HELP: Brake Bleed Conundrum with Dead Battery

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Jan 10, 2018
Atlanta, GA
Hey Ya'll,

I am in the process of bleeding the brakes on my Lx470, but I have a bit of a problem: The car has been sitting for such a long time that the battery died.

As I understand many folks are bleeding their brakes with the ignition set to the "On" position, but for me to be able to do this without engine running I have to run on an external battery jumper, so very limited juice to do it on the jump box.

My question to you all:

1) will anything happen if I bleed the brakes while the engine is on? I understand that it is an electric pump, so not sure how that all plays in ( assuming it wouldn't matter if the engine is on then if that was the case? )

2) Can I and should I start the engine up, let it charge, and then try to do the bleed procedure with the ignition just set to on?

3) What advice would you give me in this scenario? Can I bleed with the car completely dead?

Thank you all, I would have written more words but my hands are covered in grease and oil as I try to do this real time. Hooray for DIY!
Also, would starting the engine and letting it sit to charge mess with the anything related to the actual brake system? The reason I ask is that I recently replaced many things on the brake system, the front lines, calipers, etc. and lost a ton of fluid in the process. I have topped off my reservoir but just looking for feedback on this. Thanks all!
You must have IG key on to bleed brakes. Make no difference to brakes if engine running.

Clean battery post and grease them, if dry. This will help get proper voltage to all system.
Last time I did this I fiddle -----ed around enough to drain the battery.

  1. I don't have a maintainer. Can a trickle charger hooked up during the bleeding process help?
  2. Would it be better to just let the engine run for some of the job?
  3. Or should I just become more proficient at crawling under the car and loosening bleeders? (This one's rhetorical -- I can't see it happening.)
I check voltage of battery before and after. Voltage will drop some. As voltage drops booster motor RPM drop. This results in longer time for accumulator test. How much depends on battery and how long one runs the brake booster pump. But typically a good battery will get you through the job.

Keeping a tender on seems okay, as I must use in some when doing a compression test and have never had an issue. But be advised in 200 series, Toyota recommends disconnecting battery cable, before connect a battery charger. Seems they've concerns; is it fear we'd short or is that electronic are so sensitive IDK!'s a novel idea: ;)

  • Remove battery, check fluid level and electrolytes.
  • If good, fully charge battery and 'load test' it.
  • IF battery passes load test, hook to vehicle and proceed/resume.
  • IF battery fails replace with new, hook to vehicle and proceed/resume.

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