This is part 3 (the final portion) of our Tech Tricks Tuesday on how to bleed brakes on a hybrid vehicle. If you missed last week’s post, you can read it here.
Last week we covered:
- The history of the Prius used in this write-up
- Where the master cylinder reservoir is and how to remove the cap
- The importance of the master cylinder cap
- A brief overview of the brake system
- How to properly prime the reverse brake bleeding tool
- How to get started with reverse bleeding on the hybrid vehicle
- How to proceed with bleeding the system
This week we will cover:
- Reason to not shy away from bleeding a hybrid system
- Potential reason why the fluid is lower in the master cylinder
- A “best practices” of bleeding using a Phoenix Systems Reverse Bleeder
As before, the master cylinder fluid level rose after bleeding each individual wheel. This is proof that we are achieving fluid flow with the Phoenix bleeder from the wheel hydraulics upstream to the master cylinder.
Some folks shy away from bleeding a brake system on a vehicle when it has a logo on it as shown. Don’t automatically do this. Many hybrids are fairly simple to bleed when using the Phoenix bleeder.
The next vehicle we selected to try bleeding on was this late model Ford Fusion. This vehicle has never had any brake work done on it.
Note the level of the fluid in the master cylinder. It’s lower than it should be. What is the reason? Only two logical possibilities. One it has a leak which it doesn’t and two the friction is worn allowing the pistons to move farther out in the caliper bores which lowers the visible fluid level in the master cylinder. This car is in a fleet and is driven a lot of miles each month by multiple drivers. It’s used daily sometimes for extended trips.
As with most vehicles today the bleeder valves or at least the front wheel bleeder valves are easy to access.
This image shows a rotor on this hybrid with a unusual amount of glaze and material build up (transfer layer). If this wasn’t a hybrid, this may be of some concern but hybrid vehicles use regenerative braking as their primary braking system so the actual wheel brakes really don’t do that much braking.
As shown previously, the tech places his finger over the bleeder valve end of the Phoenix bleeder and compresses the bleeders handle to assure a solid column of fluid prior to putting the rubber end over the bleeder valve and bleeding the system.
This image shows “best practices” of bleeding a wheel using the Phoenix bleeder. The bottle containing the fluid is suspended by a cord and is the lowest component in the system. The bleeder is pointed slightly upward while being used. While not absolutely necessary, some tech feel this assures a solid column of fluid under all bleeding conditions.
This may look like a complex rear caliper/brake system and may also have an electronically actuated parking brake but the system bleeds out like any other caliper system. In the case of most calipers, wheel hydraulics are wheel hydraulics. There is seldom anything very special about them.
As before, you know you had fluid movement upstream by the rise in the fluid level of the master cylinder.
After completing the bleeding of any vehicle check the master cylinder level and adjust the fluid level accordingly. Set the fluid level according to now only the full mark the full hot or full cold mark. What is hot and cold. Use some common sense. If you can touch anything in the engine compartment with any problem it may be considered cold but if you can as you wouldn’t be able to if you just shut it down after a trip it is considered hot.
Can all hybrids be bled without any special procedure or tools? That is a unknown at this time. The thing is that we decided to check out two common hybrid vehicles to see if our bleeder would work on the systems and the answer was found to be yes.