Brake sinking to floor
08-26-2017, 10:30 AM
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Brake sinking to floor
The vehicle: 87 4runner 22re sr5 non turbo with PSV valve thing deleted
The symptoms: Brake sinking to floor only when engine is running. The motor wants to stall (doesn't die) when the brake is depressed. The pedal feels firm when engine is off.
The story: I rebuilt the front two calipers after having seized pistons in both. The pistons were so seized up I had to use the lithium grease method to get them out. I spent alot of time cleaning the grease out and I"m 99% sure all passages are clear. When I reinstalled the calipers (yes the bleeder is on the top so they're not switched) I started getting the symptoms above. I bled DR, PR, PF, DF. I immediately replaced the master cylinder, which I bench bled before installing. No difference. After looking at my local junkyards I got a brake booster from a 92 2wd pickup, it looks slightly different but there was no change in my symptoms. I "checked" my check valve and I can blow in one way and not the other, so I assume that's working. I blew smoke in that vacuum line that leads to the booster and I didn't see any leaks. Seems to have plenty of vacuum when I popped off the hose and put my finger on it. I've bled and rebled and rebled both my calipers and the MC. I also don't see any bulge spots in the flexible line.
Options going forward:
I have a complete solid axle from an 83, the calipers are slightly different but I could (maybe?) hook them up to see if there is no change then it's not the calipers.
Replace check valve anyway
Adjust pedal
Return the MC and get another one
Check for other vacuum leaks elsewhere?
*EDIT* I forgot to mention I checked the rear brakes and they're adjusted out far enough to stop my from turning the drum.
The symptoms: Brake sinking to floor only when engine is running. The motor wants to stall (doesn't die) when the brake is depressed. The pedal feels firm when engine is off.
The story: I rebuilt the front two calipers after having seized pistons in both. The pistons were so seized up I had to use the lithium grease method to get them out. I spent alot of time cleaning the grease out and I"m 99% sure all passages are clear. When I reinstalled the calipers (yes the bleeder is on the top so they're not switched) I started getting the symptoms above. I bled DR, PR, PF, DF. I immediately replaced the master cylinder, which I bench bled before installing. No difference. After looking at my local junkyards I got a brake booster from a 92 2wd pickup, it looks slightly different but there was no change in my symptoms. I "checked" my check valve and I can blow in one way and not the other, so I assume that's working. I blew smoke in that vacuum line that leads to the booster and I didn't see any leaks. Seems to have plenty of vacuum when I popped off the hose and put my finger on it. I've bled and rebled and rebled both my calipers and the MC. I also don't see any bulge spots in the flexible line.
Options going forward:
I have a complete solid axle from an 83, the calipers are slightly different but I could (maybe?) hook them up to see if there is no change then it's not the calipers.
Replace check valve anyway
Adjust pedal
Return the MC and get another one
Check for other vacuum leaks elsewhere?
*EDIT* I forgot to mention I checked the rear brakes and they're adjusted out far enough to stop my from turning the drum.
Last edited by Dielawn; 08-26-2017 at 10:33 AM.
