2008 Tahoe brakes won't bleed

[ChuckWoodChuck]

Pics of the truck, please.

It's just a basic white 2008 Ltz Tahoe. It's my wife's daily. My daily driver is a 79 F-150

 

[j91z28d1]

I had a corner that felt like the brake was sticking, and had warped the rotor. I thought it might have been a failure of the rubber line. But to make sure it was a messed up caliper I replaced everything except the master cylinder and the steel lines.

I drove it a short distance after the first bleed and no matter how hard I tried to brake the abs wouldn't engage and I had barely any brakes.

if everything else is right, the theory. I say theory cause you'd need to take it apart to find out and I don't know if anyone actually takes their old parts apart to inspect. but if you have a high mileage truck, the seals in the master have only gone say 2in in the bore their whole life and a ridge can build up at the stop point, you then bleed the brakes and the pedal goes all the way to the floor and the seal jumps that ridge a few times and gets damaged.

so that's why the wood under the pedal is recommended on older vehicles. Sadly you only really see that recommendation after it's to late if you don't spend time on the boards.

 

[ChuckWoodChuck]

if everything else is right, the theory. I say theory cause you'd need to take it apart to find out and I don't know if anyone actually takes their old parts apart to inspect. but if you have a high mileage truck, the seals in the master have only gone say 2in in the bore their whole life and a ridge can build up at the stop point, you then bleed the brakes and the pedal goes all the way to the floor and the seal jumps that ridge a few times and gets damaged.

so that's why the wood under the pedal is recommended on older vehicles. Sadly you only really see that recommendation after it's to late if you don't spend time on the boards.

I am going to try and bench bleed the master.

Today I did a manual bleed followed by the automated bleed. Still didn't have much brake pedal. Tried putting it in drive and the hitting the brakes to activate the abs. That yielded firm pedal that lasted a few pumps then it went away.

Your theory on the master cylinder sounds plausible.

 

[j91z28d1]

in my experience if you pump the pedal a few times and it pumps up and feels good, then let off and wait a minute, hit the pedal again and it goes down. that's air in the systems.

when you're doing the automatic bleed, do you have 15psi of better on the master?

can you snap pics of the caliper bleeders?

 

[ChuckWoodChuck]

When you're doing the automatic bleed, do you have 15psi of better on the master?

can you snap pics of the caliper bleeders?

I didn't know the master needed to be pressurized while doing the automated bleed.

I can get pics this evening, but the bleeders are in correct locations.

 

[j91z28d1]

I don't know forsure that it matters but gm manual calls for it.

something like bench bleed the master then install fluid filled pressure bleeder set to 15psi. open one caliper at a time till fresh clean fluid comes out. then run the auto brake bleed.


no one really does this, I have doubts even the dealer techs do it.

my truck being an odd ball hybrid actually has a technical service bulletin about bleeding that says no less than 30psi while bleeding. but my system is nuts and has 6 ports in the master lol. I have no idea what ome going to do with this thing if I need to bleed it haha.

 

[ChuckWoodChuck]

So it ended up being a bad master cylinder. I opened the old one up and the rear seal has a small tear.

 

[91RS]

Are the calipers on the correct side? Seen that too many times. An ABS bleed is rarely required for caliper replacement, unless you let it run dry and if so the master cylinder will need to be removed and bench bled. You do have to do a manual bleed before the automated bleed though. The master cylinder could also be bad.

 

[Charlie207]

Too late now, but this is the best tool for bleeding all four calipers: https://www.amazon.com/dp/B000TK9FE8/ref=twister_B0BNP2Z8KR?_encoding=UTF8&th=1




Don't even need to add fluid to the pressure tank. Just use a turkey baster (or whatever) to suck the reservoir dry, top off with fresh fluid, and set pressure to 15psi. Crack the bleeder on the caliper and ensure the reservoir doesn't run dry. Do this until clear fluid with no bubbles runs into a catch can at the caliper. Lots of dirty fluid will come out.

You don't need to touch the brake pedal at all, and with the ability to swap reservoir adapter caps, one pressure tank can be used for all your vehicles for brakes and clutches.