914 Brake Master Cylinder?

[lennyhope]

I think my master cylinder is toast! Brake fluid has leaked from it and under pressure just sprays out it seems.

1. Is the 914 master cylinder the exact same as the 911 type?
2. What should I expect to pay?
3. Just get the cheapest on evilbay?
4. When replacing and there is still fluid in the reservoir I topped up (!), is it an easy job to replace for a first timer and will I need to get rid of the fluid in the reservoir??
5. Has anyone got one spare on here??

[shandyhaggis]

Hi

I got one from Mittelmotor I think it was around 99 euro - wasn't the most expensive version so I may regret the quality in the long run. I still have my old one but its equally toasty:-)

I got the 19mm 911 version - 911.355.012.02

Andrew

[Darren C]

Hi Lenny,

Your enthusiasm is admirable but your questions worry me.

My advice is to buy the best master cylinder you can afford. Genuine ATE are the best.

Get a Haynes manual and read the section on changing the master cylinder a few times before you get stuck in.

Drain the reservoir, you need to take out the two pipes from it that fit into the top of the master cylinder.

Buy a proper brake union spanner if you dont have one (like a ring spanner but with a cut out to feed over the pipe) this will stop you rounding off the pipe unions.

Make sure you locate the reservoir hoses fully in the top of the master cylinder rubber gromets. Ideally mark them with tipex or white paint before you take them off the old master cylinder so that you can see how far to push them into the new one to make sure they locate fully.
Dont forget to adjust the pushrod (under the pedal board) when you have the new one fitted. The adjustment will change and you need to set the pedal free play.

Make sure you bleed the brakes fully afterwards to get all the air out and be patient it will take time.

Good luck.

[rhd racer]

All as per Darren's advice.

Collect the old fluid into a container and you can dispose of it with the oil at the local tip. You will lose so much I would push the old fluid out via open bleed nipples and effectively change the fluid at the same time. It will have definitely absorbed some water over time and is an often overlooked service item.

It's not a hard job, just needs some thought and a willing helper. For info, a standard 14 uses a 17mm MC, and the 19mm one from a 911 is a tried and tested upgrade (ie the same shove on the pedal applies more pressure as the larger Pistons move more fluid).

I would take the opportunity to check all your brake lines at the same time as there is no point doing all the hard work and then having to replace a line for the next MOT. check the proportioning valve on the rear bulkhead for leaks too. Also buy a full set of new bleed nipples, these round off with age as are very soft to start with.

HTH

Wayne

[jackstowers]

All as per Darren's advice.

It's not a hard job, just needs some thought and a willing helper. For info, a standard 14 uses a 17mm MC, and the 19mm one from a 911 is a tried and tested upgrade (ie the same shove on the pedal applies more pressure as the larger Pistons move more fluid

Wayne

I thought it was in fact the opposite and the larger cylinder requires more pedal pressure to achieve the same braking effort but less travel

[davep]

Getting the reservoir line ends into the MC can be very tricky. Before you start, be certain that the two washers (one per line) are under the rubber grommet that holds the metal line ends into the MC. A proper replacement part will have the two washers and the two grommets, plus the brake switch. The old washers from the used part can be used if the new MC does not come with them. New copper washers for the banjo fitting would be a great idea. New rubber lines for the reservoir connection are a good idea also; these are usually blue in colour to indicate brake fluid compatibility. Loosening the reservoir is a good thing to assist in getting the lines in place.

[middlefour1]

Also available from Kontakt in London, 020 8654 8837. I have used them lots of times and found them to be very good and usually a lot more competitive on price.

[middlefour1]

All as per Darren's advice.

It's not a hard job, just needs some thought and a willing helper. For info, a standard 14 uses a 17mm MC, and the 19mm one from a 911 is a tried and tested upgrade (ie the same shove on the pedal applies more pressure as the larger Pistons move more fluid

Wayne

I thought it was in fact the opposite and the larger cylinder requires more pedal pressure to achieve the same braking effort but less travel

That is correct David, the factory fitted a 17mm cylinder for a reason, it works.

[rhd racer]

Point taken - it must be that they are matched to a larger bore piston in the caliper then, so they need more fluid to operate. (Hence my four pots require a 21mm m/c). I'll get my coat!!!

Not sure why people back on about a 19mm then with standard caliper said, that being the case...

[914 KEV]

That is correct David, the factory fitted a 17mm cylinder for a reason, it works.

The reason the 914-4 ended up with a 17mm master cylinder over the 19mm had nothing to do with development of the 914 brakes through testing.

VW were using 17.46mm master cylinders across their range at the time and had been for many years, most of their cars used drum brakes all round and when they introduced disc brakes options to their cars in the mid-sixties nothing changed, while Porsche had been using 19.05mm since the 356B, when they introduced disc brakes to the model.

For the 914-4 they used the VW standard of a 17.46mm master cylinder and for the 914-6 would use the Porsche standard of 19.05mm. No development to find the best size, just a simple one manufacture uses one size while the other uses the other!

While the new 411/412 was being developed the VW engineers opted to fit a 19.05mm master cylinder to their new car which had the same front brake callipers and discs as the 914 but used as used the type 3 brake cylinders on the rear.

Half way through 1972 the front callipers for the 411/412 had been redesigned to allow for a fatter brake pad to be used and as the offset of the brake discs would also change and the new brake discs would be fitted with wheel self-centralising also.
At this time also VW changed the master cylinder size across their range from 17.46mm to 19.05 as more and more of their cars were now being fitted with front disc brakes over the drum brakes.
As the 914 was not using a VW part for the master cylinder, it stayed unchanged.

I do believe that if the 914 was using a VW part master cylinder, from mid 1972 the 914 would also have changed to the 19.05 master cylinder.

Porsche and VW development engineers along with ATE were now agreeing that when disc brakes were fitted over drum brakes on the front of the cars the optimum size brake master cylinder when using brake discs was 19.05mm.

If the 411/412 had come out slightly earlier, then I would think the 914-4 and 914-6 would have been fitted with the 19.05mm master cylinder from day one!

[middlefour1]

Well done Kev!!

[jwhillracer]

OK Kev, next question!
Why did Ate, VW & Porsche use 11/16" and 3/4" master cylinders, and not metric sizes?

JW

[914 KEV]

Andy I see you post the same question in more than one place at the same time!
Hopefully here on DDK you will receive a more thoughtful answer from the answer posts!

One thing you didn’t post here is the photo of your master cylinder showing the leaking brake fluid, so I have posted it below.



To me the leak is from the input line(s), either the plastic to metal connector on the end due to rust or the grommet(s) that holds it in place due to them perishing or not pushed fully home the last time the master cylinder was changed!

Lots of good advice already post above and I would like to added from my experience of replacing around a dozen 914 master cylinders over the years.

When I have the job of remove and refit the master cylinder I remove the fuel tank first.

Removing the master cylinder is the easy bit, refitting the input lines back into the new grommets and pushing them all the way home is the hard bit! (New ATE master cylinder will come with the washers and new input grommets that davep mentioned)

The input lines go through grommets in the bulkhead under the fuel tank.
With the grommets removed and the reservoir holder removed or the blue hose connection to the reservoir removed, the input lines can unclipped from the bend over metal holders and then lowered through the bulkhead so you have a lot more room to attach them back into the grommets properly. Once the master cylinder is back in place the grommets can then be refitted. The grommets push in from above and can't be refitted from below.

[914 KEV]

OK Kev, next question!
Why did Ate, VW & Porsche use 11/16" and 3/4" master cylinders, and not metric sizes?

JW

Is this due to the pattern holder being a British company (Dunlop?), as they would have be using imperial sizes and not metric?

[lennyhope]

Thanks chaps.. Much obliged as usual. Dont worry for me too much