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So after finally getting a C3 after a while of searching, it is a dream come true. It has a few gremlins, but the brake system has to be the biggest - No surprise there.
The issue: The car is a no-booster manual brake system and has very little stopping power. The stopping distance of the brakes is near an unsafe level and pushed to the floor, the wheels never lock up. The petal is firm and I cant detect leaks.
I have followed recommendations from other posts and gravity bled all 4 tires and bled the system with 2 people.
There are 2 new calipers on the car and two older ones, but no leaks. The master cylinder is new and was installed by the PO. I do not know if it is bench bled.
After bleeding the brakes there was little improvement.
Suggestions? Should I consider replacing hoses, calipers or the MC? Where should I start?
The car, as mentioned is a 73 4 speed - manual brakes.
2025 c3 ('74-'82) of the Year Finalist - Unmodified
2019 C3 of Year Finalist (appearance mods)
Hi and welcome!
Start at the master cylinder.
Remove one brake hard line and insert a plug at that fitting.
Your brake pedal should move very little and be rock hard.
Reinstall the hard line and test the other line the same way.
If the pedal goes down on either test the M/C needs to be bench bleed, rebuilt or replaced.
Plugs are in the HELP section of the auto parts store inside the bleed kits.
The rubber lines can deteriorate and act as a check valve but that symptom usually results in a brake that can't release.
Could the prior owner have installed a master for power brakes?
This is the first thing I thought too. The manual brake master cyl has a smaller diameter piston which creates about the same pedal travel as a power brake system, and puts more pressure to the brakes. If it has a power brake master it will feel like a power brake system with the engine not running, hard pedal, and not as much braking.
If you have a firm pedal, I would look at the disc pads. Do they have brake fluid on them? Are they glazed? Is the rotor glazed? Properly working disc brakes for C-2 and C-3 work very well. Jerry
2020 Corvette of the Year Finalist (performance mods)
2019 C3 of Year Winner (performance mods)
2016 C3 of Year Finalist
Make sure the plunger rod is in the manual hole on the brake pedal arm and not the power. Closer to the top is manual. When you bleed it make sure you start at right rear (furthest point from MC then get closer. Dont forget you need to bleed both sides of your rear brakes. My 68 has 2 bleed screws on the rear brakes. Yours might too.
If thats right I would drain the master cylinder, replace the fluid then pressure bleed the system. Theres probably water in your lines and brakes. I did this to mine and it solved my pedal problem. Good brakes now and have been since November.
Last edited by Rescue Rogers; Apr 26, 2016 at 12:19 PM.
My vote is for the wrong master cylinder. It sounds to me like you are just not generating enough pressure in the braking system. GM used the same casting for most of their master cylinders in those days. They just bored the casting out to different dimensions for different applications. I'm betting you have the wrong one.
2025 c3 ('74-'82) of the Year Finalist - Unmodified
2019 C3 of Year Finalist (appearance mods)
Originally Posted by Rescue Rogers
Does the power MC have the deep or shallow hole?
I don't remember for sure but I think
Manual has a 1" bore and a deep hole
Power has a 1 and 1/8 bore and a shallow hole.
Let's see if anyone else agrees.
You guys are amazing. I'm going to measure the bore and check the petal position as soon as I am home. I am traveling for work until Saturday. I'll let you all know what I find so we can keep troubleshooting.
You guys are amazing. I'm going to measure the bore and check the petal position as soon as I am home. I am traveling for work until Saturday. I'll let you all know what I find so we can keep troubleshooting.
So the MC is off and it is a 1" bore with a deep hole. That sounds like a manual MC from what you've all posted. Other thoughts?
Last edited by Eddie13f; Apr 30, 2016 at 04:37 PM.
Bleed the proportioning valve to make sure the check valve is in proper position. Bleed the front first. Loosen it and have a partner push the pedal to the floor and hold it until you get it tightened back up. Then do the back one the same way. Paul
2020 Corvette of the Year Finalist (performance mods)
2019 C3 of Year Winner (performance mods)
2016 C3 of Year Finalist
Did you check to see if the pedal push rod is in the correct hole? The PO could have put.it.in wrong. Check the AIM diagram in post 7. it shows the clevis in the top hole
Last edited by Rescue Rogers; Apr 30, 2016 at 08:35 PM.
Did you check to see if the pedal push rod is in the correct hole? The PO could have put.it.in wrong. Check the AIM diagram in post 7. it shows the clevis in the top hole
Thanks for this tip as well. I checked the push rod position too and it syncs with the picture. I will bleed the proportioning valves, and I plan to replace the MC anyway since it is off. I'm going to drain the system and bleed it all tomorrow.
2020 Corvette of the Year Finalist (performance mods)
2019 C3 of Year Winner (performance mods)
2016 C3 of Year Finalist
Good luck!!!!
Did you have any water in your system? I put a small tube from my vacuum pump on the bleed screw and bled it into the platic jar just to see whats coming out. It took me multiple attempts to get the pedal to stay high. It would pump up hard but took a while and alot of fluid to get it off the floor.
If all else fails try and get a power bleeder to force any contamination out of your system. New they are around $75 but maybe you can rent of borrow one.
Last edited by Rescue Rogers; Apr 30, 2016 at 08:46 PM.
Good luck!!!!
Did you have any water in your system? I put a small tube from my vacuum pump on the bleed screw and bled it into the platic jar just to see whats coming out. It took me multiple attempts to get the pedal to stay high. It would pump up hard but took a while and alot of fluid to get it off the floor.
If all else fails try and get a power bleeder to force any contamination out of your system. New they are around $75 but maybe you can rent of borrow one.
Here is an update: I started drain the system and found some good dark fluid and a few particles. I inspected the rear calipers and found that the pistons were scraping the walls and probably were leaking, so that's a start. I have new ones on order. This also gave me a good excuse to tighten my E-brake!
We will see what new calipers do, and hope for the best will a flushed system.
1973 C3 Brake Issues
