Boost Ratio of Servo's

[Rek]

After trying to link the RHD brake pedal to a LHS sited servo via connecting rods, I have given up.

There are a few remote servo's which are available for track day cars but I need to be able to compare these to the boost ratio of the standard brakes so they are effective, but don't send me through the screen and into the middle distance if I think about braking.

I've looked around but can't find this anywhere.

 

[Ian C]

I had a Tii which had been converted to rhd (badly) that used a small hydraulic master and slave cylinder to actuate the lhd servo/ master cylinder. It worked fine.

 

[Rek]

Thats interesting. Was the lhd servo mechanically operated? If so then it must be some attachment which converts mechanical to fluid operation. I also have a couple of spare tii servo's which I might experiment with.

I had a Tii which had been converted to rhd (badly) that used a small hydraulic master and slave cylinder to actuate the lhd servo/ master cylinder. It worked fine.

 

[Rek]

Can anyone help out with the boost ratio of the standard servo's on my 1971 CS?

 

[Ian C]

There was a simple master cylinder which was probably a clutch master of some type instead of the rhd brake master, actuated by the normal rod from the brake pedal. I suppose the "slave" pictured needs to give a 1:1 ratio of movement. This system gave a good pedal feel and was trouble free, but I don't know how you would do it with the twin booster setup

 

[Honolulu]

I take it that the boost ratio is the ratio of input force (your foot on the pedal) to output force (force on the operating rod which actuates the master cylinder). This is related to clamp force of the pads on the rotors through the area of the caliper pistons and the brake pads.

Remember too that the brake pedal itself is a lever, so the force the master cylinder receives is the foot force multiplied by the ratio of pedal length from the pivot to the actuating rod, divided by the pedal length from pivot to your foot.

The problem is how to measure the ratio in a way you will find useful, and this is compounded by your not stating how you want to proceed with whatever number you get.

It's easy to measure the force of your foot on the pedal... how to assess the clamp force at the rotor? I suggest a pressure gage on the flex line leading to the caliper. Don't know if the Blue Books have any data about this, but I **think** they do, and that's where I'd suggest you go looking.

 

[Rek]

Thanks for this - it might be the answer to my problem. I will start to research the parts needed.

There was a simple master cylinder which was probably a clutch master of some type instead of the rhd brake master, actuated by the normal rod from the brake pedal. I suppose the "slave" pictured needs to give a 1:1 ratio of movement. This system gave a good pedal feel and was trouble free, but I don't know how you would do it with the twin booster setup

 

[steely dan]

Can anyone help out with the boost ratio of the standard servo's on my 1971 CS?

I have a copy of a step by step ATE brake servo overhaul for the E9 gifted to me by the author when i was trying to find a seal kit for my the remote servos on my early E24 . The servos are identical on both models.
In the text it states ,
" The BMW sales brochure for the E9 states that the servos increase the breaking effort 4.3 times above that which foot pressure alone might provide ."

Unfortunately the author has asked me not to publish the article and as it is copyright I cannot .
I looked into replacing mine with other similar items fitted to some British Leyland cars but their boost ratio was circa 1-1.5.
HTH's
Don

 

[Rek]

Thats it then 4.3 times. It's quite a bit.

Thanks for this, and what a great source.

I have a copy of a step by step ATE brake servo overhaul for the E9 gifted to me by the author when i was trying to find a seal kit for my the remote servos on my early E24 . The servos are identical on both models.
In the text it states ,
" The BMW sales brochure for the E9 states that the servos increase the breaking effort 4.3 times above that which foot pressure alone might provide ."

Unfortunately the author has asked me not to publish the article and as it is copyright I cannot .
I looked into replacing mine with other similar items fitted to some British Leyland cars but their boost ratio was circa 1-1.5.
HTH's
Don

 

[Rek]

Just realised - from the "foot", so the pressure increase through the master cylinder needs to be taken into account as well.

Doh! Slide rule out.