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Kenodog · Joined: 25 Jun 2003 Posts: 2669 Location: Vancouver,B.C.

So looking in the engine bay of my new 931 and something I notice right off the batt is the brake master cylinder and booster. They are rusted beyond repair.

So my question is since we have a set of 951 Brembos going on the car is there a bolt on different set-up ? I only ask because the actual 931 master cylinders and boosters are waaaay more money than a 944 or even 951 unit.

Thanks,Leigh
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1979 Euro 931, Olive
1981 931, Sabine
1991 Ford Ranger XLT 4x4, Ricky
1996 Ford E-350 ex-FedEx Van
2014 Mazda CX-5 (Kinderwagon)
2019 KTM 790 Adventure
2024 KLX300
2024 KLX140

Euro924S2 · Joined: 06 Mar 2008 Posts: 215 Location: UK

I may be wrong but I think it's essential to change to the 951 cylinder if your using the brembo's - something about stepped bore in the MC. Look at ideolas performance planning guide -sure it says in there ....
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UK spec '83 N/A with 931 motor with Eaton MP62 'charger @ 15psi. EFI - 565cc inj. Standalone Adaptronic ECU. 951 FMIC. Ally rad. Twin throttle. Recirc valve. Custom manifolds and CAI. 232bhp

morghen · Joined: 21 Jan 2005 Posts: 9095 Location: Romania

I'm runing 1983 924 NA booster and MC on 928S4 big red calipers.
I drove it quite fast on the autobahn...also in the city...brakes feel great..car stops fantastic.
However i will be refreshing the booster and replacing the MC with a 951/S2 unit.
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Raceboy · Joined: 01 Mar 2004 Posts: 2327 Location: Estonia, Europe

I have swapped both regular 951 Brembos and 951S Brebos woth late (1980 and up) master cylinder with both late and early boosters, works well each time.
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'83 924 2.6 16v Turbo, 470hp
'67 911 2.4S hotrod
'90 944 S2 Cabriolet
'78 924 Carrera GT replica
'84 928 S, sold
'91 944 S2, sold
'82 924S/931 "Gulf", sold

'84 924, turbocharged, sold.
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ideola · Joined: 01 Oct 2004 Posts: 15550 Location: Spring Lake MI

It shouldn't be too hard to find a boost and master cylinder from a late model '44 or '51 that is being parted out. While several combos may work, in my opinion, it's best if you can keep the master cylinder matched to the calipers.

The other thing I would highly recommend is modifying the brake lines from the 931's X-split to a front-rear split. Here's a good source for the correct metric bubble flare tees and unions which will help with this job. When I did the conversion on the Club Sport, I was unable to find a bubble flare tool, so I scavenged a short section of hardline from a donor car and was able to bend it (using a proper brake line bender) such that it was not necessary to cut any of the stock lines; I simply used one union and switch where the tee was in the line to do the switchover. Pretty straight-forward once you get under the car and see where the splits are.
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erstwhile owner of just about every 924 variant ever made

Grenadiers · Posted: Thu Mar 07, 2013 6:02 am Post subject:

I bought this OTC-6504 bubble flaring tool from Summit Racing. I used it to make my own hard fuel lines, reusing the 10mm stock lines. The tool is for brake lines, but has a 10mm application.

http://www.summitracing.com/parts/otc-6504
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'83 944 Track car.
'88 924S Track car.
'89 944 Turbo
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2012 Jeep Wrangler
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Dutch924-racer · Joined: 23 Jul 2007 Posts: 1081 Location: The Netherlands

The diameter of a 924T brake booster is the same as the 944/ 951 one I believe.

I am using a 942S aloy stepped master cilinder, the diameter 19/23mm is the same also as a 951, I think.

I also converted my 924 turbo to a fornt/ rear separate system.
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937 trackday car
Series 2 engine
951S turbo and intercooler
Fast road camshaft
Forge recirculation valve + boost controller

!tom · Posted: Thu Mar 07, 2013 4:59 pm Post subject:

Why convert from the X arrangement to front/rear split if you're keeping the M/C that isn't stepped?

The way I see it, in the event of a brake failure, with the X arrangement, you can stop with 3 wheels (both rears via hand-brake, and one front). With the front/rear split, worst case scenario, you've only got rear brakes.

What benefit could the front/rear split provide with a non-stepped master cylinder?
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78 924 NA
5-lug

vatoisimo · Joined: 31 Aug 2008 Posts: 134 Location: Kent, Wa

Great Stuff! I just got done doing the 5lug conversion on my 924 from a 81. powder coated the calipers, and it looks nice. A question about the master cylinder. The 4 lug m/c has 3 hard lines coming out: 2 in the front, and 1 in the back. The 5 lug m/c has 3 hard lines coming out: 1 in the front, and 2 in the back. Do you just switch them around? Can you use the brake fluid tank off the 4lug on the 5lug? Thanks for all the help you guys! Oh, ordered some brake lines from the garage too

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

Why is altering the factory setup "highly recommended?" That is a big job, what is the benefit you feel justifies it?
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WeiBe (1987 924S 2.5t) - 931 S3

Kenodog · Joined: 25 Jun 2003 Posts: 2669 Location: Vancouver,B.C.

Whoa hold on a second...
I started this post so someone that has changed master cylinders/boosters could maybe make a list of what exactly is needed to do the job. Like I said I have a set of Brembos and the torsion bar carrier/trailing arms from a 951 and just need to know which model year brake booster etc. to buy that will work. And like I also mentioned I dont want to use a 931 unit because I am looking to buy new and a 931 set up is about 3X that of a later model set up.

Thanks,Leigh
_________________
1979 Euro 931, Olive
1981 931, Sabine
1991 Ford Ranger XLT 4x4, Ricky
1996 Ford E-350 ex-FedEx Van
2014 Mazda CX-5 (Kinderwagon)
2019 KTM 790 Adventure
2024 KLX300
2024 KLX140