Rear brakes not good enough

[Polarsilver]

i use the Compbrake Bias Valve Screw Type V2 Knob Type it is ISO9001 Certified .. the body is alloy & excellent quality .. look on Compbrake site this type Bias Valve is about £40.
I have this Combrake Bias Valve fitted ( in easy to get at position ) on three cars in the supply line to Rear Brakes for the reason i have modified the Front brakes so not a standard set up.. easy to fine tune them to suit & my start set up is fully close the vale & then open two full turns that is about right & then fine tune rear braking effort from there .. be very careful as"if the rears lock up start again as the rear brake pressure is too high "
I have past experience with Brake Testing Vehicles at Mira & also have an ex army inertia brake test kit but the reality is .. i just find a straight quiet road & then set up the Compbrake valve to suit what i think is the best braking set up, as i just need the assurance the thing will stop in the shortest distance when needed & yes my Classic Insurance is declared to have with modified brakes ;

ps the rear std subframe valve is replaced with a "T" fitting.

[1071bob]

I've done some tests on these bias valves, my 1071 has standard S calipers and 5/'8" rear cylinders. When I made up the rear brake line assemblies I pressure tested them at work to 3000psi without the bias valve piston fitted, with the piston re-fitted the valve shut off at 350 to 400psi. Not super accurate as the gauge used was calibrated from zero to 10,000 psi.
With the car finished I did some more checks:- with the brake pedal jammed on the torque required at the front wheel to turn was 100lb/ft while the rear drums were just able to turn @ approx 10 lb/ft.
Also checked the handbrake, with the brake pedal released and the lever pulled to the first click gave me 70lbs/ft to turn the drum and with the lever pulled to the second click it went up to 140 lbs/ft. worth noting that I have the later longer handbrake links in the drums. Using the torque wrench was very useful to equalise them side to side by adjusting the cables.
Now for the bad news, I can't find the notes which would tell me what spring I fitted in the valve I had three springs available, 11 coils @1.9mm gauge and 13 coils @ 1.66 gauge. Will have to wait until I do some road tests.

[Catmint]

Thanks Catmint. I think that might be someone else using mintex shoes. Mine are new standard shoes, but I did wonder if the material isn’t as good as the old nos ones. And as people have mentioned whether they are the same size.

Sorry, yes it was, I was reading the thread from the beginning, but not looking at users. Might be worth a try, an easy swap

[Peter Laidler]

You have missed your true vocation Bob (1071 Bob...) You should have been one of those 60's era apprentice masters in the old industry 3 (or 5) year apprentice schemes. Or one of the engineering Laboratory Technicians at Uni. I can still remember some of those great names who cajoled us through our practical exams. I wonder where the great apprentice master Mr Surtees is now. Or Mr Tolan, the lab tech who would open the engineering workshops to allow us to use the machines and test beds over the weekends.

Yep, your articles remind me of them Bob.....

PS. Good idea to use a simple torque wrench adaptor to adjust the handbrake load equally

[MiNiKiN]

I don't know if this was mentioned previously, but it may be worth checking the contact pattern of the brake shoes.
I usually check the shoes by covering the pad surface in white chalk and then rotating the drums with lightly applied brake (so you can still rotate them)
Then I take the drum of and check where the chalk has been ground of and where not. Often the shoes only grip in a very small area, which then tends to start glazing. Glazing of course significantly reduces the friction and braking force as such.

My trick is to use an old drum that has a 2mm greater ID so I can fit some emery paper around its inner diameter (either use self adhesive emery or skateboard grip tape) Then fit the drum and rotate whilst applying light brake pressure. Such the shoes will evenly get matched to the drum dia and you increase actual friction surface.