Stock MC size?

[///Matt]

68 Satty, 4-wheel drums with booster... who knows what size the MC would be?

Also: since I put Wilwoods on the front only, what size MC do you think SHOULD be there?

 

[R/T Boy 67]

It should be 1 inch, for drum brakes. The size for discs depends on how hard you want to push on the pedal. You should get a disc brake master with a big reservoir regardless. I have a 1 1/32 master on my manual discs. Some people prefer 15/16. Dr diff has both. Try it with your 1 inch master just to get a feel for it, then decide on a disc master.

 

[///Matt]

The car drives ok right now with the stock MC and metering valve (after putting the front discs on)... but it’s got some funny behavior I want to get rid of. Basically a delayed application of the front, regardless of pedal push, like the fluid is being restricted from getting to the discs promptly.

Wilwood tech support has been... unhelpful... to now. Their (slow to get) answer was “buy our 1 inch master for $400.”

 

[R/T Boy 67]

The drum master has a residual pressure valve built in that you should remove from the front brakes. That will not cause your problem however. The only valve that should be in your drum system is a pressure differential valve that turns on the dashboard light. If you installed a valve from a disc car it would have a metering valve that delays pressure to the front brakes. I would by pass what ever valve you have in there and install an adjustable prop valve in the rear line, and give it a try.

 

[///Matt]

The drum master has a residual pressure valve built in that you should remove from the front brakes. That will not cause your problem however. The only valve that should be in your drum system is a pressure differential valve that turns on the dashboard light. If you installed a valve from a disc car it would have a metering valve that delays pressure to the front brakes. I would by pass what ever valve you have in there and install an adjustable prop valve in the rear line, and give it a try.

Yeah... I have the wilwood prop valve in the toolbox, and plan to eliminate the stock metering, just haven’t done that yet. Got curious about whether I “should” need a different MC size. Kinda ridiculous that wilwood told me to try and change to exactly the size that should already be in the car... and I told them i have the proportioning valve not-installed and they never even suggested to “well put that on”

On an aside, where might I find/remove the RPV for the front, since they aren’t drum anymore? Is it integral to the MC, or is in inline/in the block?

 

[69L48Z27]

The delay could also be the larger bore. I did a right stuff OE looking 15/16" and spliced in a prop valve to hold off the rears from locking up. Manual setup.

 

[///Matt]

The delay could also be the larger bore. I did a right stuff OE looking 15/16" and spliced in a prop valve to hold off the rears from locking up. Manual setup.

Don’t manual vs power brakes call for different bore sizes? Or is it strictly a pedal-ratio difference?

 

[69L48Z27]

Yes and yes. There's are different sizes for different styles.

If I ran manual disc/drum it's 15/16". This gives you more pedal travel and feels like a power setup. If the same setup is power I would run 1" or up to 1 1/16". Drum/drum power or manual seem to be 1 1/8" or right around there.

Also, no need to get rid of the factory distribution block as long as it's not blocked. You'll need to split lines somehow.

 

[R/T Boy 67]

The rpv is integral to the mc. It is behind the brass tube seat. Screw a small sheet metal screw in the hole in the seat and pull it out with vise grips. It is a little rubber valve. If you are carefull you will not hurt the seat. You should still get a disc mc.

 

[R/T Boy 67]

If your rear shoes have a lot of clearance it will delay everything.