Archived Brake Pedal to Floor !!!

[R C Cola]

Coming down the mountain this AM and pedal all the way down as I pulled up to the stop sign. Raining hard, with trailer, litely loaded (16000 gross) yes that is lite for me. Trailer brakes stopped me! This is not a new problem. So far, new pads and shoes, new rotors, master cylinder changed 3 times, booster twice, flushed 3 times, crops up intermittenly. ??? Mechanics are stumped, but I haul commercial so this has to be dealt with. I did not want to lose the load I was carrying as the customer would have a cardiac if we lost his 1950 (about) Chev 3 window fully restored pickup. I appreciate any input you can give. Thanks... . R C

 

[Forrest Nearing]

man, I'd replace the calipers and rear wheel cylinders... and probably all the soft lines too!! shouldn't cost you more than a couple hundred bucks... if it happens after that, I'd sell the truck, it's cursed



maybe the prop valve too?



Forrest

 

[Paychk]

What kind of master cylinders? rebuilt or new? I had a problem and the 4th one (new wagner) fix it, all the others were remans.

 

[B.G. Smith]

Brakes

If the pedal goes to the floor and you are not losing fluid, it is still the master cylinder. bg

 

[R C Cola]

Brake work

Rear wheel cylinders are new. The most recent master cylinder is new from NAPA. At this point I am wondering about soft brake lines and or anti-lock.

Not a mechanic so I have to listen, learn, and think over. Thanks ... R C

 

[B.G. Smith]

Brakes

There is no provision for the anti lock system to return fluid to the master cylinder. If you had a brake line soft enough to allow the pedal to go all the way to the floor it would swell up the size of a golf ball. There are two piston/cup seals in the master cylinder, one behind the other. For the pedal to go all the way down from a normal position, both piston would have to bypass fluid. A caliper or wheel cylinder would have to leak fluid to the outside (It could be trapped in the dust boot for a while). The booster has nothing to do with the fluid except assist in pressurizing it when you apply the pedal. In your sig it indicates a 3500 with SRW, is that a 03? I thought they had disc all the way around?? bg

 

[keimmmo]

Does your truck have rear anti-lock brakes? I had a similar problem on my 92 when the anti-lock cylinder failed.



Steve

 

[Paychk]

If it is a "350" that would be a 1st. Gen. truck

 

[Paychk]

The most recent master cylinder is new from NAPA.

I would source a NEW AMERICAN MADE cylinder, such as Raybestos, Wagner, Bendix, Kelsey Hayes.



PS Most have value lines of parts, that is a code phrase for Taiwan or Chinese parts.

 

[dseabaugh]

my truck has done that a couple of times in 80,000 miles in panic stop situations. It has had new mastercyliner, etc. too. The only thing I can say is the second time you press the pedal it is good. It has never done it any other time and both time s were when I had to hit the pedal quick. It is kind of unnerving. Good thing I keep good trailer brakes.

 

[R C Cola]

BG

That is a 91 350 and I think anti-lock on rear only. R C

 

[Hemiless]

Like B. G said if you are not losing fluid it has to be the master cylinder bypassing internally. Or the master cylinder piston is sticking in the cylinder giving the pedal free travel and no brakes.



Best of luck to you but I wouldn't haul any more loads with it or even drive it till you have the problem fixed. It would ruin your life and someone else’s life if you were to kill or injure someone because your brakes failed. Especially if you knew about the problem ahead of time then that would be negligence plan and

 

[53 Willys]

I just went through this. After the third master cylinder I finaly found a bad front wheel bearing. Caused enough runout to make the pedal go to the floor ocasionally.

 

[R C Cola]

Brakes

53 Willys

Bad front wheel bearing, wow now that is a strange combination for symptom-problem relationship !

I just checked the fluid and the large reservoir is slightly low... I think I better look hard for leaks in the system. That pedal problem has been with me for a while and I just assumed it was back again. ... ..... R C

 

[dslmacdown]

If you have ABS check the controller. Sounds like a bad dump valve, years ago I had a Chevy that replaced the master cylinder four times and couldn't get rid of a spongy pedal. Changed the ABS controller and fixed the problem, the dump valve was leaking.



MAC

 

[dseabaugh]

Another possiblility is that you have a bad wheel bearing allowing the rotor to wobble with the hub. This would cause excesive clearance between the rotor and pad and would cause the condition you have described.

 

[B.G. Smith]

53 Willys

Bad front wheel bearing, wow now that is a strange combination for symptom-problem relationship !

I just checked the fluid and the large reservoir is slightly low... I think I better look hard for leaks in the system. That pedal problem has been with me for a while and I just assumed it was back again. ... ..... R C

What he is talking about is the rotor running out of round so bad that it compresses the piston in the caliper far enough that it takes all the pedal travel to get it back to the pads. Of course, in a situation like that, if the master cyl. is full, it would force fluid out at the cap. With the engine running, try pressing slowly on the brake pedal until it gets solid, then let up slightly but not enough for the pedal to return to the top, then press again slowly, if the pedal continues to go lower, good indication of leak, if master cyl. stays full that is where ther leak is. bg

 

[bmoeller]

Short vesion- Check rear shoe adjustment.



Long version- Had a braking problem with a C-70 Chevy grain truck. Pedal would to the floor on the first try usually. Had to pump it it once or twice more to get a good pedal. What it was, the brake shoes were not adjusted up tight. Had 3 wheels adjusted, but the adjusters were stuck on the other wheel. Once the last wheel was adjusted up, you had pedal on the first shot.

 

[keimmmo]

On my '92 with rear only anti-lock brakes, the anti-lock cylinder went bad. I am talking about the cylinder on the driver's side inside the frame rail just behind the rear end. Acted just like a master cylinder with an internal leak. I replaced the master cylinder with a good quality NEW cylinder and there was NO change!!!



I had a big load on and needed to get down the road. To verify that the valve/cylinder was the problem, I bypassed it with brake tubing. Solved the problem, but I had no anti-lock. I ordered and replaced the cylinder ASAP.



I have seen this problem on other vehicles too. It is not unheard of! However, it usually is not even mentioned in shop manuel trouble shooting guides as a possible cause of a brake pedal "falling away".



Steve

 

[R C Cola]

Anti-Lock

Steve..... You may be on to something. I will check this out first thing in the morning. I plan to top off with fluid ( it is down a little). Check carefully for leaks. Then bypass this valve. As I understand it the brakes work fine without it but might lock up if I get on them too hard. All the older vehicles I grew up with were that way and I learned to ease up on the pedal to get them to not lock. I am in the boonies now (on vacation) and can replace the valve when I get into a larger town. I also need to research and see if the wheel cylinder change some of the guys are doing will be of benefit to me.

I think they are going to a larger wheel cylinder (not sure) and getting better brakes on the rear end. Right now I have the 3" shoes on the rear with the single rear wheel. R C