Trouble with New Hydroboost

[Mister Val]

Hi forum. It's been a while since I have posted!

Just installed a new hydroboost kit from Forte, somewhat late in my build. The brake pedal only travels about half as far as it used to (pre-hydroboost), and doesn't seem to be fully actuating the master cylinder. It has basically no resistance, and then sudden won't move. There's no sense of impact at the end of travel, more like a "soft" stop.

Tried bleeding the brakes with and without a vacuum pump, no change. The pedal moves the fluid just enough to see, but not enough to expel any air or fluid. The brakes are not grabbing the wheels. Nothing is physically obstructing the pedal. No leaks at any of the connections.

Everything worked prior to installing the hydroboost, so at this point I am stumped. My best guess is that something inside of the pump or master cylinder is impeding the push rod. Anybody have suggestions or experience with an issue like this?

[Lidodrip]

I have Forte's hydroboost kit with a Wilwood tandem master cylinder and getting the brakes fully sorted took some time (and created a fair amount of frustration along the way). Personally, I found the system hard to bleed, but that was likely due to a couple of issues that needed to be addressed. Fortunately, my brake system now works great even with the stock FFR brakes/pads. Below are the steps I ended up following, but there are many others on this forum who are much more experienced with brakes and I would defer to their advice:

1. Bench bleed the master cylinder - I found the Wilwood tandem master cylinder really needed to be bench bled to get all the air out. Even using a pressure bleeder didn't seem to get all the air out. In order to bench bleed the MC, you need to remove it from the hydroboost unit (remove the two nuts holding it on). If you are using remote reservoirs, keep them connected to the MC and follow the Wilwood directions for bleeding.

2. Check the hydroboost push rod length - There is an adjustable push rod in the hyrdoboost unit that transfers the force from the hydroboost to the MC. When you take the MC off from the hydroboost, you will get access to the push rod. Mine was too long and it caused brake drag. If it is too short, your brakes will engage late and potentially not fully engage. The push rod is easy to adjust with a threaded end and locking nut. I used an inexpensive brake booster adjustment tool help get this dialed in.

3. Reconnect the MC and hydroboost unit

4. Pressure bleed the brakes - I found this better than vacuum bleeding and it was much faster and easier.

5. Brake pedal clevis - This is likely the reason why your brake pedal does not travel the full distance. Forte uses a Wilwood clevis to connect the hydroboost to the brake pedal, and unfortunately, the brake arm hits the bottom edge of the clevis and limits the pedal travel distance and hence the piston movement in the MC. The Wilwood clevis is made out of thick aluminum and I found that filing down the lower square edge (to a 45 degree bevel) gave me all the travel I needed without compromising the structural integrity of the clevis. You do need to make sure the bolt head of the hydroboost that connects to the clevis is flush with the clevis and not protruding (I had to cut mine down a little). I also have my brake pedal high to the point where it almost hits the square tubular frame brace - this gives the most amount of travel.

Feel free to reach out with any questions.

James

[dbo_texas]

Endless fiddling with mine to get it to work properly. My kit came with the hydro-boost from the previous builder and it has probably been the #1 issue I regret keeping in my build. Several reasons for that, all documented in my build thread. Some caused by my own lack of understanding how the system worked, and a few issues caused by bad parts. Keep at it - I'm sure you will get it sorted. You might also give Mike Forte a call. Despite my thoughts about the setup, he has always returned my call (sometimes on the weekend) and has helped me work through the issues until I was satisfied. Worth a shot. He doesn't provide any instructions for installing or setting it up properly, so a discussion is probably a good starting point.

[Mister Val]

James and Darryl - thank you both for the advice. Finally got it working! I ended up taking the MC and booster back off of the car. Bench-bled the MC again (I think it was binding due to some air in one of the pistons), and shaved down the clevis on the pedal. For anyone else having difficulty with this in the future, I found this article helpful:
Troubleshooting no fluid pressure at the rear brakes (https://shop.wilwood.com/blogs/news/troubleshooting-no-fluid-pressure-at-the-rear-brakes)