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311 General Brake Tech Section

Brake Lines

Brake lines are 3/16th inch tubing and for the most part use 3/8 x 24 fittings. Useful info if you plan to fabricate your own lines.

Brake Master Cylinder

Early year use a single reservoir brake master cylinder and later years use a dual. In the dual, the front reservoir is smaller and operates the rear brakes - the back reservoir is considerably larger and operates the front brakes. Keep fluid above the lines on the cylinder. Once the fluid falls below the line you must refill with brake fluid and bleed the system to get rid of any air bubbles. If the fluid level is falling, look for leaks at each wheel, along all brake lines and inside the car (out the back of the master where it connects to the brakes). Fluid that leaks out of the back of the master cylinder is a sign that the seals inside are no good - you will need to rebuild or replace. The dual masters have become very pricey.

More info on front brakes

More info on rear brakes

Bench Bleeding the Master Cylinder

Okay so we have replaced rear wheel cylinders, shoes, front rotors, calipers, pads and all three rubber brake lines. Or we have rebuilt or replaced the master cylinder. My brakes are mushy-what is up with that?? Well, we now have air in our brake lines and need to bleed the system. Bench bleeding the master cylinder is highly recommended before reinstalling. Bench bleeding will remove the air and replace it with fluid. It is kind of a messy job but well worth the effort. Bench bleeding requires a short length of tubing with the correct fitting on one end (early) and two pieces for the later dual brake M/Cs. Remove the fill cap or caps. Install the tube or tubes routing the tube from the fitting back up into the reseviour as close to the bottom as you can get it. Secure the master in a vice so you have both hands free to begin pushing in on the rod. Put brake fluid in the reseviours being careful not to put too much in. Now begin pumping on the rod. Add fluid if you need to but pump until there are no air bubbles present. You can now install the brake master in the car.

Bleeding the Brakes

There are several ways to bleed/flush the brakes. The old way is below. An alternate gravity method is described by Dave Kaplan!

A couple of words of advice-if you are having difficulty getting the bleeding completed look for sediment or debris blocking the bleed holes. One owner reported finding a piece of the foil from the brake fluid bottle in his system. No names!! Bleeder screws filled with rust/crap. Run a 1/8" drill down the center of the bleeder to clear any blockage.

Bleeding the brakes is not difficult but is better accomplished with an assistant to pump the brake pedal or by using a Motive Power Bleeder. I have used the single person siphon brake bleeders and they are worthless. I did prefer using a warm body until I discovered the Motive Power Bleeder. You can visit Motive's web site by clicking here! Once you have tried it you will never have to worry about getting help to bleed your brakes again. There is however a small modification you need to do to make the Motive Power Bleeder work properly on the roadster. I was having a very hard time getting a good seal on the lid that clamps to the master cylinder. The firewall is too close on the rear reservoir of the dual circuit and the early single. My solution was to cut about a half inch off of the lid of the Motive Power bleeder cap and the rubber seal attached to it. It works great now and I always get a good seal. Bikermike came up with a much better solution for the cap. DIY solution for ~$10

Parts:

  • 1 x rubber stopper with one hole - size 7.5 ($1.50) http://www.sanjosescientific.com/products/rubber-stopper-1-hole-7-5
  • 1 x fender washer - 2" diameter ($0.40) - Drill 2 holes for zip ties
  • 1 x flared steel tubing - 1/4" OD (cut a $4 piece of brake line in half)
  • 3 x zip ties - to clamp to master cylinder
  • 1 ft x 1/4" clear tubing ($0.39)
  • 1 x 1/4" NPT to 1/4" hose barb fitting ($3) to connect to Power Bleeder fitting
  • 2 x old hose clamps (free)

Also, you can install speed bleeders in place of the old bleeders to make bleeding even easier yet. They are 3/8" x 24 TPI thread. Speedbleeders part number is SB3824 for both front and rear. You can visit their website to order!

Andy Cost (texas auto-crosser) always recommended raising the rear of the car, due to master cylinder being at an angle makes it difficult to get those last air bubbles out of the end. This makes practical sense as it also provides easier access to the rear brake cylinders.

Bleeding brakes has been discussed a few times in the forum and the consensus is that you start bleeding at the wheels that have the longest run of brake line from the master cylinder. For a stock LHD roadster the lines to the driver side criss-cross the car from left to right to left since the original design was RHD.

So the sequence for both LHD and RHD cars with stock brake line routing should be:

  • Rear-left
  • Rear-right
  • Front-left
  • Front-right

First top off the brake master cylinder with brake fluid. Next locate the brake bleeder on the wheel cylinder. Fix a 2 foot long piece of 1/4" or 3/16" clear tubing over the bleeder nipple and place the other end in a clear seal able container. Have your partner in crime pump the brakes up and hold the pedal to the floor or use your newly acquired Motive Power Bleeder to put pressure in the system. Crack the bleeder valve open with an appropriate wrench until you see bubbles and fluid come out. Close the valve. Ask your partner to pump 'em up again and hold 'em or if you are using the Motive-just move onto the next bleeder valve. Crack the bleeder valve and look for a clear stream of running brake fluid before you move on to the next wheel. Using the buddy system you must keep an eye on the level of fluid in the brake master because if you run it too low you will have to start all over again - but with the Motive Power Bleeder you do not have to worry about this as there is plenty of fresh fluid in the Motive's tank.

Keep doing this to all four wheels in the sequence noted above. By the time you get to the front wheels your partner should notice more firmness when pumping the brakes. Lastly, you can bleed the brake master. This should provide you with aggressive stopping power. The stock brakes work great as long as all of the components are functioning as they should.

Another note of interest is the cracked firewall syndrome. The firewall around the brake master tends to flex a lot due to a poor design. After some time the metal fatigues and eventually cracks. So when you aquire one of these little jewels take a look at that area of the firewall. This can happen on both late and early cars. Stan Chernoff has developed and sells a brake brace to cure this problem for the later cars with dual master cylinders. You can contact Stan from the Vendors page. I welded up a repair plate on my '66 and this seems to have cured the problem.

General note: The early cars '67 and before have a single master cylinder. The 67 2 liter and 67.5 and above have a dual master cylinder.

Brake fluid is nasty stuff-do not get it on your paint, in your eyes and please dispose of it properly.

That pretty much covers bleeding and general brake questions.