Changing the Brake Master Cylinder on a Porsche 930
Harken back… Remember that time I took my bay-bee onto the track?
And afterwards I changed the oil and found particulate in my catch pan?
And then I went through and cleaned out the engine and didn’t find a single sign of that particulate? Well, I took a big piece of the particulate, stuck it in a jar of clear new mobile 1 and let it sit.
Its been sitting for 3 months now and… it’s still there, unchanged. Alone the mobile 1 will not remove that particulate. So sitting in a cold garage I now know that the oil didn’t magically dissolve the particulate. Yes, it could still be magic that made it go away. Jury still out I suppose.
So, damage #2:
After driving on the track I noticed the brake was spongy. Figured I better bleed them.
And I made a stupid and costly mistake.
See, I don’t have a pressure or vacuum bleeder, so I push the old fluid out of the calipers using the old “kid pushing the brake pedal” technique. And I bled the calipers and found some bubbles in the blackish fluid that came from fronts. So figured that was the ticket. And
then I found the pedals weren’t spongy any more, instead the pedal would slowly drop as I sat at a stop light, which indicates a leaking master cylinder. How is bleeding related to leaking master cylinder? Really, it never leaked before the bleed.
The mistake I made is this: the car is 35 years old. Brake fluid absorbs water from the air, you must flush it every 2 or 3 years. If you wait 6 or more years (like my previous owner must have) then the steel bore in the master cylinder will start to rust from the water in the fluid. The rust is hard and gritty. There will be no rust where the cylinder’s pump plunger moves, its being polished smooth all the time. But in areas where the plunger never travels the rust will grow tall and mighty, sort of like the great barrier reef.
When I instructed my son to depress the brake pedal further than usual it caused the plunger seal to pass over the rust and the seal was destroyed.
The lesson here is, for an old car you must bleed using a pressure or vacuum bleeder. If I’d done that I wouldn’t know there was rust and the master cylinder would have worked perfectly for another 35 years.
So.. if you are a manic type and can’t live with the possibility of rust in your MC you can bleed an old brake system with the pedal and destroy it, then buy a new one and it will be nice and shiny. Or, if you’re a more pragmatic type you can appreciate that there is probably rust there, assume there is, buy a pressure bleeder for $30-60, and you can bleed brakes without destroying the MC. Anyhoo.
I need to rebuild the master cylinder, but reading on the internet the rebuild is no good unless you can fix the corroded bore, and the bore can’t usually be fixed, it’s usually pitted so instead it must be re-sleeved. Resleeving means drilling out the master cylinder bore and putting in a stainless (or brass) sleeve. Since those materials won’t rust this fix is considered a “forever fix”.
Unfortunately most of the cool folks that do resleeving have left us. Moved to more profitable pastures. I did find a legend of the brake repair industry locally here in seattle: “Goldline Brakes”. I called him and had a wonderful discussion. He says
resleeving is quite time-intensive to do right and he would need to charge $450 or so to rebuild my master cylinder (with resleeve.) He said it wasn’t cost-effective unless you had a collector-class vintage american car where the parts were no longer available. As mine was still available new for $250 he strongly recommended I just buy a new one, and then pleaded that I flush the brake fluid every 3 years. There is another place online that you might try: White Post: http://www.whitepost.com/brake.html maybe cheaper. Maybe not.
So on advice of wonderful man at Goldline I ordered a new MC from pelican, it arrived in 2 days.
I have the 911 Projects Book by Wayne. It has a whole section on master cylinder replacement, and yet again there are a bunch of details and steps that are just left out. Pisses me off. Here is a link to the free online instructions, which also leave out steps but is better than the book.
Now that I’ve done the swap, knowing the steps and what tools to use, I think I could do it again in 90 minutes, but the first time, unknown steps left out, it took me five hours, and that’s not including a trip to target for a turkey baster for draining the
Work in driver side foot well:
– Get your SUPER BRIGHT LED WORKLIGHT, plug-in, turn on and shine it towards the pedal area.
I got this at Costco and its fricken’ amazing. Mega bright and DOESN’T GET HOT!
-Remove the carpets on the driver’s side floor.
-Undo the two bolts at the base of the accelerator pedal.
-Pull accelerator pedal loose from ball fitting.
-Put the pedal and bolts into a bag or bin for when you put them together.
-Now you can remove the carpet that is under the brake and clutch pedal. Note how at
the top of the carpet there are two metal brackets which go through holes in the
carpet – the carpet is held in place with two plastic ribbons. Carefully slide the
carpet loose through the notches. Once top edge of carpet is free you can pull it
over the top of the pedals. No need to force it, be gentle, there is room if you do
one pedal at a time.
-Now remove the wooden pedal form. One bolt at base, then pull back and wood is
free. Plenty of room to take wood panel out over pedals. Admire the nice high
-Look how brake pedal connects to a gold plated lever that comes through the top of the foot box. The pin that holds the two connected is itself held on with a spring clip through the end of the pin. Pull spring clip free with pliers, then push pin out.
-Now follow top of foot box back from brake pedal, you’ll see a bolt in the middle of the roof of the foot box, this bolt actually goes into the bottom of the master cylinder, holds the master cylinder in place. Remove it and put it somewhere safe.
At this point you are done with the driver’s side, rest of the disassembly will be in the front trunk space.
– Lay out garbage bags over the driver’s side fender. This is to protect the paint especially from any brake fluid you might leak. Have some shop towels and a little water around it wash up any spilled brake fluid.
– Move your SUPER BRIGHT LED WORKLIGHT and shine it towards the brake booster. You will really need light to see what you are doing here.
– Fold back the carpet from the top of the trunk, you don’t need to remove it, just fold it away from under the dashboard. You need to get it clear because you’ll be removing the panel that hides the ventilation.
– When you remove the carpet you’ll see the brake reservoir on top of the large black brake booster. The booster is bolted to an aluminum mount that is itself bolted to the floor of the trunk. The master cylinder is being the booster, you can’t really see it.
– Remove the ventilation panel, there are 4 bolts with washers and lock nuts. Put away in a safe place.
Now you’re into it, remove some awkward ventilation stuff. You need to so don’t argue.
– There is a flexible black plastic hose, 1.5″ diameter that is behind and below and to the left of the brake booster. It connects on each side using large hose clamp. Undo and remove.
– There is a POS paper duct that runs behind the brake booster, actually right over the master cylinder. Undo one end (hose clamp) and gently feed it back under the dash. You can get it out of the way, you’ll need to in order to reach the top of the master cylinder. Careful, it is paper and seems fragile.
– Brake fluid time: put on your nitrile gloves, make sure the plastic bags are intact over the paint, go into the kitchen and steal your wife’s turkey baster. Drain the reservoir, I just sucked out fluid until it was empty. With the small baster it took me 10 or so sucks.
– Stuff some water-moistened shop towels underneath the brake vacuum booster. This will absorb and control the brake fluid that flows there.
– Reach back with 11mm FLARE WRENCH and one small turn at a time undo the metal brake lines that go into the top of the master cylinder. Once the lines are loose they will drip a little brake fluid. Don’t freak, just be sure and clean it all up and wash the area with water once the master cylinder is out. The nuts are quite hard to reach. There is room all around so find a comfy wrench position and go slowly.
– Undo the brake vacuum booster from its aluminum stand (4 bolts).
– On the side of the stand is a 17mm nut. This connects the stand to a gold-colored rod that goes to the base of the brake pedal. Undo the bolt and put it somewhere safe. The brake fluid reservoir is held by a bracket that is itself held by two of these bolts, so now reservoir is only held in place by two hoses that plug into the top of the master cylinder.
– Remove reservoir, just twist and pull and the two hoses will pull free. The master cylinder has two rubber rings that the hoses plug into, just a press fit. Just pull them free, no drama. Reservoir and its bracket are now loose. Yes, the hoses will spill a little more brake fluid.
– Remove the 4 bolts at the base of the aluminum stand. The stand, the vacuum booster and the attached master cylinder should all be loose now. You’ll see there is a ventilation control cable that passes directly over the junction between the master cylinder and vacuum booster.
– Jiggle the assembly free (base, vacuum boost, master cylinder.) Work slowly, don’t let the brake lines get caught and bend. Take your time to get the master cylinder under that damn vent control cable. It’s not necessary to remove the cable (though tempting it looks difficult to reconnect correctly.)
– Hurrah! Horray! It is out! Now use a wet sponge and wipe up the brake fluid. Wipe it all down with clean water which will neutralize the brake fluid. Clean out the turkey baster with soap and water, let it air dry, then sneak it back into the kitchen drawer before she gets home, hide the evidence! (Kidding honey!)
– Now separate the master cylinder from the vacuum booster, two bolts.
– Clean off all the parts. Sand and fix up the paint if there’s any corrosion. I just painted mine with fluid film, a non-toxic lanolin-based substance that prevents corrosion.
Install is the reverse of above. Here are my notes:
– You will have a new o-ring between vacuum booster and your new master cylinder. Rub it down with a lubw, I used napa syn-glide.
– O-Ring onto master cylinder.
– The instructions say to bench bleed the master cylinder. I didn’t bother because I didn’t want the mess. The pump primed itself quickly, no drama.
– Bolt master cylinder onto vacuum booster. Use only 25NM of torque which is not much at all.
– Put everything back with extreme care to use correct torque settings. Brake lines to master cylinder use only 11NM of force! That is just a little bit snug, with a short wrench.
– Remember that bleed screws on calipers use almost no torque, TWO Newton Meters is just a bit more than 1 foot pound, so pretty much nothing.
– Nice opportunity to vacuum out behind the pedals.
– Only other thing that gave me grief was snapping the accelerator pedal back onto the ball, I held the metal ball rod with pliers, pushed really hard and the pedal clicked on. Wasn’t easy though.
– Bleeding: you should do the passenger rear caliper first, then the driver rear, then the passenger front, then the driver front. Each caliper has 2 bleed nipples. Take your time and don’t let the reservoir run dry! Quite a bit of fluid is needed, was easy to see when it was done because I’d previously used ATE Super Blue (since discontinued.)
Anyway, end of the day the brakes are now SOLID. No softness and no spooky slow pedal descent while waiting at red lights. Woo!