88 C4 brake issues
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Joined: Oct 2020
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88 C4 brake issues
Good morning I'm new to the corvette world. I just picked up a 56K 88 C4 very clean it has a brake problem the LH front caliper will not release. I have flushed the fluid, R&R rubber hoses, LH caliper, bleed RR,LR,RF,& LF. Checked power to ABS pump. Discovered there is no fluid gravity flowing to the LH front, only get fluid when it is being bleed. Any help would be appreciated. Could it be the master cylinder is stuck internally? Thanks
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Joined: Mar 2020
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So I just went through something very similar on an 87. I bought it and it had sat for several years before I got my hands on it.
Like most neglected cars the brake fluid was awful in this car. It was dark black and the brakes worked like ****, the pedal traveled all the way to the floor and the car barely stopped. I flushed the brakes and installed new calipers all around. The car also needed a new brake booster. After all that the pedal travel was great and response was great but the car pulled to the left when braking.
I narrowed the problem to the front right wheel because that wheel was very difficult to bleed. The pedal required excessive force to bleed. I changed the soft line, mangled the seized line nuts doing that and had to replace a bit of hard line. Still no dice, car pulled to the left while braking and FR wheel was excessively difficult to bleed.
Then I found from a post on this forum that the seal in the master cylinder sticks after sitting for about a year. Someone comes along and presses the brakes and the seal breaks off and sits in the line. When you flush the brakes the piece of plastic drifts down to the abs pump and lodges itself in a channel in there. Some fluid can get past but the plastic remains unmoved.
One poster suggested reversing the line from the MC to the problem wheel. Run a temporary hardline to a union on the problem wheel, then link a rubber hose to the hardline from the master cylinder and run that into a bucket. Step on the brakes and feed fluid into the master cylinder. This may dislodge the plastic stuck in your master cylinder. That trick didnt work for me.
I ended up buying a used ABS pump from another user on this forum.
Like most neglected cars the brake fluid was awful in this car. It was dark black and the brakes worked like ****, the pedal traveled all the way to the floor and the car barely stopped. I flushed the brakes and installed new calipers all around. The car also needed a new brake booster. After all that the pedal travel was great and response was great but the car pulled to the left when braking.
I narrowed the problem to the front right wheel because that wheel was very difficult to bleed. The pedal required excessive force to bleed. I changed the soft line, mangled the seized line nuts doing that and had to replace a bit of hard line. Still no dice, car pulled to the left while braking and FR wheel was excessively difficult to bleed.
Then I found from a post on this forum that the seal in the master cylinder sticks after sitting for about a year. Someone comes along and presses the brakes and the seal breaks off and sits in the line. When you flush the brakes the piece of plastic drifts down to the abs pump and lodges itself in a channel in there. Some fluid can get past but the plastic remains unmoved.
One poster suggested reversing the line from the MC to the problem wheel. Run a temporary hardline to a union on the problem wheel, then link a rubber hose to the hardline from the master cylinder and run that into a bucket. Step on the brakes and feed fluid into the master cylinder. This may dislodge the plastic stuck in your master cylinder. That trick didnt work for me.
I ended up buying a used ABS pump from another user on this forum.
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Joined: May 2001
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From: Fairfax Virginia
Hello there 1967 Camaro!
Welcome to the Corvette Forum!!
I too have been lucky enough to have a 1988 Corvette and have had it for about 25 years almost. Be aware that the 1988 Corvette is a "One year only Brake System". Your master cylinder will have two brake lines connecting to it.
One is for Brake Fluid In and the other for Brake Fluid Out. The fluid all goes to the ABS box behind the drivers seat. Inside the ABS box the fluid is sent to the three brake areas. One is the Right front, the other is the Left front and the last is for the "Rear". What this means is you don't have individual actuation of the rear calipers, they both act in unison which is a bit weird. On my 1988 C4 Coupe I let the car set for about 18 months and when I tried driving it I pressed hard on the brakes to verify their operation. As soon as I pushed hard the pedal went all the way to the floor. Bad feeling to say the least. Fortunately the parking brake worked great and no damage was done.
The bad thing about what happened above is that since 1964 all Cars made in the United States are required to have dual chamber master cylinders. If you have one of these then if you have a leak in the rear your front brake will still work. Don't try this with your 1988 C4, if you have a brake fluid leak at speed you better have a working parking brake or downshift really fast. The brake system in the 1988 C4 did not meet the federal requirements from what I have experienced.
My leak was at the entry point to the ABS enclosure and simply rusted thru the steel tubing. I bought a complete set of Steel Brake Lines for the 1988 from Classic Tube up in New York State. They were difficult to install and then like you are experiencing problems getting the air out of the system. Some people use gravity feed but that is not going to work well as the rear line has a big loop where it goes up between the rear wheels.
To get rid of the air I bought a Phoenix Reverse Bleeder which pushes the brake fluid up from the bottom of the system and completely fills the system. The ABS system has to get bled but I think it does some sort of bleeding when it first starts up as you can hear relays and solenoids operating in the ABS system. I also have a Snap On MT2500 scanner which helps because the folks at Snap On made a cartridge to troubleshoot the Bosch ABS system. I have been trying to get my hands on one because it is supposed to really help in the bleeding process.
I wish I could have suggested that when you replace the rubber hoses that go from the brake lines to the calipers you could have upgraded to the type of Rubber hose that has a braided stainless cover. The braided hoses make the pedal feel "better" and helps the brake feel more solid. I would never replace the rubber with plain rubber as they have a 10-15 year life expectancy.
You could try a vacuum pump to get the fluid through the system, there are lots of methods and tools for bleeding the brakes. My Phoenix Reverse Bleeder works the best on both my C3 and C4. One other service provided was to be able to bleed GM clutches like the one we had in out Chevrolet pick up. Pushing the fluid up with the air is the best way I have found myself, it is a bit messy the first time but after that it makes the job a breeze.
If the Oxygen sensor is over 24 months old it is time to install a new one. The OBD1 O2 sensors have a short life span and are supposed to be replaced every 24 months or 50k miles. If you are not sure how old it is then change it, you will be happier getting the maximum out of your Corvette.
Welcome to the Corvette Forum!!
I too have been lucky enough to have a 1988 Corvette and have had it for about 25 years almost. Be aware that the 1988 Corvette is a "One year only Brake System". Your master cylinder will have two brake lines connecting to it.
One is for Brake Fluid In and the other for Brake Fluid Out. The fluid all goes to the ABS box behind the drivers seat. Inside the ABS box the fluid is sent to the three brake areas. One is the Right front, the other is the Left front and the last is for the "Rear". What this means is you don't have individual actuation of the rear calipers, they both act in unison which is a bit weird. On my 1988 C4 Coupe I let the car set for about 18 months and when I tried driving it I pressed hard on the brakes to verify their operation. As soon as I pushed hard the pedal went all the way to the floor. Bad feeling to say the least. Fortunately the parking brake worked great and no damage was done.
The bad thing about what happened above is that since 1964 all Cars made in the United States are required to have dual chamber master cylinders. If you have one of these then if you have a leak in the rear your front brake will still work. Don't try this with your 1988 C4, if you have a brake fluid leak at speed you better have a working parking brake or downshift really fast. The brake system in the 1988 C4 did not meet the federal requirements from what I have experienced.
My leak was at the entry point to the ABS enclosure and simply rusted thru the steel tubing. I bought a complete set of Steel Brake Lines for the 1988 from Classic Tube up in New York State. They were difficult to install and then like you are experiencing problems getting the air out of the system. Some people use gravity feed but that is not going to work well as the rear line has a big loop where it goes up between the rear wheels.
To get rid of the air I bought a Phoenix Reverse Bleeder which pushes the brake fluid up from the bottom of the system and completely fills the system. The ABS system has to get bled but I think it does some sort of bleeding when it first starts up as you can hear relays and solenoids operating in the ABS system. I also have a Snap On MT2500 scanner which helps because the folks at Snap On made a cartridge to troubleshoot the Bosch ABS system. I have been trying to get my hands on one because it is supposed to really help in the bleeding process.
I wish I could have suggested that when you replace the rubber hoses that go from the brake lines to the calipers you could have upgraded to the type of Rubber hose that has a braided stainless cover. The braided hoses make the pedal feel "better" and helps the brake feel more solid. I would never replace the rubber with plain rubber as they have a 10-15 year life expectancy.
You could try a vacuum pump to get the fluid through the system, there are lots of methods and tools for bleeding the brakes. My Phoenix Reverse Bleeder works the best on both my C3 and C4. One other service provided was to be able to bleed GM clutches like the one we had in out Chevrolet pick up. Pushing the fluid up with the air is the best way I have found myself, it is a bit messy the first time but after that it makes the job a breeze.
If the Oxygen sensor is over 24 months old it is time to install a new one. The OBD1 O2 sensors have a short life span and are supposed to be replaced every 24 months or 50k miles. If you are not sure how old it is then change it, you will be happier getting the maximum out of your Corvette.
