QUESTION
I have just rebuilt my Girling brake master cylinder with a kit supplied by Lotus Marques.
Note - I have rebuilt the master due to its age and 43 years of regular use.
Prior to dismantling and rebuilding the master cylinder it was working fine.
When I dismantled the master cylinder it appeared to be in good shape and no corrosion at all in the cylinder.
It all went back together well and the brakes bleed was fine.
When I drive the Seven now, the first brake pedal press results in a lot of pedal travel and almost no braking.
On subsequent applications of the pedal, the brakes are firm and work fine.
If I let my Lotus Seven sit a while the same thing happens (only on the first press of the pedal does the issue come up).
Do you think this may be an issue with the little seal on the far end of the internal assembly (not the one around the piston)?
L.C. - Massachusetts, USA
ANSWER
This problem may be one of two things - residual air in the hydraulic system or the tiny non return valve not operating correctly in the master cylinder
Assuming you have systematically bled the brake system and there is NO residual air, then the foot valve at the back of the master would be suspect (not sealing properly)
During the master cylinder cleaning operation, did you polish the flat surface at the end of the bore?
This part of the cylinder difficult to inspect but this surface needs to be spotlessly clean for the seal to operate correctly.
Lotus Marques routinely overhauls brake master cylinders and bench pressure tests them for safety purposes.
This test is carried out by installing a pressure gauge in the outlet port, filling the reservoir with fluid and applying pressure to the push-rod.
To do this, the master cylinder is placed in a wide opening bench vice where pressure is applied to the cylinder and push-rod.
The vice is gradually tightened to a convenient pressure so the gauge reads 50psi and left over night.
The next morning the pressure gauge reading is checked to determine whether or not the master cylinder is sealing properly and if it is ready to be re-installed.
Copyright © 2020 Lotus Marques
I have just rebuilt my Girling brake master cylinder with a kit supplied by Lotus Marques.
Note - I have rebuilt the master due to its age and 43 years of regular use.
Prior to dismantling and rebuilding the master cylinder it was working fine.
When I dismantled the master cylinder it appeared to be in good shape and no corrosion at all in the cylinder.
It all went back together well and the brakes bleed was fine.
When I drive the Seven now, the first brake pedal press results in a lot of pedal travel and almost no braking.
On subsequent applications of the pedal, the brakes are firm and work fine.
If I let my Lotus Seven sit a while the same thing happens (only on the first press of the pedal does the issue come up).
Do you think this may be an issue with the little seal on the far end of the internal assembly (not the one around the piston)?
L.C. - Massachusetts, USA
ANSWER
This problem may be one of two things - residual air in the hydraulic system or the tiny non return valve not operating correctly in the master cylinder
Assuming you have systematically bled the brake system and there is NO residual air, then the foot valve at the back of the master would be suspect (not sealing properly)
During the master cylinder cleaning operation, did you polish the flat surface at the end of the bore?
This part of the cylinder difficult to inspect but this surface needs to be spotlessly clean for the seal to operate correctly.
Lotus Marques routinely overhauls brake master cylinders and bench pressure tests them for safety purposes.
This test is carried out by installing a pressure gauge in the outlet port, filling the reservoir with fluid and applying pressure to the push-rod.
To do this, the master cylinder is placed in a wide opening bench vice where pressure is applied to the cylinder and push-rod.
The vice is gradually tightened to a convenient pressure so the gauge reads 50psi and left over night.
The next morning the pressure gauge reading is checked to determine whether or not the master cylinder is sealing properly and if it is ready to be re-installed.
Copyright © 2020 Lotus Marques