scottjamison

Hi all, I am still having brake woes with my 68 BB. Below is a history of my travel through brake hell. Any ideas are most appreciated!!!!

I Started with new Wilwood calipers and rotors

• I had them installed at Midas
• When I got the car back, the brakes were spongy
• I bled them like crazy including the MC. Not much improvement so I figured something else in the system was hosed.

Then I decided to just replace everything over the winter when I did the suspension, steering, wiring, engine, and trans.

• All new brake lines, junction blocks, MC, Booster
• I used a standard 9" GM Booster
• I also made sure the calipers were square with the rotors. Perfect fit.
• Even after extensive bleeding, they were still spongy

I decided to replaced MC with Wilwood MC

• I talked to Wilwood's techs and they suggested a 1" bore because I have very low vacuum
• I bench bled it, put it in and bled the whole system like crazy
• Still spongy

At that point I threw my hands up and took it to a shop (not Midas)

• They noticed a small leak from one caliper so I had the garage replace the seals
• They checked the length of the rod and verified it was correct as well. Bled it like crazy again.
• They talked to Wilwood's tech 3 times trying to figure out why it was still spongy but Wilwood just kept saying I should go to manual brakes because my vacuum is so low (5 Hg).
• Still spongy.

So I decided to see if I could easily address the low vacuum as an expirement.

• I bought a vacuum pump and installed it
• It gives me a constant 20 Hg vacuum
• The brakes are slightly better but still spongy. There is nothing the first half of the pedal and they won't lock up even on wet pavement.

At this point, I called Wilwood again. Now they are telling me that my MC (that they SAID to get a 1" bore) is too small and not pushing enough fluid for those calipers (4 Piston all around) and I need a 1 1/8" bore. Then they continued to suggest I go with manual brakes.

I don't like the vacuum pump. Its big and heavy and loud and doesn't completely fix the problem.
My question to you guys is, does this make sense? I am willing to switch to manual and build custom brake lines for it if I have to, but I don't want to go buy yet another master cyl if it is not going to make a difference.



Help!

HeadsU.P.

WOW! Shame on Midas, shame on Wilwood.

So, how many days a week are you going to C3 Brake Therapy sessions? Those meetings never get any smaller now do they? Rumor has it, that they are going to open a wing of Mercy Hospital just for us insane brake jockeys. They will administer an injection of Dot-3 into your arm every morning.

Anyway,
A Spongy Pedal or a Firm Pedal really has nothing to do with the power booster. With the engine off, the pedal should be firm. The power system only assist so that you can use your barefoot pinky toe, to lock the wheels up instead of both feet with iron boots on. The booster is strictly an assist. Either you have a firm pedal or not.
And no, you can not put Viagra into the master. It only works for four hours.

I too, would not want a Vac pump running constantly. However, I wonder if a after-market vacuum canister would help in your situation with only 5" of vac? .
Keep at it, you will get it worked out.

jersey68l36

Verify the line pressures at each caliper. First thing is to ask Wilwood what the pressure is suppose to be, once you know what the pressure value is suppose to be, obtain brake pressure tester, 43237-2 from KK Moon that I seen selling on Amazon for about $100, before changing master cylinders.

Driving with ps with a motor that has low vacuum results in not spongy brakes, but a rock hard pedal, but little stopping power. A spongy pedal means there is still air in the system, You did bench bleed the existing master cylinder? The idea is to obtain a hard pedal then address the problem with low vacuum, such as converting to hydroboost or add an auxiliary vacuum reservoir to feed the existing brake booster.

scottjamison

Ok your Viagra comment just made me laugh out loud in the middle of a meeting at work!
Well done!!!!

Fredtoo

The 1" master is too small for power brakes, it is supposed to be bigger.
Bigger WILL be firmer.

However, you should still be able to lock the brakes.

How new are the brake pads? New pads take time to bed in, and the pedal will firm up as they do.

Can you open the cover of the m/c and see how much pedal travel you have before the compensation posts close?

scottjamison

The pads have about 600 miles on them now.
I will take a look at the MC and see about the posts. I know that when I start pushing the pedal with the MC open, I see the fluid move right away.

ronarndt

I also have a 68 that had a brake problem, although not as severe as yours. jersey68l36 said "A spongy pedal means there is still air in the system". Especially since you replaced everything on your system, there are countless nooks and crannies for air to hang up. It only takes a very small air bubble to affect the firmness of the brake feel. You did not mention the method you are using to bleed the brakes. I found that pressure bleeding worked best for me. Also, if the air is hung up at a bend in the tubing or a rough spot in the casting of a caliper, it may be difficult to dislodge it . I had air in one caliper and finally used the vibration from my air hammer to rattle it loose, while running the brake fluid thru under pressure. You may want to have a helper tap on the brake lines, junctions and calipers to get the last air bubble out. Once you solve the brake firmness you can address the low vacuum issue with the power brake booster. Good luck getting your brakes fixed.

scottjamison

Hi. Thanks for the info.
Yes, I should have mentioned how I bled them. I used a pressure bleeder several times. Pulled the calipers off (back) so I bled them upright, banged on them with a hammer, then the shop I took it to did all of the same several times.

Fredtoo

@ 600, they are bedded in.

When you see fluid moving, that means the piston is moving, but it is not yet pressurizing the brakes.
There should be some "push back" of fluid into the reservoir, but not too much.
Once the piston moves past the compensation port, the master starts to build pressure in the brake lines.

The other thing to look for while you are doing this is to see if there are any bubbles that escape when you lightly push the brake pedal back and forth a little.
If there is air in the master, this action tends to work it out.

HeadsU.P.

H-m-m-m-m-. I think we are on to something here. You took the back calipers off to bleed. No need for that and how did you do that with a steel brakeline attached and what held the pads in place? You are over-thinking the bleeder must be pointed up theory. And I think when you reinstalled the calipers you introduced air again, maybe.

Whats the odds that the pressure bleeder itself is introducing air? Leaky tank, fittings, hose, shut-off valve, lid on the MC, etc?

scottjamison

I didn't have to unhook the lines. The lines to the calipers are braided steel hoses. Not hard steel. They flex. I put a wood block in between the pads when I pulled them off the rotor.

Pressure bleeder was brand new and definitely was not leaking.
I know the vertical part seemed like a reach, but I have tried everything.

HeadsU.P.

On mine, steel line to the rear calipers, rubber hose to the trailing arm.

Also, on your Motive unit. Are you using clear tubing so you can see what's going or not going (bubbles) into the MC?

scottjamison

Gotcha. Yeah mine are rubber from the block to the control arm, then into braided steel.
Yeah, clear tubing from the pump to the adapter on the MC so I can see everything.

SwampeastMike

When replacing the rubber lines all around on my '79 I had similar frustration with a spongy pedal. Did vacuum, brake pedal method and gravity bleeding (I don't have a power bleeder) over a couple of days but the pedal stayed continually soft. At one point the rear half of the master cylinder got extremely low on fluid but I'm nearly positive it never ingested air. When new to me the pedal was similarly spongy, the system was filthy and RF was barely (if at all) working due to a clog. Vacuum bleeding followed by gravity bleeding one wheel at a time and car lifted one side at a time worked fine. I went through at least two gallons of fluid before it ran clean from all the bleeders. From the very first application (which was also the first press) the pedal was wonderfully firm and all the brakes worked perfectly. I had replaced nothing but fluid.

Back to the problem time. Again I worked one wheel (and side) at a time, used only vacuum bleeding until I saw no more air in the fluid. As said before the pedal was crap and nothing seemed to help. After sitting a while there always seemed to be more air. Exasperated I put it up on four stands with the front slightly higher than the rear. I closed all bleeders, removed the master cylinder cover, took out about 1/2 the fluid with a turkey baster and had a helper slooowly press the brake pedal. Sure enough there were bubbles in the stream shooting up from the bottom of each master cylinder chamber. With a bunch of towels wrapped around to keep the fluid from getting anywhere it shouldn't I had my helper continue to slooowly press the pedal again and again as I replaced fluid as necessary, kept the fluid from doing bad things and watched for air bubbles. Once there were no bubbles after a few presses I filled the chambers put on the cover and let the car sit at least 15 hours. I then vacuum bleed about 8 ounces each from all six caliper bleeders in what is often called the "proper" order. I lowered the car, and backed out of the garage. The first press of the pedal was a little spongy and I drove in the direction of the local Corvette specialist who I use on very rare occasion. After that first press the pedal (and braking) have been perfect!

I still don't know what I did wrong (or right) or if my last-ditch sequence will work similarly for you but it may be worth your (and a helper for a short while) time.

------------

Oh. I must agree with some of the previous comments that essentially say shame on the "professionals" who have been giving you advice. I'm far from an automotive braking system expert but I know enough about hydraulics and how power assist works to know that a spongy pedal MUST be due to something compressible (think air) in the system!!!! Very low vacuum in a power system will make the pedal rock hard--certainly not easy! A master piston of too small diameter may not give you enough force at the caliper pistons for good braking but again you won't get a spongy pedal!

NewbVetteGuy

I had a similar experience. There was just no way I could get it bled without a 2nd person. The 2 person method was the only thing that worked and it's worked quickly and consistently.

Adam

Fredtoo

I did some quick math, and the the mater cylinder you have is about 20% smaller than what is recommended.
That means the pedal will be 20% softer (more pedal travel) for an equal line pressure.

scottjamison

I will open up the MC and try it some more when my wife gets back from her trip just to double check again that there is no air (since my twin bro moved back to Phoenix so rudely!!! ).
She loves brake bleeding!!!

0Todd TCE

I don't disagree with the bore size assessment but let's start with a basic question: You don't say but I'm guessing you've fit the Wilwood D8 calipers to the car. When they bled the rears did they (either shop) remove the rear caliper for a moment and bleed it in the vertical fashion rather than mounted on its side? If either shop gives you the deer in the headlight look you've found the problem. You cannot purge all the air without tilting it straight up for the process- air will be trapped in the pistons when secure on its side.

*And no vacuum or pressure bleeding will not be a shortcut to this necessity. You''ll still want to put the bleeder nipples on the top. (and a something between the pads)

JBL Specialty

You might want to see which hole on the brake pedal the booster is in. I think it should be in the lower hole

scottjamison

Yep, bled vertically. Several times.