Master Cylinder screw extraction- with pictures

[ohgood]

Have you noticed the master cylinder screws are made of peanut butter painted grey ? I did today.

The fluid was starting to turn ugly again, so I started the process of bleeding the brakes. The first screw came out fine from the front master cylinder. The second turned to mush. Yep, I stripped the phillips head.

Took a quick trip to lowes, picked up the replacement stainless machine screws and 1/4" ID vinyl hose, stopped by autozone for DOT-4, and then got started.

If you're lucky enough to have a left hand drill small enough not to damage the threads in the master cylinder, go for it. The heat of the drilling and the reverse twist does a nice job of removing stuck things. I didn't have one for this.

There was allot of corrosion under the pan head screws, you can see it here:


After I used a 1/16" center drill, I used a 82 degree counter sink to remove more of the head. The goal was to remove enough of the inside of the head to make the removal a little easier, but not damage the master cylinder cover. Here's the countersink next to the screw for comparison:


With the old screw countersunk plenty, a sharpened and hardened tool steel (ok, anything can be hardened) punch was used. If you're careful, you can lay over the remaining bit of the head, and use it as a striking point to rotate the remaining screw. If you try at 45 degree angles or so and work your way around the remaining screw head, it will loosen quickly.  I mentioned it was made of peanut butter painted gray earlier- it really folded that easy:



Now, with a little persistance, the screw worked loose, and started turning easily. After the initial 1/4 turn, the rest was only finger tight. See the corrosion on the screw, and in the countersink:


You can go through the trouble of measuring the screws with thread gages, and/or calipers,


but the 'wall of known thread pitches' at ACE Hardware usually does what I need, and it's a M4 .7 x 16 @ $.45 each that works for me:

You can use this method for almost any flat head / button head / pan head machine screw. They're a little more difficult than regular bolts, and sometimes require re-tapping the threads. Regular bolts would mean I'd just use an easy out, or left hand drill, since they're usually bigger.


I put the new stainless screws in with a little gasket goo so hopefully there won't be any more corrosion under the heads from the aluminum.

My niece helped me bleed the brakes, for whatever reason she didn't mind hanging out in the garage today. Nieces are cool!

[Ronin]

Good post dude!....Thank's for the pic's 

[bucks1605]

Nice post! I guess I was lucky, mine came out smooth and easy.

[qwertydude]

Good looking out next time I replace my pads and fluids I'll be sure to buy new screws. Peanut butter does not a good fastener, except it sticks to the roof of your mouth, guess you could make your gaskets out of it.

[mhavel]

Anti-Seize FTW

[beRto]

Thanks for the write-up! 

[lilbill]

Thanks for the post...my screws seem to have come from the same peanut butter factory as yours 

[GeeP]

I can see you were busy making fancy center punches instead of production at your last job.   

[ohgood]

I can see you were busy making fancy center punches instead of production at your last job.   

well, they started life about 15 years ago, and as you can see they've been ground down a few times

they've saved my butt quite a few times, or at least a few customer's wallets