Question: Bleeding brakes but the pedal is still spongy.

[90whtlightning]

Hello
I have a 1990 C4. I changed out the MC and booster, brake lines and calipers then flushed and bled the system; however, I still have a spongy brake peddle. Do I need to bleed the ABS pump/ system as well? If so, is there a way to do it without a abs scanner? I would appreciate any help.

RC

 

[Hib Halverson]

Hello
I have a 1990 C4. I changed out the MC and booster, brake lines and calipers then flushed and bled the system; however, I still have a spongy brake peddle. Do I need to bleed the ABS pump/ system as well? If so, is there a way to do it without a abs scanner? I would appreciate any help.

RC

In the early years of Corvette ABS, GM did a great disservice by not publishing service information covering how to bleed the ABS modulator on a car with ABS-2S.

If you have air in the ABS modulator on a 90, you may be able to get some of it out by installing a pressure bleeder and at the same time using a TECH1 with the Bosch ABS ALDL adapter, to run the "Mode 4: ABS Tests" while bleeding the appropriate brake caliper.

If you don't have the T1 and the correct adapter, you're likely screwed but you could try installing a pressure bleeder then cracking the fittings on the ABS modulator valve.

 

[90whtlightning]

Thanks for responding.

In the early years of Corvette ABS, GM did a great disservice by not publishing service information covering how to bleed the ABS modulator on a car with ABS-2S.

If you have air in the ABS modulator on a 90, you may be able to get some of it out by installing a pressure bleeder and at the same time using a TECH1 with the Bosch ABS ALDL adapter, to run the "Mode 4: ABS Tests" while bleeding the appropriate brake caliper.

If you don't have the T1 and the correct adapter, you're likely screwed but you could try installing a pressure bleeder then cracking the fittings on the ABS modulator valve.

I don't have the T1 and correct adapter, so I will just have to try the pressure bleeding and cracking the fittings on the ABS. You are correct that it is not in the service manual about bleeding the ABS. thanks again.

 

[Robertwav1]

I don't have the T1 and correct adapter, so I will just have to try the pressure bleeding and cracking the fittings on the ABS. You are correct that it is not in the service manual about bleeding the ABS. thanks again.

Yes, I would think the ABS should definitely be bled. The reason I say this is because on a 93 (I know it's different) the ABS/ASR module must be bled immediately after installing a bench bled master cyl. The FSM also give me a rotation in which the wheel calipers should be bled starting with the right rear, left rear, right front and then left front. Anytime a steel pipe is broken or disconnected from the master, the module must be bled.

 

[90whtlightning]

How did you bleed yours? Did you need a T1 and adapter?

 

[90whtlightning]

I see you are from Apollo Beach, Fl. I used to live in Riverview when stationed at McDill.

 

[90whtlightning]

Where could I possibly find a "TECH1 with the Bosch ABS ALDL adapter, to run the "Mode 4: ABS Tests" "
Or does anyone know what a suitable substitution would be to get the job done?

 

[Hib Halverson]

Yes, I would think the ABS should definitely be bled. The reason I say this is because on a 93 (I know it's different) the ABS/ASR module must be bled immediately after installing a bench bled master cyl. The FSM also give me a rotation in which the wheel calipers should be bled starting with the right rear, left rear, right front and then left front. Anytime a steel pipe is broken or disconnected from the master, the module must be bled.

While it is true that ABS modulators should be bled, 90 and 93 use different modulators and the 93 unit is easier to service.

 

[90whtlightning]

Hello Hib

Is there a substitute for the T1 and Bosh ABS ALDL adapter that I can use to bleed my system? Is it possible to use a newer bi-directional scanner that will enable me to bleed it?

 

[Robertwav1]

I see you are from Apollo Beach, Fl. I used to live in Riverview when stationed at McDill.

Wish I could be of more help to you. like stated our cars are different. Mcdill, was there for the air show this year, F-35 impressive and the guy flew it like he was driving a car! Of course the blue angels which I haven't seen in probably 30 years are just as impressive. Lot's of people around me work at Mcdill.

 

[LLC5]

Is there a substitute for the T1 and Bosh ABS ALDL adapter that I can use to bleed my system? Is it possible to use a newer bi-directional scanner that will enable me to bleed it?

There is an old school first edition/Fred Flintstone way of doing it if your abs works properly that may help you. Drive the vehicle and slam on the brakes in a safe area with NOONE behind you, thus activating the abs and solenoids which should purge the air forward, you may have to do it numerous times, but safely of course. Keep in mind that your brakes and abs have to work properly before trying this procedure, if they don't then absolutely do NOT try it.

 

[90whtlightning]

There is an old school first edition/Fred Flintstone way of doing it if your abs works properly that may help you. Drive the vehicle and slam on the brakes in a safe area with NOONE behind you, thus activating the abs and solenoids which should purge the air forward, you may have to do it numerous times, but safely of course. Keep in mind that your brakes and abs have to work properly before trying this procedure, if they don't then absolutely do NOT try it.

Hello LLC5

I see you are a Master Mechanic. If I were to purchase a bi-directional scanner that is compatible with the 1990 C4 and capable of actuating the ABS system for bleeding. What would you recommend?

 

[LLC5]

Hello LLC5

I see you are a Master Mechanic. If I were to purchase a bi-directional scanner that is compatible with the 1990 C4 and capable of actuating the ABS system for bleeding. What would you recommend?

As long as you are able to cycle the abs solenoids you should be ok, usually those scanners are big money.

 

[90whtlightning]

The brake system as a whole does appear to work properly to include the ABS. When driving fast and getting on it, I can brake and the system functions well and will slow the vehicle down. The sponginess is noticeable when a steady application to the brake peddle is applied at a slower speed. like, say around 25-30 mph. Now if I stomp on the brake, it will work properly. Does that sound like air in the ABS or standard air in the system?

 

[LLC5]

The brake system as a whole does appear to work properly to include the ABS. When driving fast and getting on it, I can brake and the system functions well and will slow the vehicle down. The sponginess is noticeable when a steady application to the brake peddle is applied at a slower speed. like, say around 25-30 mph. Now if I stomp on the brake, it will work properly. Does that sound like air in the ABS or standard air in the system?

By sponginess do you mean that the pedal doesn't get firm, or that the brake pedal is firm and the pedal travel to get to firm is too far?

 

[90whtlightning]

By sponginess do you mean that the pedal doesn't get firm, or that the brake pedal is firm and the pedal travel to get to firm is too far?

If applied slow and steady at lower speeds the peddle will bottom out but if applied hard the peddle will initially be hard then sink to bottom out. I still have breaks but not as good as I think it should be.

 

[LLC5]

If applied slow and steady at lower speeds the peddle will bottom out but if applied hard the peddle will initially be hard then sink to bottom out. I still have breaks but not as good as I think it should be.

That sounds like air in the system or a bad master cylinder.

 

[90whtlightning]

its a new master cylinder.