Brake Issue
Thread Starter
Instructor
Joined: Dec 2006
Posts: 114
Likes: 0
From: Florida
Brake Issue
well i recently started feeling this in my 96 lt1....when every i start the car in the mornings(or when the car is around 160degrees or lower) the peddle goes almost to the floor pretty much all the way down...when i drive the car in traffic well the car starts to heat up goin to around 190degrees(for yoru info i have a 160degree thermostat) the brakes or brake peddle gets really hard an sensitave that i bearly tap the brakes and you can feel the car brake....iv also parked the car and rocked it back and forward because it is an automatic...well when i go an try to rock it the car completely doesnt move at all...and when i open the hood and rock the tires back and forward i can hear the brakes pretty much locked on to the caliper...this only happends when the car is above 170degress...at 170 the brakes are normal...anything past 170 the brakes get harder and the peddle gets stiffer...anything under 170 the peddle is really spoungy...does anyone have a clue as of what is going on here?...also the brakes have been slowing me down badly...not like its suppose to
Team Owner
Joined: Aug 2000
Posts: 40,156
Likes: 45
From: San Pedro CA
it's most interesting that temperature has any relationship to brake function.
however, the symptoms you are describing lead me to beleive that the booster is failing.
Depending on mileage, I would consider a booster and master.
First, I would bleed the brakes and replace the fluid with Valvoline Synpower Brake Fluid. Great stuff.
If that doesn't work... gee... toughy. The soft pedal implies a bad master cylinder. The hard pedal implies a bad booster. I am wondering if both have failed... or are failing.
bleed the brakes, that will expose a bad master.
however, the symptoms you are describing lead me to beleive that the booster is failing.
Depending on mileage, I would consider a booster and master.
First, I would bleed the brakes and replace the fluid with Valvoline Synpower Brake Fluid. Great stuff.
If that doesn't work... gee... toughy. The soft pedal implies a bad master cylinder. The hard pedal implies a bad booster. I am wondering if both have failed... or are failing.
bleed the brakes, that will expose a bad master.
Thread Starter
Instructor
Joined: Dec 2006
Posts: 114
Likes: 0
From: Florida
well the temp shouldnt have anything to do with it but...i have noticed that thats when the problem is at..when the car is 190ish the peddles hard an when its 160ish its spoungy...ill have to try and bleed...what type if bleed would you rather me try from caliper or from master?
Team Owner
Joined: Aug 2000
Posts: 40,156
Likes: 45
From: San Pedro CA
from the caliper. there is no reason to bleed the master independantly.
Start at the right rear and move to the left rear, right front then left front.
If the master is toast, you will ID that rather quickly.
Start at the right rear and move to the left rear, right front then left front.
If the master is toast, you will ID that rather quickly.
Thread Starter
Instructor
Joined: Dec 2006
Posts: 114
Likes: 0
From: Florida
so all for tires need to come off...man i wish i had a life lol...ill get on it asap...well this will be my 1st time bleeding my vette..i have on other cars before but not a vette....would i have to have someone in the car pumping the brake then bleeding...then pump then bleed correct?...i want to ask anything i can before i start...i want to do this right and the right way...others were jus hey help out...but this ones serious, any special tools for this one?
Safety Car
Joined: Feb 1999
Posts: 3,504
Likes: 4
From: Mexico Beach FL
Here's a theory:
Has the brake booster or master cylinder been replaced lately?
Has anyone adjusted the brake booster rod?
If there is no free play in the pedal, the booster rod may be holding the master cylinder piston so the cup is not returning behind the "relief" port.
If the cup is not behind the relief port when the pedal is released, the under-hood temperature can cause the brake fluid to expand and cause partial brake application when the pedal is in the released position.
Therefore, braking would be affected by temperature.
Tom Piper
Has the brake booster or master cylinder been replaced lately?
Has anyone adjusted the brake booster rod?
If there is no free play in the pedal, the booster rod may be holding the master cylinder piston so the cup is not returning behind the "relief" port.
If the cup is not behind the relief port when the pedal is released, the under-hood temperature can cause the brake fluid to expand and cause partial brake application when the pedal is in the released position.
Therefore, braking would be affected by temperature.
Tom Piper
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Safety Car
Joined: Feb 1999
Posts: 3,504
Likes: 4
From: Mexico Beach FL
Here is another thought.
I don't remember what year it affected, but there was a recall on a C4 where the brake pedal would contact the dash panel up under the driver's side and not let the brake release completely.
The master cylinder piston has two cups on it -- a primary and a secondary cup.
When the brake pedal is completely released, the primary cup HAS to retract so it is behind the vent/relief port.
If the primary cup does not retract far enough to vent the brake flluid to the reservoir, the brake fluid between the master cylinder and the calipers is trapped. That trapped brake fluid will expand (just like any fluid will expand when heated) with heat and apply the brakes itself -- even with your foot off the pedal.
Anything that would hold the master cylinder piston from returning so the primary cup can't vent will cause a problem.
Tom Piper
I don't remember what year it affected, but there was a recall on a C4 where the brake pedal would contact the dash panel up under the driver's side and not let the brake release completely.
The master cylinder piston has two cups on it -- a primary and a secondary cup.
When the brake pedal is completely released, the primary cup HAS to retract so it is behind the vent/relief port.
If the primary cup does not retract far enough to vent the brake flluid to the reservoir, the brake fluid between the master cylinder and the calipers is trapped. That trapped brake fluid will expand (just like any fluid will expand when heated) with heat and apply the brakes itself -- even with your foot off the pedal.
Anything that would hold the master cylinder piston from returning so the primary cup can't vent will cause a problem.
Tom Piper
Team Owner
Joined: May 2002
Posts: 24,337
Likes: 25
From: San Diego , CA Double Yellow DirtBags 1985..Z51..6-speed
1.) Quit driving the car for godssakes.
2.) Remove your master cylinder from the booster (leave brake lines connected).
3.) Crack a brake line loose there or crack a bleeder open for a second and retighten it, to remove any vacuum from the brake circuits.
4.) Measure depth from the bolt flange on the m/c to the cup in the piston. Easiest way is stick a pencil inside, and mark the side of it for the distance.
5.) Compare this with your booster pushrod length. (from where the m/c bolts up).
6.) Use vicegrips and a rag to hold the booster pushrod while screwing the end nut in to match the length you need. Make it a tad bit shorter just to be safe.
If the booster doesn't let the brake circuits open to the reservoirs, the amount of fluid in there stays fixed. When it's cold, that fluid shrinks, and sucks the m/c piston in, or the caliper pistons in, and you get extra play in the pedal. When you drive the car and heat up the brake fluid, it expands and causes the brakes to engage partway.
2.) Remove your master cylinder from the booster (leave brake lines connected).
3.) Crack a brake line loose there or crack a bleeder open for a second and retighten it, to remove any vacuum from the brake circuits.
4.) Measure depth from the bolt flange on the m/c to the cup in the piston. Easiest way is stick a pencil inside, and mark the side of it for the distance.
5.) Compare this with your booster pushrod length. (from where the m/c bolts up).
6.) Use vicegrips and a rag to hold the booster pushrod while screwing the end nut in to match the length you need. Make it a tad bit shorter just to be safe.
If the booster doesn't let the brake circuits open to the reservoirs, the amount of fluid in there stays fixed. When it's cold, that fluid shrinks, and sucks the m/c piston in, or the caliper pistons in, and you get extra play in the pedal. When you drive the car and heat up the brake fluid, it expands and causes the brakes to engage partway.
Last edited by CentralCoaster; Jun 3, 2007 at 09:31 PM.