Air in brake lines?????

[aebcpama]

Help!!!
Starting about a month ago, I have been getting air in my brake lines?
I own a 44,000 mile 2004 Tundra Access Cab Ltd 4x4 with TRD.
Front brake pads replaced last summer, rear shoes are good.
No leaks anywhere, have not lost a drop of brake fluid. In frustration
I have replaced a right rear wheel cylinder and the master cylinder
with no luck in finding the problem. After bleeding the brakes, I get a hard pedal. After three or four days of driving, the pedal goes to the floor.
Can pump up the brakes and hold the pedal, but I keep getting more air into the brake lines. The right rear line has the most air when bleeding.
Have been to the dealer twice with no success, they are as stumped as I am.
Anyone in the forum ever have a similar experience?
Any mechanics have any suggestions of how to fix this?
Thank you,
Aebcpama

[Mickey]

Originally Posted by aebcpama

Help!!!
Starting about a month ago, I have been getting air in my brake lines?
I own a 44,000 mile 2004 Tundra Access Cab Ltd 4x4 with TRD.
Front brake pads replaced last summer, rear shoes are good.
No leaks anywhere, have not lost a drop of brake fluid. In frustration
I have replaced a right rear wheel cylinder and the master cylinder
with no luck in finding the problem. After bleeding the brakes, I get a hard pedal. After three or four days of driving, the pedal goes to the floor.
Can pump up the brakes and hold the pedal, but I keep getting more air into the brake lines. The right rear line has the most air when bleeding.
Have been to the dealer twice with no success, they are as stumped as I am.
Anyone in the forum ever have a similar experience?
Any mechanics have any suggestions of how to fix this?
Thank you,
Aebcpama

Who replaced the front pads? Your fluid should have gone done as the front pads wore down. As far as still getting air in the system and not losing any fluid the master cylinder would have been where I would check. You state you had that replaced. Was the old one no good or was it still okay? I assumed a professional replaced these. Did they give you the old one back? Just because they state they replace the cylinder doesn't mean it happen or the rebuilt one has the same problem. Let us know what happens.

[aebcpama]

The dealer replaced the front pads last summer. I bought a new master cylinder from the Toyota dealer (not a rebuilt) and had my mechanic install it.
Yes I have the old one. The new one performs exactly like the old one, so I assume the old did not need replacing. The service manager and parts manager at the dealer doubt that the new one is defective right out of the box!

[Codiac]

I was thinking about this last night. I am not a Toyota expert but I know that if some ABS systems get air in them you need a special tool to modulate the ABS to get all the air out. I have heard that the ABS system builds more pressure than standard brake systems and turns air into a foam that is much harder to evacuate than in standard brake systems. You might check into this.

[Mickey]

Originally Posted by aebcpama

The dealer replaced the front pads last summer. I bought a new master cylinder from the Toyota dealer (not a rebuilt) and had my mechanic install it.
Yes I have the old one. The new one performs exactly like the old one, so I assume the old did not need replacing. The service manager and parts manager at the dealer doubt that the new one is defective right out of the box!

I also had a Ford Dealership tell me they never had problems with a computer before. BTW it took them 10x to fix computer. Keep us updated.

[aebcpama]

Update as of 5/26/08! My Tundra has spent four months at the dealer, run up a tab of over $3500 in work orders, Toyota rep has worked on it five different times, called the factory engineers and the problem is STILL not fixed. THe Toyota rep covered $2000+ of the repairs leaving me with over $1500 expended to date. The only things not replaced yet are front calipers,
ABS unit ($1500+) and all of the brake lines.
After bleeding the brakes, driving less than 100 miles the brakle padal goes to the floor?
Anyone know how to get the factory to step in buy back a 39 month old truck with 44000 miles that can't be fixed?

[notevenclose]

Bore seal between vacuum assist and master cylinder falure? Can they pressure check the master cylinder?

You say you are not losing any fluid but gaining air in the system...does the level in the reservoir increase? If not, you are losing fluid and it is being replaced by air. This could be a cracked line, loose fitting, etc. If I'm not mistaken, you can see brakefluid with a blacklight in the dark...you could try that to trace for a leak. Otherwise, you could have them add a dye to the fluid and replace the fluid later.

Maybe try to heat the fluid up by dragging the brakes and see if you can find a leak?

Just throwin stuff out there...

[aebcpama]

Thanks for your ideas. Master cylinder has been replaced twice with a brand new one and again with a known good used one. Confirmed that it is not the
master cylinder!
There is NO fluid loss and yes the fluid does come up in the reservoir when the air enters the brake lines. It has been suggested that there is a hole,crack(?) somewhere in the system that is so small that air can enter but fluid cannot leak out? I have stood on the brake pedal for 5 minutes trying to force fluid out to find a leak but had no luck with that either?

[notevenclose]

Originally Posted by aebcpama

Thanks for your ideas. Master cylinder has been replaced twice with a brand new one and again with a known good used one. Confirmed that it is not the
master cylinder!
There is NO fluid loss and yes the fluid does come up in the reservoir when the air enters the brake lines. It has been suggested that there is a hole,crack(?) somewhere in the system that is so small that air can enter but fluid cannot leak out? I have stood on the brake pedal for 5 minutes trying to force fluid out to find a leak but had no luck with that either?

Sounds like a fitting or seal then...possibly cross threaded, loose, or scratched. When you apply pressure to the fitting, the fluid seals it by pressing the o-ring or expanding the brakeline and when the pressure is released, air can pass into the low pressure area. Probably, when the fluid is heated, the air leak is sealed and when the fluid cools, the pressure drops(boyle's law) and the air enters the system.

If the right rear is the most full of air, I'd start checking fittings and seals. If the dealer replaced the pads or had the right rear brake apart at all, they could have over-extended the brake pistons popping them out...by letting someone inexperienced work on them perhaps? Then, when they re-installed them, they compromised the seal around the caliper piston with contamination. Could have a fitting come loose as well.

Keep us posted.

[Deznutjob]

Sounds like you may have a problem with one or more of your caliper pistons.