C3 Stroker

Just installed a new Wilwood brake system (calipers, pads, rotors, master cyl.,braided hoses) on my '69. Everything seems to be installed perfectly. Bench bled master cyl. and bled system w/ Power bleeder 3 times. Not an air bubble to be found. When I start it up and press the pedal, it goes to the floor! (I have power brakes). I tested the master cyl. alone, plugged, pushing manually and it will hold hard pedal OK; I attached the front line only, leaving the rear plugged; pushing manually it works OK, but with engine running and booster assisting, the pedal goes straight to the floor!......the same thing happened testing the rear line. I pumped the Pressure Bleeder up to 25 lbs.; no leaks anywhere in the system. Possible bad booster?.....unknown trapped air?....booster worked OK before.......?????

norvalwilhelm

What about the rod for the master cylinder? If the internal hole in the new master cylinder is deeper then the stock master the plunger in the power assist will not push on the new master cylinder. I had this exact problem and it was the rod.

carhound

This will be interesting for me. I have done the same thing and I have done everything to get brakes on my 69. I have suspected the rod, but I have ajusted and adjusted it but to no avail. Everything new(twice) everyway to bleed (more than I care to count). Good luck to you C3, hope you can help us both. Please keep us posted.

norvalwilhelm

It's a little late now but you need to compare the back of both master cylinders. Look at the stock master then compare the indent in the new master to compare the depth of the hole in the back piston. If the rod is too short you can push all you want and the piston will never be touched by the rod.

C3 Stroker

The pushrod piston/hole arrangement is exactly the same measurement as the previous (stock) master cyl.......I even lengthened the rod 1/8" for added assurance. I checked fluid movement in the master while slowly depressing the pedal and there is no slop or delayed activation...

427V8

What size master do you have?
Which calipers do you have?

You should be using the 1 1/8" bore master clyinder if you are using large piston calipers and a power booster.

Did you convert from Manual? If so your pedal ratio will be too high. You need to switch the push rod to the lower hole, the one the brake light switch is on now. Then of course you need a new brake switch bracket.

norvalwilhelm

If the bore size is wrong you still get brakes, just too much pedal travel but you still get brakes. Same with using the wrong hole. Brakes work but you might run into the floor.
If the brakes feel like there is absolutely nothing there I would still suspect the rod. I chased this around for a few nights until I found the rod wasn't contacting the master cylinder piston.

C3 Stroker

Thanks, Norval, (also 427V8)...you seem to have nailed the problem. Today I talked to a tech at Precision Brakes Co. (from whom I bought the system) and explained the problem. He said it acted like wrong bore size and re-checked the specs on the master cyl. that was sent......sure enough, it was the wrong one! Too small a bore size for the Dynalite 4 piston calipers. (only 15/16" bore, definitely wrong.) He explained that only a slight mistake in bore size can make the difference in "rock hard" pedal and "to the floor". He sincerely apologized for the error and immediately shipped out the correct one. (Overnight delivery, I should receive it tomorrow). I'm hoping and believing this will solve the problem........thanks,all, for your replies

carhound

norval, I have the VBP o-ring calipers. Would it be alright to use the 1 1/8 master cylinder with these?? I looked a 69 up on VBP web site and they list a 1" for 67-76 and 1 1/8 for 77-82.

427V8

Power brakes use a 1 1/8" MC
Manual uses a 1" MC