I am installing a brake booster and dual master cylinder on my 1958 Ranchero. How do I adjust the pushrod on the booster so that it is the proper length for the master cylinder? I know how to make the pushrod longer or shorter, I just need to know what length to make it for a given master cylinder. Thanks.
Sorry if I didn't state my problem clearly. The pushrod on the brake booster is adjustable. It fits into the recess in the master cylinder piston, but I do not know how much clearance to leave between the end of the pushrod and the "bottom" of the piston.
That is what Phil just told you. Put the rod in to the master and adjust till there is clearance without touching .I use 1/8 3/16. Can be simply measured with thin stiff wire. Good luck Jack
Greetings I was concerned with that too. I desgned a sheet metal gauge to fit the piston in the master cylinder and then made a gauge to fit the booster push rod. When these fit the master cylinder and the booster, I placed them on a surface end to end to measure the clearence.
Wind the adjuster out as far as it can. When you push the M/C onto the booster you should feel the M/C piston making contact before the cylinder seats on the booster. That will be the amount you need to wind in the adjuster PLUS 20 thou or half a millimeter. You need that amount of clearance, but only that small amount. Any more and you will have too much freeplay in the pedal. You can check it with a small piece of modelling clay or similar. That is the way I was told by a well known brake part supplier here in Australia and have never had any problems.
The boosters I've worked on were usually set with .040" max clearance, but using midroad's .020" as a minimum should be OK. Just make sure the booster has max vacuum applied when measuring the clearance, normally around 20" Hg.
Could someone please walk me through the procedure for adjusting the pushrod with the booster OFF the car. Do I need to hock the booster up to a vacuum pump? Thanks.
Use a pump or long length of hose to a running engine, but the booster has to have vacuum applied to correctly measure the push rod to master cylinder clearance.
I don't think so. I evacuated the brake booster to 20" of vacuum and the pushrod does not move. (I would not have expected it to move, as that is the situation when the vehicle is running and the brakes are NOT applied). Of course, the pushrod moved when I push in the brake pedal rod to admit air to the atmosphere side of the diaphragm. BUT, the pushrod measurement I need is the static distance, which does not change whether the booster has vacuum or not.
I've never had the booster on vacuum when setting them. Always worked fine. You can do it on the bench if you secure the booster.
The position of the booster push rod can move/change when vacuum is applied, and is why all boosters at the brake component/booster manufacturer I tested for had 20" Hg applied, company SOP. You may not see any movement, but considering the very small clearance you're measuring, ANY movement could cause pre-load on the master, or excessive pedal travel. You asked for advice on how to set the push rod clearance, and now all of a sudden you're a booster expert. You do what you want, I tried.
I set my boosters up on the car with no vacuum, all GM units and have had no issues. I normally set them up with the pedal having slight movement before it pushes on the rod, not much, just enough to know for sure that the master cylinder piston can retract all the way when the pedal is up. I also have the master mounted on the booster when I set up the free play. If you are mixing and matching parts make sure the booster rod is pushed straight into the booster and not pushed at an angle which will destroy the booster.
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