Bad Power Brake Booster?
Thread Starter
Cruising
Joined: Aug 2008
Posts: 10
Likes: 0
From: San Jose Ca
Bad Power Brake Booster?
I’m having brake/ booster problems on a 74 Corvette and I think it’s bad… did a search on another website and found this thread:
if you think the booster is leaking run the engine for a minute
shut it off and let the car sit for a while, then pull the check valve out- if there was a sucking sound (vacuum left in the booster) then its not leaking
http://www.camaros.net/forums/showthread.php?t=135202&highlight=power+ brake+booster
Ran the car for a while and let is stand for 2 min. and the booster had no vacuum when the check valve was pulled. Main thing is no brakes – soft pedal. I’ve replaced master cylinder, front brake hoses and front calipers. Planning on replacing rear Calipers also… Just been throwing money at it but I would like to make a little progress…
What do you think? Bad Booster?
Mark (AKA Z28 Mark)
if you think the booster is leaking run the engine for a minute
shut it off and let the car sit for a while, then pull the check valve out- if there was a sucking sound (vacuum left in the booster) then its not leaking
http://www.camaros.net/forums/showthread.php?t=135202&highlight=power+ brake+booster
Ran the car for a while and let is stand for 2 min. and the booster had no vacuum when the check valve was pulled. Main thing is no brakes – soft pedal. I’ve replaced master cylinder, front brake hoses and front calipers. Planning on replacing rear Calipers also… Just been throwing money at it but I would like to make a little progress…
What do you think? Bad Booster?
Mark (AKA Z28 Mark)
Team Owner
Joined: Jul 1999
Posts: 65,492
Likes: 230
From: Orange Park Florida
Mark, do a search on brakes for the C3 and you will be totally overwhelmed, pick out some of my fairly recent comments
it's a LOT of reading....
after that, if you have specific questions post or PM/email me....
it's a LOT of reading....
after that, if you have specific questions post or PM/email me....
Racer
Joined: Dec 2004
Posts: 319
Likes: 4
From: Suisun City, CA
It sounds like you are on track. Since you replaced the master cylinder and front calipers, you should have that brake, if the booster was functional. Good luck and keep us posted on your success.
Thread Starter
Cruising
Joined: Aug 2008
Posts: 10
Likes: 0
From: San Jose Ca
I did the search thing and I still think it’s bad… makes that swoosh / sucking sound. I doesn’t sound too easy to change but I guess I have to-to see if this helps out.
Mark (AKA Z28 Mark)
Mark (AKA Z28 Mark)
Team Owner
Joined: Aug 2006
Posts: 24,125
Likes: 15
From: Columbia Missouri
Here's an easier test.
With the engine off, press the brake pedal repeatedly. Does it firm up quickly?
If yes, the booster is holding vacuum. If no, it's not holding vacuum.
If it firmed up and held vacuum, start the engine with your foot pressing on the brake pedal. Once the engine is started the pedal should soften and depress some. That's normal.
With the engine off, press the brake pedal repeatedly. Does it firm up quickly?
If yes, the booster is holding vacuum. If no, it's not holding vacuum.
If it firmed up and held vacuum, start the engine with your foot pressing on the brake pedal. Once the engine is started the pedal should soften and depress some. That's normal.
Le Mans Master
Joined: Dec 2007
Posts: 6,422
Likes: 591
From: McHenry Illinois
I agree with some of the above, but a soft pedal usually means air in the system. The booster may have a problem with the check valve or even a leak in the diaphragm, but the first issue is the soft pedal and that's not caused by a bad booster. IMO
Thread Starter
Cruising
Joined: Aug 2008
Posts: 10
Likes: 0
From: San Jose Ca
The pedal doesn’t firm up at all (well maybe a little since the front calipers) but it goes straight to the floor. The C/V appears good… open one way and not the other. . I may replace the hose to the booster as it is as hard as ever. I’m using a vacuum pump (electric) and I believe that I’m getting most of the air out but it isn’t continues fluid when it’s being bleed. As I stated I’ll probably be doing the rear calipers today and then make the big decision about the booster… not looking forward to doing the booster.
Thanks for all the info and please keep it coming.
Mark (AKA Z28 Mark)
Thanks for all the info and please keep it coming.
Mark (AKA Z28 Mark)
Last edited by Z28 Mark; Aug 24, 2008 at 04:34 PM.
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Burning Brakes
Joined: Oct 2006
Posts: 1,006
Likes: 28
From: Lutz Florida
Bad booster usually = hard pedal, not soft. Also if the booster is leaking and not holding vacuum other strange things can happen - like your car starts not idling well, or the engine dies out or almost dies out, when you depress the brake pedal.
Is the booster push rod adjusted to length properly for your new MC?
Is the booster push rod adjusted to length properly for your new MC?
Limping across the line
Joined: Oct 2002
Posts: 5,299
Likes: 109
From: Peoria Az
You've got air in the system you need to pressure bleed the brake system. Vacuum bleeders just dont cut it on these 4 piston calipers.
You draw air from around the bleeder threads before it draws all the air from the piston reliefs in the caliper.
You draw air from around the bleeder threads before it draws all the air from the piston reliefs in the caliper.
Advanced
Joined: Aug 2008
Posts: 70
Likes: 1
From: corpus christi tx
im having the same prob, but i replaced the brake booster last week, bleeded out thethe new calipers...( i have not put the down yet from the stands so i cant tell if i m brakeing or not)
but my pedel is frim if i hit the brakes with the car off... but when i turn on the car,, pedal hits the floor. i cant fig it out ether
but my pedel is frim if i hit the brakes with the car off... but when i turn on the car,, pedal hits the floor. i cant fig it out ether
Le Mans Master
Joined: Mar 2001
Posts: 6,640
Likes: 287
From: Ann Arbor Michigan
The pedal doesn’t firm up at all (well maybe a little since the front calipers) but it goes straight to the floor. The C/V appears good… open one way and not the other. . I may replace the hose to the booster as it is as hard as ever. I’m using a vacuum pump (electric) and I believe that I’m getting most of the air out but it isn’t continues fluid when it’s being bleed. As I stated I’ll probably be doing the rear calipers today and then make the big decision about the booster… not looking forward to doing the booster.
Thanks for all the info and please keep it coming.
Mark (AKA Z28 Mark)
Thanks for all the info and please keep it coming.
Mark (AKA Z28 Mark)
Thread Starter
Cruising
Joined: Aug 2008
Posts: 10
Likes: 0
From: San Jose Ca
I think you may be right about the air in the system and the vacuum pump. May have to buy a preasure bleeder. Didn't cheek the rod on the booster before I installed the M/C. I too still have the car in the air and when I start it it goes right to the floor!
Mark (AKA Z28 Mark)
Mark (AKA Z28 Mark)
Team Owner
Joined: Jul 1999
Posts: 65,492
Likes: 230
From: Orange Park Florida
I think you may be right about the air in the system and the vacuum pump. May have to buy a preasure bleeder. Didn't cheek the rod on the booster before I installed the M/C. I too still have the car in the air and when I start it it goes right to the floor!
Mark (AKA Z28 Mark)
Mark (AKA Z28 Mark)
OK, first thing you do is go to a parts house and get a T fitting for the front brake lines....and fit it in there in place of the 'proportioning valve'....it's actually just a switch, then put the rear brake line directly to the rear section of the m/cyl....you will need a brass adaptor fitting in there, but been so long since I had a iron m/cyl I forget if it's front or rear....
give that a shot before you mess with the booster....it maybe bring enough pedal back for you....those brake bias switches tend to leak air but not fluids....I proved that long time ago....
Heel & Toe
Joined: Aug 2008
Posts: 16
Likes: 0
I went through all these steps on my 1969. Ultimately, it was a bad brake booster. If your car has the original one in it, you might as well replace it anyway.....PLUS I suspect it will correct your problem. It is not tough to replace -- as I recall it took me about 30 minutes. Be sure to replace the hoses while you are at it.
Good luck.
Good luck.
