2003 LC with Traction control and VSC. Where is the accumulator pump pressure sensor located? Also, where is the high pressure relief valve located? I imagine they are both on the manifold block between the master cylinder and solenoid board, but would like to hear from someone that has actually torn one down. Thanks.
Brake accumulator pump pressure sensor
- Thread starter TenderTendon
- Start date
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2001LC
SILVER Star
I'll assume you're asking, because you've a brake master issue setting off ABS DTC (code) activated. You're now, trying to fix the issue?
forum.ih8mud.com
Brakes ...... Overdue write-up.
First and foremost: Brakes should only be worked by those, with high level of mechanical abilities and experienced with brake systems. With the age of all 100 series today, in our aging fleet. Any issue, with brake master assembly. IMHO, best and safest course of action. Have the whole brake...
forum.ih8mud.com
- Thread starter
- #3
I have already read that thread. It doesn't address my issue. Do you know where the pressure sensor and relief valve are located?
- Thread starter
- #4
Well, I finally got around to digging into this and found a couple of things that make complete sense. It also perfectly explains the symptoms I was having.
First off is the pressure switches. They were on the manifold block, as I suspected, but weren't what I expected. I expected to see a couple of strain gauges, but instead I found heavily sealed, spring loaded pistons actuating very high quality micro switches. My low pressure micro switch tested perfectly fine. Using 4 wire Kelvin clips, the switch consistently had less than 0.07 ohms resistance, even after 50 actuations. Pretty impressive for a switch with such a low activation force. The high pressure switch failed big time, and I suspect this is the cause of many, if not most of our master cylinder/pump failures. This switch started off with approximately 0.1 ohms resistance, but after 10 actuations, I noticed the resistance keep rising. After 30 or so actuations, the switch had a resistance of over 200 ohms. Not good... This explains why my accumulator pump wouldn't shut off after I drove 30 minutes or so, even though the pressure was too high. These micro switches would not be that difficult to replace, with some basic soldering skills. There could also be another common failure mode of the high pressure switch, but not a problem with the switch itself. A master cylinder with little or no maintenance could have a lot of moisture in the system and could cause the spring loaded piston to corrode and lock up, never actuating the micro switch. Same result, different cause. Unfortunately, I see no way to get these pistons out for cleaning or replacement. It seems the whole piston assembly is pressed into the manifold block, with no way to remove.
Next up is the high pressure relief valve. It wasn't on the manifold block as I suspected, but at the end of the master cylinder, behind a pipe plug. This relief valve is not adjustable and non-serviceable (for obvious reasons). I can't really see how the valve was installed, but I suspect it is with some sort of breakaway bolt (similar to the bolts holding the VIN tag on our engines). It could also be pressed in. However they did it, it's obvious they didn't want anyone messing with it. This relief valve is tapped directly into the pressure port from the pump/accumulator and bypasses directly into the front chamber of the brake fluid reservoir. It was obviously doing the job it was designed for.
I have some micro switches on order. I'll follow up when I get them installed and do some testing.
Pressure switch pistons:
Micro switch:
High pressure relief:
First off is the pressure switches. They were on the manifold block, as I suspected, but weren't what I expected. I expected to see a couple of strain gauges, but instead I found heavily sealed, spring loaded pistons actuating very high quality micro switches. My low pressure micro switch tested perfectly fine. Using 4 wire Kelvin clips, the switch consistently had less than 0.07 ohms resistance, even after 50 actuations. Pretty impressive for a switch with such a low activation force. The high pressure switch failed big time, and I suspect this is the cause of many, if not most of our master cylinder/pump failures. This switch started off with approximately 0.1 ohms resistance, but after 10 actuations, I noticed the resistance keep rising. After 30 or so actuations, the switch had a resistance of over 200 ohms. Not good... This explains why my accumulator pump wouldn't shut off after I drove 30 minutes or so, even though the pressure was too high. These micro switches would not be that difficult to replace, with some basic soldering skills. There could also be another common failure mode of the high pressure switch, but not a problem with the switch itself. A master cylinder with little or no maintenance could have a lot of moisture in the system and could cause the spring loaded piston to corrode and lock up, never actuating the micro switch. Same result, different cause. Unfortunately, I see no way to get these pistons out for cleaning or replacement. It seems the whole piston assembly is pressed into the manifold block, with no way to remove.
Next up is the high pressure relief valve. It wasn't on the manifold block as I suspected, but at the end of the master cylinder, behind a pipe plug. This relief valve is not adjustable and non-serviceable (for obvious reasons). I can't really see how the valve was installed, but I suspect it is with some sort of breakaway bolt (similar to the bolts holding the VIN tag on our engines). It could also be pressed in. However they did it, it's obvious they didn't want anyone messing with it. This relief valve is tapped directly into the pressure port from the pump/accumulator and bypasses directly into the front chamber of the brake fluid reservoir. It was obviously doing the job it was designed for.
I have some micro switches on order. I'll follow up when I get them installed and do some testing.
Pressure switch pistons:
Micro switch:
High pressure relief:
2001LC
SILVER Star
Nice researching work.
Now you know why. I recommend against the use, of these so called remanufactured brake masters.
I'm hesitant, to give any advice on brake master, other than:
Brake Master are a one and done. When time comes, we bit the bullet and replace the whole booster assy w/master.
Now you know why. I recommend against the use, of these so called remanufactured brake masters.
I'm hesitant, to give any advice on brake master, other than:
- Replace the whole unit, when failure occurs or sign of premature failure are noted.
- Flush often, with Toyota brake fluid. (Don't mix brands of fluid)
- Do not overfill or spill brake fluid on master.
- Keep driver side fender well mud flaps in place.
Brake Master are a one and done. When time comes, we bit the bullet and replace the whole booster assy w/master.
