Adjusting Brake Booster

"Derek Lawler" wrote in news: snipped-for-privacy@individual.net:

has a procedure for adjusting the brake booster. You have to make some special tools by grinding down standard wrenches.

Thanks for the link, Jim. Will turning the nut on the booster damage it? What goes on inside the booster? Derek

"Derek Lawler" wrote in news: snipped-for-privacy@individual.net:

I don't think so;

IIRC,there's an adjusting nut and a locknut to keep it from moving-those are what you have to adjust,and why you need the modified wrenches;they are

12 point nuts,like the inside of a 12 pt.wrench.You adjust the freeplay between the booster pushrod and the brake master cylinder's piston.

AFAIK,the booster uses engine vacuum to assist the pedal force on the rod that pushes the brake master cylinder.There's a rubber hose from the booster to the engine's intake manifold to supply vacuum. As far as what the internals are doing,I don't know for certain.I imagine there's some sort of opening valve to modulate how much vacuum gets applied to the diaphragm that adds force to the pushrod.

"Derek Lawler" wrote in news: snipped-for-privacy@individual.net:

What's your pedal freeplay like? Should be less than 5mm.

I don't want to go to the trouble of pulling the booster back enough to run the clevis back further, since I would have to take off the brake lines from the MC and those nuts on the booster studs are impossible to get to ---especially the right top one--I used a piece of tubing on a 12mm socket to get the threads started and then tightened using a universal joint on an extension. Maybe I could hire a midget to do this for me next time. I also have not ground down a couple of comb wrenches to fit over the adjustment nuts. Would line wrenches work on this---I haven't tried? If I did that and screwed the rod further in how would I be able to tell about the clearance? The diagrams are good as are the photos but after looking at it over and over I still am not clear about the MC and pedal freeplay. I am ready to turn it over to someone who has done this before and pay them for it. I have brakes and could live with it this way I suppose---pedal free play "feels" like 5mm. The engine stalls on me as I roll to a stop as if one of the plug wires is off (not the case) but I wonder if the guys that did the tranny didn't make the throttle adjustment as it shows in the book. Could the valve in the vacuum hose be a problem? I went to buy a new one at the dealer and they want fifty bucks for that little nylon valve! This car is old enough that most younger mechanics probably haven't worked on one so I am reluctant to turn it over to anyone yet.

Derek--quite puzzled, but thanks very much for your input.

"Derek Lawler" wrote in news: snipped-for-privacy@individual.net:

You don't do that. You adjust by turning the threaded pushrod itself in or out until correct freeplay is achieved. Study the text and photos, then study your own car's arrangement.

You'll surely find they will be too thick and the wrong angle. As you've already seen, space is stupidly tight under there.

When you push the brake pedal with your fingers, push *VERY* lightly. An extremely delicate touch is needed here. Freeplay will be VERY light compared to the effort needed thereafter. See here for why there's freeplay in the first place:

the second graphic.

It ought to be quite obvious. If you feel no lightness at all at the top of pedal travel, possibly freeplay is currently zero, which can be a bit of a concern.

The valve is just a one-way valve. Pull it off the booster hose. Now blow one way through it, then the other way. There should be no flow one way, but flow in the other direction. These normally don't go bad. And even if they do, you'll find scads of them for dirt cheap at the wreckers. AFAIK, most Hondas use the exact same valve.

How tightly are the REAR brakes adjusted? If they're too loose, you'll get long pedal travel, even if the parking brake seems OK.

Thanks again for clarifying this procedure. You are one who can "suffer fools gladly." I appreciate your patient explanations. I must commend you on the site you have set up for us Honda lovers with explicit diagrams. Now I will go and grind a couple of cheap tools to fit. I will also check the adjustment of the back brakes as you recommend. Derek