Porsche 944 Brake conversion on 1303

[Dodgy]

Hi H2OSB
Yeah I have seen Gerrelt's install of the 944 rear ARB, and lots of other good stuff on his site
I'm not so keen on the u-bolt mount, cantilevered off the torsion tube TBH.
Plus right now I have the luxury of an upside-down pan for easy access, a welder and plenty of time to develop another approach.
My intention is to make the install factory looking, as much as possible.
Pros and cons to both methods. Of course his/yours doesn't require welding on the pan or ARB, or extending the ARB ends, reducing stiffness.
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'75 1303 (current project) owned since 1989!
'72 Squareback - full resto completed 2008 - now sold
356 Speedster kit, completed 2005 - now sold

[Dodgy]

[Tvättbjörn]

[offtherailz1]

Enjoying the reading here and on the links. This is all beyond my current mechanical abilities, but I know Memminger do a 1303 abs install, I wonder what they use?
_________________
“ My worry is, that if I die suddenly, my wife will sell everything VW for what she thinks I paid for it.”

Cuppa tea man, living in a latte world.

1973 1303, one previous owner, my Dad
1975 1303, Fourth owner, mum 1975 to 2014, me from 2017
https://www.thesamba.com/vw/forum/viewtopic.php?t=711269&highlight=
https://www.thesamba.com/vw/forum/viewtopic.php?t=740901

[Dodgy]

@Tvättbjörn: I am using the Porsche single-piston sliding calipers, not the 4-pots, does this change your advice / experience?
The 944 calipers appears to have different bore front/rear to set bias. I'm not sure the brake balance should be the same with rear engine? Plus a lighter car of course.
I will look up the mechanical booster, sounds intriguing...
Not sure a hard stop from 200km/h is something I will have to plan for in this car!

@offtherailz1: A while ago I found some info on the Memminger install. I think they use a T4 or T5 ABS module. With factory Beetle brake parts, as far as I can tell?
They mount the module inside the trunk, but I prefer to keep all the high pressure lines on the floorpan, a little closer to factory.
I have some ideas about engine, but that is a LONG way off yet..
_________________
'75 1303 (current project) owned since 1989!
'72 Squareback - full resto completed 2008 - now sold
356 Speedster kit, completed 2005 - now sold

[Tvättbjörn]

[tzepesh]

I have used Bug MC with both setups, single piston, or 4-pot. Nice pedal feel, never had an issue with hitting the bottom. I did not like the Porsche MC at all. As Tvattbjorn mentioned, it has very short throw, very hard feel and my legs cramped after a few brakes...
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'74 1303S, L98B Viperngrun (extra glitter), German Look
'64 1200, Sea Blue, under restoration

[Dodgy]

Thanks Tzepesh
Now I have one reccommendation each way!
Would appreciate hearing anyone else's experience
_________________
'75 1303 (current project) owned since 1989!
'72 Squareback - full resto completed 2008 - now sold
356 Speedster kit, completed 2005 - now sold

[H2OSB]

I'm running Boxster rear calipers on the front and 944 rear sliding calipers on the rear, all with a 1303 "disc brake" MC. I had planned to use the stock 1303 MC but a couple guys I know who know Porsche brakes on Beetle conversions suggested the slightly larger MC since I may be standing on the pedal at autocross events. I've heard and experienced, MANY times, the 1303 factory MC does a fine job with disc brakes, the pedal just feels a bit softer compared to drum pedal feel.

My other Super (1973. Just sold it about 3 months ago so this is recent data) had four wheel discs with a stock MC (typical disc brake conversion kits) and would stop on a dime. If I had autocrossed that car before all my research and $$ expenditures for the car I still have (1974), I would have just used Topline conversion kits (maybe with the new EMPI calipers...just because I like them) and a factory drum brake MC. I'm not certain why people often say the factory MC cannot control disc brakes. It worked flawlessly for me. In fact, my first Super I had back in the mid 90s had full 944 brakes front and rear and worked fine with a stock MC. I never even knew, back then, swapping the MC was a thing. It worked fine. Later I heard about people using a VW MK1 Golf MC, which was/is the 20.6mm MC everyone sells as the Beetle "disc brake MC". The 20.6mm is, incidentally the one I'm using on my current car, however, it's not a driver yet, so I can't compare to stock. I will say it's got some big shoes to fill, IMO, to equal the stock 1303 MC.

I'll say this, Dodgy..if you just keep the stock MC, I don't believe you're going to feel like you made a mistake.

H2OSB
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(o\_i_/o) I'm not a vegetarian because I love animals, I'm a vegetarian because I hate plants.

[Dodgy]

That's great feedback H20SB, thank you 👍

From what I have read the trade-off is (obviously):
• Larger bore MC = hard pedal, short travel - less 'feel'?
• Smaller bore MC = soft pedal, longer travel - more 'feel'?

Quite a few people recommemd staying with 19mm bore MC (standard VW) so that is a good place to start, the easy option!
Unlike standard Beetles, the Supers have a 'biased' hole pattern, so finding a compatible 'upgrade' MC is a little more challenging, especially for RHD:

As long as the standard MC can shift enough fluid to move the massive 944 front caliper pistons (56mm diameter) without the travel becoming excessive, that is good enough for me!
Having ABS in the mix adds a little complication, but essentially in un-activated state it shouldn't affect the basic fluid transfer characteristics.

I'm not finished yet on rebuilding the floorpan before starting to install brake parts, but it is getting closer...
_________________
'75 1303 (current project) owned since 1989!
'72 Squareback - full resto completed 2008 - now sold
356 Speedster kit, completed 2005 - now sold

[Tvättbjörn]

[Dodgy]

Yes, that is true, also.
For the record, I am a qualified mechanical engineer (automotive industry) in my day job, so all the mods to my car are considered from a 'proper' engineering standpoint.

I know there is a risk mixing parts from different systems. The questions are:
1) do the mixed components work together successfully?
2) does the new mix of components provide an improvement to the original system?

Some of these questions are difficult to answer 'on paper'.
The 944 MC was developed for a heavier car with front engine, so the system requirements are different to ACVW. I think that is a fair argument against using the dual-diameter 944 MC.

I'm certainly not discounting your experience Tvättbjörn!
If the system is not performing properly, it can always be updated later. None of these build projects are ever really 'finished' are they?!
Here in the UK older cars are exempted from mandatory MoT tests (similar to TUV) but when complete I wiĺl get my car independently checked, always wise to get a second pair of eyes to make sure nothing is missed. Brake function & balance etc is part of that test.
_________________
'75 1303 (current project) owned since 1989!
'72 Squareback - full resto completed 2008 - now sold
356 Speedster kit, completed 2005 - now sold

[tzepesh]

Actually, the MC was not designer with focus on "heavy front". The calipers are designed for that purpose. The MC has to provide enough brake fluid volume for braking. This is why the Porsche MC has 21 (?) mm MC diameter for the front brakes: due to the large pistons, they need more fuel. It was never to distribute force (there is a topic on germanlook.net where I explained the physics behind). Also, the Porsche MC was designed for an assisted system, not direct pedal application, so the force to push it was never an issue for them. If the pedal bottoms, it means that not sufficient braking force can be obtained. I did not have any means for checking the left over travel at full brake.
The idea of smaller diameter MC is that you do not have to force the pedal down to brake (which frankly I find risky, maybe the wife want to go shopping with the bug sometime). Also, it is more about the "feel": when you have to push with less force, you can modulate the brake better and obtain what you want. My feeling with Porsche MC was that it is an ON/OFF system, and is more prone to locking due to this fact.
Moreover, I swapped from the NA brakes to turbo brakes because they act more progressively (due to different diameter cylinders). The 54mm front pistons seemed HUGE. Based on Wally's feedback, his best compromise was 42mm Ghia front calipers with 36mm Porsche rear calipers. It also gives a braking ratio close to stock, so no side is more prone to locking.
That being said, with such brake conversions, you have to learn how to brake...
_________________
'74 1303S, L98B Viperngrun (extra glitter), German Look
'64 1200, Sea Blue, under restoration

[tzepesh]

There you go:
https://germanlook.net/forums/showthread.php?t=4595&page=11
https://www.germanlook.net/forums/showthread.php?s...amp;page=2
_________________
'74 1303S, L98B Viperngrun (extra glitter), German Look
'64 1200, Sea Blue, under restoration

[H2OSB]

[tzepesh]

What is the Boxster rear piston combination and how many pistons? Just to compare to the 944Turbo calipers.
_________________
'74 1303S, L98B Viperngrun (extra glitter), German Look
'64 1200, Sea Blue, under restoration

[Dodgy]

Hmmm... some things to think about there, thanks!
_________________
'75 1303 (current project) owned since 1989!
'72 Squareback - full resto completed 2008 - now sold
356 Speedster kit, completed 2005 - now sold

[H2OSB]

I'll ask my buddy Lanner. It wasn't an original idea. He actually built a kit for Wally with the exact same set up but for his Notchback. Lanner tried, persistently, to talk me into using the Boxster rears for my front brake set up but I was bound and determined to use 914 front calipers....however...I HAD 944 spindles and discovered 914 calipers bolt directly onto the spindles. Unfortunately, 944 rotors are too large in diameter to clear the mounted calipers so after much time and $$, I finally accepted the fact it wasn't going to work(if anyone is truely considering the same path, PM me and I'll detail all of the pitfalls), so I had Lanner make me a set up that allows me to use early 924 spindles with Boxster rear calipers and rotors over custom hubs and caliper adapters.

The only thing I had to do was flip the cross over tubes and bleed valve positions so the pistons were trailing correctly (they are two different sizes). The Boxster rear calipers are truely lightweight. They make the 944 rears feel like boat anchors (in fact Lanner teases me about that unmercifully. He simply refers to them AS my boat anchors).

I'm not going to lie, the n/a 944 set up does work on a 1303. Those monster front 54mm piston calipers just do the job. They're huge and heavy and for the life of me, I can't figure out why they AREN'T making too much front brake bias, but they certainly don't seem to. In the 90s, when I first got into Supers and the Kafer Cup was a big thing in Germany, that's the brake set up all of the Kafer Cup guys were putting on their cars. That said, I have no idea if they were swapping in 944 MCs. I didn't, and the brakes worked well.

H2OSB
_________________
(o\_i_/o) I'm not a vegetarian because I love animals, I'm a vegetarian because I hate plants.

[Dodgy]

So I ran some numbers, all based on VW M/C Ø19mm / Ø19mm and 944NA calipers Ø58mm front / Ø38mm rear

1) I made my own calculation sheet, based on 'first principles', this gives brake balance 68% to front
2) I used the online calculator at https://brakepower.com/, this gives brake bias 68% to front.

Good that both methods give the same result!
68% front bias doesn't seem to excessive to me...

As it is said, "every day is a school day"
I understand why the dual/diameter Porsche M/C doesn't result in a change to the bias, as tzepesh points out (separate thread).
There are a number of other factors at play that influence the balance, such as the fact that the effective radius of the rear calipers is larger than the effective radius of the front calipers - the outer diameters of the discs are the same, but the rears have a larger hub to house the handbrake mechanism, which pushes the centres of the pads outwards.

My calc shows pedal travel should be around 100mm, which is more than standard VW brakes but should be OK, and somewhere between 17-20kgf should be enough to get max braking effort, which is not too excessive (no servo)

That seems enough to me to continue to plan with Standard VW M/C for now, and see how it feels when back on the road.
_________________
'75 1303 (current project) owned since 1989!
'72 Squareback - full resto completed 2008 - now sold
356 Speedster kit, completed 2005 - now sold

[H2OSB]