Drum brake power conversion

[jhill52]

Recently there was a discussion on converting manual drum brakes to power. It was noted that a spacer was required I believe in the back of the master cylinder so the booster output shaft could push on the MC. Dirt Donk or anyone else do you know the dimensions for the spacer?

 

[thegreatjustino]

Completely depends on what master cylinder and booster you're using.

The spacer is only needed if you're using a deep piston MC with a shallow push rod booster.

If you're using a stock EB master cylinder and vacuum booster, the slug in the piston is not necessary as the push rod from the booster is adjustable.

 

[Skinnyr1]

I just put on a vacuum booster with my drum brakes. I used a wildwood prop valve and bent up some brake lines to go to the valve and/or H block.

Once I had everything in hand, it was pretty easy. The 8" vacuum boosters are @$175 shipped to your door, and it makes a pretty noticeable difference. Money well spent.

I didn't note any spacer. You just have to adjust the piston that goes into the master from the vacuum booster.

 

[Timmy390]

Keep them adjusted properly guys.....I ran them for 10 years and on occasion it was scary

I used stock parts. No spacer or slug needed

Tim

 

[DirtDonk]

What they all said. Unless you find one specifically for your master cylinder and booster combo, you might have to make one.
I can't say they don't exist, because I've never actually searched for them as a separate piece, but you can see the ones that come with our masters in this image: https://www.wildhorses4x4.com/product/Hydroboost_Master_Cylinder/bronco-master-cylinder
It's a simple thing, but is sized for those masters specifically. We had to make one once when retrofitting a vacuum booster to a friend's '71 with stock master. The guy is a gizmo-hoarder and literally walked over to his pile-o-parts, pulled out a solid steel rod that was the perfect diameter and even had a dimple machined into one end already!
Cut it to length, rounded the tip and voila! Instant bullet spacer thingy.
I believe the o-ring in the included piece is simply to hold it in place. But it probably doubles as a secondary line of defense for that time when your master starts to leak out the back.

All this discussion about the bullet spacer thingies should not be confused with the spacer that Ford used on '76 and '77 Broncos with manual brakes. This was literally a master cylinder spacer that moved the master outward by an inch or so, when the booster bracket was not present.
Maybe this was for pedal rod length, or some kind of geometry change, or because all the masters had the shallow depth piston typical of a boosted master. But it was a real spacer to move the master forward away from the firewall.
Different from the one we're talking about that brings the back of the piston outward/rearward towards the booster rod.

Paul