C4 Brake Issue
Thread Starter
Intermediate
Joined: Aug 2013
Posts: 42
Likes: 9
From: Texas
C4 Brake Issue
The brakes in my '86 coupe with 45K miles felt spongy and required excessive pedal pressure.
I had the fluid flushed to bleed out residual air and discovered the right rear caliper is not functioning. Service tech said there appears to be a blockage in the brake line, but I find that hard to believe. These guys are not Corvette experts. I'm wondering if my ABS is screwed up, however there is no warning light on the dash display.
Any ideas on how to diagnose and correct this issue?
The master cylinder is new, and I've already replaced the front rotors and pads with slotted and drilled rotors with ceramic pad. I plan to install new rotors and ceramic pads once the hydraulic issue is resolved on the right rear wheel.
Jack
I had the fluid flushed to bleed out residual air and discovered the right rear caliper is not functioning. Service tech said there appears to be a blockage in the brake line, but I find that hard to believe. These guys are not Corvette experts. I'm wondering if my ABS is screwed up, however there is no warning light on the dash display.
Any ideas on how to diagnose and correct this issue?
The master cylinder is new, and I've already replaced the front rotors and pads with slotted and drilled rotors with ceramic pad. I plan to install new rotors and ceramic pads once the hydraulic issue is resolved on the right rear wheel.
Jack
Melting Slicks
Joined: Mar 2016
Posts: 2,778
Likes: 580
From: Langley BC
When you were bleeding the brakes was any fluid coming out of the right rear caliper?
Also I'd say have someone depress the brake pedal and see if you can see the caliper clamp down on the pad/rotor? there is only a very small bit of movement but you should be able to see it move just a little bit when the brakes are depressed.
let us know what you find.
Also I'd say have someone depress the brake pedal and see if you can see the caliper clamp down on the pad/rotor? there is only a very small bit of movement but you should be able to see it move just a little bit when the brakes are depressed.
let us know what you find.
Last edited by DMITTZ; Sep 4, 2016 at 05:32 PM.
Thread Starter
Intermediate
Joined: Aug 2013
Posts: 42
Likes: 9
From: Texas
When you were bleeding the brakes was any fluid coming out of the right rear caliper?
Also I'd say have someone depress the brake pedal and see if you can see the caliper clamp down on the pad/rotor? there is only a very small bit of movement but you should be able to see it move just a little bit when the brakes are depressed.
let us know what you find.
Also I'd say have someone depress the brake pedal and see if you can see the caliper clamp down on the pad/rotor? there is only a very small bit of movement but you should be able to see it move just a little bit when the brakes are depressed.
let us know what you find.
Thread Starter
Intermediate
Joined: Aug 2013
Posts: 42
Likes: 9
From: Texas
Melting Slicks
Joined: Dec 2008
Posts: 2,772
Likes: 64
From: Mystic CT
You can get stainless lines from many of the vendors that advertise here or the usual online speed shops. This is a part that you get what you pay for and your life rides on these working.
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Melting Slicks
Joined: Mar 2016
Posts: 2,778
Likes: 580
From: Langley BC
There was no caliper movement when brake was depressed. Apparently this condition is not new as there was rust on the rotor. No fluid escaped when the line was opened. All of this was discovered when I had the brake fluid flushed out starting left front, right front, left rear, right rear when problem was discovered.
As other have suggested start with by replacing the brake hoses they are fairly inexpensive and are probably due to be replaced. They could well be the issue.
Thread Starter
Intermediate
Joined: Aug 2013
Posts: 42
Likes: 9
From: Texas
The rubber lines go between the steel lines on the chassis and the caliper on the hub to allow suspension movement. Be happy you did not get the other failure of a locked up caliper that does not release.
You can get stainless lines from many of the vendors that advertise here or the usual online speed shops. This is a part that you get what you pay for and your life rides on these working.
You can get stainless lines from many of the vendors that advertise here or the usual online speed shops. This is a part that you get what you pay for and your life rides on these working.
Thread Starter
Intermediate
Joined: Aug 2013
Posts: 42
Likes: 9
From: Texas
Just for future reference when you bleed brakes you should start at the furthest wheel from the master and work to the closest...
As other have suggested start with by replacing the brake hoses they are fairly inexpensive and are probably due to be replaced. They could well be the issue.
As other have suggested start with by replacing the brake hoses they are fairly inexpensive and are probably due to be replaced. They could well be the issue.
Safety Car
Joined: May 2004
Posts: 4,469
Likes: 275
From: Naples FL
Keep in mind that 1986 was the very first year for the ABS system. If the fluid hasn't been changed on a regular basis it could be the ABS system. Not likely but …
btw - Here's the factory manual sequence:In the 1987 FSM page 5-7 says "Bleed the brakes in the following sequence: right front, right rear, left rear, and left front."
Richard Newton
btw - Here's the factory manual sequence:In the 1987 FSM page 5-7 says "Bleed the brakes in the following sequence: right front, right rear, left rear, and left front."
Richard Newton
Safety Car
Joined: Apr 2016
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From: N.E. Ohio OH
Finalist 2020 C4 of the Year - Modified
Loosen the rubber line to the caliper and see if any fluid is getting through when the brake pedal is applied.
That will tell you in a flash if you are getting any fluid to that point, or if the blockage is in the lines themselves or in the caliper.
That will tell you in a flash if you are getting any fluid to that point, or if the blockage is in the lines themselves or in the caliper.
Last edited by drcook; Sep 5, 2016 at 02:41 PM.
Melting Slicks
Joined: Mar 2016
Posts: 2,778
Likes: 580
From: Langley BC
Keep in mind that 1986 was the very first year for the ABS system. If the fluid hasn't been changed on a regular basis it could be the ABS system. Not likely but …
btw - Here's the factory manual sequence:In the 1987 FSM page 5-7 says "Bleed the brakes in the following sequence: right front, right rear, left rear, and left front."
Richard Newton
btw - Here's the factory manual sequence:In the 1987 FSM page 5-7 says "Bleed the brakes in the following sequence: right front, right rear, left rear, and left front."
Richard Newton
Thanks for the info, Richard. I had always heard beeding was done furthest wheel from the master to closest. However, if that is what the manual says I will use that procedure from now on. -learn something new everyday.
Race Director
Joined: Apr 2002
Posts: 10,036
Likes: 346
From: Anaheim CA
There are two separate brake circuits on the car, front and rear. It doesn't really matter which caliper you bleed first as long as you do the right side before the left side.
Last edited by Cliff Harris; Sep 6, 2016 at 02:12 AM.
Thread Starter
Intermediate
Joined: Aug 2013
Posts: 42
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From: Texas
With an ABS system the fluid goes from the master cylinder to the ABS module behind the driver's seat. From there is goes to the various calipers. Because of that arrangement, the right front is the farthest from the master cylinder.
There are two separate brake circuits on the car, front and rear. It doesn't really matter which caliper you bleed first as long as you do the right side before the left side.
There are two separate brake circuits on the car, front and rear. It doesn't really matter which caliper you bleed first as long as you do the right side before the left side.
Jack
Oil Producer
Joined: Apr 2014
Posts: 9,368
Likes: 2,735
Wood, find a gravel road, and excercise the abs pump. don't do it on a paved road. and when you do do it on a gravel road, don't get too much speed to avoid any rock chips.
excercise the abs pump and see if your brakes change. MINE DID. i have an 87.
excercise the abs pump and see if your brakes change. MINE DID. i have an 87.
Thread Starter
Intermediate
Joined: Aug 2013
Posts: 42
Likes: 9
From: Texas
It's worth a shot. Thanks.