal or problems stopping it just seems that whenever i tow something i have to stand on the brakes to stop and i recently rented a chipper to grind brush and got scared when i had to stop on a hill while pulling that and didnt think i was gunna stop at all. (i even dropped the trans to nuetral just to be sure the engine wasnt pullin)

if i do a line pressure test on the front calipers can anyone tell me what would be a good PSI number to look for.

Aussie Pete · 09-16-2003, 16:41

It sounds more like you have issues with coefficient of friction between the pads and the discs. Have they been contaminated in any way?

351w · 09-16-2003, 20:50

i dont think so AP i put new pads on when i did the caliper change even though i had 8/32 left on them.

SiX_iN_a_RoW · 09-18-2003, 17:43

have they been bedded in correctly? might be worth taking the pads off and giving them a light scuff over some concrete or similar. What pads are you using?

351w · 09-21-2003, 21:03

maybe i should have sprung for the brembo's but i didnt.
i dont know for sure but i think they were tuff stop brakes from the local parts store and i never had any trouble buying from the local places before.
these might have been made in china though and that might be my whole trouble.

Tote · 09-23-2003, 02:27

This may not be applicable to your case but I have heard of a problem with poor brake performance due to a faulty PCV valve which was not allowing enough vacuum to build up in the booster. A quick way to test is to pull the valve and check if idle drops dramatically when you block the hole. Big cams will also have an adverse effect on vacuum at idle.
Regds,
Tote

351w · 09-28-2003, 22:16

yes this is true but i have a smaller cam than stock and a good pcv so the only thing i can come up with is my proportioing valve is partially blocked or something.

Fat F100 · 10-01-2003, 00:36

I vaguely remember replying to a question similar to this before (could have been in the Truck forum), so if I'm repeating myself, too bad.
A mate of mine fitted a '89 model F-350 brake booster to his '79 model F-100 & reckons that this made a 100% improvment on his brakes. Apparently, the shaft was a little bit too long which he had cut down to the correct length & then bolted it straight on. The reason he did this in the first place was that he had a hole in the brake booster diaphragm which was letting the vacuum escape.

89F150 · 10-01-2003, 00:58

Yeah it was the same post by the same person.

351w · 10-01-2003, 22:17

oh well it still adds to the post count.