M500 brakes, thinking outside the box

[Sasquatch]

Something I would like to start a discussion on.  That is the upgrade of the M500 brakes when they fail.  I have no issues currently with my M500's brakes, but at 42 years old I am sure it is coming.  Parts are getting difficult to find.  I replaced the calipers and all the rubber hoses a few years ago, so I am not worried about that.  What I am concerned with is the very complex 3 master cylinder, 2 vacuum booster setup on the M500.


Here is my thought.  Why can we not upgrade it to a brake system out of a delivery truck?  Something with a diesel engine, front disk and rear drums.  (only talking about the master cylinder system).  Something like all those big flat bed trucks that lumber yards use.  We could pull something from a wrecking yard.  Get a Hydraboost booster and the master cylinder.  We would need to remove all the factory master cylinders and related plumbing.  Install the hydraboost and MC, get the proportioning valve from the donor truck, run new metal brake lines fitting it all in, tap into the power steering system with a new line from the pump to the hydraboost module then from the module to the steering box, and it should be good.


I am sure there would be a few issues along the way like getting the plunger rod length right, etc, but I can not find any real reason it would not work, and work well.  Then we can actually get parts easily for this new master cylinder. 


Please discuss, what do you all think?  I am trying to have a plan in place for when the day comes that I need to do something with my system.

[Elandan2]

Of course it will work. My M500 is hydroboost so the parts are already available. The master cylinder on mine was used on GM P30 chassis with drum brakes up until the nineties. The hydroboost unit is a standard Bendix unit, still available. The proportioning valve I don't know if they are exactly the same but the chassis service manual shows all the holdoff pressures at 117 psi, so that would lead me to believe they are the same in either hydro vac or hydroboost systems.

[khantroll]

I've been eyeballing the P30 trucks for years wondering if they'd fit, and I am 90% sure it would work. I just haven't taken the time to measure the perches.

[Rickf1985]

Hydraulics are hydraulics. The piston sizes at the master and at the wheels are the determining factors. So basically if you get a hydroboost unit that has the same piston sizes as the original boosters then you are good to go. If the pistons are too big then you will have short pedal travel and possibly not enough pressure at the wheels and if they are too small just the opposite.

[DaveVA78Chieftain]

M500 Hydroboost System

[Sasquatch]

Perfect, thanks.

[ByronRACE]

Hi Dave,

Found your M500 information on your website, but couldn't find a way to contact you there and ended up finding you here.

I have a bit of info that might be handy to add to your M500 site. 

As you know, the small parts kits for the rear drum brakes that are supplied by NAPA for the M500 do not include the small parts for the auto-adjuster.  Nobody has these parts.  The particularly problematic piece of this is the little adjuster spring that tends to rust-through.  None of the other automotive springs from drum brake kits that I've found have the right spring rate and/or size/shape. 

This one is a match:
https://www.mcmaster.com/9434K141/

Don't be tempted to buy its stainless cousin; the spring rate is significantly too high and seems to bind the adjuster.  The same is true for any other spring I've tried to swap in from other drum brakes; the spring rates are 2x+ too high. 

The one above works like the original and is an exact size/shape/rate match.

Byron