Jcb backhoe brake pedal pulls down

[Justin29625]

I have a 1998 jcb 217s. When I start the engine, the brake pedal pulls down, and engages the breaks. The higher the RPMs, the harder it pulls down. What might be causing this?

 

[JCB_JCR]

Sounds like something gone wrong with vac booster on master cylinder. Guessing there's a valve or vent stuck/blocked that normally vents until pedal is pressed. No idea if it's possible to dismantle though.

 

[Justin29625]

Sounds like something gone wrong with vac booster on master cylinder. Guessing there's a valve or vent stuck/blocked that normally vents until pedal is pressed. No idea if it's possible to dismantle though.

It definitely seems vacuum related. If I put the toe of my boot under the pedal and lift it up, the breaks let off, but the more throttle I give it, the harder the brake pedal pulls down. It'll just about smash your foot. When I turn the switch off, the brake pedal raises back up. It's gradually gotten worse over the last 50 to 60 hrs of use.

 

[JCB_JCR]

I'd say either poppet valve stuck or blue chamber leaking from outside. Is it rusty? Sounds like new booster needed.