944 Brake Master Cylinders

[loftygoals]

So what's the story on 944 brake master cylinders?

 

I know there is the whole Girling and ATE difference. From what I understand one difference between the two brands is the length of the push rod that activates the master cylinder.

 

The big thing I am wondering about is the bore sizes in the master cylinders. Looking various places I have found 3 different configurations:

 

• Dual Circuit 19mm/19mm
  
• Dual Circuit 23mm/23mm
  
• Dual Circuit 23mm/19mm

 

From Centric's website I find that the non-ABS cars use the 19mm/19mm MC while the ABS cars use the 23mm/23mm. But, I have found multiple sources that say all NA 944's and 924S's use the 23mm/19mm.

 

After the confusion from the Internet, I decided to actually look at my cars:

 

My 1983 944 has an original Girling unit with a 1982 date stamp. It looks like it uses the 23/19 configuration.

 

My 1983 924S has an ATE with the 23/19 configuration.

 

The spare master I have is actually a 1980's Mercedes part- 004-430-901 or H23852.0.1. This is the unit that is being sold as a low cost 944 steel replacement option by Paragon Products and 944Online. The unit I have is made by FTE and looks to be the same dimensions as the Girling unit I have. It is labeled with the bore sizes as 23/19.

 

The other thing I've noticed is some of the MC's have a bolt located between the front feeds or below the feed for the right front. My OE Girling has this bolt. Any idea what the bolt is for?

 

The second question is the steel unit legal? I found another thread here in the 944 section that thought it would be, but I think it would be good to know for sure. It is not manufactured as a Porsche OE replacement part, so it doesn't fit the rules per se. It does serve the same purpose, has the same performance, and weighs a ton more. Given those facts, I wouldn't protest anyone that was using it.

 

-bj

[Sterling Doc]

BJ, again, great research, and great info.

 

The 944S,& Turbo used brake fluid pressure regulator for the rear brakes, so there were variations in bias among the models, but for Spec purposes, I think there is only one option in the 8V world.

 

The Mercedes unit would not be legal. While it may well have no performance advantage, from a rules perspective, it's a moot point. Getting into justifying non-standard parts based on their performance potential is a very messy business. It's a can of worms we can't get into.

 

Rebuilt OEM MC's can be had inexpensively, or you could swap in the unit from your street 924S, and use the Mercedes unit in the street car.

[944-Spec#94]

The MBZ master cylinder is border line legal.

 

 

Remember here is quote from our rules.

 

2.1 Parts

All parts must be stock from one of the eligible year models, except where otherwise noted.

Aftermarket parts designed and sold as direct replacements for stock genuine Porsche

original equipment parts with no change in performance or weight may be used and will be

considered “stock” for the purposes of these rules. Subsequent sections of these rules which

specifically state “genuine Porsche OE” will allow use of only original factory produced parts or

genuine Porsche OE replacement parts. This is intended to allow general use of non-Porsche

branded replacement parts in place of genuine Porsche parts in non performance critical

areas to reduce costs. Aftermarket parts that are sold and/or designed as improvements to

factory parts are not considered direct replacement parts for the purposes of rules

compliance.

 

Note the key area as highligted. The MBZ master cylinder is being sold as a direct replacement for the Porsche OE cylinder, but was not design to be use in the Porsche application. So therefore it meets only one requirement of an aftermarket replacement part. If the part were not made by MBZ and was made by an aftermarket supplier and they listed the 944 as an application then it would meet the "designed for" clause. I have not checked, but I believe the meeting the "as sold for" clause by what is on Paragon or 944-online. Even so if it is steel body vs the aluminum body it may not meet the no change in weight clause either.

 

One thing to understand is that if protested or found at inspection I would expect the burden of proof be on the competitor to prove "sold for", "designed for", and "no change in weight or performance" clauses in the rules So probably not worth the hassle.

[loftygoals]

I brought this up mainly as a Public Service Announcement. There are lots of Master Cylinders being sold as direct replacements that are not actually direct replacements. This isn't just the MB steel unit. There are units being sold from Centric, A-1 Cardone, Raybestos, Wagner, and others that are not actual 23mm/19mm split masters.

 

I wasn't planning on using this MB master I have. Well, I was until I discovered that it was a MB unit and I realized that it weighs a ton. I've had this thing sitting on a shelf since 2008. I guess it's going to sit there a little longer.

 

Oh, one other things about the MB master, it is being sold as a replacement for all 944's.

 

One final thought: A 944 Spec car will be best served by an actual OE new replacement or a rebuilt OE unit. These cars already have to much rear brake bias and anything other than the 23/19 split will only increase this problem. The steel units are cheaper, but weigh a lot more. Stick with a OE replacement and you'll get the best performing of all the options. You should be able to mix Girling and ATE MC and boosters, but you will need to adjust the length of the pushrod for the MC used. The pushrod a threaded rod attached to the brake pedal and held by a lock nut.

 

Checking the length of the pushrod is a good idea even if you aren't replacing the master cylinder. On my car, I have a full inch of travel before the pushrod engages the MC. I will be lengthening the rod to take up some of the slack. This will also raise the pedal height under braking making heal-toe easier.

 

-bj