Strange break issue
Thread Starter
2nd Gear
Joined: Oct 2008
Posts: 2
Likes: 0
Strange break issue
I've been around C3 corvettes for years, so finally I bit the bullett and purchased a 74 L82 Coupe that actually runs and drives. I've owned a 75 L48 Coupe for abotu 3 years now that I have been slowly building but have never driven...the 74 actually runs 
The 74 has a few odd and end issues that I need to address (as soon as the budget allows), but the one that is really starting to irritate me is this....
After driving the car on the highway at speed (around 60-65 miles per hour...I am not breaking any laws) for about 10 mintues, the front breaks decide to "drag". In other words, they are applying some pressure to the rotors and it's like driving the car with your foot resting on the break peddle. Uppon breaking, the peddle is very tight and does not have proper travel.
All parts look fresh, no leaks in fluid, and the break pads look real fresh as well.
Now the only thing I can think of that could be related to the issue is that the headlight switch I feel has a bad vaccum diaphram and I am using the bypass under the dash to open up the headlight doors. With this open, there is a vaccum leak. Also, there is a "hum" coming from the power break booster. Could a vaccum leak cause this problem??
Please advise anyone. Thanks
WONDERFUL FOURM BY THE WAY
The 74 has a few odd and end issues that I need to address (as soon as the budget allows), but the one that is really starting to irritate me is this....After driving the car on the highway at speed (around 60-65 miles per hour...I am not breaking any laws) for about 10 mintues, the front breaks decide to "drag". In other words, they are applying some pressure to the rotors and it's like driving the car with your foot resting on the break peddle. Uppon breaking, the peddle is very tight and does not have proper travel.
All parts look fresh, no leaks in fluid, and the break pads look real fresh as well.
Now the only thing I can think of that could be related to the issue is that the headlight switch I feel has a bad vaccum diaphram and I am using the bypass under the dash to open up the headlight doors. With this open, there is a vaccum leak. Also, there is a "hum" coming from the power break booster. Could a vaccum leak cause this problem??
Please advise anyone. Thanks
WONDERFUL FOURM BY THE WAY
Le Mans Master
Joined: Jan 2000
Posts: 8,918
Likes: 27
From: New Hill NC
I've been around C3 corvettes for years, so finally I bit the bullett and purchased a 74 L82 Coupe that actually runs and drives. I've owned a 75 L48 Coupe for abotu 3 years now that I have been slowly building but have never driven...the 74 actually runs The 74 has a few odd and end issues that I need to address (as soon as the budget allows), but the one that is really starting to irritate me is this....
After driving the car on the highway at speed (around 60-65 miles per hour...I am not breaking any laws) for about 10 mintues, the front breaks decide to "drag". In other words, they are applying some pressure to the rotors and it's like driving the car with your foot resting on the break peddle. Uppon breaking, the peddle is very tight and does not have proper travel.
All parts look fresh, no leaks in fluid, and the break pads look real fresh as well.
Now the only thing I can think of that could be related to the issue is that the headlight switch I feel has a bad vaccum diaphram and I am using the bypass under the dash to open up the headlight doors. With this open, there is a vaccum leak. Also, there is a "hum" coming from the power break booster. Could a vaccum leak cause this problem??
Please advise anyone. Thanks
WONDERFUL FOURM BY THE WAY
The 74 has a few odd and end issues that I need to address (as soon as the budget allows), but the one that is really starting to irritate me is this....After driving the car on the highway at speed (around 60-65 miles per hour...I am not breaking any laws) for about 10 mintues, the front breaks decide to "drag". In other words, they are applying some pressure to the rotors and it's like driving the car with your foot resting on the break peddle. Uppon breaking, the peddle is very tight and does not have proper travel.
All parts look fresh, no leaks in fluid, and the break pads look real fresh as well.
Now the only thing I can think of that could be related to the issue is that the headlight switch I feel has a bad vaccum diaphram and I am using the bypass under the dash to open up the headlight doors. With this open, there is a vaccum leak. Also, there is a "hum" coming from the power break booster. Could a vaccum leak cause this problem??
Please advise anyone. Thanks
WONDERFUL FOURM BY THE WAY
Not likely, Most times this is bad rubber lines or the pushrod in the MC is adjusted too far in.
Le Mans Master
Joined: Aug 2006
Posts: 7,426
Likes: 1,559
From: mount holly NC
2025 c3 ('74-'82) of the Year Finalist - Unmodified
2019 C3 of Year Finalist (appearance mods)
Best to change all four, they may be 34 years old, then if you still have the same problem adjust the M/C push rod. PG.
Advanced
Joined: May 2007
Posts: 64
Likes: 0
From: Knoxville Iowa
While I agree that the problem could be brake lines, I would also take a look at the power brake booster,if its a power brake car. Back in the day, I had an Olds of similar vintage that had the sme symptoms,Bear in mind that the car was only about 8 years old at the time.
Senior Member
Joined: Jan 2008
Posts: 12,146
Likes: 2,038
From: Easton, PA
St. Jude Donor '10
Spoken from experience let me offer that when removing the rubber lines you need to take real care. I didn't know to buy the right wrenches initially and my hoses all stripped, then I damaged the hard lines upon removal. This was on my 77. Your 74 is older, so beware.
I have since replace the front cross over line, the hard lines on the front, the rubber lines up front, the front to back hard line, the rear cross over line, the rear hard lines and of course, the rear rubber lines. What started out as a simple rotor replacement and brake job has lasted two months and cost me a lot of time to get the job done. Spray the heck out of those fittings, use the right wrenches, and move slowly.
Good luck with your replacements...I wish I had known then what I think I know now.
Best regards,
David
77Sleeper
I have since replace the front cross over line, the hard lines on the front, the rubber lines up front, the front to back hard line, the rear cross over line, the rear hard lines and of course, the rear rubber lines. What started out as a simple rotor replacement and brake job has lasted two months and cost me a lot of time to get the job done. Spray the heck out of those fittings, use the right wrenches, and move slowly.
Good luck with your replacements...I wish I had known then what I think I know now.
Best regards,
David
77Sleeper
