First post here so please forgive any newbie mistakes. I shouldn't even be here, as the car I race in historics is actually an Elva Courier. The car has been racing in historic for 30 years, between ourselves, Brian Sampson and Winston Kim.
However, it's got 240Z drums at the rear and the wheel cylinders continue to fail. When I say fail, after about 20 laps (with new cylinders - or honed and rekitted ones) They start to weep fluid. That weep becomes a leak and then everything gets wet and messy. Every session means the drums come off, a can of brake clean gets used and if the circuit is hard on brakes, I may pull the cylinders off, hand hone them, put on some new piston seals and reassemble to get through the meeting.
I have been trying to solve the problem for 2 years and am gradually working through every possible problem without success.
So stop me now if you've had the problem and worked out what caused it!!
The backing plates are drilled, the drums have large vent holes, there's good airflow, heat isn't the problem. It seems that the problem is mechanical. i say that because after just a few races, there's a very clear wear mark in the bore, that indicates the piston is cocking. Last weekend at wakefield park, (fresh hone and new rubbers) I pulled the pistons out and just replaced the seals only for them to leak in the next race immediately. So the bore must have been compromised.
We have tried new OEM cylinders, sleeved cylinders, 2 different types of seals that are the same size, measured the piston to bore clearance (it's correct), tried little O rings on the piston neck to stop the seal sliding up and down, we are running castrol 4.1 fluid, etc etc. The shoes are always adjusted up.
There are 2 avenues left I think. Have I been reassembling the drums with the wrong spring configuration? I've tried it a couple of ways, one where the you have to hold the shoes lightly against the backing plate, before securing them with those little spring retainer arrangements. The other way round the shoes really wanted to roll off the drum. Neither seemed to make a difference.
The other is the drums themselves which are at their max of 230mm. They've been on the car for 20 years. Whilst the linings appear to wearing evenly, it's possible the drum liner surface is no longer square and the linings are cocking under load. We are taking the whole assembly over to a couple of brake guys for their feedback, because after this weekend I've just about reached the end of ideas.
Any feedback or thoughts would be warmly welcomed!