October 11, 20205 yr Hi. I have a Montesa Cota 315 1999. F Brake master cyl is a Grimeca I like to go practice pivot turns in the back yard. But recently after doing them, the front brake goes to the handlbar and i have to pump it to get something back. It happens every time I do them. I've bled the system, wound the adjuster right out, rebled. Checked the caliper and all that. But its still doing happening. (the brake stays firm when I'm just noodling about but when I go back to the pivots I lose pressure again) There are no leaks that I can see. Nothing at the caliper, hose is fine, connection look good. I even filled the fluid reservoir right up, just in case what I'm doing is allowing an air pocket to get into the line Has anyone has this issue? Who will be the first to tell me my master cylinder needs rebuilding? where is the air getting in and why?
October 11, 20205 yr Check the front wheel bearings, fork brace and caliper mount bolts, it sounds like pad knock back.
October 11, 20205 yr Sure sounds like your master is loosing pressure because of a bad seal... maybe your fluid is rushing back into the reservoir so your not seeing any leaks? I haven’t worked on the Grimeca brakes so not sure how the piston and seals are setup so I don’t know if this is would be possible Without leaking but I have had it happen in the past on an old street bike I had so thought it might be worth a suggestion.
October 17, 20205 yr Author On 10/11/2020 at 9:29 PM, totty79 said: Check the front wheel bearings, fork brace and caliper mount bolts, it sounds like pad knock back. Thanks for the info, I'll have a look at that. I do know that if I drop the front wheel down hard or over too far it can suffer quite a bit side force. I'll check the areas you mentioned...cheers
October 17, 20205 yr Author On 10/12/2020 at 3:29 AM, jonnyc21 said: Sure sounds like your master is loosing pressure because of a bad seal... maybe your fluid is rushing back into the reservoir so your not seeing any leaks? I haven’t worked on the Grimeca brakes so not sure how the piston and seals are setup so I don’t know if this is would be possible Without leaking but I have had it happen in the past on an old street bike I had so thought it might be worth a suggestion. Thanks for that. I'll have a look at that. There may be a rebuild on the cards T
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