Tricky points on brake master cylinder and accumulator/pump replacement

Tricky points on brake master cylinder and accumulator/pump replacement

Basic Background on the 2 parts

Master cylinder assembly is also commonly referred to as actuator. Basically include

• Similar to traditional master cylinder
• Circuits + valves for brake ECU to control (and coordinate with the regen braking to blend the desired braking force)
• ABS circuit
• Brake pedal pressure simulator (I think just based on compression of hydraulic cylinder)

Brake Accumulator and pump is what the name suggests

• A electric motor pump to generate pressure
• Pressure is stored in an accumulator. About size of a soup can. Store up to ~400PSI!

Since hybrid ICE can turn off during drive. Can’t use engine vacuum for power braking force like traditional ICE cars. Pressure needs to be available when ICE is off.

Part Order

TSBs list 5 different part numbers (PN). 2 are kits which many Toyota dealer online parts stores don’t list on catalog. The remaining 2 actuator parts seems to be for the smaller and larger brakes (come with larger wheels?) reference link Finally the accumulator/pump has only 1 PN.

Some Toyota dealers participate in Toyota’s frequent 20-25% sale on parts + free $75 shipping coverage. Got mine on July 4th sale from Decatur Toyota parts department for ~$900 total (no tax) for both part + gasket.

==== Hardware Replacement

Many videos online so I’ll just focus on the tricky points often skimmed over.

Remove the belly pan

Some parts/tool will likely drop and have to fish it out underneath. Probably good idea to just remove the belly pan in advance. I dropped

1. a crows foot (torquing down the brake lines)
2. The most difficult accumulator/pump silicone rubber bumper,
   
3. 2x accumulator/pump silicon rubber bumper’s plastic end fitting.

1+2 were found here. A lot of crevasses so comb it carefully. Just the hassle of raising the car (probably don’t want to car raised during most of the removal + install to easily reach the parts)



Actuator

Generally fairly obvious. 4 tricky areas

Pedal Retainer Clip

My brake pedal to actuator retainer clip looked different than most video I saw. Still goes through the pin hole but need to pry the open end while pulling the clip.

Normally not much of an issue but you are upside down body twisting position looking up uncomfortably while trying to figure this out



Clearing the hard brake lines

Removing and installing actuator require clearing the heavy actuator from the 5x hard brake lines blocking the way. Just need to gradually work them loose without bending too much.

Cover one of the hard line with a sandwich bag

Cover the hardline end that travel towards the passenger side. This thing wants to spring while working and sling brake fluid towards you. Got me in the eye! Yikes.



Threading in the bottom most brake line

Looks like many people have trouble threading this in ( link ) including me. I think the trick is not to tighten the 4 nuts in footwell area so the actuator can move a little.

I finally looked from the passenger side and realize need to tilt the hard line tip (upwards? Can’t remember) to catch the threads.

Torquing the brake lines

11 ft/lb is a bit much to ask from a small 10mm wrench. Both in required force and potential to strip with an open end. My 10mm 3/8 crows foot with torque wrench works well (just dropped the foot once that cost me an hour haha)

Accumulator / Pump

Fought this thing for 2 hours doing it first time. Here is a picture upside down. Installation involves blind install the underside.



Mainly due to

• No space to remove and install the nut on B
• Silicone bumper on A and B require sliding motion to install. Installing B easily cause A to dislodge and plastic clip to fall out.
• B silicone bumper install/removal is blind underneath the unit causing multiple problems.
• Removal and install requiring sliding towards the passenger side with a plastic hose clip and wiring harness blocking the travel. During install, unclip the hose clip to make more room. Can’t unclip the harness as the release require blind access on the backside.

Silicone bumper A

This bumper often bind and stays on the metal shaft for first timers not knowing the sliding angle. When this happens, the plastic stop inside falls off and drops. Luckily found it on the belly pan.



Installing this is blind. Shaft can easily go into one of the surrounding revolver cylinder holes. Need to inspect with mirror+light after both A+B bumpers are in to confirm properly installed.

Silicon bumper B

When install this bumper, very little space and access. Natural to pull the unit towards passenger side to create more room. This cause A to come off its shaft… and losing its plastic stop.

Install nut on bumper B shaft

Quite impossible to thread the nut onto this shaft. Finally heard of the dental floss trick and it worked like magic.

• Nut is hot glued onto the 10mm ratcheting wrench to avoid losing from falling out
• Floss is wound 4-5 loops so when its pulled, the ratchet rotate clicks
• Just place nut over the thread and pull the floss

==== Diag Tool Bleeding

Charge up the 12V before starting. After 1+ hours with the failure prone process using cheap MVCI cable, battery was 10V and all the computers went crazy. Eventually charged it up and just left the charger on the battery though the whole process.

I have the cheap MVCI clone + techstream setup (probably most people) This setup is good enough for many techstream tasks. However the bleeding and calibration sequence requires many back to back steps lasting over 10min even if completes perfectly. Unfortunately the cheap MVCI clone will drop communication in midst of process preventing proper completion.

Many people describes this problem but don’t mention how they got through it. Some say XP (native or VM) techstream setup work better. I tried VM XP and have the same problem.

This video illustrates the complete process for reference

The process seems to show the following steps

Bleed

1. First 4 corner bleeds are probably just ABS and further downstream
2. Stroke simulator bleed trapped air in that circuit
3. Front 2 corner (probably bleed trapped air from different area of the stroke simulator circuit unable to exit its bleeding screw?)

At this point, all the bleeding is done. Remainder seems to be calibration?

4. Exercise the actuator for 120s
5. Cycle accumulator pressure ~5x?
6. Linear Valve Calibration

Unfortunately, cheap MVCI tool starts to drop communication starting at step 2

I was able to complete #2 (3x total bleeds but process failed after each one) after many tries. Each failure require going through step 1 again (no need to bleed, just click next in menu) You can hear the an solenoid click when starting #2 and hear a click when communication drops or fails. Stroke simulator bleeder screw is on driver side where my techstream computer was located. This allowed quick bleed after triggering before it failed.

Was able to complete driver side of step 3. Again, mainly due to proximity to techstream computer.

Couldn’t complete passenger side of step 3. Took too long after triggering the techstream and open the bleed port. Maybe a long USB extension cable would have helped. Have techstream near passenger front caliper bleed screw : trigger, helper step on brake, open bleed screw.

Many failures on 2 and 3 and require restarting the process and just click next through all the prior menu steps to resume from failure.

Once #4 is triggered (just click next on the process until getting to #4 and hopefully doesn’t fail before. If fail, just try again and eventually will get through) #4 went through 120s without problem but failed after.

Unsuccessful triggering #5 (require going through 120s of #4 so I only tried 2x) Instead, I ran either ECB Utility Zero Down function or accumulator zero down (can’t remember) 1x. Maybe should have done it 5x? The zero down test did lower and raise the reservoir fluid like the above video.

#6 Linear Valve Offset can be triggered from ECB Utility. However, it won’t do anything (won’t hear any noises other than set code C1203 C1345) Reading utility directions says to erase memory before executing linear valve offset if actuator has been replaced. Did that and it works (made lots of noises, no codes after)

Would be nice to figure out what are individual utilities/tests that an be triggered to perform step 2-5 instead of the constant failing complete bleeding/calibration process. Triggering zero down, reset memory, and linear valve offset all completed without any problem outside of the long bleeding process.

Don’t know if there is still a little air left in the system but the car brakes great. No codes.