Brake question – I only have 1 bleed valve – on the right wheel – none on the left –
 

Brake question – I only have 1 bleed valve – on the right wheel – none on the left – is this correct?

I’m in the process of changing the rear brake “wheel cylinders” on my 85 12a. I need to bleed the brake lines as part of the change, plus while doing the change, I would like to go ahead and change out the brake fluid. My question is I only have 1 brake bleed valve on the rear wheels, the right side. The brake line comes from the front of the car to the left rear wheel, where it connects to the “wheel cylinder” then exits the cylinder and runs to the right wheel (where the only bleed valve is). So I assume that I just bleed the right rear wheel and because it’s a closed loop with the left, both will be bleed at the same time? Or am I missing something here, e.g. does the left wheel have a bleed valve that I am not seeing?

I could not find any historical articles that were appropriate - so if they exist, I would appreciate someone pointing me to them

no histerical articles to show you, but yes, if you have rear drums, that is the correct setup. I found that when you bleed the drums if you think there might be air in them, use a C clamp and compress the left cylinder and then bleed. Do that ONLY if you think you might have air bubbles in there.

Yeah, the idea is that the line comes from the master cylinder, into the left side, out of the left side, into the right, and out the bleeder valve.

So when you bleed the brakes, air bubbles pass through the left wheel cylinder as if it was just another piece of line - theoretically. Basically all this means is that you have to bleed more thoroughly to make sure that any air bubbles make the long journey through the system and out the bleeder valve. It's always better to overbleed than underbleed.

Remember, only use DOT3 or DOT4 because both of those are fully compatible with each other. DOT5 to some people might *seem* like a good idea for an upgrade, but unless you completely flush the system properly, you can't use DOT5 since it's uncompatible with 3 and 4. Besides, unless you've got racing brakes, you don't need more than dot4 anyway.

Jon

Since I'm putting on new wheel cylinders there will be air in the wheel cylinder, but assume the bleeding process will force the air out of the cylinder, e.g. the repeated braking - is this an incorrect assumption?

I've never had a problem bleeding the rear brakes, including after disassembling the whole mess in order to change the differential. (To take out the diff the axles have to come out, and the backing plates have to stay on the axles, so all the brake lines and the handbrake cables have to be removed)