Hydroboost conversion driving me crazy (Guru’s?)

For some reason I decided to convert to Hydroboost. I bought the Hydratech setup, wilwood master cyl and also converted to wilwood 4 piston front brakes. I had horrible problems with air but got them resolved. Here is my current issue.

When stepping on the brake firmly my red brake warning light comes on. The switch in the proportioning valve is tripping it. I know that this is usually caused by a difference of pressure between the front and the rears. Brake pedal feel is good with the exception of the light. I have not driven it.

I’m at my witts end with this and not sure where to go from here. Thanks for your input.




What's An Intercooler
Staff member
Unplug it.. also sounds like you need to drive it some. Sounds like you still have air in it

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The air could be way up near the master. Crack the line as a helper presses pedal. Then do the other one. Some do the pump it up, hold then crack. I found if there's a ton of air its better to open then press. Maybe just my preference.
I did bench bleed the master and did everything mentioned but I will lower the nose of the car so the master is almost level and do the line bleed again.
I have the same system and love it. I am in line with what everyone else says and suspect air in the system as it has happened to me.
Air in the system for sure. You can disconnect the lines from the master and let it gravity bleed for a while. Gotta have something to catch the mess. Then re connect and gravity bleed the wheels for a few hours making sure the reservoir doesn’t get too low.


Texas, Where are you from
original proportioning valve? If so you might consider a new brass replacement. When you are bleeding how are you doing it? I like the old, get a helper, and do the press and hold and the let it back up. I like to put a 2x4 under the pedal as the "assistant" is not always carful not to over stroke the mc. What is coming out of the bleeders? Nice new fluid? If not I'm sure you haven't bled enough. I like a clear glass jar to catch in so I can see what we have and the bubbles and such.
I sent Hydratech poctures and a video and they figured it out. The stock system has the front brakes on the rear chamber of the master cyl. The Wilwood is designed to have the front brakes on the front chamber. I had the lines in the incorrect order for this brake system. Flipped the lines and re-bled. No more issues.