When you click on links to various merchants on this site and make a purchase, this can result in this site earning a commission. Affiliate programs and affiliations include, but are not limited to, the eBay Partner Network.
My ‘79 with power brakes has always had a long pedal travel to full stop. Almost to the floor. Changing master cylinder and all 4 calipers and pads made no difference. I also notice that with the engine off and no vacuum supply, the brake pedal is rather spongy, when it shouldn’t move. Yes, i’ve bled them over and over. Need some new ideas on this…
There must be a thousand threads on here about brakes.
pressure bleed them. Never vacuum bleed them. They should be tight. spongy with no vacuum, definitely your not getting the air out.
Google search C3 Corvette brakes. You'll find a heap of threads on the topic.
There must be a thousand threads on here about brakes.
pressure bleed them. Never vacuum bleed them. They should be tight. spongy with no vacuum, definitely your not getting the air out.
Google search C3 Corvette brakes. You'll find a heap of threads on the topic.
My 79 has a firm brake pedal after pressure bleeding with a new set of rebuilt O-ring calipers.
"Changing Master Cylinder" is always a clue to a long pedal travel.
There have been hundreds of people that unknowingly purchased the incorrect master. There are different designs, especially where the booster rod engages.
C3s are very picky about which MC will work and which ones will not. Never believe a parts counter person that says:
Fits All Vettes from . . . . . . . blah - blah -blah. WRONG !
always had the issue.. maybe measure the rod distance on the master?
i went ebay on my 79 for old remanufactured and no issues.
can you elaborate on what master you got?
Filter for vacuum open to brake booster? verify. check booster for leaks?
I tend to agree with using "pressure" to bleed all the air out completely. I use a Phoenix Reverse Bleederwhich pushes the fluid IN at the caliper bleeder screw and back UP to the master cylinder. I have been doing this for years and had very good luck with the tool using it on my motorcycle, Cessna, 2 Corvettes and other cars.
There is a system made by Motive that puts a cover over the top of the master cylinder and pushes the brake fluid down to the caliper screws and those do work pretty well. I have one of the Motive units for my GM vehicles and it has been relegated to a spot on the shelf as it can't compare to the Phoenix reverse bleeders. I also have the parts to use Vacuum and even the old speed Bleeders that replaced the bleeder screw on the calipers. I have wasted a lot of money trying to learn the best way for me to bleed and flush the brakes every few years.
Knowing that the air wants to go UP and out it makes sense to me to push it from the caliper bleeder screw back UP to the master cylinder. The only negative is having to empty the excess from the master cylinder as you push the fluid up. Phoenix offers the Reverse Bleeding system with many adapters to allow you to use it in a variety of places around the shop. I have used a small pan under the master cylinder and some carefully placed towels to catch any brake fluid that overflows from the master cylinder. I waste a big bottle of brake fluid but when I flush the brakes they are "well flushed" when I am done. My C4 is the hardest to bleed completely as the ABS equipment needs to be cycled a few times to ensure the air is completely gone.
The Phoenix system also works exceptionally well with GM's Hydraulic Clutch master cylinders used on the later Corvettes. It was the only system I found for getting the air out of my clutch system on our 1995 Chevrolet Pickup. I had a shop replace the clutch and they could not get the air out so they extended to push rod to compensate for it. I ground off their extra metal they had welded on and in 5 minutes had a perfect clutch pedal using the Phoenix Reverse Bleeder. The air that was caught went up and out allowing the fluid to fill the void and give me back the correct pedal feel.
Having the correct master cylinder is critical since they are available in various different sizes. I have saved the master cylinders that have been removed from my C3 and C4 as I would like to get them rebuilt versus trading them in for the core. I would rather pay the core charge than to give up a piece that worked great for years and now needs to be rebuilt.
To elaborate what i did before I posted my SOS on this forum......
1. Replaced master cylinder - checked pushrod clearance which was .040
2. Installed new pads
3. Installed reman. SS calipers
4. Replaced all four flex lines and the front hard lines.
5. PRESSURE bled the brakes
The only component I haven't changed is the booster, and that might be next.....
Thanks for your collective feedback.
whats the run out on the rotors ,, if the rotors are thin you will never get a good pedal
I also would like to add that if you take a rubber mallet and tap the calipers before bleeding
it might help releasing the trapped air in the caliper
People are confused about the job of a booster. It's strictly an "Assist" in how much force is needed to apply the brakes.
A brand new booster will not:
Keep a brake pedal off the floor.
Will not remove spongy brakes.
And will not fix a faulty brake issue. Look elsewhere.
I always question the bleeding method of brake issues.
Was the MC bench bled in a work bench vise? And done correctly?
Were all six bleeder screws bled?
Did at any point of installing the MC, air was allowed into the system?
i.e. Attaching lines to MC
Reservoir was allowed to run dry.
Forget the booster. You still have air in the system.
I need to update the thread, but I can tell you that while I fixed some other issues, my issue was primarily the power brake booster. Here's why:
The booster died.
Bubba, although somewhat ingenious, decided to install a longer brake booster piston rather than use the proper booster with a proper piston. The engagement to the MC was never correct, though I had it adjusted to the limits of the makeshift piston.
As to the power brake booster, for my application (1974 Vette) it should look like this:
NOT this!
Notice that the piston isn't visible (it's there - I borrowed one from O'Reilly Auto Parts) on the second image as it's designed for an entirely different master cylinder, with a recessed mounting interface - that is not "correct" for my application.
Also, I could not agree more with the comments regarding a power brake bleeder. I purchased the
and I assure you it's worth its friggin weight in gold, platinum, palladium, nickel, and depleted uranium... I, too, though I had the system free of air with a vacuum bleeder but I was horribly mistaken. Run, don't walk, and get one. Please trust me/us... you'll wonder how you've survived thus far without one.
Ensure you have the proper combination of MC and power brake booster, and power bleed the system before you start throwing more parts at the situation.
Best of luck and let us know how things turn out for you! If you'd like to see what's involved in a removal/reinstall of a power brake booster, take a look at this video from TheCorvetteBen. He also highlights the issue with incorrectly sourced boosters:
The upper photo shows an "adjustable booster rod". Not all model years had that feature. Some had no adjustment. Others were adjustable via the clevis pin hole on the brake pedal assembly only.
In the above story, the booster itself could have been perfectly fine, holding vacuum. Just had the wrong booster rod.
You can see on the end of the rod its rounded shape. That meets up with the concave piston at the rear of the master. There should be a gap at that junction of around 0.060, or around 1/16 of an inch. Without a gap, the weight of the brake pedal will ever so slightly engage the master, thereby engaging all four calipers.
Also known as brake drag. The calipers are not allowed to release.
Too much gap creates a delay from when pedal is engaged, and master begins to apply pressure. This is known as a long pedal travel.
Brakes Broke??
