[wakesupremo]

After several years of struggling with my brakes I have, after a bit of advice, swapped to manual brakes. I have fitted a 4 disc master cylinder from a corvette and sorted out the pushrod length but, whilst trying to find out the proper push rod length I come across a post about the pedal return spring!!! mine has never had one, that'll explain why the pedal has been slow returning!! Where should it be and what spring? Thanks 1969 firebird convertible.

[indymanjoe]

going this route as well what part number did you use and does it work well?

[Scarebird]

The spring is not there to return the pedal as much as keep it from rattling. Manual brakes are quite good at pushing the pedal back - especially 4 wheel disc.

[wakesupremo]

Thank you for the replies.
Firstly, indymanjoe. I reused the pushrod that was there. I took the booster apart and shortened the pushrod from that until satisfactory. My pushrod already had adjustment at the clevis pin end so needed to be within 1/2 inch and then final adjustment from there.
Secondly, Scarebird. Thank you for that. Rattles don't really bother me as mine is a race car mostly on open headers anyway!!! However, There's nothing now stopping the pedal from 'lifting'. I can pull the pedal up to the bottom of the dashboard. is this correct?

[Scarebird]

Usually there is a method of retention; deep hole, snap ring or in GM's case a rubber boot to prevent lifting.

[JUDGE3]

does your brake pedal have 2 locating holes for the pushrod?

manual brake era cars had 2, one for power brake/one for manual. angle of pushrod may be making your pedal lift out and master cy not pushing it back properly.

also the brake light switch helps with the pedal stop a bit.

[wbnapier]

See photo.

[wakesupremo]

Thanks again for that. The pedal doesn't come back far enough now to touch the brake light switch. The switch is pushed all the way in but the pedal still misses it by 1/16 of an inch.

[JUDGE3]

I had to fab a new brake switch bracket for my switch to line up and "make" as it should after switching to manual. I have no spring or such, my master pushes back enough. Especially since yours is race, test the heck out of it be darn sure the pushrod has no way to fall out. Hope this helped, Eric

[wakesupremo]

Now that I have got upside down and right under the steering column I can see that theres also 2 holes for the brake light switch !!! Put it in the upper hole and all seems good. Still not happy with the pedal though still a lot of movement before any brake engagement.

[JUDGE3]

U may need a different proportioning valve, perhaps and adjustable one? Maybe another will chime in. My firebird did not have the 2 hole pedal or in the switch area, i had to change the pedal and fab the small switch bracket so your better off than i was 4 sure. Mine are rear drum front disc. For me on a hobby car, manuals cure the big cam vacumn issue and big valve cover clearance issue as well as tossin the big pwr booster in the trash!

[wakesupremo]

And so the saga continues. Ive no air in the system I'm certain but still the pedal goes to the floor. There is a glimpse of brakes right at the bottom. I thought, being as the pads are now 15 years old, maybe they're getting thin and the piston is right out on the caliper. I bought a new set of pads and went to fit them today, the original 15 year old pads have more 'meat' on them than the brand new ones. I didn't need to push the piston back to fit them!!! My next point of call is the flexi's. Are they swelling? is there a part number for off the shelf braided flexis for the front D52 type calipers?

[misterp266]

Direct replacement, DOT certified, made in USA. Bought a set for my ‘63 Safari disc brake conversion.

https://www.ebay.com/itm/33055245825...MAAOSw6lthZ5kq

[Scarebird]

Either the bore of your master is too big or more likely you do NOT have all the air out. Harbor Freight makes a air-powered vacuum setup that works well for under $30. Buy an extra bleed screw for front and rear - drill them out. Use these to bleed as they won't let air thru the threads like the stock one do, then replace with the stock screws.

Use a 1/2 gallon to be sure you thoroughly purge the lines.

[Half-Inch Stud]

Drums need the star wheel ratcheted to be darn close to apply. That brings the pedal up good.
Rear brakes apply FIRST in all cars, then fronts.

[tempest1964]

Did the OP say he was going to a 4 disc manual master cylinder?

[JUDGE3]

Originally Posted by Scarebird

Either the bore of your master is too big or more likely you do NOT have all the air out. Harbor Freight makes a air-powered vacuum setup that works well for under $30. Buy an extra bleed screw for front and rear - drill them out. Use these to bleed as they won't let air thru the threads like the stock one do, then replace with the stock screws.

Use a 1/2 gallon to be sure you thoroughly purge the lines.

I was understanding that with manual brakes, you WANT a larger bore master cy.
please explain regarding getting the right bore size. curious due to when I ordered mine, MP brakes had the kit for the swap stating the larger bore. pushing more brake fluid for the manual brake made sense to me. mine are front disc/rear drum and a new replacement type proportioning valve. also will an adjustable proportioning valve help with manual brake?

[Scarebird]

Originally Posted by JUDGE3

I was understanding that with manual brakes, you WANT a larger bore master cy.
please explain regarding getting the right bore size. curious due to when I ordered mine, MP brakes had the kit for the swap stating the larger bore. pushing more brake fluid for the manual brake made sense to me. mine are front disc/rear drum and a new replacement type proportioning valve. also will an adjustable proportioning valve help with manual brake?

Larger bore? no, they have it backwards.

Look thru any parts book; ie a 1970 GTO will have a power bore of 1-1/8" and a manual bore of 1". The larger the bore, the more fluid moved per arc swing but also more effort. The pushrod of a manual is the higher hole on the swing arm. Mopar has the same hole and the same bore size master (a sensible approach).

[Skip Fix]

Larger diameter piston yes moves more volume but takes more pedal pressure to keep line pressure the same. So harder pedal(more pressure from leg) less pedal travel to move same volume. Smaller piston moves less volume per stroke but easier to push with same leg pressure.

Imagine 100lbs leg pressure put on a 1.125" piston and the same on a 1" piston. Larger spreads out pressure over a larger surface area so less PSI.

So you have trade offs and pedal ratio plays in there , disc piston size and personal preference for fell. A lot of non power are 1". Baer used to recommend a 15/16 for manual disc brakes in their kit.

[Scarebird]

yes, Baer calipers have a slightly smaller area than OEM so a bit smaller master is in order.

Another manual master to look at is the 24mm Mopar minivan unit. It has a deep pocket for the pushrod, aluminum body with plastic reservoir and 3/8-24 ports. You will need to open up the mounting holes outward to use on a GM and make a pushrod in a lathe - and they are cheap: $34 new cheap. It is what Wilwood sells after modding them.