Brake Fluid Leak (‘81)
Thread Starter
8th Gear
Joined: Apr 2025
Posts: 8
Likes: 1
Brake Fluid Leak (‘81)
Long time lurker, first time poster…have an 81 that I inherited from my wife’s grandfather. Just replaced the master cylinder along with all new calipers (Wilwood) today, and when attempting to bleed the system, there was a substantial leak from an area just behind the master cylinder. Leakage was increased when pedal was pumped, but it’s not leaking while sitting untouched.
I had noticed last night when I removed the old master that there was some fluid built up around the brake booster attachment, but this is now a brand new MC. Is this a common issue on the vehicle? I guess my next step would be to replace both the master and brake booster? Would like to hear the group’s thoughts on this, as it’s my first time working on a vehicle, and obviously my first corvette. Thank you all!
I had noticed last night when I removed the old master that there was some fluid built up around the brake booster attachment, but this is now a brand new MC. Is this a common issue on the vehicle? I guess my next step would be to replace both the master and brake booster? Would like to hear the group’s thoughts on this, as it’s my first time working on a vehicle, and obviously my first corvette. Thank you all!
2026 Loser of the Year
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From: New Or-leens Loo-z-anna
Just a rookie guess here...Old brake fluid ruined the seal in the brake booster and the new fluid is making the leak worse. I forgot if boosters can be rebuilt DIY to keep the car Original.
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From: Sunshine Coast, Queensland, Australia
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Your booster isn't at fault here. Sounds like your new master is at fault here.
when you bench bleed your master, did you push the piston in to far? Thus destroying the seals?
This is a common issue. Lack of knowledge can easily destroy a new master. Or perhaps you got a bad one?
when you bench bleed your master, did you push the piston in to far? Thus destroying the seals?
This is a common issue. Lack of knowledge can easily destroy a new master. Or perhaps you got a bad one?
Le Mans Master
Joined: Aug 2017
Posts: 8,336
Likes: 2,810
From: Cool Northern Michigan
Sorry 81 pilot,
My comments are not directed to just you but the hundreds that fall into your category.
I never understand the thought process of purchasing aftermarket brake systems for our C3s.
It's been said they are some of the best disc brakes in the world with 4 pistons per corner, reasonable price on parts
and somewhat easy to swap-out by the weekend warrior.
Do you road race? Rally on Saturday? Drag race on Sunday? Salts Flats on weekdays?
Or perhaps your drive 120 miles an hour then slam on the brakes at the grocery store?
If the Delco lasted 40 - 50 yrs, one would think you could get another 50 years with new Delco parts, right?
I am sure Wilwood are wonderful brakes. They sold millions.
But what is the obsession with them on C3 / street?
My comments are not directed to just you but the hundreds that fall into your category.
I never understand the thought process of purchasing aftermarket brake systems for our C3s.
It's been said they are some of the best disc brakes in the world with 4 pistons per corner, reasonable price on parts
and somewhat easy to swap-out by the weekend warrior.
Do you road race? Rally on Saturday? Drag race on Sunday? Salts Flats on weekdays?
Or perhaps your drive 120 miles an hour then slam on the brakes at the grocery store?
If the Delco lasted 40 - 50 yrs, one would think you could get another 50 years with new Delco parts, right?
I am sure Wilwood are wonderful brakes. They sold millions.
But what is the obsession with them on C3 / street?
GM Cert Corvette Tech
Joined: Apr 2008
Posts: 2,559
Likes: 585
From: Anaheim Hills California
First of all welcome to the Corvette forum.
From what you are describing it sounds like the replacement master cylinder is defective. Replace the master cylinder and you should be fine.
From what you are describing it sounds like the replacement master cylinder is defective. Replace the master cylinder and you should be fine.
Thread Starter
8th Gear
Joined: Apr 2025
Posts: 8
Likes: 1
I could see that being a possibility. The car was parked for about 20 years, and had a soft pedal leading up to him putting it in storage. I’ll see if I can get the MC off and take a closer look at the seal in the booster. Thanks!
Thread Starter
8th Gear
Joined: Apr 2025
Posts: 8
Likes: 1
Your booster isn't at fault here. Sounds like your new master is at fault here.
when you bench bleed your master, did you push the piston in to far? Thus destroying the seals?
This is a common issue. Lack of knowledge can easily destroy a new master. Or perhaps you got a bad one?
when you bench bleed your master, did you push the piston in to far? Thus destroying the seals?
This is a common issue. Lack of knowledge can easily destroy a new master. Or perhaps you got a bad one?
Thread Starter
8th Gear
Joined: Apr 2025
Posts: 8
Likes: 1
Sorry 81 pilot,
My comments are not directed to just you but the hundreds that fall into your category.
I never understand the thought process of purchasing aftermarket brake systems for our C3s.
It's been said they are some of the best disc brakes in the world with 4 pistons per corner, reasonable price on parts
and somewhat easy to swap-out by the weekend warrior.
Do you road race? Rally on Saturday? Drag race on Sunday? Salts Flats on weekdays?
Or perhaps your drive 120 miles an hour then slam on the brakes at the grocery store?
If the Delco lasted 40 - 50 yrs, one would think you could get another 50 years with new Delco parts, right?
I am sure Wilwood are wonderful brakes. They sold millions.
But what is the obsession with them on C3 / street?
My comments are not directed to just you but the hundreds that fall into your category.
I never understand the thought process of purchasing aftermarket brake systems for our C3s.
It's been said they are some of the best disc brakes in the world with 4 pistons per corner, reasonable price on parts
and somewhat easy to swap-out by the weekend warrior.
Do you road race? Rally on Saturday? Drag race on Sunday? Salts Flats on weekdays?
Or perhaps your drive 120 miles an hour then slam on the brakes at the grocery store?
If the Delco lasted 40 - 50 yrs, one would think you could get another 50 years with new Delco parts, right?
I am sure Wilwood are wonderful brakes. They sold millions.
But what is the obsession with them on C3 / street?
No offense taken whatsoever! I definitely see your perspective. This car was an early inheritance from my wife’s aging grandfather, whom I would love to get back into his beloved car at least one more time before it’s too late.
He had the Wilwood calipers from a few years ago when he meant to get it back into running order but just couldn’t find the time to do so. While I certainly appreciate the thought of keeping the vehicle with OEM parts, using what he had available was far cheaper for me. Kept the old Delco calipers though, wouldn’t mind rebuilding them one day and getting them back on. No racing for me, just a Sunday cruiser and a family heirloom!
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Thread Starter
8th Gear
Joined: Apr 2025
Posts: 8
Likes: 1
Thank you! I’m hoping not, but it may be the case. I purchased it from Eckler’s, this one to be exact.
https://www.ecklers.com/1977-1982-co...-121869-1.html
Any recommendation for a different product or perhaps I just got a bad one if that’s the case? Thanks!
Race Director
Joined: May 2006
Posts: 18,699
Likes: 2,572
Thank you! I’m hoping not, but it may be the case. I purchased it from Eckler’s, this one to be exact.
https://www.ecklers.com/1977-1982-co...-121869-1.html
Any recommendation for a different product or perhaps I just got a bad one if that’s the case? Thanks!
https://www.ecklers.com/1977-1982-co...-121869-1.html
Any recommendation for a different product or perhaps I just got a bad one if that’s the case? Thanks!
Race Director
Joined: Nov 2006
Posts: 13,193
Likes: 7,792
From: Sunshine Coast, Queensland, Australia
2025 C3 of the Year Finalist - Modified
2024 C3 of the Year Finalist- Modified
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Cruise-In VIII Veteran
You bought it from Ecklers??? 
I would suggest that you look threw some of the vendor reviews in the feedback section near the very bottom of the first forum page.
scroll down past all the C8 -C1 forums and keep going. Second from the bottom, "Transactions Feedback ". I believe it's called. Read all the reviews. Make more informed decisions on parts purchases .
I would suggest that you look threw some of the vendor reviews in the feedback section near the very bottom of the first forum page.
scroll down past all the C8 -C1 forums and keep going. Second from the bottom, "Transactions Feedback ". I believe it's called. Read all the reviews. Make more informed decisions on parts purchases .
1967 Pedal Car Champion
Joined: Mar 2020
Posts: 9,053
Likes: 4,194
From: US-PNW
Agreed x2: You don't want brake fluid sitting inside the diaphragm area of the booster. Try to get as much brake fluid out as you can: suction gun, shop vac with small hose, rags.