Nickymac

That's the difference between a car that weighs close to a ton versus 670Kg! None of that happens, the pads and linings last a few seasons, and the drums have been on the car for many many years, it doesn't boil fluid, nor warp rotors. It does however leak fluid from the rear cylinders....

Thanks mate, yes i did work that out the handbrake wouldn't be in the right spot! Linings though are thick and brakes are adjusted up before each session, linings lightly touching drums when you spin them. What I have worked out is that I've swapped the cylinders over by mistake and the adjuster lever is now on the inside of the slave. The bigger linings spring and the lever are actually pushing against each other, perhaps this is contributing to the problem....

If I had the backing plates swapped by mistake during the last resto, the loads on the pistons would be reversed. The way it is now, the cylinder on the drivers side is on the left of the drum, thus the top lining is being pulled away from the piston as it actuates. Same load applies on the passenger side, although the piston is on the right obviously. If the backing plates were swapped, the top lining would be forced into the piston as it actuates and perhaps affect its performance. Just a thought.....

They are absolutely standard 240z drum assemblies, the only exception being some cooling holes drilled. You can't fit 260Z/280Z cylinders, linings or drums to this backing plate. I will take some pics though, it's a good idea, somebody may well see something. Cheers Nick

Thanks again guys for the feedback. Firstly there are cooling holes in the backing plate including a ring of 5mm holes right around the outer edge. The drum has 4 or 5 30mm holes but on the surface that faces the wheel. There are no holes on braking surface. The piston normally extends about one mm, how much further would it go when they expand? I can't imagine too far, but I might stick the GoPro down there for a session at Sandown and watch it! Brake fluid is fine at Dot 4 , there are zero issues with compatability with 3. It's when you go to 5.1 that you get probs as that's a synthetic formula. I don't think annealing is the problem, or we would have all heard of it happening with drums in the past. The taper of the lining face is the first thing to check I think as the piston is cocking somehow. I am going to try and pull the handbrake on a few clicks, if piston protrusion is the issue then it may help. But I keep coming back to the fact that the car has raced for30 years without this problem, what's changed? Once again thanks for all your help. Nick

Thanks all for responding thus far. We could probably go to a 260Z config but we raced this car ourselves back in the 80's when we originally restored it and never had a problem. The car has raced for 30 years without a problem. It's only the last few years that this has happened. The over extending theory has merit - although they are adjusted up before every race. It's conceivable that they are expanding to such an extent that the piston has to travel right out. I did read of one driver who uses the handbrake adjuster mid race to wind the shoes out a bit to cope. It's conceivable that the linings we are using now have much more grip which is causing them to work too hard and get too hot and consequently extend too far. I created some extra cooling for this last meeting, but I think that was nullified by the fact that the circuit is so hard on brakes. Sandown in 6 weeks will be a better benchmark. Thanks again for your thoughts, I sure would like to solve the problem. Cheers Nick

Hi All, 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! Kind regards, Nick