Austin Branson Posted February 6, 2016 Report Share Posted February 6, 2016 Greetings, oh sage ones, I have a 1974 ex-California CF. I suspect the left hand rear wheel cylinder has reached its sell-by date. Because it's a CF, does that mean it's a 0.75 cylinder? Is there any benefit to changing both cylinders to 0.70? The master cylinder and servo were replaced last year. Many thanks, Austin Quote Link to post Share on other sites
RogerH Posted February 7, 2016 Report Share Posted February 7, 2016 Hi Austin, fitting the bigger cylinder will reduce the force/push on the brake shoes. This will reduce the braking at the back end. Roger Quote Link to post Share on other sites
Peter Cobbold Posted February 7, 2016 Report Share Posted February 7, 2016 (edited) Austin, that Vespertini blower is leading you into bad habits, you're not supposed to use it to drive on the brakes The force exerted on the shoes, for a given system pressure, will increase in proportion to the bigger area of the larger cylinder. http://usercontent1.hubimg.com/8990332_f520.jpg That's about 14% more for the 0.75 vs 0.70 bores. Your bigger cylinders will add a bit bias in favour of the rears. Fitting the smaller bores would reduce rear braking compared with front. With bigger cylinders the pedal dead motion will increase a bit as more fluid is needed to move the pistons before they bite and system pressure starts to rise. I presume the front chamber of the master cylinder has enough capacity. Going smaller as you plan should be OK. Peter . Edited February 7, 2016 by Peter Cobbold Quote Link to post Share on other sites
Andy Moltu Posted February 8, 2016 Report Share Posted February 8, 2016 Hi Austin, fitting the bigger cylinder will reduce the force/push on the brake shoes. This will reduce the braking at the back end. Roger Won't it increase it at the expense of greater pedal travel? Quote Link to post Share on other sites
RogerH Posted February 8, 2016 Report Share Posted February 8, 2016 Hi Andy , yes that is what I've said but I'm reffering to the force on the brake shoe. It will increase pedal effort. Roger Quote Link to post Share on other sites
Peter Cobbold Posted February 9, 2016 Report Share Posted February 9, 2016 Bigger bore piston will increase the force on the brake shoe. Pressure x Area. More rear braking with respect to front. Slighty longer pedal travel. Peter Quote Link to post Share on other sites
RogerH Posted February 9, 2016 Report Share Posted February 9, 2016 indeed - but he wants to fit a smaller bore 0.7" instead of 0.75". So, more travel but more foot pressure. This will result in the font brakes braking harder compared to the rear. Roger Quote Link to post Share on other sites
peejay4A Posted February 9, 2016 Report Share Posted February 9, 2016 Less pedal travel, more pressure required to lock the rears. Quote Link to post Share on other sites
RogerH Posted February 9, 2016 Report Share Posted February 9, 2016 indeed so. Roger Quote Link to post Share on other sites
alan atkinson Posted February 10, 2016 Report Share Posted February 10, 2016 (edited) Greetings, oh sage ones, I have a 1974 ex-California CF. I suspect the left hand rear wheel cylinder has reached its sell-by date. Because it's a CF, does that mean it's a 0.75 cylinder? Is there any benefit to changing both cylinders to 0.70? The master cylinder and servo were replaced last year. Many thanks, Austin One of the more common upgrades here is swapping the rear cylinders for bigger Morgan ones. There's an article on VTR that describes how much it shortens the stopping distance, and its quite significant. Ill look for it in a bit. Edit: http://vintagetriumphregister.org/brake-conversion/ Edited February 10, 2016 by alan atkinson Quote Link to post Share on other sites
Austin Branson Posted February 11, 2016 Author Report Share Posted February 11, 2016 Many thanks to everyone for your help. I have now got the drums off, perhaps I need to explain the symptoms that lead me to suspect the cylinder. The LH rear brake is binding up, requiring me to constantly back-off the adjuster. Everything moves freely (especially the slave cylinder), so I figured the piston will be corroded, and not returning after activation. A look at the position of the piston, and it looks fine. Now I'm stumped. Could it possibly be that the adjuster is self-tightening? I know it sounds crazy, but I really am stumped. I can change the two slaves as a matter of course, if opinions suggest. Thanks again, Austin Quote Link to post Share on other sites
Peter Cobbold Posted February 11, 2016 Report Share Posted February 11, 2016 Austin, The cylinder should slide on the back-plate - perhaps it is stciking? I lubricate with a mix of molygrease and waxoyl. It should be possible to slide it to and fro by hand, maybe a cm. Or the handbrake cable or lever is sticking? cheers, Peter Quote Link to post Share on other sites
John L Posted February 11, 2016 Report Share Posted February 11, 2016 If you have the drums back on, and apply the brakes is the drum them then free, if not there could be several things. Apply the brakes and then release, if the drum is still tight, release the bleed screw this will release the pressure if any, if the drum then turns, then I think you have a problem with the rubber pipe working as a non return valve. Are the shoes on the right way round, with the release springs in the right place also compared to the r/h side? The mechanical adjusters cannot self adjust. John Quote Link to post Share on other sites
Andy Moltu Posted February 16, 2016 Report Share Posted February 16, 2016 Also check the condition of the flexible brake hose - sometimes they fail internally and function like a one way valve so the pressure doesn't relieve when you lift off the brakes. The back plates sometime wear a groove where the handbrake lever pivot is which impedes the wheel cylinder from sliding freely. Quote Link to post Share on other sites
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