02-11-2018, 09:42 PM
This is another recurrent topic. These posts are likely to come up in Search so a summary may be of use to some....
Conventional modern lining materials are designed to not fade under very severe use, and to last forever, and to be power assisted. These linings are hopeless in an ordinary Seven. But likely to be applied by brake firms who do not do a lot of old car work.
Contemporary brake performance was poor (often abysmal. Some did not achieve 50%!) and even many of the older materials are dubious (I have NOS woven asbestos era Ferodo GG7 linings and roll of the same from 1960s and occasionally see in swapmeets; dunno how this is rated relatively now?)
The current specialised soft linings by most accounts seem a major improvement. Locked wheels are claimed. In the dry! A relative rating would certainly be interesting. Various methods of testing by applying to just one shoe can be devised.
Bedding is a problem with Sevens, especially with the low mileage. Unlike most other makes the shoes are not free to locate themselves in any way so even if ground to appropriate radius off the car unlikely to seat immediately. Fitting in place to the drum is about the only way of hastening bedding. (I hate to think how much asbestos I sniffed up fitting brake shoes years ago; something to be aware of esp with NOS). The ends of the shoes may need alteration. There have been numerous posts about devices for checking shoe location and for contouring.
There is a mod of the shoes to render them partially self locating but it is somewhat barbaric, and might lead to grabbing or rubbing problems. Certainly need to avoid the latter with a Seven!
For those new to the topic Seven brakes are not too small. Except perhaps the very last rod brake models, problems arise from limited leverage, little compensation, and lack of self servo effect. If the leading shoe starts to apply itself pressure from the cam reduces and the cam cannot follow up and maintain pressure because it is restricted by the trailing shoe which has no self operating effect and in consequence a relatively weak action. With hydraulic and full Girling sytems the expander follows up and maintains full pressure on the leading shoe.)
Conventional modern lining materials are designed to not fade under very severe use, and to last forever, and to be power assisted. These linings are hopeless in an ordinary Seven. But likely to be applied by brake firms who do not do a lot of old car work.
Contemporary brake performance was poor (often abysmal. Some did not achieve 50%!) and even many of the older materials are dubious (I have NOS woven asbestos era Ferodo GG7 linings and roll of the same from 1960s and occasionally see in swapmeets; dunno how this is rated relatively now?)
The current specialised soft linings by most accounts seem a major improvement. Locked wheels are claimed. In the dry! A relative rating would certainly be interesting. Various methods of testing by applying to just one shoe can be devised.
Bedding is a problem with Sevens, especially with the low mileage. Unlike most other makes the shoes are not free to locate themselves in any way so even if ground to appropriate radius off the car unlikely to seat immediately. Fitting in place to the drum is about the only way of hastening bedding. (I hate to think how much asbestos I sniffed up fitting brake shoes years ago; something to be aware of esp with NOS). The ends of the shoes may need alteration. There have been numerous posts about devices for checking shoe location and for contouring.
There is a mod of the shoes to render them partially self locating but it is somewhat barbaric, and might lead to grabbing or rubbing problems. Certainly need to avoid the latter with a Seven!
For those new to the topic Seven brakes are not too small. Except perhaps the very last rod brake models, problems arise from limited leverage, little compensation, and lack of self servo effect. If the leading shoe starts to apply itself pressure from the cam reduces and the cam cannot follow up and maintain pressure because it is restricted by the trailing shoe which has no self operating effect and in consequence a relatively weak action. With hydraulic and full Girling sytems the expander follows up and maintains full pressure on the leading shoe.)