Dual master cylinder conversion

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Leverone
Posts: 11
Joined: Sun Jun 25, 2017 1:55 pm

Dual master cylinder conversion

Post by Leverone »

Some time ago I purchased a 1963 Monta Spyder Convertible from a broker who got it from a deceased collector. It is a concourse correct survivor except it had a color change repaint years ago (lacquer) that was done so well that no one can find evidence of the original Gold. Now it is Ivy Green. Anyway, to the point: I have replaced the fuel system, suspension, and brakes. Everything came from Clark’s. The brakes are now 100% new from pedal to shoes. When the old single reservoir master was replaced with the dual cylinder, the brake pedal now had about 1” free play. I adjusted the push rod to get the play back to about 1/4”. Per Clark’s recommendation, the bench bleed of the master was done in car using a bench bleed kit but pushing the brake pedal to the floor instead of a screwdriver in a bench vise. Then the whole new system was bled first with the old fashioned method (patient wife at the pedal) then re-bled using a pressure bleeder system. My issue is there is a good solid hard end point to the pedal, but that happens with the pedal pushed very far down, too close to the floor for my comfort. The car stops, but I would like less travel in the pedal to get there. Has anyone else had experience with these kits from Clark’s? Is this much travel normal? Will the pads bed in and self adjust (reverse) to give me earlier engagement? Any help is appreciated. Thanks!
66vairguy
Posts: 4529
Joined: Tue Dec 21, 2010 3:44 pm

Re: Dual master cylinder conversion

Post by 66vairguy »

There are a number of things that can cause your problem.

Just a few suggestions - are the brake shoes adjusted so the drums just drag slightly. Too much shoe movement will cause a low pedal.

If I recall correctly the 64's had self adjusters and especially on the rear its complex. Getting all the parts installed correctly is not easy if you didn't take pictures (or someone before you messed it up). This can cause a problem.

If you power bled the brakes I doubt air is in the MC, BUT - if dry (new) the MC should be bleed level (usually in a vice - hence the term "bench bleeding"). If only one side has air in the circuit the pedal will travel nearly to the floor before it gets firm - in fact this is exactly what happens when one circuit on a dual system fails. The center MC spring must collapse before the functional circuit piston works resulting in a lot of brake pedal travel.
Leverone
Posts: 11
Joined: Sun Jun 25, 2017 1:55 pm

Re: Dual master cylinder conversion

Post by Leverone »

Thanks. The brakes are all assembled and adjusted correctly, with just slight drag as you suggest. I am very familiar with working on old cars, so I am OK there. Your comment on the master is also where my brain was going. Much as I hate to do it, I may remove the master and re-bleed it in a vise using a rod. Lots of work, because then I will have to rebelled the whole system, but it will be worth it. I know not to push TOO far with a rod or I may damage seals, but I just don’t think all the air is out of the master.
Thanks for the suggestion!
66vairguy
Posts: 4529
Joined: Tue Dec 21, 2010 3:44 pm

Re: Dual master cylinder conversion

Post by 66vairguy »

BTW - I had a heck of a time with the new "bench bleed plugs" that come with the MC a few years back. I went back to the local parts place and the guy sighed and said "We have a lot of folks come back because those new plugs don't work well. I have a kit that you screw into each out port and the tubes go back into the reservoir and you have to keep the tubes covered with fluid in the reservoir". The kit didn't cost much and it worked well. It took about five pushes of the rod to get all the air removed (you can see the bubbles).

Note - because of the way the ports are located internally you sometimes have to tip the MC each way a little to get all the air out.
Leverone
Posts: 11
Joined: Sun Jun 25, 2017 1:55 pm

Re: Dual master cylinder conversion

Post by Leverone »

Tipping sounds very smart. I intend to do that too. I really hope that is all the problem is!
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