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dreamgts · Joined: 29 Dec 2009 Posts: 504 Location: malta

Does anyone here have a diagram of how the hydraulic fluid lines differ from the 79 model to the 81 model. I am exchanging the 1979 master cylinder and 7in booster to a 1981 master cylinder and 9in booster, the latter seem to be a good better option. I have noted though that the fluid lines on the 79 model are attached in a different manner. any help or diagrams please. thanks

dreamgts
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!tom · Posted: Wed Nov 23, 2011 2:53 am Post subject:

The 924 has always used an X split, so the connections are the same.

You might have different port locations depending on the particular manufacturer of your master cylinder.

One brake line goes to the right front and left rear. One brake line goes to the left front. One brake line goes to the right rear.

The master cylinder has the same bore for both circuits, so it doesn't matter which circuit you plumb to which pair of wheels, but you do need to make sure that you have exactly two wheels per circuit.

The stock configuration has the right front and left rear on the rear circuit, and the left front and right rear on the front circuit. You could swap front and rear circuits with no issues with the 924 master cylinder.

The 944 on the other hand has a stepped bore and different brake routing, with both fronts on one circuit and both rears on a different circuit. This stepped bore master cylinder is incompatible with the stock brake line routing of the 924.
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78 924 NA
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dreamgts · Joined: 29 Dec 2009 Posts: 504 Location: malta

thanks tom. the 79 master has 2 ports(A) on the front sides while there is another port(B) at the rear. The 81 master has 1 (B)port top front and 2(A) ports rear on sides, so I take it that if I connect the 79 master A and B to the 81 master A and B each circuit will have 2 wheels, am I correct.

dreamgts
_________________
2 PORSCHE 924 (CURRENT PROJECTS)
2 CLASSIC CORTINAS (FINISHED)
1 CLASSIC FIAT(FINISHED)
1 CLASSIC FIAT 132 2000CC(JUST PURCHASED)
4 SUV'S
2 SEDANS
1 OPEL PANEL VAN
WIFES SUZUKI ALTO

924RACR · Posted: Wed Nov 23, 2011 4:04 am Post subject:

Hmmm. That sounds backwards.

The ports closest to the booster are the larger bore, and should go to the fronts. So you should have one brake line going directly, from each of those two ports closest to the booster, to each front wheel.

The port furthest from the booster/pedal is the smaller bore. One line should go from this back to the brass "tee" and then back to both rear wheels.
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Vaughan Scott
Webmeister
'79 924 #77 SCCA H Prod racecar
'82 931 Plat. Silver
#25 Hidari Firefly P2 sports prototype

dreamgts · Joined: 29 Dec 2009 Posts: 504 Location: malta

Getting a bit confused here. 924RACR, is the method you described used for dual dagonal systems (X) or for the later type front/rear brake systems.?
As tom described it 1 port supplies 2 wheels (F & R) while the other 2(can be front or rear) supply a wheel each. So I take it that the one supplying the 2 wheels should be attached to a certain port, while the other 2 feeding 1 wheel each shold be attached to a port each.

Difficulty here though is that the master cylinders have different port locations as described.

What I have noticed on both master cylinders though is that each has 2 ports located near each other and 1 port located at another location on the cylinder. I might suspect therefore that the port located on its own feeds 2 wheels while the other 2 which are loacted near each other as described in my earlier post might feed 1 wheel each, but Im still not sure of this.

dreamgts
_________________
2 PORSCHE 924 (CURRENT PROJECTS)
2 CLASSIC CORTINAS (FINISHED)
1 CLASSIC FIAT(FINISHED)
1 CLASSIC FIAT 132 2000CC(JUST PURCHASED)
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fiat22turbo · Joined: 18 Jan 2006 Posts: 4040 Location: Portland, OR

dreamgts · Joined: 29 Dec 2009 Posts: 504 Location: malta

Ok, so I know that the 81 master cylinder and 9in booster are interchangable with the 79 master cylinder and 7in booster. I might not be asking the proper questions here, so I might be confusing you guys. I apologise if I have.

Presntly the car has the dual diagonal brake system (X) and not the front and rear system as I think fiat 22turbo is calling the 944 system.

I intend to fit the 81 items to the 79 model yet keep the dual diagonal system for now at least. I though have difficulty to understand where the fluid lines connect since as I stated earlier the porst position differ on both master cylinders. tom might have understood my query first tiem around, though I still need to know how to identify which port takes the front and rear wheel , and which ports take the front wheel and which the rear wheel since it seems that the system as described by tom works this way.

dreamgts
_________________
2 PORSCHE 924 (CURRENT PROJECTS)
2 CLASSIC CORTINAS (FINISHED)
1 CLASSIC FIAT(FINISHED)
1 CLASSIC FIAT 132 2000CC(JUST PURCHASED)
4 SUV'S
2 SEDANS
1 OPEL PANEL VAN
WIFES SUZUKI ALTO

924RACR · Posted: Wed Nov 23, 2011 7:30 am Post subject:

The deciding factor for which port to use is the MC bore size.

The different sets of ports will have different bores, resulting in different pressures for a given pedal apply. This is the beginning of your brake proportioning system.

Get it wrong, you can have excessive pressure at the rear vs. front and be more likely to lock a rear brake before the fronts.

The MC port configuration, more than anything, will determine what brake split you can use.

You CANNOT simply plug 'em in wherever you feel like.
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Vaughan Scott
Webmeister
'79 924 #77 SCCA H Prod racecar
'82 931 Plat. Silver
#25 Hidari Firefly P2 sports prototype

!tom · Posted: Wed Nov 23, 2011 7:34 am Post subject:

!tom · Posted: Wed Nov 23, 2011 7:37 am Post subject:

924RACR · Posted: Wed Nov 23, 2011 8:26 am Post subject:

Does that include the '81 MC he plans to use? Or perhaps the difference between M471 and non-?

Or is it only a concern if using a 944 MC?
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Vaughan Scott
Webmeister
'79 924 #77 SCCA H Prod racecar
'82 931 Plat. Silver
#25 Hidari Firefly P2 sports prototype

!tom · Posted: Wed Nov 23, 2011 10:37 am Post subject:

Feel free to correct the below statements; I believe them to be true but cannot independently confirm them.

All master cylinders that come from X routed cars must have no step.
All 924's come with an X routing from the factory.

Therefore, all 924 master cylinders must have no step.

The 944, with a different weight distribution, plays with brake biasing with the master cylinder, rather than the 924 approach playing with wheel cylinder/piston diameters. Therefore, in principle, a front/rear split car COULD have a master cylinder with no step, but in fact, the 944 came with a step in order to fine tune the brake bias.

In conclusion, my understanding is that this is only a concern with respect to 944 master cylinders.
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78 924 NA
5-lug

Rasta Monsta · Joined: 12 Jul 2006 Posts: 11733 Location: PacNW

!tom, correct across the board, IMO.
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WeiBe (1987 924S 2.5t) - 931 S3

dreamgts · Joined: 29 Dec 2009 Posts: 504 Location: malta

Ok both the 79 and 81 have no step in the cylinder. Therefore we are right about certain things, I also know that the 924 uses the X type brake system. I will therefore have to look for the tee which connects front right and left rear and work from there before removing the old master cylinder.

As described earlier both cylinders have 2 ports near each other placed either at the far front or far rear of the cylinder and 1 port which is located at the other half of the cylinder which also varies on both MC meaning on one the sole port is found at the rear while the new mc has this on the top front right before the fluid container. It could be therefore that this sole port on both mc's might be the port where 2 wheel fluid lines are connected. but I have to check I guess. tom when you say front right are you describing it looking from the front of the car or from the inside of the car, I am taking it that the front right is the exhaust side right ( looking from inside the car). Or is the the other way round, pls note that my car is a euor model having RHD.
Thanks to all. At least something might be used here by other members too.

dreamgts
_________________
2 PORSCHE 924 (CURRENT PROJECTS)
2 CLASSIC CORTINAS (FINISHED)
1 CLASSIC FIAT(FINISHED)
1 CLASSIC FIAT 132 2000CC(JUST PURCHASED)
4 SUV'S
2 SEDANS
1 OPEL PANEL VAN
WIFES SUZUKI ALTO

dreamgts · Joined: 29 Dec 2009 Posts: 504 Location: malta

Ok guys had to settle this the hard way. Im the info would be appreciated by anyone with similar queries.

As stated the 924 brake system is an X type dual diagonal as mentioned here.

The 79 MC ports go as follows- the lone port found at the back side is attached to both Front right and rear left wheels. The other 2 ports found on each side on the MC at the front feed front left and rear right wheels, one port for each wheel.

Since the 81 MC has different port locations , these attach as follows. the fport found on the front top of the MC connects to Front right and rear left wheels, the other 2 ports found at the rear just under the fluid container attache to either front left or rear right wheels, one port for each wheel too.
When mentioning right ref above this means the right side when looking from inside the car, in my case where the driver sits.

I had to check the hard way and jacked up the car from 4 wheels and traced the fluid lines, I needed somone to vibrate the fluid lines from the engine compartment or where attachments were noted to verify. On my car the T connectore conecting the front right and rear wheel is found right under the drivers floor panel (RHD).

I hope I explained myself well enough.

dreamgts
_________________
2 PORSCHE 924 (CURRENT PROJECTS)
2 CLASSIC CORTINAS (FINISHED)
1 CLASSIC FIAT(FINISHED)
1 CLASSIC FIAT 132 2000CC(JUST PURCHASED)
4 SUV'S
2 SEDANS
1 OPEL PANEL VAN
WIFES SUZUKI ALTO