Will booster self destruct w/no MC when started

[chrismorse]

Help Guys,

I am in the final stages of a major big brake install, waiting for bits to be machined to adapt a new bigger mc and am wanting to fire up the engine, without a mc), so i can check the new bigger oil cooler, stainless lines and thermostat -- Will the booster, having nothing to push against, over extend and blow, or am i just worrying too much.

BTW, the master cylinder is very unusual, It has a metal sleeve attached to the piston. This 5 inch sleeve holds the rod in alignment, losely, in efect, centering the rod on the booster diaphram. The rod is adjustable, but the adjuster is seriously staked around the threads, while the opposite end has a 1 inch +_ "foot" on it.

So,i am having an adaptor made with a sleeve, to support the rod, center the smaller mounting hub and allow a two bolt MC to be installed on a 4 bolt Ferrari Booster.

I remember Eric cautioning that this could get weird - well, it is, but i will persevere.

Heck, the F-50 calipers and brembo 355x32 rotors for the front were only $700 on ebay - just a start :-)

So, I am wondering if i can check out the cooler, lines and Mocal thermostat by filing with oil and starting the car, up on blocks, with no MC.

Will this be ok if i do not push the brake pedal, (as much as i would like to)????

Anxiously Ignorant,
chris

[Newman]

Start the engine and dont push the brake pedal. There is a check valve inside all vacuum boosters that only applies the "waiting" vacuum once the valve is activated by the pedal position. If this valve wasnt there the brakes would automatically apply everytime the engine started which of course would present a problem.

[chrismorse]

Thanks Paul,

I had forgotten that bit of mechanics. But what if i did touch the brake pedal, would it mess anything up?? I haven't, so am not worried about it, but just wondered, what if???

thanks again,
chris

[Newman]

Good question, never done it. The diaphram would be applied, it can only go so far inside the booster housing. Would it damage something? Probably not, it sure wouldnt explode or pop the diaphram but if something odd like it not returning would put a damper on your day. Try it and let us know take one for the team.

[velocityengineer]

Hi Chris,

I am pretty sure you are safe. However, why dont you just take the vacuum line off the Booster? No need for vacuum assist in this case.

Without the vacuum, the booster is just a mechanical transfer of the pedal force input to the MC. The diaphram should be free to stretch front to back in the booster shell.

Should be okay, but I know Martin has spent some time with the 308 pedal assembly, so maybe give him a call.

Hope this is as wierd as it will get.

Eric

[velocityengineer]

Hey Chris, something to consider when using the OE booster with your new system. In terms of pedal feel, the pedal ratio will have a big effect, as well as the MC and booster size.

But another factor to consider is the ramp rate of the booster. A booster's total amount of output vs input force is dictated by the shell size, (or diaphragm size) but the internal rod is not a direct link. There is usually some type of ball and socket device which allows the rate at which the booster actuates the output rod is controlled. There are many methods for doing this, and I am not familiar with the 308 unit internals.

what does this mean? only that it is possible to adjust an OE booster if the pedal feel is not what you want. You must uncrimp the boster and carefully get it apart and try to make adjustments, then recrimp/seal the unit, but it is possible.

Hows the system coming along?

Eric

[chrismorse]

Hi Eric,

Wow, an adjustable booster. My pedal will be quite light, may have to look into this.

I have everything except the master cylinder adaptor in hand. The 308 MC is in a class all its own. Attached to the piston is a tube. This tube travels with the piston and supports the rod, which is adjustable on the mc end and has a +_1 inch foot on the booster end. The cylinder is secured to the booster with 4 studs in a square pattern, whereas almost every other mc has a two bolt flange.

So the machinist is making three things, a longer push rod, an adaptor with a tube on it to support the new rod and a 4 bolt adaptor to cary and center the 2 bolt wilwood unit. The biggest tandem unit could find is about 27 mm.

One further wrinkle is that the studs are too short for the adaptor and they are really inthere. I did not want to hose it with PB blaster or stip the threads with double nuts, so the machinist is taking coupler nuts, 8 mm x 1.25 pitch and turning down the bottom half to fit in a recess in the adaptor. I might have everything by this weekend, except the 360 p brake cables and new brake lines.

I will post pics and specs.

thanks,
chris