first brake job

[Flieger]

I am going to embark on swapping calipers for the first time. I bought some stunningly restored S calipers for my 1971 911S. (Thanks, Neunelfer ) I am going to swap the new ones onto the car and then bleed the brakes. The pads are new, as are the stainless steel braided brake lines. I just did the pads a couple months ago and I only drive about 50 miles a week on weekend blasts (have you seen the gas prices?)

Any tips other than PB Blaster/WD-40, have heat ready, and the right tools? I have been tipped off to the copper sealing washers for the caliper banjo bolts. I am planning to clean and reuse my current pad guide pins and retaining springs.

I am going to be getting rid of the dust shield that shrouds the back side of the rotor in order to improve cooling. The inside front pads were worn down twice as much as the outside front pads.

Do I need to bleed the rear brakes also, even though I am only doing the front? I expect the answer will be yes.

[Rich Lambert]

Get yourself a rubber mallet for gently tapping the calipers to dislodge trapped air bubbles and a pressure bleeder like the "Black Label European Power Bleeder Kit" that Pelican sells. I used one of those on the last round of brake bleeding and it works great...way better than the sucker type or the pump-the-pedal method.

With the dual hydraulic circuit you could probably get away with bleeding only the front. But if it were me, I'd do all of them...just because.

[jameshtaylor]

Or just use gravity to bleed your brakes. Works fine on the early cars, saves money, and avoids buying an ugly piece of equipment that drips brake fluid everywhere you store it!

You will need: brake fluid, six or seven feet of plastic tubing sized to fit snugly over the nipple on the brake caliper (mine uses 3/16” internal diameter tubing but check yours), and an appropriate small box wrench to open & close the bleed valve. (Sears makes small 6 sided combo wrenches which are useful for recalcitrant cases; the bleed valves on my car are 7mm but some I believe are 8mm.)

Here’s the procedure: jack the car up, support it on jack stands or wood blocks, and pull the wheels so you can get at the calipers. Or do one wheel at a time if you want.
Loosen the brake fluid container cover in the trunk.
At the first wheel, position the plastic tubing so it hangs straight down (from your garage roof or door or a door or even a stick or spouse) to the caliper. Slide the box wrench over the nipple, slide the plastic tubing over the nipple, and open the nipple with the wrench.
Watch the fluid rise in the tubing until it reaches the height of the brake fluid reservoir in the car, maybe 15 inches. This will take 3-4 minutes. Tap the caliper a few times with a rubber hammer or block of wood if you want. Watch the tubing for bubbles, especially when you start. If they keep on coming after the level in the tube has risen 12-15 inches, close the nipple, remove the tubing, drain it into a paper cup, and repeat. Assuming you are bubble free after 2-3 inches of fluid have drained, however, do this once; tighten the wrench, pull the tubing off while holding a paper cup to catch the fluid, and move on to the next wheel.
Keep an eye on the fluid container and replenish the brake fluid when it's down more than an inch.
Do all four wheels & again replenish the fluid.
You are done. Gravity has done all the work. You cannot damage your master cylinder with this technique, and you don’t need a helper (if you have a garage or a tree or can rig a stick to hang the tubing from.) This should take you a maximum of 5 minutes per wheel once the car is up and the wheels are off. Forget the idea that there are bubbles all thru your lines and that pressure will somehow push them out but not the fluid. A pressure bleeder only moves any bubbles and fluid thru the lines more quickly. But they travel together. So gravity will do the job perfectly if time isn’t the object.
This process works because nearly all the bubbles generated by driving around and heating the brakes excessively are found at the very top of the caliper near the bleed valve…in effect where the heat is.
Depending on how much fluid you withdraw each time, you will find that the fluid is fully replaced every 10-15 bleedings. I track my car 5-6 times per year; bleeding pretty much replaces all the fluid over a couple of years, as recommended by many experts.

[Flieger]

Thanks for the tips. Interesting procedure.

[Flieger]

I got the calipers sone today. I will still need to do some more bleeding but they are great. I left the dust shield on because it was too much work to take off the rotor. I did not have a replacement rotor and the thickness of the current ones, using a micrometer, was .7 inch, about 18 mm. This is much thicker than the spec for the new front rotors for a 1971 911S according to Wayne's book. I checked in a few different places. Anyway, I am going to run with these rotors for a while.

Comments on the disparity in the specs?

I will take it out for a good shake down drive tomorrow and then try bleeding some more. My brake pedal is actually in a better place for rev matching downshifts.

I posted a question about the dust covers in the autocross forum and they said to get rid of them for some 993 air deflectors or ducts. Maybe I will try the dryer hose when I change the rotors.

I saved a lot of $ and had even more fun

[Flieger]

The rubber mallet came in handy for getting out the bubbles from the front calipers. Thanks for all the tips. I am going to bleed the rears today before my shake-down drive. I let the master cylinder fluid level get a little too low and I think some air got in there because the pedal is softer than with the old brakes. I did the 2 person bleeding method. I did the pumping and my dad did the calipers.The fronts were pushing clean fluid. I know it is always procedure to bleed the brakes again after a good amount of miles. In my case, that would be a couple weeks. The pedal is engaging low at the moment but is just as it was yesterday, so no leaks.

Thanks to Neunelfer and all the support from the board.

Can anyone confirm the specs for a 1971 911S front rotor thickness? I do not see how my rotors can be 18 mm thick now when they are supposed to be around 12mm. I did use the only micrometer I could find at Sears, which was not metric. .7 inch * 25.4 mm in an inch = ~18mm, right?

[Flieger]

Well, I pulled some air out of the rear brakes and the pedal firmed up a bit. The travel is still longer than before but I think this is because the pistons actually move now.

I took a run and had fun. The braking is much improved- smooth, firm and easy to modulate. I can also blip the throttle on doenshifts much easier because the brake pedal is lower and closer to the height of the throttle. The car is much more stable because I can trail brake and control it smoothly.

Now I have to keep pulling my wheels to clean the calipers, though. They are great. The car feels much more agile and stable.

[Neunelfer]

Looks great!

Seems like you've done all the right things.

It sounds like you're getting vented rotor thickness confused with solid rotor thickness.

Vented rotors new should be around 20mm.

[Flieger]

I thought that was the problem when I saw Wayne Dempsey's book had later model cars with 20-18mm thickness. I figured it was a misprint when he listed 1971 911 front rotors so thin. That was the only range of years that fit my car in his book.

I did not have new rotors ready anyway so I just was curious as to the thickness.

[Flieger]

I see now on the Pelican site it says for a 1971 911 front rotor new is 20mm, wear limit is 18mm.