cmac2012

I dug into my rear brakes for the first time. I’ve had the truck about 12 years, maybe 60 K - 1989 G20.

I’ve put in brake shoes maybe 10 or 12 times in my short life (71 now). I always remember it being a challenge, this one perhaps more than the rest. Thank God for smart phone video and photos. Thanks also to Jaguar for inventing disc brakes.

I of course, referred to the left side to work on the right side. I was thinking to put in slaves on both side, but the left shoes were so good, and if it ain’t broke, don’t fix it. The right shoes are also very good, but soaked with fluid.

The interesting challenge on this one was everything was a mirror image except the emergency brakes. On both of them, the brake lever was on the right side. Oh well, with my copious photos and video I made it through.

The master cylinder has two reservoirs. The smaller front one was pretty much empty. The larger one back still had enough fluid. The warning light alerted me to an issue, I hadn’t seen the “brake” that large in the past.

I was going to bleed it the old fashion way, with a helper. But this one is not behaving normally. I had removed all of the old fluid, which was a tad dirty, in the larger reservoir. Filled them both.

But the pedal won’t go to the floor with the spigot open. I’ve tried vacuum bleeding on other vehicles with the Mityvac and haven’t done too well with it.

Thoughts?

Triaged

I like gravity bleeding. It helps with my lazy side where I can just walk away for a while with the bleeder open and come back later to see if anything is dripping out. Just full the reservoir, open a rear bleeder, and wait.

No rear wheel anti-lock on it?

tech2

does it have a metering/proportioning valve that needs to be opened to allow fluid to pass to the rear.

cmac2012

Thanks for the replies, sorry to disappear like that.

I have also found gravity bleeding to be somewhat effective. I drove pretty carefully on a test drive the first time I did it, which was the new calipers, rotors, and pads on the front of this vehicle about a year ago.

I tried it on the rear brakes with this job, it seemed OK, but not optimal. I was about to drive up to Washington state from the bay area, about 800 miles. I have a good mechanic buddy, not just a buddy, he runs a good shop and he had time to get me in the next morning. It is unusual with the double reservoir, but he was able to make it work it with me working the pedal.

It sure seemed to be working better after than before. We did all four wheels, so anything lacking in the front calipers was also addressed. Not sure the gravity bleed gets all of the old dirty fluid out as well as a pressure bleeding. Who knows. We need a transparent, cutaway type, set up to really see how this stuff works.

cmac2012

I don’t know the answer to that. I’m only halfway educated on these things.

Triaged

I suppose I left out some information. I have had good luck with gravity bleeding getting fluid to the wheels when the system was empty and regular bleeding didn't seem to work. However once I got fluid to the wheels I did finish off with conventional two person bleeding which went quickly.

mountainmanjoe

before ABS, cars had proportioning valves. They are typically mounted on the rear suspension. As the vehicle rocked forward during hard braking, it would shift brake pressure towards the front wheels (to prevent the rear wheels skidding as they are unloaded). Air can get trapped here.

tech2

i;ve seen p valve on trucks in the mid 2000 that had abs. follow the lines from the master cylinder to the abs pump...look for a square block with a rubber cap and tag.

mountainmanjoe

Interesting. Why? They do the same job: modulate brake pressure.
Was the ABS not sufficient to stop skids?

tech2

not sure why they were both there. I can only speculate. definitely made bleeding the rear brakes easier when they stopped putting them in.


my 81 regal has a p-valve. i have to buy the tool...$25 tool is now $100