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  #1  
Old June 10th 2011, 10:12
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Need info: 1303 Master cylinder stroke

Hi

I need to find out the master cylinder stroke for a stock 19 mm 1303 disc brake master cylinder.

In the Bentley manual it lists
All 1970 front 15.5 mm, rear 12.5 mm
113 & convertible front 17.5 mm, rear 11.5 mm
Karmann Ghia (disc brakes) front 14 mm, rear 14 mm
Sedan 111, 1971 on 15.5 mm, rear 12.5 mm

I'm assuming that it would be the same as the Ghia master cylinder as they both have disc brakes.

Steve
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Old June 13th 2011, 07:42
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Why do you need to know Steve?
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Old June 13th 2011, 09:42
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Hi

I will spill my guts here, I'm trying not say too much on my local sites, you never know who is looking.

I recently got my STI powered bug on the road, had it all checked off by an approved engineer, passed by another examiner, paid all my fees etc.

Then I took the car home and pulled the car apart to finish some wiring issues and just a general tidy up, a week later I was told to bring the car in for a more thorough examination, a random check on the approved engineers is what they said was the issue.

They have a few issues with my car, they reckon that my stock 19 mm master cylinder can not properly cope with my upgraded brakes, I'm running 996 rears on the front and Boxster rears on the rear, both these callipers use 30 & 26 mm pistons.

These are the figures that I gave to my engineer to show that my master cylinder is suitable for the task.

One calliper has a piston area of 2x 30 pistons = 1413.71669411541
And 2x 28 pistons = 1231.5043202072
Total piston area for one Porsche calliper = 2645.22101432261

A stock VW Beetle calliper has 2 x 40 mm pistons, total piston area for one calliper = 2513.27412287183

Incidentally a Type 3 VW uses the same size master cylinder, its callipers use 42 mm pistons. Total area = 2770.8847204662

Another issue is my wheel base is too long by 30 mm, the 944 alloy trailing arms must have done this.

I was trying to find the stroke of a 1303 master cylinder to give the engineer more ammo, I'm pretty sure it would be the same on all disc brake VWs.

I'm using a Volvo 240 master cylinder reservoir, does anybody know the volume of one of these? another thing that worried them if my reservoir was big enough.

There are other issues but will I keep quiet about those for now, one is hilarious.

Steve
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Old June 13th 2011, 13:10
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Steve, don't forget to make the point that monoblock calipers need far less fluid that sliding calipers as there is less slop in the assembly..
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Old June 14th 2011, 05:41
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Quote:
Originally Posted by Steve C View Post
another thing that worried them if my reservoir was big enough.

There are other issues but will I keep quiet about those for now, one is hilarious.

Steve
I find the above (bold) statement hilarious enough already.. your sure he's an engineer?
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Old June 14th 2011, 06:06
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Hi Wally

I actuality fitted a Volvo 240 master cylinder reservoir, so it would be slightly bigger than the Beetle one I guess.

What they are getting at is, if I fill my reservoir and I drive the car until the brake pads are worn out, I will not run out of fluid.

I cant keep it quiet any more, they suspect that my Beetle is Mexican Beetle that I've put on an early pan, I've pointed out to them that a Mexican Beetle has a flat front windscreen and a torsion bar front suspension and my car being a 1303 has a curved windscreen and McPherson struts.

The reason that they suspect this is, is that I bought new wind-up glass for my door windows from the USA, they were made by VW Mexico, so 2 windows made in Mexico, front windscreen and flipper windows were made in Australia. My rear window is a heated German one and and my pop outs were made in Germany as well, its a wonder that they didn't suspect that is was an Australian or German Beetle lol

Steve
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Old June 14th 2011, 06:56
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Volvo 240 master cylinder?

Goggle suggests it's 22.2mm bore
but this perhaps indicate a 22.2 / 15.75 set up. No info on stroke.

http://seekpart24.com/volvo/240-p242...der-100026#all

Also read page 7 of below. It seem that the twin circuits were split diagonally and the twin bore set up was to reduce pedal pressure if one circuit failed. So I guess both circuits have the stepped bore and it is not a method of setting up brake bias.

http://www.volvo244.pl/images/broszury/1978-240.pdf

Another option?

Kerscher sell a 20.64mm cylinder to suit porsche brakes. It is an ATE unit from a Renault Traffic van. ATE part number 03.2120-1142.3


If I recall correctly.... the bug master cylinder has quite a long stroke. I always assumed this was to allow for poor adjustment of the rear drums.

Last edited by Bruce.; June 14th 2011 at 07:09.
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Old June 14th 2011, 20:26
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Hi Bruce

I'm only using the Volvo 240 resevoir, I still have a stock VW 1303 disc brake 19 mm master cylinder.

Steve
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Old June 14th 2011, 21:05
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swap to a kombi 24mm perhaps?
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  #10  
Old June 15th 2011, 01:20
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Hi

Its not the master cylinder that they are questioning, its the reservoir size. The 19 mm master cylinder gives me great pedal.

Steve
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Old June 16th 2011, 11:50
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Steve, the stroke of the m/c is a red herring IMO. You are quite right about the comparison of the Type 1 and type 3 calipers that show that they both are fed by the same m/c and that the Porsche calipers fall as a size between them. Ergo the stroke cannot be an issue. The 'normal' (if there is one) clearance for the pad to disc contact is 14 thou (0.3556mm) so you can calculate the amount of fluid to take up the clearance. Thereafter the amount of pad/fluid/seal compression is variable depending on the pad material, fluid type, seal type and not forgetting the hose expansion. It is impossible to predict accurately therefore how much the piston will travel - it can only be determined by trial and error.
Another point worth mentioning is the difference in pad sizes between the Porsche and the VW pads. Assume that the Posrche pad is 20% larger than the type 1 pad and given by your figures the Porsche piston area is 5.25% larger then the compression force/unit area on the Porsche pad is LESS that that on the VW pad for a given pedal pressure. Therefore, a) the pad doesn't heat up so much so as to soften the material and b) there is less force to compress it.
Think on this: Alfa Romeo developed their 116 V6 Rally/Circuit car that was homologated with twin standard calipers at the front and the standard single caliper at the rear. The vehicle is also homologated with a standard dual master cylinder of equal 25mm pistons for the front and rear. Doubling the piston area at the front had little untoward effect on the braking or driving ability of the car and excessive pedal travel was definitely not an issue. Also given that the rear m/c piston had to travel 4 times the length of the front piston as the difference in caliper piston sizes front/rear are about 2x in standard format if m/c piston volume had been an issue it would have been profound in this set-up.
It seems to me that your checking engineers don't know enough about the theorey of braking systems and appear to be applying illinformed and unfounded intuition. God save us from amateurs!
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  #12  
Old June 17th 2011, 06:18
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I see that I misunderstood your question and as per above...... what a piece of nonsense.

I guess you could fit a larger reservoir if they insist but what about a slightly different solution. Could you fit a fluid level sensor in the cap (the usual OEM place I think) linked to a warning light? That way the size of the reservoir (verses the fluid requirements of worn out pads) becomes redundant.

You might be able to find a random cap that fits the 240 bottle or butcher another cap to get the sensor out.

Just another option to consider.
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Old June 17th 2011, 07:00
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Hi

Thanks guys, good technical answers as usual from this site.

They will base their calculations on the fluid used to fill the movement of the pistons from new pads to worn out pads.

The front pads on my car 18 mm from new and the rears are 15 mm.

I haven't done the calculations yet but they need to see that I have enough fluid to left over in the reservoir after the pads have completely worn out, I guess that they have to make sure the car is idiot proof.

I'm pretty sure that they will need to see 1.5 times the fluid needed after the pads are worn out.

I'm getting a spare Volvo fluid reservoir tomorrow so that I can show it to the engineer and he can use its calculate the capacity.

Steve
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Old July 4th 2011, 11:56
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Hi Steve,
Did you get anywhere with this? My rough calculations show that the fluid resevoir need around 125ml per division, thats 1/4ltr in total.

Clive
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  #15  
Old July 4th 2011, 19:24
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Hi

I'm still dealing with the local engineers, I got hold of another reservoir the same as mine, its actually a Empi one the same as sold by CB.

Using kitchen measuring devices it holds about 175 ml

Steve
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