The Stovebolt Site Forums The Parking Lot Big Bolts 1968 C60 brake issues

I've got some odd brake issues that I was chocking up to just believing these old trucks have poor brakes, but I misled myself.

When we hit the brakes the engine idle changes. There's a hissing sound but its not air brakes and it takes a crap ton of foot pressure to apply the brakes. I don't understand whats happening. I had the single on the firewall master cylinder replaced a few years back and when I reflect on it the brakes were good back then.


I'm gonna dig through the resources here and figure out how to get new soft brake lines, and a caliper just started leaking, but I need some advice on this hissing sound with the idle change.

Sounds like you have a bad vacuum booster. The hissing sound you here is it leaking when your pushing the pedal. The engine staggers because of the vacuum leak created by the booster, your pedal is hard because you have no assist from the booster.

Dang, I had it replaced with master cylinder. A bad vacuum line to it wouldn't do that though so that's the only thing it could be.

Thank you

Is the vacuum booster directly mounted to the master cylinder? I would think it is a divorced HydroVac as found on the older trucks. A working HydroVac will make noise and create a small disruption in idle quality, but you should have good power assist if all is healthy.

It's directly mounted like newer trucks.

I've got a bunch of f550 parts trucks with hydroboost I'm considering stealing from...

The vacuum booster for this trucks is $380

Can you disassemble the booster and inspect the diaphragm?

Never done anything like that before, but i can give it a shot.

Can you post pictures and ID info of the existing brake booster and master cylinder? I've got an original 1968 Chevy Truck Chassis Overhaul Manual that has the diagrams (cut-away assembled and exploded disassembled views) along with the instructions for the overhaul process. I'd be glad to snap pictures of the correct brake booster/master cylinder info from the book and post them here, once I can confirm which one you have.

The problem with repairing the brake booster is not taking it apart, the problem is finding replacement parts for the diaphragm. Most vendors don't stock individual pieces as much as the do replacement assemblies.

diaphragm is bad gonna go down that direction... the parts so expensive I wish I could swap Hydro boost right now

i think i used to have the dual one that got swapped for a single, has a more modern master cylinder..
i can get another vacuum booster or go superduty hydroboost.
ive got superduty parts trucks


https://southwestspeed.com/products/150-103?variant=47184387244313

i was thinking i put on this pump, use 10an to 6an adapters, plumb the steering box to the return with perhaps a cooler (im non powersteering right now.) and use a superduty hydroboost which i should be super easy to mount. it looks same mounting as the vacuum booster.

or should i just put $400 into another vacuum booster ?

If you can justify the time, try the hydroboost modification, it won't cost you very much in materials. If it doesn't work out, revert back to original.

I did the Hydrobooster swap and love it, this thing stops like NOW! I used a booster and Master Cylinder from a '90 GM Motorhome . Mine is mounted under the floor which added some complications. I made the lines myself, as well as the Booster Mount Bracket. I added the Power Steering pump and Alternator bracket.

As your mounts to the firewall it should be somewhat easier. I should tell you that my setup is a 4 wheel disc brake conversion. I had less than $300.00 in the Hydrobooster setup.

Heck yeah!
what Powersteering pump did you use?

They Power Steering pump is is from a '67 C10 with a 230. I suffer from ADHD (Automotive Disassembly Hording Disorder), I don't throw any thing usable away.

TUTS 59 - Pack rat fever is contagious as well.

i picked up a powersteering pump and bracket, gonna do the hydroboost swap. ive got two f-550's to steal parts from, gonna do same to my 1955 s14400 probably too

so we put it on finally, acts insane when you hit brakes. stiff, then weird and pushes in, then shoves you right back...
Im gonna try putting the ford remote reservoir on where its on the original truck, between the steering box and hydroboost. i think somethings not right without it.

i want a power steering gearbox. anyone got one?
it would probably help to have the system put together the way its meant to be and also be nice to have powersteering.

If you know what you are looking for, post an ad in the Truck Parts Wanted forum as that's the correct place for such a question.

That pedal feel doesn't sound unlike the last Hydroboost truck I drove. It is a much different pedal feel than a regular vacuum boosted brake.