Cannot get a firm pedal in my "67 after trying all bleeding methods

[Joseph E.]

Manual brake car, rebuilt and sleeved MC, ss sleeved calipers, new rubber lines from frame to calipers, DOT 5 fluid, no air coming out in the bleed lines. I've used all methods I could find in the archives to bleed the brakes on this car but none have provided me with a firm pedal. The master cylinder was bled before being installed on the car. There is no air coming through the bleed lines when the valves are opened yet I still have a pedal that will go to the floor with a moderate amount of effort. I disconnected the connection from the MC to the brake light switch and plugged the MC with steel plugs. When I stepped on the pedal, it moved a very small amount and then was as solid as a rock and would not budge. The lines were connected again from the switch to the MC and the system was bled but the pedal is still soft and will go to the floor with little effort. All connections are tight and leak free with no fluid coming out of any of the hard line connections, rubber line connections or the calipers. There are no drips or puddles of fluid under the car anywhere.
I've bled about a dozen brake systems on the vehicles that I own over the years and have never encountered a situation that has me this stumped. I keep coming back to the MC. Is it possible that the MC is bypassing even though the pedal was rock hard when the MC was isolated from the from the rest of the system? Any suggestions would be most appreciated. Thanks.

Joe 45420

[Stephen L.]

Re: Cannot get a firm pedal in my "67 after trying all bleeding methods

Joe, I had a similar problem on a MOPAR. I did multiple bleeds and each time thought I had all the air removed. As it turned out the calipers were switched right to left during installation and the bleeder valves were not at the top point of the caliper. They did bolt right into the caliper mounts. Maybe you have a similar problem. I don't recall if a corvette caliper can be mounted incorrectly as its been awhile since I did my corvette brakes.

[Joseph E.]

Re: Cannot get a firm pedal in my "67 after trying all bleeding methods

Stephen,

Thanks for the reply and I'm not sure that corvette calipers can be switched and installed on the wrong wheel. Anyway, the bleeders on all four of my calipers as installed on the car in are at the top and highest point of the caliper. I was looking through the archives and found comments about the Motive Products power bleeder. Does anyone have opinions regarding this system or pressure bleeding a C2 system filled with DOT 5 fluid? Thanks again.

Joe

[Ray G.]

Re: Cannot get a firm pedal in my "67 after trying all bleeding methods

The viscosity of the DOT 5 is much thicker than organic DOT 3 brake fluids. It takes much longer for the bubbles to rise to the top in the lines and calipers. Actually takes several sessions with a few hours between each.
We install 1/4 transparent tubing on the bleeders, making sure those transparent tubes go up as they leave the bleeders before draping down and dripping into a container.
Open one front and one rear bleeder at the same time and observe the fluid exiting. If there was DOT 3 in the system before you started it will be mixed with the DOT 5. The mixture will not harm the system.
Rapid movement of the brake pedal will create bubbles also.
If The fluid does not flow from a particular bleeder, use normal bleeding procedure but only push the pedal down one time. Do not pump the pedal.
my .02

[Joe R.]

Re: Cannot get a firm pedal in my "67 after trying all bleeding methods

Joe,

There are two bleeders on each of the rear calipers.

Hope you found those.

JR

[John F.]

Re: Cannot get a firm pedal in my "67 after trying all bleeding methods

I had the same problem bleeding my 67 years ago. Then someone told me to wrap the caliper with a towel and pound on it with a rubber mallet while bleeding. Where previously there were none, when pounding there were bubbles in the tubing. Even with this method, it took the wife and I several iterations with a day or two between to get a firm pedal.

[Domenic T.]

Re: Cannot get a firm pedal in my "67 after trying all bleeding methods

Joseph,
I did my 67 back in the 70's and had exactly the opposite problem (pedal to firm).
I made pressure bleader and bled from the bottom up pushing the bubbles up. I recovered the dot 5 at the master cylinder and re used it to do the other lines with no waste.
I didn't like the feel of my pedal (to hard).
My brakes are manual and I think power brakes would have had a softer feel. But the power bleeder is the only way we bleed brakes here and it only takes one person to operate.

DOM

[Paul S.]

Re: Cannot get a firm pedal in my "67 after trying all bleeding methods

Stephen,

...I was looking through the archives and found comments about the Motive Products power bleeder. Does anyone have opinions regarding this system or pressure bleeding a C2 system filled with DOT 5 fluid? Thanks again.

Joe

Joe, a Motive Powerbleeder does not play nice with DOT 5--while some have said you can use a Motive Powerbleeder at low pressure, it did not work for me. At 5 PSI which is barely more than gravity bleeding I continued to see tiny air bubbles in the flow from the bleeder screws. I ended up bleeding using gravity bleeding followed up with the two man method. I got all the air out and a firm pedal (on a power brake 67) although not quite as firm as DOT 3/4.

I agree with the advice to use a mallet and pound on the calipers to force air out. I used a rubber mallet on mine. Stephen, I assume you are not finding a leak anywhere.

Finally, did you bench bleed the MC, thoroughly?

[Stephen L.]

Re: Cannot get a firm pedal in my "67 after trying all bleeding methods

Joe, On the MOPAR I was referring too, the calipers can be mounted mechanically on either side of the car; however, the bleeder screws were not at the upper most location in this position and I didn't notice that. After I corrected that problem, I was able to successfully bleed the brakes with DOT5 using a handheld vacuum pump. My 67 Corvette also has DOT5 fluid and there were no problems bleeding that system using the 2 person procedure, so in my opinion either procedure works.

[William F.]

Re: Cannot get a firm pedal in my "67 after trying all bleeding methods

You're making it hard on yourself by insisting on using DOT 5. A lot of previous threads don't think there's any advantage, and as you see, problems with getting all the air out.

[Al R.]

Re: Cannot get a firm pedal in my "67 after trying all bleeding methods

Joe, I've been fighting this off & on since Feb. I finally contacted CSSB, whom I bought the MC from. They told me to raise the rear of the car up high enough, so that the front of the MC pointed downward and then rebleed and to insert a small wire in the smaller hole in the rear reservoir to release any trapped air. Might try this to see how it works. Didn't for me , so they sent me another MC. Will try installing it this weekend and see how it works. Will let you know. You can PM me for further clarification on the bleeding if you wish.

[Joseph E.]

Re: Cannot get a firm pedal in my "67 after trying all bleeding methods

I have DOT 5 in all of my cars and have never encountered such difficulty in bleeding the system as I'm experiencing with the '67 that I'm working on now. The biggest advantage of the DOT 5 for me is the fact that it does not absorb moisture like other fluids will which may eventually cause problems with brake lines and calipers if it is not regularly changed. Yes, the master cylinder was thoroughly bench bled to ensure that all air was removed prior to its installation. After reading all of the replies, I think I have air trapped in one or more of the calipers that is just being a SOB to remove. I'll try the gravity bleed method combined with the use of a rubber mallet to try and dislodge the trapped air over the holiday weekend. Will let you all know how I make out. Thanks to all who replied. Have a safe and happy July 4th!

Joe 45420

[Gerry G.]

Re: Cannot get a firm pedal in my "67 after trying all bleeding methods

I know the pain..Have you adjusted the pedal free play??? Have you checked to see if pedal returns to its stop.weak return spring or misin stop on column.

[Bill M.]

Re: Cannot get a firm pedal in my "67 after trying all bleeding methods

Dom I had a problem like that on my 67 years ago it drove me nuts. It turned out to be drivers side rear hose. I always bled my braked by myself. This was such a pain I had one of my sons helping and he saw the line balloon when I leaned on the pedal. We changed all of the hoses an all good.

[Richard M.]

Re: Cannot get a firm pedal in my "67 after trying all bleeding methods

Gents, You likely didn't notice but this thread was posted 10 years ago.