Tonka

Only because I've started asking on here and anyone else with a similar prob may one day read the whole thing to the end in search of a solution and wonder what eventually happened, so I'm trying to help them too. I only just found that link from googling my problem. Thanks again for your help.

I think I may have found something else relevant. Should the rear wheel cylinder be located at the top or bottom of the backing plate ? I found a rear brake exploded diagram here: and it seems to show the cylinder at the top, my rear wheel cylinders are at the bottom, that's how they've always been. Where should they be ? Maybe my rear brake backing plates are on the wrong sides and upside down ?

The brakes work again, but have always felt spongy. I still imagine that any air in the sytem will always go to the top and liquid to the bottom, I don't understand why an increase in pressure would make the air fall down into the liquid. As the bleed nipple appears to not be at the very top I still can't get how the air it's meant to remove gets down through the liquid to where it's positioned on these rear wheel cylinders. It will have to remain as one of life's mysteries for me for now. Thanks for your help.

Thanks, if that's the correct original engineering design then I'm just amazed and now a bit more curious. Inside the wheel cylinder is there any fancy porting that somehow directs the air from the airspace at the top of the cylinder down to the bleed point ? I can't get my head around why any engineer would design something that would defy the underlying principal of liquid to the bottom and air to the top. To save me pulling my wheel cylinders out and looking, can you remember if the ports for the hydraulic line and the nipple are just plain holes drilled straight into the main body cavity of the cylinder straight in line with where the respective line and nipple screw in ? And yes a dual circuit master cyl is now the plan.

Datsun 1000 B20 ute, 4 wheel drums and a single circuit master cylinder, lost all brake fluid yesterday after the flexible hose to the diff split and the pedal hit the floor. Went to a friends place real close by and he helped fix it. Then when we went to bleed the rear brakes he looked at the rear bleeder nipples and said "why is the bleeder nipple located lower than the brake line, how does that allow the air to escape ?" Good question. We looked at swapping the rear wheel cylinders but that wouldn't change the bleed screw positions, looked at rotating the cylinder 180 degrees but then the handbrake mechanism wouldn't line up and looked at swapping the upper hydraulic line with the lower nipple but they are clearly different threads. Ended up parking backwards on a steep slope and jacking the front up about a meter to get the line and the nipple positions just level to get the air out as we pressure bled it. The front wheel cylinders have the bleeder nipple at the top so no issue with conventional bleeding techniques. So the question now is, is this all normal ? Or maybe have the rear wheel cylinders been replaced previously with another type that fit perfectly but are designed for another vehicle to mount at some other position ? Anyone got any clues as to what's going on ? Or seeen/heard of a similar issue ?