LUVTruck.com

Is there a reason I would need to have my engine running to bleed the brakes on my stock 79 LUV? I changed the master cylinder and am pretty sure that I got all the air out during the bench bleed. Also, how many times should I bleed the same line? Does the air get pushed out first? (How does that work?)
Thanks in advance.

I bled them with the engine on (still don't know the benefit). The last bleeder was full of foamy air and DOT3. I have brakes now! (yay).

FSM ssys there is a seal that can be damaged if the brakes are bled without the engine running, but it doesn't say which seal or where.

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'78 Chevy LUV,1.9,4sp,headers,31's,SAS Dana 30,Dana 20,SOA rear w/Aussie Locker, rough body, bought new 12/4/78.
'87 Trooper,2.3,5sp,headers,31's,ball joint flip & spacer,Aussie Locker rear,Superwinch hubs,brush guard w/5.5K winch,more to come.

When I did mine (just the rears), I went through quite a bit of fluid. I didn't quit until I stopped seeing bubbles in the bleeder.

Jack

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'83 Isuzu P'up Diesel LS - Original Owner
JoeIsuzu@IsuzuPup.com
IsuzuPup.com

I think it is some kind of relief valve in the vacuum booster that supposedly can be damaged. I have yet to have a failed booster on any of my LUVs and have bled the brakes with the motor off several times. Sometimes you don't have a choice when you're trying to repair brakes before motor.

The thing I do worry about is when bleeding them on an old master cylinder that I haven't removed and repaired, I use a block of wood under the pedal to prevent it from going much below the normal pedal travel. It keeps the piston in the master cylinder from getting pushed into an area of the bore that it hasn't seen since new which is usually full of trash and grit. That fouls the seal and you end up replacing the MC soon after bleeding the brakes. Granted if you've had brake failure that led to the pedal going all the way to the floor you've probably already got problems with the MC seals, but not repeatedly bottoming the pedal might make it last a little bit longer.

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95 Isuzu Trooper Daily Driver
86 Isuzu Trooper reliable backup
77 LUV 2wd stock beltway blaster (resting)
79 4x4 LUV project: 2.6L, 5spd, 31s (eventually)

MEPR: Man, my 4x4 makes all other LUVs look good

Running the engine while bleeding brakes pulls a vacuum on the booster which is the nominal mode of operation. There is probably a diaphragm in there that would be damaged if you weren't pulling the vacuum by idling the engine.

Wanted to mention that you can get Russel Speed Bleeders in a metric size that will fit the Chevy LUV rear brakes. I have them on my truck, put them in there when I swapped rear ends. They are the bleeder screws that have a check ball in them so all you have to do is sit in the cab and pump the brakes -- no pumping till the pedal's hard and then opening the bleeder screw. I ordered my Speed Bleeders from Summit Racing, I have also seen them at various auto parts stores. I don't have my order history to tell you the exact one.