924Board.org

[Joes924Racer]

Got this out of a 1980 924 thing is the wheels were gone so i dont know if it had disc brakes ,theres a 23 stamped on the body..how
can i tell if its meant for a disc braked car.

_________________
1979 porsche 924 Na
1980 porsche Turbo 931GT Replica
Have u ever driven a turbo.

[gohim]

Doesn't make any difference whether the master cylinder came from a car with four wheel disc brake or not. From 1980 on, the same master cylinder was used whether the car was a Turbo (like the one that the master cylinder in the photo) or from a NA (normally aspired) car, whether the car had four wheel disc brakes or the discs and drums. Both setups used the the same master cylinder.

The 1980 master cylinder was different from the 1981 and later master cylinder, in that in 1981, the brakelight switch was moved to the pedal cluster inside of the car, and removed from the master cylinder (where it had resided since the 924 was introduced).

The 1980 throught 1985 (83-85 Euro models) even use the same master cylinder rebuild kit (brakelight switch is not included).

[Joes924Racer]

Does that mean this is at least an 81 mc in that it has no
brake light hook ups.
_________________
1979 porsche 924 Na
1980 porsche Turbo 931GT Replica
Have u ever driven a turbo.

[Smoothie]

Yes - that and the electrical connectors on the cap say it's from '81- .
_________________
"..it's made in Germany. You know the Germans always make good stuff."


'82 924T, US version, dark green metallic, 5 speed Audi 016G gearbox

[gohim]

You can use the master brake cylinder from an 81 on an earlier model by installing the brake pedal stoplight switch (hole should already on be on the pedal assembly).

The wires originate inside of the car, and are run under the hood with the main wiring harness. You can isolate the wires for the brake stoplight switch on the master cylinder, then pull them back through the firewall to attach to the new switch on the brake pedal assembly.

After that, if you need another master cylinder, you will find the a new late model master cylinder between $20-$40 less than the earlier one with the brake stoplight switch.

If you are going to use the master cylinder that you have, you should switch to the one without the connection for the clutch master cylinder. Replace the grommet/bushings when you pull the tank off. Use the old cap without the wires for the brake fluid level indicator.

[Joes924Racer]

this is great one more question are my brake lines routed wrong
for this mc to work like it should I still have the 79 924 lines
_________________
1979 porsche 924 Na
1980 porsche Turbo 931GT Replica
Have u ever driven a turbo.

[Smoothie]

The OE configuration of your brake lines is correct for that (and for any 924 non-stepped (straight 23mm)) MC. The lines change for a stepped 23-19mm (or other stepped size) MC.
To answer your other question posted elsewhere - the MC needs rebuilding.
_________________
"..it's made in Germany. You know the Germans always make good stuff."


'82 924T, US version, dark green metallic, 5 speed Audi 016G gearbox

[Joes924Racer]

so I have a question: Is this mc is just like the stock drum braked mc
that im currently usen ??...
with the discs. Do I need the stepped mc
_________________
1979 porsche 924 Na
1980 porsche Turbo 931GT Replica
Have u ever driven a turbo.

[gohim]

The 1980 and later 924 brake master cylinder is 23+mm internal diameter.

The 1979 and earlier 924 brake master cylinder is 19mm internal diameter.

The Sebring 79 Special Edition 924 with four wheel disc brakes used a 23+mm master cylinder (different part number from the one used with later 924 production).

The internal diameter of the brake master cylinder was increased to increase the fluid pump capacity of the master cylinder because more fluid is required for the four wheel disc brakes. The diameter of the vacuum booster was increased to keep the pedal effort the same as that of the earlier cars with the smaller diameter brake master cylinder.

All 924 cars got the increased size master cylinder and vacuum booster in 1980 because of production costs. It would not pay to stock and install two different sizes of these parts. This is the same reason that the normally aspired 924 got the internal tank fuel pump. The internal fuel pump was required for the Turbo engine, and it was cheaper in the long run if Porsche did not have to build and stock the fuel systems with and without the internal fuel pump.

I have seen some early cars that use the original size brake master cylinder and vacuum booster, some with the larger 23+mm master cylinder and the original vacuum booster. the owner of these cars said that they stiopped fine, and the brake pedal effort was not too high. I have not driven any of these other cars, so I have not experienced a direct comparison.

My 81 came with the larger master cylinder and brake booster to begin with. When I did the conversion, if it had not, I would have installed the larger diameter parts. Porsche increased the diameter of the parts for a reason. So it seems that if you want the parts to work the way they were designed to, you should install them the way that they were designed to be used. At this time I am running stainless teel braided, teflon brake lines, ATE aftermarket replacement 924/944 front calipers and 85/1 944 rear calipers (that a rebuilt with new seals, pad hardware, and new brake pads before installing) with the balance of the rear brake parts from a 85/1 944 (although my parking brake cables came from a 924T with five bolt wheels). The brake pedal feel, stopping power, and brake balance are perfect for me with the wheels (had a set of 6 X 15 phone dials powder coated the original shade of silver) that I am using (only mistake I made was buying the Pirelli tires that I got).

As far as the controversy regarding using the 924 straight diameter master cylinder, or the 944 stepped master cylinder. I suggest that you do the conversion and drive the car with the suspension and wheels and tires that you intecd to use, on the surface that you intend to drive the car on. The early 944 (82-83), and the 924 (with five bolt) used the same part number front and rear calipers (all five bolt) 924, 924S, and 944 (79-8 use the same rear calipers), and front and rear rotors. But the 924 had cross connected brake system, and the 944 had the front and rear brake circuits. The 944 carries more weight in the front than the 924, and has larger rear tires than a 924. Because of this, Porsche used the stepped diameter master brake cylinder on the 944 to alter the brake balance without installing the proportioning valve that was added on the 16V, and Turbo 944 (which had even higher front weight than the 944). And note that the 944 stepped master cylinder was used with both the 924/944 five bolt front caliper and the later 944 caliper.

What I have been telling people all along is to get one of the 23+mm 924 brake master cylinders with the larger brake vacuum booster if they have an early car that came without. Don't worry about whether you have the 924/944 front calipers or the later 944 calipers (just make sure that you get a matched set). Get the wheels and tires that the car is going to be driven with, and do the four wheel disc brake conversion with good used parts (all parts checked to factory spec with new seal kits in the calipers, new brake pads, and rotors within factory specs). You need to check any used rotor you may be considering using because the Porsche factory spec only allows for 1.5-2.0mm of wear from the new rotor thickness spec. That is not much wear thickness. Complete the brake conversion, break the tires and brake pads in, and test teh brake balance to determine if any changes are necessary, before you start changing parts.

Because of these other factors, you need to get the parts installed, and drive the car. You may not be happy with the brake balance, and want to add the stepped master cylinder, and/or the proportioning valve after driving the car, or you may simply change the tire or wheel size, or the spring/torsion bar rating to get the car where you want it.

[Joes924Racer]

Seems its time agina to crawl underneath and find out the layout of my lines again and rebuild the mc or get a stepped. either way
it seems I may have some more line work to do. Thanks.
I already did the conversion and am runnen big 215 60 16s
new pads are broke in and seated the 19mm mc
is barely doin the job it stops better than drums though
the front to back ratio is screwed cause its a 19mm mc.

I could rebuild this 81 23 mm mc.. I imagine
or get a stepped mc for a 944. While Im waiting
Ill map out the lines and see about getting it set up
like a 944 with the tee in the back or cause im
remembering that I have the tee up front on the
passenger side. Thanks.
_________________
1979 porsche 924 Na
1980 porsche Turbo 931GT Replica
Have u ever driven a turbo.

[gohim]

Are you sure that you got all of the air out of the master cylinder when you substituted in the 23mm?

It is very hard to get all of the air out when the master cylinder has been dry (like the master cylinder that you tried to install). Especially when new brake pads are installed in the calipers, because the caliper pistons are fully retracted and it is difficult to get the brake fluid through the caliper in a volume high enough to carry the air trapped in the lines out of the system.

Dry master cylinder are hard to bleed because the seals don't seal without fluid, and you can't get fluid into the master cylinder without pumping with fluid.

You were able to put your old master cylinder back in with minimal problems because it was already full of brake fluid.

Before buying any more parts, you should try bleeding the brake system again. You can try bleeding the master cylinder before installing it by filling the tank, and plugging all but one of the fluid outlets, and carefully pumping the master cylinder (slowly, don't let it go dry again) until clean fluid comes out without air, then cap that outlet, and do the next in succession. You will still have to do a thtough bleed after the master is back in the car, but at least you will have somewhere to start from.

As a rule of thumb, I use a full 32oz can of brake fluid when bleeding/replacing the brake fluid in my cars with a MityVac. The old pump and release method takes a helper, takes longer, and never seems to remove the air as well as the MityVac can.

I start by replacing the old fluid in the tank (when I am replacing fluid) and filling it with fresh brake fluid. Then I go to the wheel with the shortest fluid line, and start bleeding. I bleed until the fluid comes out clean, without any air. Then I continue to bleed the caliper until I pull an additional full container of clean contaminate free fluid from the caliper. After securing the bleed valve, I continue to the next closest caliper, and repeat the same process until I have done all the calipers (or wheel cylinders on the car. I usually go around a second time and draw an additional container (I think the container is 4oz or 6oz) of clean uncontaminated fluid from each wheel.

The mistake that most people make when bleeding brakes is not using/letting enough fluid pass through the system to ensure the removal of all the air/old fluid/contaminates. You gotta be ready to use enough fluid to get the job done. Brake fluid is cheap compared to the cost of a ruined brake system, or brake failure when you step on the pedal.

Personally I recommend a new replacement master cylinder when a master cylinder indicates the need for replacement. Every master cylinder that I have ever replaced has leaked fluid out onto the vacuum booster. If you have a soft pedal, there is usually another reason (worn brake pads or shoes, leaking caliper, wheel cylinder, or brake line. Or in the case of the 86 Jetta that I bout a couple of months ago, a leaking rear brake proportioning valve.

[Joes924Racer]

Seems a thorough bench test is in order. first off.
I think I was to excited the last time & forgot to
bench bleed the 23 so I went back to the 19
One of the rear wheels
didnt produce enough fluid the last time with it.
When I push the plunger it makes a sucking sound.
so maybe I can bleed it up. Am I gonna be able to
push the plunger with 2 lines plugged shoud be able to
I use a vaccum pump with stock valves then switch to
speed bleeders if the mcs on the car. Brake booster
issue not a prob pedal travel
doesnt worry me with it. Brake light switch for the pedal
is the issue as I dont have one. Anybody can help here.

I can get a prop valve with 7 repeatable distint settings for
brake bias. Its not the knob style its swivel handled.
I was gonna get a line lock type since I left the park brake
parts at the boneyard. Cost 84.00 line lock type is cheap way
to go.

We have uphill downhill twisties in the counrty here
so its nice I cant brake hank and turn as fast as Id
like plus the rear is to high though the pedal is to soft
and has alot of travel its the damn 19mm mc.

How about a brake balance bar.

Anyway Im off to Olympia Washingtonfor the night
gonna atend a wedding seems terris older brothers
daughter is getting married shes been maken the
cake in the kitchen here all week. I rented a hotel off of
101 in olympia for the nite as there to much family at
her bros house. So well do the wedding and reception
eat some food go back to the nice newly remodeled hotel.

Return sunday and Ill work on installen the 944 catback
I got from Phogfire1. Its heavy so Im getting it put
on like it should usen the intended points along the
drive tube. I dont want to brake my header.

Thanks for setting me straight on the brake systems.
with all the great info ... K
Joes924racer[/u]
_________________
1979 porsche 924 Na
1980 porsche Turbo 931GT Replica
Have u ever driven a turbo.

[gohim]

The vacuum booster will not effect the travel distance of the brake pedal. It will affect the amount of pressure that it takes to activate the brake. You will have to push the pedal harder to make the car stop.

The larger the diameter of the master cylinder, the higher the volume of fluid you are pushing, and the more effort you will need to push the master cylinder push rod the same distance.

The vacuum booster assists you by amplifying the amount of pressure that you exert on the brake pedal. The travel distance will remain the same.

If the pedal is soft, you have air in the system, and/or a bad master cylinder. Someone wrote under another topic that NAPA has the correct rebuild kit for the master brake cylinder. When I was younger a sucessfully rebuilt every master cylinder that I ever worked on. As time went on, I stopped rebuilding when I realized that I if I shop, I can buy a brand new master cylinder for very little more that the cost of rebuilding the old one, if I sell the old one as a core. On top of that, I have not rebuilt any 924 master cylinders because the genuine rebuild parts kits for for around $80, and I have purchased several new ones at different swapmeets for no more than $25. I ended up selling my spare new master cylinders for around $80, the same price as a rebuild kit.

[Joes924Racer]

Just finished up bench bleeding this thing
used my vaccum pump and pushed the rod in
a bit it puts out alot of fluid from each and every hole.




Stop light switch it just fits in the hole
is this all Ill need. What does it hit to be pressed the firewall?
Do I need 2 of them like on the 80 and earlier mc.




Oh by the way I had a great time the motel Ok and the speed limit
70 and above basically the whole way outside of Oregon Damn
I had fun liven in the gorge on the washington side. Its been awhile though. If this switch install is as easy as it sounds this looks like a done
deal
_________________
1979 porsche 924 Na
1980 porsche Turbo 931GT Replica
Have u ever driven a turbo.

[Smoothie]

Click for larger pic -

_________________
"..it's made in Germany. You know the Germans always make good stuff."


'82 924T, US version, dark green metallic, 5 speed Audi 016G gearbox