Adjusting Brake Booster

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Derek Lawler - 22 May 2006 01:55 GMT

After tediously getting the brake booster out of my 1986 Honda Civic sedan
(AT just rebuilt, 1.5L engine) and replaced with a rebuilt one I could not
get it through the firewall without removing the 2" clevis connector so I
had to back out the replacement far enough to put it on from the inside and
then put the pin and cotter pin in place. Bled the rebuilt master cylinder
on the bench then bled all four wheel cylinders. However, the pedal goes to
the floor and since I can't screw the clevis further back on the booster's
threaded rod I am trying to back off the rod from the booster where there's
a locknut. Using pliers I managed to back it out a fraction of an inch. Is
this the right way to go about it? I would appreciate any input on this. I
do have braking but the pedal goes too far down for my peace of mind.
Derek

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Jim Yanik - 22 May 2006 03:15 GMT

> After tediously getting the brake booster out of my 1986 Honda Civic
> sedan (AT just rebuilt, 1.5L engine) and replaced with a rebuilt one I
[quoted text clipped - 9 lines]
> I do have braking but the pedal goes too far down for my peace of
> mind. Derek

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

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Jim Yanik
jyanik
at
kua.net

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Derek Lawler - 22 May 2006 18:25 GMT

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

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Jim Yanik - 22 May 2006 23:03 GMT

> Thanks for the link, Jim. Will turning the nut on the booster damage it?

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.

> What goes on inside the booster?
> Derek

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.

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Jim Yanik
jyanik
at
kua.net

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TeGGeR® - 23 May 2006 11:31 GMT

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

http://www.tegger.com/hondafaq/mastercylinderreplace/adjustment.html

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TeGGeR®

The Unofficial Honda/Acura FAQ
www.tegger.com/hondafaq/

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Derek Lawler - 24 May 2006 03:43 GMT

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.

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TeGGeR® - 24 May 2006 04:12 GMT

> I don't want to go to the trouble of pulling the booster back enough
> to run the clevis back further,

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.

> since I would have to take off the
> brake lines from the MC and those nuts on the booster studs are
[quoted text clipped - 4 lines]
> couple of comb wrenches to fit over the adjustment nuts. Would line
> wrenches work on this---I haven't tried?

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

> 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.

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:
http://www.tegger.com/hondafaq/mastercylinderreplace/howworks.html
See the second graphic.

> I have brakes and could live with it this way I suppose---pedal free
> play "feels" like 5mm.

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 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!

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.

> 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.

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.

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TeGGeR®

The Unofficial Honda/Acura FAQ
www.tegger.com/hondafaq/

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Derek Lawler - 24 May 2006 05:29 GMT

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

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