4 wheel drum power brakes too touchy

[JohnJohn]

I would like to drive my trail rig more on the road. It has 4 wheel drum brakes now but the PO added a power booster from Duffs.
My only problem is when I hit the brakes at speed it almost puts me into the dash it stops so fast. The brakes are way to touchy to be safe.

Any tips on making them less sensitive?

I will be converting them to disk at some point but I would prefer to run it the way it is for now.

 

[70_Steve]

Which master cylinder are you using? You might consider installing a master cylinder with a slightly smaller bore. TAkes more pedal stroke to move the same volume of fluid.

When I converted to hydroboost I went with a MC with a 1 1/16" bore. Gave me a good pedal feel with lots of feedback. I can easily lock up my 35's, but the feel is very controlled.

That was with Disk/Drum and now Disk/Disk.

 

[Apogee]

I would like to drive my trail rig more on the road. It has 4 wheel drum brakes now but the PO added a power booster from Duffs.
My only problem is when I hit the brakes at speed it almost puts me into the dash it stops so fast. The brakes are way to touchy to be safe.

Any tips on making them less sensitive?

I will be converting them to disk at some point but I would prefer to run it the way it is for now.

Do you have any brake modulation at all, or is it like a light switch (on/off)? The reason I ask is that if the booster fails in a certain way, such as a cracked air valve body, then it will apply full boost as soon as you touch the pedal rather than progressively like it should, which could explain your symptoms.

Otherwise, a larger bore master cylinder would generate less pressure for a given pedal effort and would be a relatively easy way to mute the responsiveness of the brakes.

 

[JohnJohn]

I don't know for sure but I think I am running the manual drum MC.
I happen to have a 77 disk/drum MC in my barn. I could see if it has a smaller bore.

 

[Apogee]

FWIW, the factory drum/drum MC had a 1" bore, as did the '76/'77 disc/drum unit.

 

[broncnaz]

I think Id go with a larger bore MC. A smaller bore puts out more PSI which may make the brakes even more easy to lock up while you will get a longer pedal travel it wont reduce brake pressure it will hit harder.. A larger bore will reduce PSI and increase the effort needed to make the brakes work of course it will shorten the pedal travel.

 

[Timmy390]

I ran the stock drum/drum MC on my 74 with power booster and drums for 10 years. NEVER had a problem like that. My issues was keeping them in proper adjustment. I had many "oh crap" moments when breaking hard.

Make sure you have the brakes adjusted properly. Maybe try adding more rear brake and less front. I say this because you didn't say the rears were locking up. My guess is the fronts are adjusted tight, very tight.

Tim