924Board.org

Yundar · Joined: 13 Jun 2020 Posts: 4 Location: Glacier Washington

Hi All, I have been a quiet reader on this board for a little bit. I am bringing a 1980 NA back to life slowly but surely! I have experience in other Porsches, both 944s and 70's 911s. This is my first 924 and I got it to play with and tinker around. The car was off the road for 17 years and disassembled. It has taken me about two years to get it to the (barely) drivable state.

My question is this... I am ready to do a five lug brake swap on it and have an 83 944 as my donor. Reading through Ideola's posts I only see the brake lines mentioned once. Has anyone completed this swap using the stock master cylinder and the stock cross over brake lines? I have seen posts saying to swap brake lines and posts on other forums saying you don't need to. On one of Ideola's write ups it just mentions changing a tee to convert to front and back braking. Has anyone tried this route? Just looking for some advice before I start this next project. Also I was intending on swapping the entire rear suspension as a unit to gain the factory rear sway bar mount. Any tips there? Thanks, Andy

MikeJinCO · Posted: Tue Jun 15, 2021 11:23 pm Post subject:

The threads on brake swaps get quite confusing. The 5 lug conversion works best using the stepped 23/19mm dia MC from the 944/924S however that requires changing the brake lines to a front/rear split from the existing diagonal. The stock one is 19/19. When I did my track car it was much easier as it was gutted down to the tub and I used cupronickel tubing that bends easily and a flaring too I got from Eastwood. Easier, but not a pretty or neat installation. A fellow known as Itom from your area once did a conversion with no change in plumbing and said it worked fine. I think that is how the 5lug optioned cars were set up also
.
You ought to look at the later PET later(after 80) MC changed to the one on the 944(See Clarks Garage PET's) as there was one change of the 924MC about 1979 to change the brake light switches. They also changed from a 7" to 9" brake booster that can interfere with the throttle cable location coming thru the firewall.

I'd try Itom's method first and find out if it works for you. Change the flex lines to braided SS at the same time. I had to change to the 944MC as mine was dead and I couldn't find a rebuild kit at the time.

All cars after 77.5 should have the same adjustable rear suspension with sway bar mounts welded to the TB carrier. You can even put the 19mm adjustable rear sway bar off the 968 on a '78 by changing the bushings. If somehow you don't have the sway bar mounts, they are available from Porsche and can be welded on and some folks have used a large diesel exhaust clamp 4" or so(measure) to hold them to the tb carrier rather than weld.
_________________
Mike

'67 MG Midget Dp
'71 Ocelot Dsr Kawasaki 1000(under rebuild)

Rasta Monsta · Joined: 12 Jul 2006 Posts: 11723 Location: PacNW

When I did this on my 80 turbo I used the master that came in the car and didn't touch the brake lines. Worked fine. Added Brembos later, also worked fine.
_________________
Toofah King Bad

WeiBe (1987 924S 2.5t) - 931 S3

Fasteddie313 · Joined: 29 Sep 2013 Posts: 2596 Location: MI

The “stepped bores” do not change the bias between the different masters, it only changes the travel of the secondary piston in the event of one split or the other loosing brake pressure..

The steps are to tune what happens when a brake line blows out, to activate the other side when one looses all fluid..

Their is really only 1 pressure piston, the second one just floats between the 2 chambers to separate them and then is there to manually push one or the other incase either side looses all fluid/pressure..

The splits don’t really matter either, other than the safety mechanism..

Corner split uses the same size pistons, because both are same fluid volume when one fails..
F/R split uses the stepped safety system, because fronts/rears have differing volumes..

931 and early 44 brakes are the same other than the corner or F/R split..

Neither system has any bias control other than the sizes of the caliper pistons, which are the same..

I think a corner split car could be changed to a F/R split by adding one additional front brake line, or rebranding and extending the one, and changing up that TEE that is under the bell housing area..

I looked into doing a bunch of this stuff a long time ago, but never got around to actually doing any of it..
_________________
80 Turbo - Slightly Modified

Rasta Monsta · Joined: 12 Jul 2006 Posts: 11723 Location: PacNW

Fasteddie313 · Joined: 29 Sep 2013 Posts: 2596 Location: MI

!tom · Posted: Thu Jun 17, 2021 5:40 am Post subject:

My swap used the stock MC and stock routing.

No issues.

Not the stepped bore M/C either.

Stepped M/C should be run front on one circuit, rear on the other.

Non stepped M/C can be run with either routing. The factory deemed the X routing was best, so I saw no reason to change it.

I agree that the advice suggesting the step affects pressure is incorrect; the step affects volume. Using a stepped M/C in an X configuration is incorrect.
_________________
78 924 NA
5-lug