Don Terrill’s Speed-Talk

Yeah, I'm trying to build servo/vacuum brakes into my hotrod,

Using a 7" dia single diaphragm booster, which has 3.375" bolt spacing.

It should be the "COMMON GM" bolt spacing.

So my question is: What year/ model GM master cylinders have this pattern?

Need 0.875" bore and wish for a modern aluminum body master. Will something from the 80's work, or is this common GM. stuff only on the 60's and 70's model years?

Oh- give me a hint here, fellas.

I am just a noob when it comes to US classics; had my head buried in euro- cars most of my life....

Cant say for later models but i dont think gm had a small bore master. Its usually 1" or 1 1/8. Well the 60s models that i know of used those sizes.
Must it be american? Pretty sure you would be able to find an A.T.E booster and mastercyl from a german car.


chevyfreak.

Hi. Yes, you are right. However- a New 7" ATE booster for an Escort MK2 is something like 350$, and the 7" US/Hot Rod boosters are like 60$, so there's the reason...

I'll look aout for a 7" 2. hand ATE

I know price is sometimes to main thing when building a project.
Would have thought for you getting european parts would be easier. The ford models here , well the english bodies had girling brakes. Unless you refering to the later german bodied cosworth .

I wanted to import a 9" booster from summit for my impala with disc brakes im fitting. With exchange rates and the shipping by the time it gets here it has escalated 3 fold.

Found a booster at a friend that he says came from an opel/vauxhall model, and with luck the bolt pattern for master was the same. The pushrod that activates master was different.
The disc brake conversion also done with parts that fits and works but not for the chevy. Hubs came from opel senator. Uses same bearings just spaced further apart.
Bmw discs and calipers also from the senator. Actually stripped one for parts (i have 5 of the opel v platform cars) so had everything.
And yes, i still have the xr6 cortina if you were wondering.

Chevyfreak.

Cant say on all the brands over there in germany but over here all the german cars opels , vw/audi, bmw and mercs runs ate brake systems.

Chevyfreak.

Just saw your post here, chevyfreak. Regarding Chevy master cylinders having 7/8" piston bore...... I am not aware of any of the newer aluminum bodied brake master cylinders having this bore size. In the early to mid-1960s, there were 3 piston sizes available on GM cars. Most had 1" piston size, whilst a few of the power brake setups used 1-1/8" pistons. There was also a 7/8" piston size. These are more rare and were for the high performance drum brake option having sintered iron drum brake lining. All of these had cast-iron bodies and were single piston, single reservoir design for drum brakes.

If you are needing a dual outlet 7/8" piston master cylinder in a modern aluminum body, I would suggest first looking at European and Japanese cars to see if there is a similarly sized master cylinder that will work for you.

Another option might be to have a local machinist sleeve a larger bore GM master cylinder and bore/hone it to accept a 7/8" piston (assuming that you can come up with a piston and seals that size for the unit in question). There are some newer aluminum body American master cylinders for disc brake applications having metric equivalent of 1-1/8" for front brakes and 7/8" for rear brakes. These may be a starting point for you. I stumbled across one when I was searching for a different piston size the other day (e-Bay listings). Sorry, didn't make note of application, though. Of course, you would need an adjustable proportioning valve to work out front and rear brake bias if you decrease front piston diameter and pedal travel will increase as well.

Best regards,

Harry

1978 Malibu 3.3L/229ci V6 used a 7/8 dual outlet, cast iron though, with plastic reservoir. Mounts on an angle.
https://www.rockauto.com/en/catalog/che ... inder,1836

1977 Malibu used a 7/8", dual outlet, cast iron, integral reservoir, level mounting.
https://www.rockauto.com/en/catalog/che ... inder,1836

Both use the same fittings, 9/16-18 & 1/2-20 inverted flare.

When I recently made a power-to-manual adapter plate for my car, using the 1978 Mailbu MC, my scratch pad shows I measured the mounting bolt spacing as 3.425". Spacing for the 1977 MC is the same.

You will need to pay very close attention to the pushrod seat location on whichever MC you choose, and fiddle with the brake booster pushrod length accordingly. That is CRITICAL for power brakes and adapting a manual MC onto a power booster isn't something you can just bolt up and go.

POSSIBLE ALTERNATIVE, ELECTRIC MASTER CYLINDER

http://www.abspowerbrake.com/ehpm.html

That looks interesting. I wonder how the brake feel is? After spending ten years helping work with the manufacturers on brake system performance and feel I have become a little bit of a snob. At least I can admit it.

Paul

FC-Pilot wrote: ↑Sat Nov 30, 2019 12:33 am After spending ten years helping work with the manufacturers on brake system performance and feel I have become a little bit of a snob. At least I can admit it.

Paul

Speaking of, any hints as to why the pedal on my '06 Envoy, and about every GM truck of that era, feels like stepping on a 10lb wet marshmallow even with everything bled properly? Just really poor rubber hoses? Inherent design of the ABS (accumulators)? A squishy spring instead of a pushrod between pedal & booster? (OK it's not that last one, but that's what it feels like)

Is it intentional, some misguided attempt at 'driver comfort', part of the NVH obsession they went through for a while? Dunno about everybody else, but a brake pedal that feels like it's not connected to anything doesn't give me a whole lot of 'comfort'. Blech.

It is funny you bring that up. The mid 90’s trucks and suburban had a head of the department who’s wife liked the suburban but wanted a nice soft pedal. Sadly we all got crappy pedals because of it. Luckily they fixed it, but slowly. At least they got their act together. Toyota on the other hand still feels like crap. When car and driver reviewed the latest Camery and had negative comments about the brake pedal feel, Japan came back and instructed the US brake engineers to tell them “you don’t know what you are talking about and that they (Toyota of Japan) knows what is best for the American consumers”. I will laugh about that one till the day I die.

As a whole the best feeling brakes I would say is Ford. I really like some models of VW and other individual models around the industry. The best programming I have felt is the regenerative braking of the Chevy Bolt. Without using any brake pedal, just the braking paddle on the wheel can bring you to a complete stop better and smoother than most drivers can. When we tested it at Toyota the management had the car tied up for three days playing with it and shaking their heads saying how far behind we were.

Paul

FC-Pilot wrote: ↑Sat Nov 30, 2019 12:33 am That looks interesting. I wonder how the brake feel is? After spending ten years helping work with the manufacturers on brake system performance and feel I have become a little bit of a snob. At least I can admit it.

Paul

That looks almost exactly like the Powermaster setup that Buick used on Grand Nationals.

It feels about halfway between vacuum brakes and Hydroboost. I prefer it for this reason. It is basically Hydroboost or the equivalent that Audi used in the 90s (pressure "bomb" looks identical too!) but with an electric pump to use pressurized brake fluid instead of power steering fluid.