Scotty, I have another rookie question.
I have a 2004, Audi Allroad Quattro, with 300,000 km, Automatic. I recently put it on car stands to check the rear brakes. The right rear brake was sticking because partly, I believe, of an emergency brake line that wasn't completely releasing. I took the caliper apart and tried to spin and press the piston back in place -- it was super tight, but eventually, after a few times seemed to free up.
When the car is on Jack stands, with tires on, I spun the tires and the right one seemed to have a bit more drag than the left one. And they didn't spin as freely as I would expect. Is that common on AWD cars? Should I have put it into neutral to test the spin of the rear tires? At the time.. I just left the car in park and turned the tires as best I could.
Any thoughts or suggestions would be helpful.
Jackson
They won't spin as freely as you're thinking they will. You're spinning the differential on that axle, and likely the driveshaft as well. I'm not completely familiar with AWD vs 4×4 like a truck has, but there has to be some kind of center differential to let the front and rear wheels spin at different speeds. There's gonna be thick gear oil in there as well that's going to resist being spun.
Earlier this year I had the front end of my truck up in the air to do shocks and spun the wheels, since they were modified to be permanently locked to the center axle and I wanted to see how much effort it took to spin the drivetrain. I was surprised, it took quite a bit and the wheels wouldn't coast like I expected. I was getting 14 MPG driving like that. I swapped to manual hubs and ended up freeing around 3-4 MPG by unlocking the front wheels. All of that resistance is why AWD cars get worse gas mileage than standard 2WD vehicles. There's a lot of heavy parts to be moved.
When you're pressing caliper pistons back in, make sure you remove the cap on the fluid reservoir so you're not building back pressure. I would also do as @MountainManJoe said and try spinning the axles with the calipers off to see if the wheels still don't spin at the same rate.
Hey Thanks, @MountainManJoe and @Justin-shepherd, good information. I was worried a bit, but the car seems to fly down the road.. so, I will call it good! What a great site for information. Thanks again.
it depends what it was dragging on. Did you try turning the axles with the calipers off?
Hey @Retired,
Yes, I believe it was the rear right caliper sticking... I changed it out and now the back calipers are good. I have a new problem -- The front brakes are dragging now -- with the abs fuse out it's the right tire, and when I put the abs fuse back in, the left tire drags. Grr... I think it's either the caliper or the abs module, or the brake master cylinder...
This car is kicking my butt, can the master cylinder cause both front brakes to drag, or just one to drag at times? I'm trying to figure it out.. but it's kicking my butt.
History on the Car:
2004 Audi Allroad 2.7T
Current Symptoms – Wheel drag slowing car, and eventually locking up tires so car doesn’t move.
History:
August 27 - Rear right brake seemed to be dragging on jack stands – when pushing the emergency lever up, it seemed to free brakes. – Emergency brake mechanism – seemed to help free up the wheel.
August 28th – Accidentally toped up Brake reservoir with power steering fluid drove for 10 minutes – got home, recognized the mistake, and siphoned out fluid in brake reservoir as best I could.
August 30th – Drove the car to Calgary
Sept 13th – Return drive from Calgary
Sept 15th – Pressure bleed brakes with motive Brake Bleeder at 16 psi.
Sept 20th – Drove to Calgary
October 4th – Upon starting the car, drove the car for 15 minutes, at which time Front left gradually got stiffer and stiffer until the engine didn’t have enough power to move the car – completely locked up—front left rotor was hottest, with mild smoke. All rotors were hot. Break down happened beside a mechanics garage – bled off the pressure and drove car into the garage. Scanned system – Code for Brake pressure sensor. Mechanic disconnected brake pressure sensor by the reservoir. I left the mechanic's garage, and 20 minutes later – the wheels locked up again.
Towed to Canadian Tire – Second scan – Brake pressure sensor again. The mechanic went through the car, determined that drag on the right rear tire drag was telling the computer to compensate on the other tires. The mechanic said he pushed the emergency cable up on the caliper, it released.. and that’s what he thought was wrong with it... We went for a short test drive around the block.. and the rotors were all hot, he said that was normal – it didn’t seem normal to me. Left Canadian tire in Calgary – didn’t push the brakes hardly at all, outside of Lethbridge, checked rotors for temperature, front felt cool, rear right was warm – dragging
October 5th – Changed rear right Brake Caliper with a new caliper. Test drive around the block, rear rotors are now cool to touch, but, front rotors are dragging. Especially the front right much hotter.
October 5th – Removed fuses 16, 41 & 42 – to disable ABS, ESP and EDL. The problem persists; the front right brake still gets hot, drag on the car – I didn’t drive to lock up.
Released pressure on brakes using bleeder screw – car coasts amazing, and with no drag – unfortunately, eventually I will have to use the brakes. Used only emergency brake to transport car to Volkswagon Dealership.
A careful moving car, as the brake pedal isn’t pumped up – minimal braking power at present.
Inner Thoughts and Research:
I have no idea!
After checking the Audi forums, some think it’s the master cylinder return port not working properly, which causes the brake fluid to get hot, expand, and cause further braking issues until the car stops.
I’m thinking it could also be the ABS module not opening and closing correctly, which is causing pressure to not return to the master cylinder…
Another person said it could be a pressure sensor by the brake reservoir and yet another said the brake booster check valve isn’t functioning correctly.
I really have no Idea; I am suspecting all of the above is the problem.