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Tech Talk with Master Power Brakes

Tech Brief Follow-Up: the Booster Pin to Master Cylinder Gap

Posted by toby on Feb 15, 2014 9:53:19 AM

Those of you who read our newsletter may recall a recent article discussing the booster pin to master cylinder gap and how an incorrect gap can cause a soft pedal.  In the article, we shared a picture that prompted one of our readers to send us a note.  Here is what he had to say:

Criticizing the experts: I believe your Booster Push Rod Gap illustration is in error...are you not showing a "manual MC" with a deep recess for the push rod? It appears you are using a (Power) with a manual MC instead of a MC with a dimple plunger. True or False?

Obviously, our reader has a sharp eye…and he is reading our posts…so we thought we would share our response so we can clear up any confusion:

I'll answer your question by saying that you aren't wrong and we aren’t wrong. You are correct that traditionally a power master cylinder would either have the insert in the master giving it a short dimple or the master cylinder wouldn't need the insert and would have the dimple machined into the pushrod. We did photograph a master cylinder without the insert and your sharp eye noticed it. This can work for a brake booster if the pushrod from the booster is of the longer style. This is actually quite common on Ford brake boosters and master cylinders where a shallow hole is hardly ever seen. I think the goal in the photograph was to illustrate the drastic possibilities one way or the other and not to say this is the only way a power master cylinder can be. However, you are correct that the master cylinder and the booster the way each is shown, they wouldn’t work together without something changing or being added to the equation since the master cylinder is a deep hole and the booster is a short pin.

We hope this helps with any confusion that may have been present. As always, we greatly appreciate the feedback from our customers. It only allows us to better help you in the long run!

Topics: brakes, classic car, How To Series, push rod, soft pedal, brake boosters, master cylinder

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