Technical Soft pedal, would like to use brake hose pinch pliers to check system.

Having issues with getting a firm pedal in my car with four drum brakes. Using silicone fluid, which I know can be a challenge due to aeration of the fluid. But I have been extremely careful while bleeding using low rates of pedal apply, not pumping the pedal, etc.

If I used brake hose pinch pliers at each individual corner, I may be able to isolate the source of the soft pedal by eliminating one corner at a time. If I bought four pliers, I could determine if the issue is in the master cylinder itself potentially by cutting off all four corners?

My concern using the pinch pliers is collapsing the brake hoses and damaging them. These hoses are less than two years old, so they shouldn't be prone to cracking, etc.

Thanks,
Mike

 

If it were my car and you put hose pinchers on the brake lines, I would beat your *** into next week. Figure out a different way.

 

Do they actually make "brake hose pinch pliers"? That is a scary thought. If you drive over your garden hose with the car somewhere down the road it will probably fail. I would expect the same to happen with brake hoses except the results would be a lot worse. If someone had pinched my brake hoses I would replace them.

Charlie Stephens

 

No sweat mate! Just use vice grip pliers.

 

Only 3 rubber hoses, so no way to get to all "corners", unless you have IRS?

Try a Mighty Vac, or spring for a pressure bleeder...you'll get it

 

those will work just fine. Done it before never had a problem. (Obviously if the hose is all cracked and beat up jut change it but u said thy were only two years old) also if u aren't getting any air out bleeding then maybe suspect the master. Have someone step on the pedal and make sure each wheel is "locked" up. Just had this on my impala. Changed wheel cylinders and couldn't get a pedal and had very little pressure while bleeding

 

If you're using a pressure switch in the line for brake lights, it needs to be upside down or the air in it will be trapped and give you a soft pedal.

 

Like another poster said, if you have typical brakes, and no IRS, you can't really isolate the sections of the system as you mentioned. Also, you're making an ***umption that the your soft pedal is being caused by air in the line and by pinching off, for example, a front line, that the air is somewhere between the point where you pinched the line and the termination of the fluid circuit at the wheel cylinder. What's to say there's no air in the system between where you pinched the line and the master cylinder.
You would be well served by not trying to invent your own trouble shooting methods. Stick with the basics:
Visually inspect for leaks. Is the MC bench bled? Observe the hoses in the system while the pedal is being pumped. I have seen "new" brake hoses swell and contract as pressure is applied and then released, yielding a soft pedal. If these three things check out, are you being overly gentle with your bleeding technique? Are you using an ***istant to help bleed? Make sure that the correct bleeding (pump with bleeder closed, hold pedal, crack bleeder, close bleeder, then release pedal) is being employed.
Although pinching off a hydraulic brake hose doesn't really appeal to me (if the hose doesn't get immediately damaged, you may shorten it's service life) I can understand the use of pinch off pliers as a service tool to prevent fluid loss during component service procedures but not as a trouble shooting aid.
While I never understood the use of silicone fluid in a street driven vehicle, if you're concerned about the fluid getting bubbles in it, you may just want to gravity bleed the system if your MC is higher than the wheel cylinders.

 

i would start by adjusting all four wheels tight and see if the pedal gets hard.

 

Thanks for all the replies. Correct, 3 pliers would do the trick, except this is on a '63 Corvette, so 4 would be needed because it does have IRS. The issue is not really a "soft pedal", I should have described it as a pedal with too much travel. The pedal gets firm and I have good braking force, but its close to the bottom of travel (close to where the pedal hits the floor). The intent of the pliers is to isolate which corner could be causing the additional travel. The front seems to be adjusted properly, but the rears are tough because you are rotating the halfshafts at the same time and its hard to tell what's brake shoe contact vs. what's driveline torque.

I am going to try adjusting the shoes again and maybe one more bleed before I try anything else. Thanks again for the feedback.

 

The usual trick in the old days to adjust drum brakes was adjust until the wheel no longer turns. Then back off the front about 5 clicks and the back about 8-10 clicks. It is a bit hard to do with brakes that have self adjusters.
I would adjust yours until tight and check your pedal.

 

Soft pedal? Master under the floor? Lots of fun bleeding. I jack up the rear first high and the the front. Real pain in the ***.

 

If your pedal is hard but low, you have an adjustment problem. Either at the drums or your push rod adjustment at the master. I would do as others have said and adj all 4 drums so they dont turn and recheck pedal height. If its still low then your issue is probably in the pushrod, be careful not to over adj it as you can block the compensating port and cause your brakes to lock up as fluid isnt allowed to return to the resevoir.
Pinching the brake lines isnt an unherd of practice, I dont recommend it but sometimes its the only way to isolate an issue. Rubber has memory and it will return to its original shape, if it doesnt it needs replaced anyways. The issue is with hoses that have a hard plastic liner inside of them. That liner will not go back to its proper shape after being pinched and will cause you an issue, the restriction will cause a slight delay in application and release of that brake. GM usually have this liner.
Hope this helps, good luck

 

What is the bore of your master cylinder? Too small bore will cause excessive pedal travel.

 

Then explain the zillion or so mounted on Ford masters over the years that worked fine. As long as the switch is below the top of the master it will be okay... and no loops or un-necessary joggles in the lines.

I would look for leaks at every connection.. and why are you using silicone fluid? Make sure it is compatible with all your rubber parts.

 

Air rises in brake fluid so the air will stay in the brake switch even if it's lower than the master cylinder. Some of the older switches had a piston almost level with the bottom of the switch and don't hold much air. Some replacements are longer and can hold air causing a spongy pedal. If this is a Corvette it likely has a pedal switch.

 

All of the Ford type switches I've seen have been small. The one that came with my CPP proportioning valve was that style.

 

if you can pump the brake pedal and it gets harder, there is air in the system.