Front brakes not working??

[zzrodder]

Took the Hennway out for an end of season drive, rear brakes started to squeak as coming to an easy stop, also happened last weekend . The old finger on the drum test told me the rears were smokin' hot and the front calipers cool. Obviously the rear brakes are doing all the work, but why? I took off the rear wheels, brakes look good, 6 months old, not dragging, the drums came off easily. Inspection of the front discs also look good, also 6 month old pads, no scoring or weirdness. Master cylinder is full, no leaks anywhere. The entire brake system is 1978 Ford F150. pedal, booster/master, proportioning valve, etc., pedal feel is normal. With a front wheel off the ground, I gave it a spin and pushed the pedal by hand (engine off) and the wheel stops.[S
My primary suspects are the proportioning valve or the master cylinder, but I hate changing out parts on a wild ass guess...
Anyone have an idea how to test these parts to find the problem??

 

[BlueNorther]

that M/C looks like the larger reservoir is closest to the booster, the front brake line should be connected to it, and the smaller chamber to the rear drums.

also you may need an adjustable proportioning valve to turn down the pressure to the rear brakes and work the front harder.

try a panic stop on a dirt surface, the fronts should lock up first.

that type of M/C is notorious for not bleeding all the air out of the the front system, did you bench bleed it before installing it?

 

[zzrodder]

that M/C looks like the larger reservoir is closest to the booster, the front brake line should be connected to it, and the smaller chamber to the rear drums.

also you may need an adjustable proportioning valve to turn down the pressure to the rear brakes and work the front harder.

try a panic stop on a dirt surface, the fronts should lock up first.

that type of M/C is notorious for not bleeding all the air out of the the front system, did you bench bleed it before installing it?

It has been on the road since 2006 with no alterations, working fine 'till now -after seeing your post I just checked it now to make sure the large reservoir is going to the front brakes - yes. (oh boy, that would have been embarrassing!) I honestly can't remember if I bench bled the master after 12 years - it may be worth a shot just bleeding the front brakes anyway. The dirt road test is also good advice, thanks.

 

[redidbull]

First thing that came to mind for me was also the prop valve. Is it adjustable or fixed? With the reservoirs filed that would be the next place I'd looked. Jim

 

[smallfoot]

I believe the adjustable proportioning valve only controls things by being able to adjust flow to the rears. That's the only thing it does on mine.

 

[Old Iron]

Make sure the inside part of the prop valve is still centered.

 

[zzrodder]

First thing that came to mind for me was also the prop valve. Is it adjustable or fixed? With the reservoirs filed that would be the next place I'd looked. Jim

I believe the adjustable proportioning valve only controls things by being able to adjust flow to the rears. That's the only thing it does on mine.

Make sure the inside part of the prop valve is still centered.

It is the original prop valve from the 78 F 150 (can’t see it in the pic, it’s down on the frame). A separate adjustable prop valve added into the rear line would no doubt compensate for the rears grabbing first but does not address the root cause of the problem. I guess I’ll need to remove the prop valve and find a way to test it or just get a new one.

 

[05snopro440]

I think you're on the right track, try bleeding the brakes first and then see how it is. If it's still an issue, then the proportioning valve can be your next target.

I'm wondering if some fluid is bypassing the piston in your master, but that's just a long shot.

 

[Dr Crankenstein]

I would also start with bleeding the fronts. If they bleed normally, you can probably rule out the combination valve and master cylinder...

Your 6 month old pads... are they ceramic? If so, chuck those pads in the nearest orchard, cut the glaze off your rotors and put organic pads in their place. (I'd tell a long-winded story, but I'll wait for your findings.)

.

 

[redidbull]

I too was fooled by the ceramic hype on my Wife's Mustang GT. Never again. Jim

 

[zzrodder]

I would also start with bleeding the fronts. If they bleed normally, you can probably rule out the combination valve and master cylinder...

Your 6 month old pads... are they ceramic? If so, chuck those pads in the nearest orchard, cut the glaze off your rotors and put organic pads in their place. (I'd tell a long-winded story, but I'll wait for your findings.)

.

I too was fooled by the ceramic hype on my Wife's Mustang GT. Never again. Jim

Hmmmm, good question, I don't recall putting in ceramic pads but since I have CRS, anything is possible [S .... going to do the bleed and look at them today - is there an easy way to tell if they are ceramic?

 

[05snopro440]

Hmmmm, good question, I don't recall putting in ceramic pads but since I have CRS, anything is possible [S .... going to do the bleed and look at them today - is there an easy way to tell if they are ceramic?

I've never dealt with ceramic pads, but could you check with a magnet or would that not work?

 

[Dr Crankenstein]

is there an easy way to tell if they are ceramic?

I've never dealt with ceramic pads, but could you check with a magnet or would that not work?

A magnet will stick to the friction surface of a semi-metallic pad, it won't stick to organic or ceramic.

Organic and semi-metallic pads make black dust. Ceramic pads make very little dust... tan or light grey, depending on the manufacturer's "recipe."



By process of elimination...

- If a magnet sticks to the friction material, you have semi-metallic pads.

- If a magnet doesn't stick, you have organic or ceramic pads.

- If a magnet doesn't stick and the dust is black, you have organic pads.

- If a magnet doesn't stick and dust is non-existent (or light in colour) you have ceramic pads.


I have no idea if this post applies to your issue, zz, just sharing a friend's experience and eventual solution, which I should have explained yesterday...

A couple of years ago ,my friend (Brian) bought a very well kept, low mileage, warmed up '80 Camaro Z28. (Black on Black.) Nice car, clean as a whistle, "needs nothing". Brian put some delicate miles on the car (like it was made of glass) and everything was right in his world... a few tours went by and he soon tested its limits... goes like stink... stops like a lingering chili fart...

Brian (a good backyard mechanic) tore his hair out chasing the problem... he went through the brakes over and over again, only to discover he had "brand new" ceramic brake pads that couldn't cut the mustard. "Glass on glass" was his description... pedal feel never changed, but the car now stops like it should on conventional brake pads.

Again, I have no idea if my ramblings apply, just sharing what my friend experienced and the (unbeknownst) easy solution to his problem...

.

 

[zzrodder]

Good info Doc, thanks. I'll do the magnet test / dust exam in the next couple days. Today I bled the fronts, didn't seem to spit out any air but they did take a few goes to get it flowing. Doing it solo with a 2x4 between the pedal and the seat to hold the pedal down so that may have limited the amount of fluid coming out on each try.....
Took it for a 2 mile test drive and did several hard stops (on blacktop) - not able to lock up any wheels but it stopped straight every time and in a normal distance. Front rotors were hot and drums were very warm, nowhere near as hot the other day when they were squealing. So now I'm a bit puzzled, did the bleeding fix it?? I did whack the calipers back and forth while the wheels were off - they seem to be very stiff in their mounts on the spindles. These Ford calipers are held in place with a metal block, spring bar and retaining bolt. I'm wondering if the calipers are just not floating properly on their mounts, not letting them move around as the brakes are applied? Should the mounting points be lubed and if so what is the right stuff?

 

[MercuryMac]

ZZ, your stiff caliper piston suggestion has awakened me. I am changing my wife's Explorer rear brake calipers, because the pistons seized into the calipers. You may be onto something there. Good luck.

 

[akatao]

I have always lubed the slides usually with what is called caliper lube that not being available I have used never sieze .

 

[zzrodder]

ZZ, your stiff caliper piston suggestion has awakened me. I am changing my wife's Explorer rear brake calipers, because the pistons seized into the calipers. You may be onto something there. Good luck.

In my case, it's not the pistons seizing up, it's the mounts that the caliper sits in that is holding it too tightly.

I have always lubed the slides usually with what is called caliper lube that not being available I have used never sieze .

Thanks, I'll check those things out.

 

[BlueNorther]

those are "sliding abutment style" front calipers, these work OK as long as you lube the **** out of them.

I used a EP wheel bearing grease (extreme pressure), along with taking a coarse flat file to the groove and all the surfaces on the caliper and mount touched by the slides and the anti rattle spring ( that funny curved "flat" spring thing).

when lubed and filed clean they only move about .002" - .004" each time you apply pressure.

 

[Dr Crankenstein]

I'm wondering if the calipers are just not floating properly on their mounts, not letting them move around as the brakes are applied? Should the mounting points be lubed and if so what is the right stuff?

You might be onto something and more. Since you posted this thread, I've read and understand a good shock to the combination valve can reset the valve to its "neutral" position, at least until it sees irregular front/back pressure again...

Anyhow, if your calipers were not floating freely, I surmise your "hits" and panic stops freed the calipers and re-educated the combo valve.

When I do a brake job, I slap some anti-seize compound on every metal to metal contact. High-tech geeks may disagree, but I've used common, general purpose anti-seize since I knew how to spell it...

.

 

[zzrodder]

I took BN's advice and took the calipers off, filed, wire brushed and lubed all the contact points between the calipers and mounts - you can see how rusty the mount is in the first pic. I used a specific lube for brake parts, high silicone that won't melt off. things seemed to go back together easier, I'm pretty sure this is where the problem is. Oh yeah, the magnet test confirms they are metallic pads, not the dreaded ceramic.
Naturally, the insurance just ran out end of October, if the rainy weather now hanging around now lets up I'll get a short term permit to get in a couple end of season drives before heading south for the winter.

It occurs to me that when I installed the new pads last season, I compressed the caliper pistons with a C Clamp but did not remove the MC reservoir cap (didn't want to spill brake fluid on the paint.) - maybe it upset the prop valve and now bleeding and messing with things has reset it like Doc surmised [S. Fingers crossed that it's OK now. Thanks again everyone for the advice.[cl