Which 944 M/c

[What-r-u-doing]

I guess the issue you are having or don’t want to have, is a piss poor pedal and spongy brakes.

The question is why do I have spongy brakes.
1- You have air in the system
2- You haven’t done the job correctly
3- You have missed matched the components of your conversion


I won’t even go into answering question 1 and I will only touch on question 2.

Question 2 - You haven’t done the job correctly
E.g. if you have used second hand rotors and they have heaps of radial run out in them, you will never get a sharp pedal why because each time the rotor turns one full rotation the pads and hence the calliper piston will get knocked back too much and you have to reset the calliper and piston back to the disc rotor face before affective braking takes place, the first pump or two are crap then the pedal firms up.

Question 3 - You have missed matched the components of your conversion
IT doesn’t really mater what type of brakes you want to run on your car, 944s, 944Ts, Big reds, Brembos, Willwoods or even AP racing callipers, what maters is that the all the components in your system work together.

So as we are trying to improve the braking of a rear engined car we can carry more brake on the rear wheels that say some one with a Nissan 180sx turbo –why because we have more weight over the rear wheels.

If you compare a drum brake VW beetle to a the above Nissan with 4 wheel disc brakes you would find that the beetle has roughly the same sized drums and shoes front to rear compared to the Nissans and you would also find that the beetle would be placing more brake effort on the rear wheels % wise than the Nissan.
Lets assume that you modified the Nissans brakes to give you the same % front to back as a Beetle how would the Nissan behave under braking well if I was a betting man I would be putting my $$$ on the fact it would lock up its rear brakes first and you would lose control.

Now you think I don’t know what I’m taking about cause you Daddy’s got a old Chevy pick up with drums all round and the rears are as big as the fronts and lets assume that the master cylinder has the same bore size on the front and rear circuit so that means roughly 50% of the total braking effort goes to both the front and back, with me so far.
And as you know at least ohh 65% if not 70% of the vehicle weights on the front wheels and it doesn’t lock up its rear brakes all the time.
How ever your Daddy’s pickup truck has a think called a load sensing proportioning valve in the rear brake line, so when you have 3 tons of sugar and copper line in the back you get all the braking effort available to the rear wheels at the rear wheels when you only have that old hound dog on the back you may only be getting 13% of the braking effort on the rear wheels. Still with me?

So if we were trying to buy parts for our killer conversion would we want to use the complete system off a Honda CRX, Nissan 180sx, Porsche 911, Porsche 944T or Porsche 944.
Well it would be better to use the components off a vehicle with approximately the same weight distribution as your car –still with me.
I’m going to make some big assumptions here, cause I’m to lazy to look it up so lets say a 911 has a weight distribution of 55R/45F and a 944T and a 944 has 45R/55F and a CRX as 28R/72F and a Beetle is 55R/45F, what vehicle’s braking system would be the best to use, the answer is a clear as mud, the 911 followed by the 944 and to be on the safe side its better to have more braking on the front than the back. By the way the above is an assumption and is only there to prove a point, I don’t care if a 911 is 49R/51F or a CRX is something else.

So why is it when you use early 911 rotors and callipers and a Beetle master cylinder the brakes are awesome, or 944T 4 pot callipers and rotors and a stock Beetle master cylinders the brakes are good??? Yet when we use 944 single piston sliding callipers and rotors and a stock beetle master cylinder the brake pedal sucks, and you can’t even get a hard pedal???

Here are some quotes I found when looking at this site and these are made me put pen to paper, well fingers to keyboard.

As quoted by Boygenius
“I'm no brake expert but I would think that the piston size in the 911 master cylinder would better complement a rear engined car than the 944 unit. Then again using the 944 brakes could change the characteristics of the 911 master cylinder.”

As quoted by Wally
“Because of the rear engine and 'reverse' weight distribution of the bug compared to a front engined/watercooled car, mounting the same m/c seems pointless to me. Fitting a m/c with 21/19 cups rear/front would make more sense to me...”

As quoted by Jezza
“I think I will fit the 944 master cylinder, its front to rear ratio (having actually done the calculation now) isn't as bad as I suspected it would be.”

What Boygenius and Wally have said is so far from the truth it scares me that they are allowed to modify their cars and drive on the same roads as me.
At least Jezza is close to the truth but by looking at his other comments it must be by share luck or he was able to seek some professional help.

The answer is if you use a beetle master cylinder the hydraulic volume and pressure is incorrect for the single pot front callipers, if you only fitted the rear 944 brakes and checked it you would have a good pedal, fit the front and it goes out the window, the Beetle master cylinder bore size is 19mm front and back, and the 944 master cylinder is 23mm front and 19 rear, so do you see why the 944 rear callipers would work on the stock beetle master cylinder.

But in fairness to the above guys yes when swapping from the beetle m/cylinder and 944 callipers to the 944 m/cylinder and 944 callipers it will affect the front rear brake bias, but only cause the front callipers were not MATCHED correctly with the beetle master cylinder.
But god only knows how you came to that conclusion.



And again its true that changing your master cylinder size will affect your front rear brake bias, look at any real race car and you will find they have a thing called a balance bar, with two master cylinders, this is do they can change the pedal effort between the cylinders and if its not enough they can change cylinders with out too much drama to alter the front rear brake bias..


If you are going to modify your vehicles braking system or mix and match brake or suspension components please seek professional help, they know what they are doing.
Yes it may cost more in the first place but it could save your life, or at least stop you from crashing your car.

That’s my 20 cents worth….