Booster info.

[swamp rat]

Nether of my manuals have any pertinent info on swapping out a power booster in regards to pedal adjustment or even the proper clearance of the push rod that activates the master cylinder, how would you check that rod to make sure its not pushing the master cylinder valve body when bolting the units in?

[hugger6933]

One of the easiest is gonna bolt it up and see if the wheels drag then shim accordingly. Or the other if you insist on doing things the uh right way would be measure the length of the rod from the brake pedal to the firewall then compare with your new unit. If you are using a factory booster of the right origin [for your type truck] you should be in the ballpark right off, if not that is why most that do custom type setups use a 3/8 union nut [you know the real long one] and cut the rod off the pedal of their truck and the booster and the mate them back together then weld them up. Or some prefer to cut threads on the rods so they can screw the nut on to join the two. On some pedals there are two different holes close to each other and one is for man brakes and one is for power it will change the stroke of the rod and lessen the touchyness of the pedal in those cases. Jim

[swamp rat]

Well, too late to measure the rod from the brake pedal to the firewall, i already removed the stock stuff and turned them in for a core. The new booster is suppose to be a stock replacement but the body of it is different from my old booster, and the little push rod that goes between the booster and master is shorter than the old one as well.

With just the booster on and i push the pedal with my hand it looks like the rod moves about 1/2" before it bumps into something that i assume is the diaphragm. I figure if someone can help and tell me this is adjusted ok or to much throw ect then i can remount the master cyl and use a little silly putty or something to see how much clearance is left on that rod between the two.

[swamp rat]

Still need to know if the booster rod that hooks to the pedal linkage be fully extended with the foot off the pedal?

[Longhorn 70]

The way I figured out the end of the pushrod to the M/C piston was

Steal modeling clay from my 5 year old daughter. I know I know
Put a pea sized ball on the end of the push rod
Bolt up the M/C
Unbolt the M/C and remove it carefully.
Pull the clay off and measure the thickness.

I adjusted it so there is just a few thousanths of clearance. I found THIS INFO that had good tips.

[swamp rat]

Originally Posted by Longhorn 70

The way I figured out the end of the pushrod to the M/C piston was

Steal modeling clay from my 5 year old daughter. I know I know
Put a pea sized ball on the end of the push rod
Bolt up the M/C
Unbolt the M/C and remove it carefully.
Pull the clay off and measure the thickness.

I adjusted it so there is just a few thousanths of clearance. I found THIS INFO that had good tips.

Yes i plan on doing this too, i have a ball of clay, I appreciate your reply greatly. I will study the link in depth.

Where my main concern lies now is on the pedal side of the booster, is the incoming rod is suppose to be all the way out (toward the firewall) when you adjust pedal freeplay or is the rod suppose to be moved in a bit into the stroke? Also how much freeplay at the pedal? I figure if this adjustment is wrong then everything else will be wrong too.

[Longhorn 70]

I believe the pedal should be set so that it has limited freeplay, ⅛" or so WITHOUT moving the push rod out. You should also check the spring to make sure it holds the pedal tight to the bumper of the pedal mount.

Don't forget to adjust your stop light switch too when changing the pedal adjustment.

[swamp rat]

I was reading this link (Thanks Longhorn 70)

http://www.autoshop101.com/forms/brake05.pdf

It gives 3 tests for the booster, i have verified that the one way valve is functioning properly.

What i'm not sure of is if the other two tests need to be performed with the master cylinder bolted up and the lines bled?

One test is to place foot on the pedal and see if the pedal drops about 1" when started, my pedal didn't move.

The other is to hold the pedal down and shut off the engine, the pedal is suppose to stay down for at least 30 seconds, mine comes right up as soon as my foot is removed.

[cdowns]

the factory servivce manual is very cheep and readily available from vendors and is chuck full of all this type of info to do the job right and in tolerance

[swamp rat]

Originally Posted by cdowns

the factory servivce manual is very cheep and readily available from vendors and is chuck full of all this type of info to do the job right and in tolerance

I have the PDF, if it was in there i wouldn't be asking......

[cdowns]

well it isd in the book that is why i said it was it the BOOK