Need info on fixing leaking accumulator

I'll start by saying I'm not very familiar with the Gen 3.

You may want to read this thread:
Error code C1391 | PriusChat

 

I find it curious the way we're slowly transitioning from Gen2 to Gen3 work... I now have an opportunity to do my first head gasket and am still trying to decide if I really want to go down that rabbit hole?

 

I still have a prime condition 2008 in the driveway that needs the abs assembly replaced and I'm not sure if I want that rabbit hole either. I even have 6 of the assemblies on the shelf ready to try. Just haven't made the time, and not 100% certain I want to. For being in a pandemic, life sure has been exceptionally busy............

 

yea... it's all about the bubbles... As in getting bubbles out of the cooling system or the braking system... Avoiding those hassles make Prius repair work fun! Of course once we get good gear gear and technique by facing the challenge we'll likely wonder why we avoided it for so long?

 

Attached is a service bulletin regarding Brake Booster Pump Assy replacement, and I'll pm you a Repair Manual link.

 

One thing about that pdf, on page 20 they show a torque (31 inch pounds) for tightening the two nuts, and they were able to calculate that torque because they know the length of the specific torque wrench they tell you to use, and the length of the custom "brake pump wrench" extending it.

From the picture, they look about equal, so that's probably about 62 inch pounds at the nuts. If you're using your own improvised tools, the math may be different.

 

There is no easy or cheap solution when the pump accumulator won't build pressure fast enough. It needs to be changed. It is a very common problem.

Some might risk a used pump but since this is brake by wire and essential, most spend the money for new parts. A metal diaphragm in the unit leaks, usually taking out the abs/brake ecu/master cylinder in the process.

Even if you replace both units, the brake stroke simulator portion has to be calibrated and a special flushing technique is required, both using Techstream.

There are various versions of the master cylinder making a used option more difficult. Used sellers generally don't know this so it would be prudent to have the donor vin for part compatibility verification. The Toyota part number is not on the master cylinder.

I would appeal to Toyota Corporate for a repair even though you must be over 150,000 miles.

This recent video details the replacements short of the Techstream process.

 

There's also something tricky with the pump unit, there was a revision to it, and (IIRC) rather than revise the part number, they just rotated the label on one of the "beer cans", through 90 degrees. Or maybe they did revise part no too?

 

Another inexpensive option is to refresh the brake fluid. I've experience some significant improvements in the pump run times after replacing the brake fluid. It's a relatively inexpensive thing to try.

 

Sometimes a part of the problem is nitrogen leaking out of the accumulator. If it does, it gets into the brake fluid, and there are two problems:

1. There is less nitrogen in the accumulator, so it goes from max to min pressure faster, and the pump has to run more often. (This is just like a house on well water when there is not enough air in the pressure tank.)
2. There are nitrogen bubbles in the brake fluid. Every time you brake, they have to be compressed, which takes extra fluid. When you release, they re-expand and blow the extra fluid back to the reservoir. This means more fluid is used for each use of the brakes, and the pump has to run more often.

Both 1 and 2 contribute to the frequent pump runs. When you do a fluid replacement (or just go through the actuator bleed sequence, which requires some new fluid but not as much as full replacement), you can get the bubbles out of the fluid, which fixes 2. Nothing you do puts the nitrogen back in the accumulator, so the 1 part will keep steadily getting worse (and eventually giving you the 2 part again, probably sooner than the last time). But at least dealing with the 2 part gives a noticeable improvement that can last for a while.

 

Fortunately, the accumulator on a Gen 2 can be replaced independently from the actuator assembly just by unthreading it from the valve body block. I think it's a 15 or 17 mm hex on the end of the accumulator. You just need to discharge the accumulator to the reservoir via techstream to bleed all pressure from the brake system prior to loosening. Not sure if it's possible on the Gen 3. Pretty sure the accumulator can be unthreaded, just not sure if there's adequate room to do it.

 

Flushing the fluid will fix it for about a day. Been there done that. The gen3 has a separate pump accumulator.

 

Attached are the non-Techstream and Techstream brake bleed methods, from Repair Manual. @ChapmanF has noted in past that the Techstream method may be required if there's anomolies in the firewall gizmos.

To clarify a very obtuse bit of the non-Techstream instruction, the order they say to bleed is F/R, F/L, R/L and finally R/R.

 

It's always worth a reminder that those sections of the manual are not brake bleed instructions.

They are brake fluid replacement instructions. In fluid replacement, you start with a system full of fluid, no air, no need for bleeding. You let old fluid out and new fluid in, no air, no need for bleeding. These instructions will work for that.

If there is air but it is only in the wheel cylinder lines or calipers, you can also get away with these instructions. If there's air in the head end, you can't, and have to bleed with Techstream. Techstream will walk you through doing the fronts two times, two different ways, to bleed the two different circuits; no non-Techstream procedure is provided for that.

If you are doing a simple fluid replacement and take your eye off the reservoir and get air in, you will also need to bleed the head end, and will need Techstream to do it.

 

How would I go about doing that and has anyone done it before