Over many decades, I have never had an engine running when bleeding brakes (after a caliper replacement, etc.). My cousin (knowledgeable, whom I respect) said "Oh yea, you have to have the engine running". Does it matter? I guess it would be a bit easier for the person pushing the pedal. And you may get a bit more force. But does it matter?
Engine on or off when bleeding brakes?
- Thread starter AJB0009
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I've always done it engine off. When the brake bleeder is open you don't need as much force to move the fluid through the lines, and the last thing you need is someone pressing the pedal and a ton of fluid being forced out of the open bleed screw.
Get yourself a vacuum bleeder so you don't have to count on someone else and to do a better overall job.
My 1990 Ford Ranger will not bleed rear brakes with the motor off. Rear anti-lock system requires the motor running to get any fluid from the rear drum brakes. Guess it just depends on the vehicle.
No part of the ABS system is driven off the engine, as in, there is no belt driving the ABS pump from a pulley on the engine.
True, maybe the key has to be on and in run position? That said, 1990 was a long time ago, and I feel like ABS was unchartered territory back then.
I've used the vacuum pump for a while now, too much pain to find a second person. Have yet to figure out though the air bubble issue, as it never has a good seal and I'm left guessing when it's good enough.
FWIW, I did a caliper on my truck years ago, would not bleed and get a good pedal. Gave up, took for a short spin, and voila! proper pedal after one more bleeding attempt. Local mechanic said that some vehicles need that. So I keep that in mind when I have issues, sometimes after brake work it just needs a bit of a drive (carefully) if it feels like it's off.
IMO engine always off! You don’t want the mess or the potential fluid injection. If you have to you can turn the key on to activate ABS to help bleed but again engine always off.
Just my $0.02
Just my $0.02
Off.
Well, an electric motor drives the ABS pump, so maybe. But the ABS system isn't activated unless a wheel is skidding so not sure what that would do. Some systems require a scan tool to activate the solenoids to get fluid flow through the pump itself.
I do both. First when off then on. On my gmc the pedal wouldn't finish bleeding until there was vacuum in the system from running then it fully purged. But i don't know if that's specific only to the gmt 800 so i just can't say for sure in your case. I used a little kit they sell at the parts store.
True. My big concern here is that I don’t know if that abs pump design and control mirrors today’s setup-back then they had some wacky stuff, like rear only abs or three channel abs.
I remember looking at the ABS 'module' on an old Ford pickup that had 'Rear ABS' . It didn't look like much more than a valve of some sort way back on the frame rail. No pump at all. No idea how it worked and that was ages ago. I'd imagine it just dumped pressure off the rear drums, somehow.
Some Fords have rear brake proportioning valves that are attached to the suspension. When you brake and the vehicle nose dives, lifts the back suspension and it reduces the brake fluid pressure to the rear. Good luck bleeding brakes with the rear end lifted.
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Or a pressure-bleeder. If it's a stubborn bleed, some vehicles bleed better nose-up. I suppose ABS pumps might like to be running, but doubtful. Engine off.
