[iceman411]

My '71 LeMans Sport convertible came with factory power discs in the front, drums in the back. very common....
Now, the engine i have in the car only produces 5-6" of vacuum with the cam in it at idle.
My thoughts were to remove the power booster and adjust the new stainless lines and just go with it.

I also just picked up a vintage Cam Dynamics vacuum storage can (NOS) that I thought of trying if i keep the power booster.

I cant remember the last time I had a classic car with power brakes. Not sure what Im missing, if anything..

On my last car, 1969 GTO with this actual engine. it had factory discs with the standard manual drum master and it worked pretty good for a manual brake car...
Not sure if the power master cylinder i have will function as a manual brake set up without the booster.

Or... maybe there's a master cylinder with the correct line fitting diameters that also has a correct mounting bolt pattern that may work as well?

Im sure someone on here has come across this before. Thoughts?
Thanks, Mike

[JLMounce]

I would absolutely switch to manual brakes. I did this last year and don't regret it.

They are somewhat spendy, but the Wilwood manual master will come with several size provisions for various line sizes to the proportioning or combination valve. The booster will use a 4 bolt bendix pattern, while any manual master will use only the top bolts. Some applications may use a doubler plate between the firewall and the master cylinder.

In regards to the vacuum storage can, I'm not a fan of these. My reasoning is that depending on how the car is driven, it may not be there for you when you need it.

The can will hold the maximum vacuum it sees while the engine is in operations. As an example if your light cruise vacuum is 12", the can will hold 12" and you'll have that available to you when you hit the brakes. However, while at idle it's only going to store that same 5-6" of vacuum. What happens if you get a little frisky from the light, bury the throttle and don't make any vacuum for a while. If you slam on the brakes here, you've got no vacuum in storage and no brakes in a possible panic situation.

For a race car that you just need some brakes at the big end once, these can work well. On a street car where you may need your brakes at any given moment, they become a liability. Vacuum pumps are only marginally better because they tend to be a bit on the slow side. If you're too far above sea level they also don't work well and tend to burn themselves up as they'll never make enough vacuum to turn off.

[iceman411]

Well, I bought the manual brake push rod, cup, seal and clasp. Today I removed the 9" booster, relocated the portioning valve a bit, relocated the new stainless brake lines, along with cutting and re-flaring the ends... No i didn't forget the nut(this time) and mounted the master to the firewall...
Actually looks a lot cleaner and less busy. I like it....

Now, to bleed the entire brake system again and see how it feels.


Get to it to get through it...

Mike

[Scarebird]

I have the exact same car, but highly modified. The bore on your power master should be 1-1/8"; too big. A 1974-80 GMC half ton manual master will work perfectly, just need to modify the pushrod to fit you 71 with a coupler nut.

[george kujanski]

The master shown has the front brake reservoir in the rear. Check your existing master to determine if the rear of your reservoir is for the front brakes also. My '67 is the opposite, the front of the master goes to the front brakes.

George

[iceman411]

Originally Posted by Scarebird

I have the exact same car, but highly modified. The bore on your power master should be 1-1/8"; too big. A 1974-80 GMC half ton manual master will work perfectly, just need to modify the pushrod to fit you 71 with a coupler nut.

Yes, Ive watched a lot of your build and am familiar with your car...
Ill look into the master with the smaller bore... I believe you posted a link to Rockauto on this master in another post... On mine, I have two different diameter line fittings(line diameters are different too) for the brake lines...... Is the truck master the same, or do I need to have matched line fittings to run it... ?
What would I expect the brakes to be with the larger diameter bore master I have right now compared to the 1" bore master you suggest?
Curious is all...

Mike...

[chrisp]

Are you using a pcv valve ?