I have read to check the length you press the pedal you should see bubbles after about 3/8 to 1/2 inch of travel.with power brakes do you check this with or without the engine running.

 

nothing to do with the engine so engine is off......you are looking for the first bubbling up of bubbles..... not much to see so dont expect a volcano.....and its not really bubbles of air more bubbles of fluid

 

can somebody expand on the actuall adjusting of this rod?

 

The rod needs to have a tiny bit of end play between it and the piston in the master cyl.

 

Mine was converted to power brakes.hard pedal just has too much travel.my rod the came with the manual mastercylinder was a fixed non adjustable rod.one that came with the kit was also a fixed length rod.I just wanted to eliminate that as to why I have so much travel.I have hurd of threaded adjustable rods between the mastercylinder and booster but never have seen one.

 

I usually get a dollar a peek, but I'll give you a look for free.



The short rods aren't adjustable.
If adjusting the rod, adjust it out until there is a small gap between the master and the booster flange, then turn it in 1/4 turn.
There is a fancy gauge made for this, but not really necessary.

 

rugerm44,
I am curious as to why you are asking this question. What is the symptoms of the brakes, or are you just setting things up.

The reason I ask is that I am getting ready to replace my m/c because the brake pedal goes to the floor, and I have done the other checks for bleeding brakes, new fluid, replaced the rubber hoses, installed new booster check valve, did a brake booster check, and the last thing will be to replace the m/c.

There is one more check with power brakes, and that is the position of the actuator rod connection to the brake pedal. I think the bottom hole is for power brakes and the upper is for manual brakes. I have power brakes and the pin is in the bottom slot.

So then I was thinking about the actuator that depresses into the m/c, and I have the same question as you. How do you determine or measure if the rod is the correct length.

So my question to you is, why are you asking. Are you having similar problems/issues, or just curious as to the setting.

kdf

 

I went out to the car and pressed the pedal down hard.only got a tiny disturbance the front reservoir and that took a couple of hard pumps of the pedal.so let me get this right the adjustable rod is in the booster and pushes on the fixed rod that gose into the back of the mastercylinder.its all brand new.Im just trying to figure out why so much pedal travel.It dosent give you too much reserve when the pedal is that close to the floor.

 

Hello
I reread one of your posts and see why you are asking now. You are converting from manual to power brakes.

Noonie may be able to answer better, but I think the adjustable rod is in the brake booster. From looking at the m/c repair kit the rods in the diagrams are a fixed length.

kdf

 

The car stops on dime just too much travel.thanks that explains a lot.I guess you have to press on the pedal with mastercylinder removed to get the rod to protrude adjust the rod.makes you wonder why they didn't already adjust it or at least mention it in the paper work that came with the kit.this may very well be my whole problem.

 

That alone tells you there is air in the system.

 

It is impossible to mix an OEM long piston with a short rod, or a short piston with long rod. They either won't fit or won't work at all.
If you have a rebuilt booster with fixed rod, then the rod may not be the correct length, but may only be close to correct.
There is no adjustment at the pedal rod, just threads to r&r the clevis.

With the engine off, you should be getting a hard pedal at a max of 1" at the pedal pad, providing you have no air.
Check to make sure you really have an 1-1//8" master for the power brakes. I have had them misboxed before. Just pull it off far enough to measure, don't undo the fluid lines.

Long


Short


Both

 

Noonie thanks for the photo. There is a lot more difference in the lenght than what I thought would be there. I can see that mixing the two just wont work.

On my car there is a possibility the previous owner replaced the brake booster. Is the brake booster Corvette specific, or is there one size that fits Camaros, Chevelles, etc. One size fits all.

If they are model specific then could the rod be different sizes for different models. That may explain some of the problems I have with excessive brake travel.

I am planning on buying a new m/c this weekend. At least I will know what to look for. And I plan on taking my current m/c to the store to compare dimensions at the counter before I buy.

kdf

 

I can't get the mastercylinder out far enough to measure the piston dia.I have power bleed this thing 3 times.right at a gallon of fluid had passed thru the system.If its got air in it it must be trapped in the mastercylinder somewhere.I also have a brand new reproduction power brake mastercylinder from zips sitting in the box.I measured it and its 1 1/8.also measured the depth of the hole in the piston.1 1/2 inches.same as the manual brake mastercylinder I took off of it.the on it now is the second new one I have put on it.has about 5 miles on it.bought the power brake kit from Corvette central.sent the mastercylinder in the kit back thinking it might be the. Problem.the one on it came from ecklers.needless to say a little frustrated is an under statement.

 

I just went through a long process of tracking down brake problems on my girlfriend's 68

It had manual brakes when she bought the car 9 years ago so she paid someone to convert it to power brakes. Every time I drove her car the brakes scared the crap out of me because even though the pedal was hard there was a lot of travel, and the brakes never felt like they were grabbing nearly enough.

This is what I found when I finally got into it:
1) Because of the camshaft installed in her engine it only produced about 8" of vacuum at idle. I installed a electric vacuum pump to fix this.
2) The brake booster was installed improperly. He drilled 4 new mounting holes and mounted the booster about an inch higher than it should have been.
3) The linkage from the booster was attached to the wrong hole in the pedal arm. He attached it to the top hole like the manual brakes were. This is also probably why he mounted the booster too high on the firewall.
4) The booster was not the correct one for a C3 vette. It was the same dimension and had the same bolt pattern, but the studs were all metric threads, and it did not provide anywhere near enough boost (with good vacuum).

It was only after installing the electric vacuum pump, mounting the booster in the proper location and linking it to the correct pedal hole that I finally figured out that the booster was incorrect. When I replaced it the brakes finally work as they should.

 

The booster is in the right place and the clevis and rod are hooked up where they are supposed to be.the kit was supposed to be for a 71 that came with manual brakes.stranger things have happened.Im just now getting back to it.I finished installing the vintage air kit and now its time to sort the brakes out.when I get over having the crud Im going to pull the mastercylinder off one more time and see if the booster has an adjustable rod or not.vaccum at idle is about 17.I will double check that reading but would low vacuum cause excessive pedal travel.If that's the problem I will go to an electric vacuum pump.

 

I have a very sick feeling that they sent me a booster for 77-82.I measured the thread pitch on the studs that mount the mastercylinder and a 1.5mm pitch gauge fits perfectly.when I installed it I didn't pay much attention to it.after checking the size of the nut it fits a 17mm wrench tighter than an 11/16.
Dose anyone know off hand what size the nuts are on the 77-82 mastercylinder.If I remember right the77-82 takes a shallow piston mastercylinder not the deep one used on 68-76.I can't see and part numbers on this booster.outside of the stud size for mounting the mastercylinder is there anyway to tell with it on the car.If Corvette central sent me the wrong one I don't think I will be doing business with them ever again.all that work for nothing.I have been worrying with this thing off and on for months just to find out they sent me the wrong part.If so words can't express my anger.If this indeed is a 77-82 booster will a 77 up mastercylinder with shallow piston fit the threads on my brake lines.

 

Almost all the boosters we are getting today are the same, I think they all have the metric bolts. I would think to get the correct booster you would have to rebuild an old one.

 

They have different part numbers in all of the catalogs that I have dug through.whats the difference between the two as they came from the factory.

 

You can undo the master bolts and then undo the 2 bolts for the dist block/prop valve and that weill give enough slack to pull the master away from the booster so you don’t have to rebleed the system.
Make sure you have the 1/18” master.


The short piston master won’t have an adjustable rod.
17” of vacuum will give less line pressure than 21” of vacuum but will also give a harder pedal.

Gm changed to metric fasteners on their booster in 1982.
Having the short combo vs the long combo makes no difference at all as far as your brake performance or pedal travel.

You can get the short or the long combo or individual pieces at any NAPA and probably a little better quality. Never had a problem with them.

Why don’t you post a pic of what you have. It’s pretty easy to tell.