switching from power to manual brakes

[cheno2]

I have a 69 coronet, 4 wheel wilwood disc, wilwood m/c, stock drum brake prop.valve,adjustible prop.valve and new power brake booster. I have a harder than normal pedal, I know i'm short on vacuum(only 12 inches). I have gotten used to the hard pedal but can never make the brakes lock front or rear. Pedal seems better during AUTOCROSS under hard decel and hard braking but wont lock up no matter where prop.valve is adjusted. Was thinking of going to manual brakes because don't want to put on aux. vac. pump and also would like to "delcuter engine compartment". What kinda of "difference in feel" would i have betweent the two. I do know i would have to change m/cyl.

 

[Propwash]

Try a vacuum canister.......a lot cheaper than a $300 dollar vacuum pump kit..lot less noisy as well. Might cut it for you. What do you mean by hard pedal? As in like the power booster isn't doing anything or as in the master cylinder bore size needs to be reduced because it brakes well, just hard all the way through till hitting its max extension?

 

[cheno2]

It feels like week booster (had that before that is why it has new booster) definitely made hard pedal better . It actually doesn't have much of pedal travel. Like I said decel hard in low gear is a noticible difference but still wouldn't say it's perfect.

 

[Propwash]

It feels like week booster (had that before that is why it has new booster) definitely made hard pedal better . It actually doesn't have much of pedal travel. Like I said decel hard in low gear is a noticible difference but still wouldn't say it's perfect.

Think you're on the right lines with the sub-par vacuum issue then. 12 is getting down there.

If you go the vacuum pump route, you can use the supplemental vacuum pumps out of the early 80's J-Body GM cars with a 1.8 liter, like the cavalier, celebrity, 6000. Save yourself a ton over those "vacuum kits". Especially if you find one in the boneyard.

 

[lewtot184]

you may have a combination of low vacuum and too large master cylinder piston. check to see if the master cylinder has a 1.125" bore. if so try a 1" bore master.

 

[Cranky]

Think you're on the right lines with the sub-par vacuum issue then. 12 is getting down there.

If you go the vacuum pump route, you can use the supplemental vacuum pumps out of the early 80's J-Body GM cars with a 1.8 liter, like the cavalier, celebrity, 6000. Save yourself a ton over those "vacuum kits". Especially if you find one in the boneyard.

Around here, all of those cars were crushed many years ago! I don't even see them on the road anymore either...

you may have a combination of low vacuum and too large master cylinder piston. check to see if the master cylinder has a 1.125" bore. if so try a 1" bore master.

I did the same thing on a 66 Belvedere. Dont' remember the final bore size but my brakes got better for the same pedal effort but I did end up with a bit more travel.

 

[cheno2]

I have researched that route. Do them older ones shut off/ turn on at a pre-determined vacuum level. Also will the provided enough vacuum to operate booster?

 

[Propwash]

http://www.jalopyjournal.com/forum/archive/index.php/t-491044.html

http://www.gmcmotorhome.com/tech/vacuum_pump/index.html

http://www.chevelles.com/forums/archive/index.php/t-57721.html

Guy in town has a '66 Coronet with one. Woks well. Pretty radical cam in his ride