So we're at the stage in my 62 reassembly that I was able to drive it around the yard a bit, and it became quickly apparent that there is an issue with my brakes. It has all new lines, new shoes & wheels cylinders, new rotors, new calipers, new pads, cleaned & reassembled LSPV. Only original, un-touched parts are the booster & master.
Anyways, the issue is an inconsistent and unreliable brake pedal.
- If I push the pedal quickly (not necessarily hard, just quickly), the pedal grabs at close to the top of the travel, the pedal feels firm, and stopping performance is good. The pedal holds steady at whatever position without sinking down.
- If I push the pedal at a "normal" pace, the pedal grabs a bit further into the travel, but steel feels firm when it does grab, and stopping performance is fine. Pedal still holds position as long as I keep pressure applied.
- If I very slowly press the brake pedal, it will slowly sink down until it hits the floor. There are no leaks, and the fluid level is not changing in the reservoir (if anything it seems to slightly increase when this happens). There is absolutely no braking at all except for the last 2-3mm of travel - so it's not just the booster going crazy and sucking the pedal all the way down.
- In any of the above scenarios, if I release some (but not all!) brake pressure and then apply more pressure - the pedal will sink an inch or so each time. So I can stomp the pedal, have a rock-solid pedal feeling, if I repeatedly slightly ease up and then re-apply, I can get the pedal to sink all the way to the floor.
The symptoms don't really seem to match up with air being trapped in the master (pedal is not spongy at all), so my feeling is that one or more of the piston cup seals are worn/damaged, and don't seal unless they're under a lot of pressure. Unless that's just what these Aisin master's do if they're air-bound? My only other theory is that something is going on in the LSPV - but I made sure I bled it thoroughly, and I don't think it has enough volume to swallow the entire master cylinder's stroke worth....
I'm not afraid to rebuild the master - but the brake system did sit for ~10 years without any fluid in it. So I'm afraid the brake master might have some rust in the bore. Probably just simpler and easy to replace the master. Is there any particular preferred brand, or one to stay away from? They all seem pretty reasonable.
Anyways, the issue is an inconsistent and unreliable brake pedal.
- If I push the pedal quickly (not necessarily hard, just quickly), the pedal grabs at close to the top of the travel, the pedal feels firm, and stopping performance is good. The pedal holds steady at whatever position without sinking down.
- If I push the pedal at a "normal" pace, the pedal grabs a bit further into the travel, but steel feels firm when it does grab, and stopping performance is fine. Pedal still holds position as long as I keep pressure applied.
- If I very slowly press the brake pedal, it will slowly sink down until it hits the floor. There are no leaks, and the fluid level is not changing in the reservoir (if anything it seems to slightly increase when this happens). There is absolutely no braking at all except for the last 2-3mm of travel - so it's not just the booster going crazy and sucking the pedal all the way down.
- In any of the above scenarios, if I release some (but not all!) brake pressure and then apply more pressure - the pedal will sink an inch or so each time. So I can stomp the pedal, have a rock-solid pedal feeling, if I repeatedly slightly ease up and then re-apply, I can get the pedal to sink all the way to the floor.
The symptoms don't really seem to match up with air being trapped in the master (pedal is not spongy at all), so my feeling is that one or more of the piston cup seals are worn/damaged, and don't seal unless they're under a lot of pressure. Unless that's just what these Aisin master's do if they're air-bound? My only other theory is that something is going on in the LSPV - but I made sure I bled it thoroughly, and I don't think it has enough volume to swallow the entire master cylinder's stroke worth....
I'm not afraid to rebuild the master - but the brake system did sit for ~10 years without any fluid in it. So I'm afraid the brake master might have some rust in the bore. Probably just simpler and easy to replace the master. Is there any particular preferred brand, or one to stay away from? They all seem pretty reasonable.
