5.1:1 last time I checked

Sorry to bring this thread back to life, but I researched and unfortunately a stepped bore master cylinder does not affect brake bias. :-( I hope I am wrong, but I think I'm not. They call those master cylinders (quick take up) and they are made to work together with low drag calipers..

Have a look here.

WTIW, I think you're right. I 'feel' (pun intended) the size of the bore of the master cylinder is mainly meant to match the total size of the caliper pistons, so pedal travel remains acceptable.

Thats correct. The primary piston (23mm) fluid actuates the rear piston 19mm. They are not mechanically linked unless in event of one circuit failure, so equal pressure in both front and rear master cylinder pistons. The step is for volume not pressure.

I've built many bugs with 944na, 944t, 986, 986S/996 with stock beetle 19mm dual circuit mc with great results. Pedal feel is really good, except the 944na where it is slightly low... if that is unacceptable to customer then I put in the 944mc.

With split busses I typicaly build them (944na, 986, 996 etc) with early modified single circuit mc. Yup single circuit, works awesome. Due to pedal ratio the 944NA brake system on single mc works well without as low a pedal as beetle. Again for higher pedal I can use 944mc as option but typical isnt an exercised option by my customers. (Single bus is 22mm mc).

I think this thread will be revisited frequently over the years...like I'm doing now, because we all go through what this thread is trying to address. I talk to Flat all the time, trying to figure this all out. Basically, I've decided to run n/a 944 with their single 35.9mm pistons on the rear, and some variation of 42mm 2 pot calipers on the front. I chose this based upon word from two guys who's empirical data I totally respect (not that I don't respect others, but these two guys, we can mostly all agree have a lot of experience to base their opinions upon), Steve Carter, and Walter. Both of these guys whether recently or in the past have told me they had VERY balanced brake set ups with the above mentioned sizes. In Walter's case, he used 40mm stock Ghia type front brakes, and with Steve, he said it was late T3 front brakes (which are the same as early Porsche 914/VW T4). That's enough for me. Well, in reality, I was ok with what Steve told me a couple of years ago, and Walter recently confirmed it.

The rear is very easy on an IRS Beetle. I just bought the tubes and swans Lanner (aka Flat) sells and the set up is an easy and direct bolt on with factory VW parking brake cables.

The front is not quite as straight forward, but ultimately not super difficult. Right now, I've got the 944 front spindles on my car, due mainly to the fact I bought the damn Kerscher ball joints and would hate to throw that much money away. So I'm trying to work out how to attach early 914 front calipers to the 944 spindles. The bolt spacing for the caliper(s) is the same as the 944, however, when the caliper is set on the 944 rotor, the holes are about 1/2 a hole too far away to bolt up. Oddly enough, the offset is very close to right on. If you're wondering how I'm make calipers meant for solid rotors fit over 20mm wide vented rotors, I will tell you (per info gleened from Eric Shea of PMB Performance), the 10mm spacers and all hardware from a 70-83 Porsche 911 REAR M calipers can by used to make the calipers fit (width-wise). The rear M calipers is the exact same casting as the EARLY 914 front caliper (thus also use the same pads), with spacers added.

Perhaps a FAR easier way to approach this...and one I may fall back on, CSP from Germany sells a kit that has 20mm wide vented front rotohubs in the 5x130 PCD I need. These rotors go directly onto the stock 1303 spindle and the calipers have the same bolt spacing as your typical Ghia caliper (not sure the exact measurement, but it's less than the 3 inch bolt spacing of the Porsche 944 spindle). These calipers are made to bolt to any of the many Super Beetle caliper adapters needed for those of us who don't have Super Beetle disc brake spindles (pretty much everyone in the States) and give the correct offset over the rotors. The advantage of this: It's a bolt on solution and I'd be done with it. The disadvantage: The rotors are specialized (though I BELIEVE made by Sebro) and I have no idea the source of the calipers, in the event either has to be replaced in the future, who knows if CSP will still exist and thus the parts available. In reality, CSP has been around for many many years and will likely be around for many many more. That said, I REALLY like the idea I could walk into most any auto parts store in the States and buy either calipers or rotors if need be, should I choose to use the Porsche parts. I'm going to give the Porsche parts the good college try. Honestly, all I need is an adapter to mount the calipers and I'll be good to go. I'm going to try making a pattern from plexiglas.

H2OSB

Hi John,

Very true indeed: stock front disks and 944 n/a rears on stock MC is what gave me rock hard pedal and awesome brake balance!
In fact, liked that so much that for my 'daily driver' project, I got a set of fresh stock sized disks in 5x130 from CB, because I liked the alu hub a lot. By now I have acuired parts for a rear 944 20mm disk set up (vented/drileld of course :D) as we, so I'am close to the swap :-)

http://www.keversite.nl/fotoalbum/fotos/144773.jpg

Here you can just see (through the rim) the also new, drilled, 944 n/a rotor bolted to the rear IRS hub:
https://farm5.staticflickr.com/4518/...7e8c0a37_b.jpg

Wally--

Do you have any old n/a 944 rotors handy? I've often wondered how close those hubs are to working with 20mm wide 944 rotors

john

These wheels make me break into a cold sweat. I want a set something fierce for autocross tires

You will even more if I tell you what they weigh :cool: (just 5,3 kg, similar to the magnesium gas burners iirc)

You mean trying to put a rear 944 n/a rotor onto one of these alu front type 1 hubs?

Don't think I don't know that. Flat has a set of the even LIGHTER ones he teases me with pictures of from time to time. Someday.....

No, the front. It attaches the same way as the CB rotor. I've also considered getting a set of those hubs/rotors, removing the rotor and turning the hub slightly to fit inside a late 944 rotors (the ones that fit OVER the hub).

Ah! Now I see why you said used n/a rotor :rolleyes:
But euh...no, sorry. Due to me trying to minimize parts hoarding a bit, I brought all old rusty rotors to the dump.. sorry.

Oh, do tell! Are they also 5,5 x 15" ?

It's all good. Can you please measure the bolt circle of the rotor attachment bolts? The 944 has a 126mm bolt circle.

I actually kinda got on the guy at CB who designed those hubs/rotors. I asked "why would you re-invent the wheel, so to speak, when Porsche rotors are readily available?" He had no answer.

They're about 10lbs per wheel (not sure what that is in Kg). Incredibly light. Yes, 15x5.5 with the same offset as your wheels. Only, they're made of unobtainium and incredibly expensive. If you happen upon a set for a good price (well, more likely, individual wheels), they're worth it, but unless you have a Porsche owner income, you'd be well ahead to just get custom race wheels made. https://rennlist.com/forums/924-931-...ver-spare.html First wheel you see in this thread. Holy crap, if you read through the thread with the wheel pic, one guy sold a wheel to the original poster for $10 plus shipping. He could turn around and resell that wheel for $500 in the right place.

Interesting!
I think all porsche rotors (except the 914 rears) are vented and they wanted something for the type 1 market?

I'll try to measure the bolt spacing ;-)

Their source for un-drilled rotors has dried up so they needed something to offer a 5x130 pcd for the front. A lot of potential...which I don't think they realized (well, perhaps not until I started bugging them about it)

Interesting indeed.
I just measured it, but was difficult to do. I needed to sort-of eye-ball it a bit, but I think its about 112-113mm bolt spacing. What is the 944 n/a ?

They are big bolts however, like M10, not the M6 of the original 944 n/a front hubs.. (on which 911 3,2 rotors in 24mm thickness also fit BTW, but you may already know that).

I suspected it wasn't the same :( They didn't even consider the Porsche rotor when they created those. The n/a 944 bolt circle is 126mm. I did know the later rotors would fit. Flat told me that some time back (in the event I could use those 44mm 964 C2 rear calipers on the front). I wonder if n/a 944 rotors could be re-drilled in the off spaces to fit the CB hubs? 944 rotors are dirt cheap (I bought my set for $13 per side). I MAY try experimenting to see if it would work.

Edit: NVM, I just went out and looked at my 944 rotors. There's not enough meat to the inside of the 126mm bolt circle to drill M10 holes, much less on a tighter bolt circle. If the CB hubs don't have enough meat outside their bolt circle for a M6 holes, it's a non-starter

Is it that difficult to find 944 n/a hubs then? I thought they just needed two (or even just one?) adapter sleeves for the bearings to fit the beetle spindles? 944 is alu too and the CB hubs can't be bought separate iirc?

Nah, that's doable. They are getting a bit more difficult to find, but I think I have 3 sets. The difficult part is finding someone to do the machine work. Flat does that work, but he's only at it part time and has a huge que of people who want his work. Most of my local machine shops try to send me elsewhere. They don't like one-off projects and cannot comprehend why I'd put custom brakes on a Beetle.

CB hubs cannot be bought separate, but the hub/rotor is not expensive compared to, say, custom made hubs. You can buy the rotors separate. They're about $50 per side, versus the hub/rotor together for about $159 per side. Buy the set, remove the rotor and resell for $45. Cheap hubs, made for the VW spindle and in a 5x130 pcd.

Ah, yeah, I saw a 356 outlaw or some custom coach one with these back then. That is also where I got the idea to use these. I had one set welded +1,5" for the rear only for drag racing a few years ago and they holded up fine. Welded very easy, so very good quality alu I was told :-)
I had one in 16", but without the outer holes, but still rare I think. Edit: I see this was the hot one...and I sold it for what I got it indeed an outlaw builder for 250 euro's...
Mine are older 928 spares ;-)

BTW the 356 ones are 11 lbs. Pretty close to my 5,3 kg (11 lbs or so) I think, but yeah, very rare!

Hmm, there is plenty 'meat' to drill a wider pattern I think. Seems pretty solid, but the disk is still on it. I'll look sometime coming days to get you more info ;)

The trouble with drilling into the hub in the offspaces is that's where the studs are. Is there enough room inline with the current holes to drill an M6 hole? Perhaps offset betwixt the M10 holes and the studs?

https://farm5.staticflickr.com/4518/...7e8c0a37_b.jpg[/QUOTE]

Man, I really like those rims. What car did they come from? Are they 15 inch?

To answer that, I took a few pix for you. In short: yes, I think there is enough meat and room for additional M6 studs ;)
In fact, the CB whole hub is dimentionally very close to the early 944 hub.

https://farm5.staticflickr.com/4721/...f8b757c9_b.jpg

https://farm5.staticflickr.com/4612/...2748acac_b.jpg

https://farm5.staticflickr.com/4612/...741fc7a5_b.jpg

@Francelle: the answers to your question are already given in the posts above ;-)

Ok, I will read again.

Thanks Wally for the great pics. That hub has a lot of potential. That said, it's looking real good with my 914 caliper on 944 rotor set up. Write up soon to follow. Turned out to be FAR easier than expected...particularly with how little I've spent.

Little update. So the brakes I'm doing for the front of my 1303 are the following: I'm using Porsche 944 spindles with a "flip-it kit" to relocate the direction of the tie rod ends. Due to this, I'm also using Kerscher ball joints. For the actual brakes, I'm using 944 rotors that have had the DIAMETER reduced by 1 inch (25mm). This allows a typical Porsche 914 caliper to bolt onto the 944 spindle and have enough swing clearance for the rotor to fit inside. The rotors diameter PERFECTLY places the 914 (D30) pad on the rotor. Now, obviously, 914 calipers are made for 11mm wide solid rotors and the 944 vented rotor is 20mm wide. This is corrected by salvaging the spacers from a set of Porsche REAR M calipers.

The Porsche rear M calipers is the SAME casting as the 914 EARLY front calipers, so if you can find a set of the rear calipers in good condition, all of the hardware can be used (bolts, spacers, pad hangers). This is important because both the 914 caliper and the rear M caliper use non-standardized M7 bolts, the M calipers bolts being the infamous Ribe bolts (pronounced ree-bee) which have been out of production for about 40 years, and cost roughly their weight in gold, assuming you can find them. That said, the longer bolts are required to compensate for the width of the spacer, however, one could use the longer of the two original 914 caliper bolts as the shorter bolt once the spacers are in place, and just get longer bolts for the other spot. In my case, the rear M calipers I purchased had three of the Ribe bolts ruined due to some previous owner attempting to use the wrong tool to remove them. A Torx head of the correct size can be used to remove them, however, torquing them, it's suggested by "those who know" to use the correct Ribe bit.

Both Lanner Khan (aka Flat) and my machinist friend (who turned down the rotors) thought me silly for what *I* did, which was purchase the correct length M7 socket head bolts from a company called Tola-tool in Germany(Tola-tool was the ONLY company I could find who offered both the correct length AND hardness (12.9) for brake caliper use.). Both suggested re-drilling the holes in the calipers to M8 (a standardized size that is FAR easier to obtain) in the case of Lanner or 5/16th inch (also standardized) in the case of my machinist friend. The reason this was silly was the fact the shipping from Germany to California was almost exactly TWICE the cost of the bolts themselves...which weren't cheap. I elected to not re-drill the calipers out of fear there simply wasn't enough material in the calipers to do this. In the end, I'm happy with the bolts. Cry once, as they say.

So, the results of my mods made for a very slick setup that seemed almost meant to be. The caliper is centered over the rotor perfectly with the use of a 2mm shim placed between the caliper mounting ears and the spindle. However, as I was fitting everything together I discovered my first (and really only) major hurdle. The outside of the caliper body hits the HUB edge when everything is bolted on place. I had been fitting everything up with a pair of junk split 914 calipers with the pistons removed to make trial fitting easier. I tried to clearance the calipers a bit but discovered there simply isn't enough material on the body where the piston lives to take material away. Fortunately, I know Flat. Lanner has had a set of 944 hubs on his bus for years that he has turned down by 8mm in overall diameter. I know from my caliper clearancing effort, I only need to remove approximately 2.5mm for the caliper to clear the hub, so 4mm is more than enough for good clearance, thus I'm sending them up to Lanner to have him turn them for me.

Thats some dedication!

A picture of the finished set-up would be cool :)

Yeah, eye candy:)

Quite honestly, I've thought of going with something easier to put together several times, but I've spent too much on those damn calipers (the German bolts AND the sacrificial Porsche rear M calipers) to abandon them.

Sadly, I sent out on this path simply because I wanted vented rotors on the front, to match my vented rotors on the rear (straight 944 rear brakes).

CSP offers a kit that give 20mm wide rotors with a 42mm piston caliper. These bolt to any typical caliper adapter made for a 1303 without disc brakes (or the ever rare disc brake spindles), thus they have 2.25 inch bolt spacing. Unfortunately there is no way for me to get these for less than a LOT of money. CIP1 is the importer for CSP products in the States. They will special order the kit for me for $1300. Now, that's for JUST two rotors and two calipers, not including shipping. WAY more than I'd like to spend. The other alternative for me, if I must have vented rotors, is having someone like Flat make a set of caliper adapters that bolt to 1303 spindles and having the 944 hubs modded to fit the 1303 spindle.

That all said, I think the turning down of the 944 hubs will yield the results I seek.

Pictures of the finished brakes, will, of course, follow.

I have 944NA brakes now on 1303S, with stock 19.05mm master cylinder. I have a set of 944T 4 pot brakes that I will swap on my car, so I've been reading a lot on brakes lately. This thread was a wealth of information. So I tried to plug in some data in the "formulas" used before:
1. 944NA brakes (54mm and 36mm slave cylinders) with 19.05mm pump.
(54/19.05)sq=8.0352.
(36/19.05)sq=3.5712
Resulting ratio is 2.25. So huge front bias. Same result if using 23.8mm pump or stepped 23.8/19.05mm pump (explanation why stepped pump is not affecting bias is here: https://www.germanlook.net/forums/showthread.php?t=2183). The stepped pump just increases the volume of brake fluid going to the front slave cylinders and makes the pedal harder. This explains what I saw during "MOT", a high efficiency of front brakes (80%) compared to rear (40-50%), this being correlated to front and rear weight. So I do not see any other option except bias bars (or dual pumps) to overcome this issue.
Pedal feel is great from my point of view, soft and long travel. I hate hard and short pedal.
2. Considering 944T brakes (40/36 front and 30/28 rear) with 19.05mm pump (same would be with any other pump):
((40+36)/19.05)sq=15.9161
((30+28)/19.05)sq=9.2697
Ratio is 1.717, so still front biased, but much less. Now, considering the same piston sizes were used in 930 with a 23.8mm pump (no step), and that the 930 is has a closer static/dynamic weight ratio to Bug (both rear engined), compared to 944 (front engined), it seems these brakes will be much better suited for a Bug, ratio-wise not power-wise. I'll try with the stock 19.05 pump first, I have read a lot of positive feedback on this setup.

But a question that still remains is why did 944T have a stepped pump with the 4 pot brakes and 930 straight pump, if the step in the pump actually does not affect bias. Just for volume?

Did I understand this correctly? Some older calculations took into consideration for the ratio the master cylinder different steps, but that seems to be false according hydrodynamic laws. That would hold true if the two pistons in the master cylinder would be hard connected to each other, which they are not.

Yep.
Thats my experience anyways.

Thanks Wally for the confirmation. So it seems that 944T brakes would actually fit better the Bug than the 944NA.
I have a curiosity: how do you know which brakes lock up first, front or rear? Do you just feel the car in a specific way? I locked my brakes up a couple of times on hard braking in traffic, but I can not tell which ones did. I just heard the wheels squeak, no deviation from straight line. Can you feel that in specific conditions, on track, for example during hard brake on cornering? I only use my car in normal traffic, which also means some mountain roads, so I did not race it nor do I intend to do so. My "feeling" of the car is that of a normal driver, I have no idea how it is on a track (hm, it was only once at a VW meeting where we had a small autoX track, but that was long time ago and I had no mods).

Oh, I really do feel if front or rear locks up first, very clearly. It happens sometimes on an emergency brake situation or if you simulate one.
You really should feel it!
My advise would be to wait for rain and then just stand on it in different situations and in those street situations/surfaces in the wet, it should still never lock up rears first from a safety standpoint.
Just please be carefull when you try this. Be very sure you have room on the road to slip/skid a little and no other cars behind or in front of you ;-)

Anyone mind going over the math for why a stepped MC does not effect the preasure output by each cylinder?

A dual MC is set up with a floating piston between the two separate cylinders.

https://i.imgur.com/8L2UI7y.jpg

if we assume we are at steady state (piston no longer moving, just generating more or less force), that the brake line ports are plugged, and that this piston is not connected by a bar and the spring force is minimal when breaking, the pressure in the primary circuit (P1) is going to be the input force (Fin) divided by the plunger area (A1). Without any solid connection or added force between the two channels, Fin must be equal to the force the fluid in the first circuit applies to the floating piston (F1) must be equal to Fin. Secondly, the force the floating piston applies to the second circuit (F2) must be equal to the force applied by the fluid in the primary circuit. This force (F2) is equal to the pressure (P2) in the piston multiplied by the area applying the pressure (A2). Therefor, if the area of the two circuits are not identical, the pressure within them will be different as well

https://i.imgur.com/zyKaxyp.jpg

I'll just leave this here not to confuse people.
eskamobob1, I agree partly to your argumentation. But what you have drawn is exactly what it is NOT in the stepped pump (the pistons of different areas are NOT hard linked together). The forces and pressures you computed are correct however if the secondary piston would look like that. But the inside of the pump looks like in the picture from the link https://www.germanlook.net/forums/showthread.php?t=2183. Meaning that the force applied to the second piston is NOT the input pedal force, but it is derived from the pressure of the first: pressure in first chamber (P1) is Fin/d1 (say 400N and 23mm as in the picture), and the force on the second piston is P1*D2 (19mm for second piston). Thus the pressure in the second circuit is the same as in the first circuit.
Your idea would work if the pump would look like below inside, but as far as I know, it does not...