Espy1949

Just had a vacuum booster replace in my 93 the adjustments between the brake cylinder and the vacuum booster is not correct
Since it's an easy adjust I've been adjusting the rod between the booster and the MC an 1/8 of a turn and reinstalling it and testing the car out my question is how hot would the rotors get after driving it six or eight miles stopping 8 or 10 times
What I'm reading with my digital thermometer is 160 to 170degrees f parked for a few minutes. in the meanwhile I checked the temperature of the wheels themselves and the front we're about a hundred and ten and the rears were around 95. I'm in sw florida around 78 degrees ambient.
my reason for adjusting is I'm not feeling that power brake feel when i touch the brakes it seems like you're putting your foot into the pedal a little too far before you feel anything and of course as I've been adjusting it out it has been getting better but I do know it's a sensitive adjustment and you can lock them brakes up pretty quick. Therefore I'm monitoring the temperature of the rotors as well as how the pedal feels when I drive it
Any input would be appreciated thanks guys

Hot Rod Roy

If you're driving at 80 mph, and stopping the car 8 or 10 times within 125 ft. each time, the brakes will be smoldering hot! But I don't think that's your question.

If the push rod between your booster and your m/c is too long, your brakes would be dragging by that time, because as the brake fluid warms up, it expands because of the heat, and the expanding fluid would not be able to flow back into the m/c as it should, because the m/c piston is blocking the vent port in the m/c. If the push rod is too short, you'll have excessive pedal travel before the brakes actuate, and the pedal will be too close to the floor when you press on the brake pedal.

It's easy to verify the correct length of the push rod. Remove the cap of your m/c, and with the engine off, open the drivers door and stand on your left foot while you're pressing on the brake pedal with your right foot. Watch the surface of the fluid in your reservoir. You should see a spurt of fluid as soon as the brake pedal moves. If you don't see a spurt, your push rod is too long. If the pedal moves more than about 1/2 inch before you see the spurt, the push rod is too short.

If your brake fluid is clean, you should be able to see the piston move in its bore by looking into that vent port. You'll probably need an assistant for that test!

Espy1949

thanks for getting back to me the reason I was adjusting it is because I felt they had too much pedal travel therefore I didn't really feel the grab of the brakes right away since I last posted I made a small adjustment took it for a spin brakes seem better pedals almost probably where it should be I checked the temperature the rotors they were about 230 degrees ( slight variation from r to l) I don't think that's excessively hot, and i did work the brakes quite a few times while I was on my test run. driver side Rim is 120 while the passenger side Rim is 110.
I have in the past experienced brakes locking up because the rod was too long generally you will feel the pedal begin to swell a little because the brakes are being applied while you're driving but that's not what's going on with me thanks for getting back to me and any other info you may have I'm all ears thank you

Hot Rod Roy

If you insist on using your thermal monitor to test your brake temperature, you'll need to drive the car without using the brakes! If your brakes get hot when you haven't used them, your push rod is too long. They will normally get a little warm, even if you don't use them, because your brake pads are touching the rotors.

The "spurt test" is MUCH easier!

Espy1949

got it adjusted to where theres better pedal feel and brake response. what had happened was the tech who installed my booster either adjusted the rod or it should've been adjusted, because my brakes locked up. at that point he adjusted it but my foot was going into the pedal a little too far before braking.
i tried the spurt test but really didn't see any activity. however to b sure i'm gonna have my wife operate the brake while i watch. thanks for your advice hot rod roy.

92ragtop

I've just checked my FSM, bu cannot find any reference on how to adjust the rod between the booster and the MC. Could please post on how this is done?

Hot Rod Roy

Not a Corvette, but it's the same principle.

Espy1949

The adjustment is fairly simple remove the master cylinder Two Nuts and disconnect the wire that senses the fluid level you're able to slide it off and get it out of your way just enough to make an adjustment at that point you'll see the little hex head you can pull that shaft right out it won't come out of the booster but it will come out enough for you to put a pair of pliers on the knurl and make adjustments from there I will caution you that a tiny adjustment goes a long way you can cause your brakes to lock up if you lengthen the Rod too much which is what I'm going through right now because I had a mechanic install the booster for me and he either adjusted it or it came out of adjustment so I've been playing around with it. after you adjust the hex, probe around and it will slide right back into booster

krackenvette

DO you have pictures or a estimated distance that rod sticks out of the booster?

Espy1949

The rod wants to be about 1/8 inch recessed inside the opening .not out. use a credit card on edge to span across the center of the push rod and adjust accordingly in or out. the does rod pull out enough to make the adjustment i think its an 8mm nut
if for some reason the pushrod is tooo short after adjusting to the max you can get a bolt and cut it to length and lock it in place. i have done this sucessfully
make syre to fill the resevoir to the FILL line to allow for thermal expansion keep me posted