Brake Master Cylinder Replacement

Hello everyone,

The brake pedal on my 1973 911T is getting very sticky indeed, so much so that I need to reach down and pull the brake pedal back every time I apply the brakes!

So, I've decided its a good idea to change the master cylinder.

Questions:

1) Have any of you ever done this, and if so, could you give me some simple instructions? The article on this website is for cars with power brakes - the procedure seems different for the older models, as the Haynes manual talks about removing the panel under the steering rack and getting to the cylinder that way.

2) Should I change the pedals at the same time? The problem may be due to a broken brake pedal return spring, although I doubt it, as the problem has been getting steadily worse for some time now, whereas a broken spring would suddenly go (I assume).

As always help is very much appreciated!

- roGER

Roger:

I used to have a 1974 911, and when this happened to me, it was not a faulty brake master cylinder that needed replacing, but rather the bushing which absorbed brake fluid and swelled up.

Yes, you will still have to either replace the master cylinder, or rebuild it, but you'll also have to replace the bushing(s) at the pedal cluster.

All three pedals are "housed" in this cluster, and when brake fluid runs down the shaft from the master cylinder, the fluid swells the bushing. You can replace the bushing with either OEM bushings, or brass. If you use the brass, they will not swell the next time your master cylinder leaks.

This is an "easy" fix, though time consuming. You'll also have a little effort to remove and re-install the return spring, but a nice weekend will allow you to bask in the sun while you do......Andras

There is nothing technically complex about this job! It is in an area with difficult access, if you happen to have much 'bulk' and the pedal assembly should be disassembled, cleaned, treated for rust damage, and have all of the plastic bushings replaced with factory parts, not brass replacements some folks sell! The way the master cylinder is mounted is identical to a VW Beetle, so, if you have ever worked on or seen one of their master cylinders, fear not!

Flare nut wrenches are required if you do not want to damage the fittings! Sears has metric sets, as do others. Since you are going to 'open' the hydraulic system to the atmosphere, it is the logical time to change all of the brake fluid, a task Porsche recommends every two years, but very few owners pay any attention to! All four calipers should be removed and drained completely! The brake lines should be blown out with compressed air, as should the calipers! With the age of your vehicle, I would recommend the replacement of the four flexible rubber hoses with OEM parts. You may need to clean the area around the pedal assembly of any rust damage and apply Rustoleum or a similar paint. The pedal cluster is often quite stubborn to disassmble after rust damage has occurred. A sturdy bench vise, propane torch, and heavy mallet is often required for disassebly. Penetrating oil alone is not likely to be of much help! A Haynes manual would be of some assistance in this messy and dirty job! I suggest reading before starting the job, so you will be familiar with the layout and arrangement of the various assemblies. If there is any doubt about the health of your clutch cable, this would be a good time to change it, too!

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Warren Hall
1973 911S Targa

[This message has been edited by Early_S_Man (edited 03-27-2000).]

Thanks very much for the information both of you!

Warren - why do you not recommend going the brass replacement way with the bushings? I'm just curious, as to why its a bad idea.

Regarding the points in both mail messages, points - too true! From my preliminary investigation, the pedal/footwell area IS rusty, and I will have a damn good clean-up around there.

I have a set of flared wrenches in sizes 7mm-14mm (I used to have a 15mm as well and can't find it anywhere!). Hopefully these will be sufficient.

This morning I soaked the entire area in WD40, and managed to get enough movement to drive (very carefully) a couple of miles.

Saturday is now officially reserved for this task, assuming I can source some pedal bushings by then. Pelican provided a master cylinder very quickly - it was only ordered yesterday.

Thanks once again for the advice gentlemen - much appreciated.

- roGER

Roger, I don't like the brass bushings for a couple of reasons ... the factory used plastic for a reason, that pedal cluster is intended to NOT need lubrication, opereated dry, which it does for years, quite well! The area collects 'dirt' and brass bushings need lubricating to work silently, oil or grease collects dirt ... kind of a never-ending cycle of destruction! I use silicone brake fluid, so I never have had a problem with the bushings in my car ... they are still original!!! In my opinion, if you change your glycol brake fluid every two years, completely, as recommended ... you won't have problems with pedal cluster bushings in the future. Or, you can switch to silicone brake fluid, and be assured of minimal brake system deterioration in the future!

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Warren Hall
1973 911S Targa

Thanks a lot Warren - that makes sense.

I'll post another reply here in a week's time (I'm away next week).

- roGER

Just a quick update -

I've managed to remove the pedal cluster ready for rebushing.

Removing the pedal cluster is a swine of job!

Not because anything is very difficult, but the lack of space makes everything difficult!

If any of you attmept this job, here's some useful info:

A quarter inch socket set is very useful, as are a set of small spanners and long screwdriver (flat head)

The bolts on the floorpan holding the pedal cluster down are 10mm.

The screws holding the master-cylinder/pedal cluster to the front bulkhead are 13mm.

The large bolts holding the suspension arm/steering rack cover are 17mm.

The small bolts holding the steering rack cover at the front are 10mm.

Next week - replacement of the master cylinder and rebulit pedal cluster...

Roger: I will be taking on the same task that you did (replacing master cylinder and rebuilidng pedal cluster) on my 912 in about 2 weeks. I was just wondering if you ever got the car back together and how did it go? Also did the new bushings make the pedals a lot smoother?

Thanks!

Hello,

The pedal set is with Pelican being rebuilt.

As soon as it comes back I'll put it back on
and let you know how it is.

- roGER

This is a question for anyone who has used the bronze bushings for a pedal cluster rebuild: What were your impressions of the fit of the bushings in and on the pedal cluster parts?
I ask this because I am in the middle of a rebuild and I was NOT impressed with the fits at all. All the bushings seem loose on the OD (the part they fit in), and the parts that fit inside the bushings seem loose as well. I guess looser than I'd like or expected. The new bronze pieces for the accel linkage where even loser than the original plastic parts they where meant to replace. Has this been the experience of anyone else? I more than half considering using OEM bushings. Comments please?

Chris
Black 78 SC

I don't know because I'm still waiting for the rebuilt pedal cluster to arrive... It should be here today and the fit of the parts will be the first thing I check...

- roGER

I recently rebuilt my '71 pedal cluster with a bronze bushing kit that I bought right here at Pelican Parts. The bushings fit very precisely with no play in ID or OD. Once reassembled, the pedals have virtually no movement back and forth and move freely in the direction they're supposed to, a huge improvement in driving. I guess either your parts have worn, or your bushings are the wrong size for some reason.
I went with the bronze because I wasn't impressed with the performance of the original plastic ones. Some of them had worn almost completely through after 130K miles, leaving the pedals free to flop around in all directions. This with no evidence of any past brake fluid spillage, which I understand would cause swelling, not wear. The bronze ones are oil-impregnated for self-lubrication. They would be unaffected by a leaking master-cylinder disaster, and I can't imagine they would wear any worse than the plastic ones, but who knows?

Well folks,

Here's the latest news on this long story:

My pedal cluster wasn't rebuildable - according to the good folks here at Pelican, the base was dented and distorted, and someone had bodged up the "axle" tube that holds the bushings by welding it!

How on earth all this damage occured is beyond me - an accident perhaps?

Anyway, Pelican were very good (again!) and sent me a rebuild unit "off the shelf."

I installed this "new" unit this morning.

Once again, I must stress that the lack of accessability is a BIG PROBLEM with this job.

If you are not thin and have small hands like me, you may have major problems. Connecting the throttle cable and the clutch cable are tricky.

After quite a struggle I actually connected the throttle cable BEFORE I installed the pedal cluster. I then fitted the pedal cluster into place. Using electrical tape to tape the brake and clutch pedals together made this job a bit easier. This is because the clutch pedal is sprung so that it wants to go down, while the brake pedal wants to stay up! Try and thread the brake pedal actuating rod into the master cylinder while you do this - its VERY TRICKY and you must be patient.

When you attach the floorpan screws that hold the pedal cluster to the bottom of the car - don't do them up too tightly! That way you can tighten the master cylinder nuts and get a good "snug" fit at the front. Then you can tighten the floorpan screws down.

When I came to connect the clutch cable, I ran into another problem. Because the pedal cluster was different from the original, the clutch cable was now far too slack!
Fortunately, I managed to adjust it at the pedal end. To do this, loosen the lock-nut (10mm) and then grip the end of the outer cable with a self locking wrench. You can now turn the brass fitting "down" the cable to shorten it. There's about 1cm of travel provided, and it proved to be just enough.

Reverse gear engages without grinding although I'm going to adjust the cable at the clutch end this week-end, as at present the clutch disengagement occurs right at the end of the pedal movement, and it doesn't feel quite right.

Apart from that, the pedal cluster replacement has been a great success. The throttle feels MUCH better, and the original problem, which was a sticking brake pedal, has disappeared.

On Saturday I hope to replace the master cylinder, which was the original subject of this topic!

- roGER

Final update:

I replaced the master cylinder this week-end.

Its actually a fairly straightforward job, provided you have the correct tools (namely, flared wrenches).

Here's a few of points that may help you
if you do this job.

* Have a large paper cup or plastic bottle or
something to collect the brake-fluid that
pours of the pipes when you disconnect them.

* Undo the pipe-connectors in order, smallest
diameter first (10mm). Then disconnect the much larger brass nut that holds a coupler unit to the side of the master cylinder(17mm?). Then disconnect the master cylinder attachment nuts (13mm).

* If you do all of the above, you'll find it relatively easy to undo the two pipes from the resevoir that fit into the top of the master cylinder. These pipes are a friction fit - just pull them out of the rubber fittings.

* As always, the biggest problem is space - there's not a lot of room under there, although its child's play compared to the infamous pedal cluster.

* IMPORTANT: When you fit the new unit, ensure the rod from the brake pedal to the master cylinder is correctly positioned: If it isn't, you'll have to disconnect everything and start again (guess how I know this?!?).

Obviously, you'll have to bleed the brakes when all is fitted up. The bleed nipples are 7mm. Make sure you have a good quality box or flared wrench that fits across the flats to do this. Alternatively, if you have a DEEP 7mm socket (that fits across the flats) that should work as well. I maanged to semi-round off two of the bleeders before I realised what had happened - learn from my mistakes!

A big THANK YOU to everyone who's helped me during this saga, especially Warren and the folks at Pelican who were generous and efficient in dealing with my beat-up old pedal cluster unit.

- roGER