QuestionHi Jim,
I just got my first Spitfire, a 1978. It runs well and my dad and I are doing little things to make it better. My dad thinks there may be a leak in the brake master cylinder and he got a repair kit so we can do it tonight. He thinks this because you have to pump the brakes to make them work best. I've looked online and can't find any resources for repairing the braker master cylinder. Do you have any tips? Sincerely, Kate
AnswerHi Kate,
Congrats on the new toy.
The brake master cylinder isn't too bad to rebuild if you (or your father) have any experience with rebuilding hydraulic components.
It is critical to have a proper set of tools before you get started. You'll need a 7/16" flare wrench (for the hydraulic fittings) and a pair of circlip pliers to dismantle the brake master cylinder itself.
First off, before you get started you'll need to drain all the old fluid out of the reservoir. Brake fluid (DOT3/DOT4) is caustic and will destroy the paint on the car (and isn't much good for your skin either) so it's best to siphon out the old fluid (or open a brake bleeder with a drain tube into a catch can) to empty the reservoir.
From the reprint of the factory manual:
1 Remove the master cylinder, detach mounting bracket and drain the brake fluid.
2 Remove the reservoir (4 screws)
3 Remove the internal nut securing the tipping valve to the master cylinder body
4 Apply slight pressure on the push rod to allow the tipping valve to seat and withdraw the tipping valve.
5 slide the dust cover clear of the cylinder to expose the circlip retaining the push rod and remove the circlip.
6 Withdraw the pushrod
7 Withdraw the primary and secondary plungers complete with seals and springs.
8 Separate the plungers and the intermediate spring.
9 Prise up the leaf of the spring retainer and remove the spring and center valve sub-assembly from the secondary plunger.
10 Withdraw the valve spacer, spring washer and valve seal from the valve head.
11 Remove the seals from the primary and secondary plungers.
12 Thoroughly clean all components.
13 Examine the cylinder bore for wear, scoring and corrosion. If damage or wear is evident a new tandem cylinder must be obtained.
Assembling
14 Fit new seals to the primary and secondary plungers
15 Fit a new valve seal, smaller diameter leading, to the valve head.
16 Place the spring washer on the valve stem ensuring that the convex side of the washer is adjacent to the valve.
17 Fit the valve spacer,legs leading
18 Fit the spring retainer to the valve stem, keyhole leading.
19 Slide the secondary spring over the spring retainer and offer up the secondary plunger.
20 Slide the secondary plunger and the valve assembly between the protected jaws of a vice. To ensure cleanliness, clean paper should be placed on the vice jaws. Compress the spring and using a small screwdriver, press the spring retainer hard against the secondary plunger. Holding the retainer in this position depress the leaf of the spring retainer against the plunger. Remove the plunger and valve assembly from the vice and check that the retainer is firmly located on the plunger.
21 fit the intermediate spring between the primary and the secondary plungers
22 Generously lubricate the cylinder bore and plungers with clean brake fluid and insert the plungers into the cylinder.
23 Fit the push rod and the retaining circlip and rubber boot.
24 Depress the rod and insert the tipping valve. Fit seal and securing nut and tighten nut to a torque of 35 to 40 lb ft.
25 Fit the reservoir.
If this all makes sense, go for it. If not, you're better off letting a local professional brake specialist handle the job.
Cheers,
Jim
