Hi

I recently had the brake servo replaced and on the drive home all four calipers stuck solid. I managed to get a local mechanic to release them and he screwed back the pedal which allows the car to drivce but they still stick slightly. I can release this by slightly lifting the brake pedal which \i don't even notice moving. Recently my wife was driving the car and they stuck on and started to smoke which caused her alarm. This was the first and she says last time she plans to drive the car and is unfortunately along with my two daughters are suggesting strongly I sell the car and get a 'practically' car LOL. Any help would be gratefully accepted. I did go back to the garage who replaced the servo but they said it was not their fault, needless to say I won't be back

 

I was actually at a loss, what a "brake-servo" might be - but my browser told me: It's the brake booster. This might help others with an answer for you.

Meanwhile, until you get a reply from someone, who had that same issue before, it does sound reasonable, what my browser tells be about this issue:

>>>>>Brake sticking after a brake booster swap on a Jaguar S-Type is typically caused by incorrect installation or adjustment of the internal push-rod, which prevents the master cylinder from fully releasing pressure.

Primary Causes

• Push-Rod Adjustment: The most probable cause is that the push-rod inside the servo is extended too far or not properly located in the master cylinder piston. This keeps the master cylinder piston engaged, blocking the fluid return port and causing the brakes to drag.
  
• Pedal Connection: The footbrake pedal may not be connected correctly to the servo’s pedal push-rod, maintaining constant pressure on the system.
  
• Servo Venting Failure: If the servo’s internal valve fails to vent vacuum pressure after the pedal is released, the booster continues to apply force to the master cylinder. This can happen if the servo was damaged by depressing the pedal to the floor during bleeding or repair.
  

Secondary Factors

• Bleeding Procedure: Improper bleeding techniques, such as pumping the pedal excessively without support, can damage the servo diaphragm or cause internal binding.
  
• Master Cylinder Issues: In some cases, the master cylinder seals may have failed or the piston may not be returning fully due to corrosion or debris, independent of the booster swap.
  

Recommended Checks

1. Verify Push-Rod Length: Ensure the internal push-rod is adjusted correctly so it does not rest against the master cylinder piston when the brake pedal is fully released.
   
2. Inspect Pedal Free Play: Check that there is adequate free play in the brake pedal to allow the servo to disengage completely.
   
3. Test Vacuum Hold: Use a vacuum gauge to ensure the servo holds vacuum properly and vents correctly when the pedal is released.