Alero Brake Change Help Needed

[oldmike]

Hate to keep bothering everybody, but I have another question. I'm turning the rotors and putting new pads (if needed) on my 02 Alero GLS, v6, auto, 16" wheels. I've already had the front rotors turned and reinstalled and used my Haynes manual to start reassembling. 85 ft-lbs torque on the caliper mounting bracket. Cleaned up and found pads were thick enough to reuse. Mounted caliper. Now ready to bolt it on. Haynes book says 23 ft-lbs for front and 81 for rear. Here's the dumb question - do they mean front bolt of the 2 that hold caliper or do they mean front wheels and rear wheels? If front and rear wheels, which I suspect, why would rear be 81, so much more than front? Hope someone has a shop manual to verify these numbers against. I would really appreciate it very much.
Thanks, Mike

[BNaylor]

To start turning the rotors if the original GM disc is a bad idea. They won't last and may make noises when coming to a stop even though braking may be good and there are no vibrations or disc lateral runout. Next using old pads regardless of condition is a bad idea too. Always use new pads to do the job right the first time.

The higher torque figure is typically for the caliper mounting bracket bolts. The lower figure is for the caliper bolts and caliper sliding pins (X2). Any higher and the caliper mounting bolts will snap off. Be sure to use hi-temp brake lube on the caliper sliding pins but clean out old lube first. And that the rubber boots are serviceable.

[oldmike]

Bob,
Thanks for the quick answer. I agree, new rotors would be better, but these appear to never have been turned. The pads were nearly new by thickness so I was just trying to save a few bucks. The caliper mounting bracket bolts were 85 ft-lbs and this is what I did. What confuses me is in the table of torques in my Haynes book, it said very definitely caliper mounting bolts were 23 ft-lbs for front and 81 ft-lbs for rear. I plan to relube the caliper slide pins, boots are OK. Can anyone verify the rear brake torque numbers on the caliper bolts?
Thanks, Mike

[BNaylor]

Originally Posted by oldmike

Bob,
Thanks for the quick answer. I agree, new rotors would be better, but these appear to never have been turned. The pads were nearly new by thickness so I was just trying to save a few bucks. The caliper mounting bracket bolts were 85 ft-lbs and this is what I did. What confuses me is in the table of torques in my Haynes book, it said very definitely caliper mounting bolts were 23 ft-lbs for front and 81 ft-lbs for rear. I plan to relube the caliper slide pins, boots are OK. Can anyone verify the rear brake torque numbers on the caliper bolts?
Thanks, Mike

If they are the GM rotors you can safely go one turning but thats it. After a few hundred miles I had to replace the rotors after turning since there was a noise when you came to a stop which was very annoying. I switched to Raybestos PG rotors with Performance Friction Carbon Metallic pads.

Sorry I don't have the torques specs for the rear calipers and caliper mounting brackets but 85 lb-ft for the front caliper bracket is correct and 23 lb-ft for the front caliper bolts. I don't recall ever recall using 81 lb-ft for the rear caliper bolts which seems too high to me. For most GM cars 33 lb-ft is acceptable for the rear.

[oldmike]

Bob,
I'm going to finish up the front calipers using 23 ft-lbs. Then when I get the rears off and ready to go back on, I'll try to get GM specs from a dealer.
Thanks again, Mike

[BNaylor]

Sounds good Mike. Please post the rear torque figures so other can know when they view the thread. Also, while you are on the rears be sure to adjust your emergency/parking brake. The cable does not have an external adjuster like many GM cars. Under the rear disc/top hat rotor is the parking brake pad shaped sort of like a C - horse shoe. At the top you should see a star type adjuster. This will bring the parking brakes back in where it should be when you pull up on the parking brake lever.

[xeroinfinity]

I believe the haynes manual is wrong on the rear torq specs for the caliper mounting bolts. I usualy just do them the same as the front 23-24 ft lbs..

One way to verify would be to set your torq wrench to the 23-24 Ft Lbs and try loosening the caliper bolts.
If it loosens them then that is the torq value, iF it just clicks try raising the torq wrench values.

Though it might be easier to call a service shop. lol

All caliper braket mounting bolts are 85 ft lbs.

[BNaylor]

I agree with the lower torque figure which is really just common sense. Also, recall the caliper bolts are not typical GM where the caliper pin is also the bolt. The caliper pin and retaining bolt is separate. I recall having to use an open end wrench to hold the caliper pin while tightening the bolt down. I used around 30 lb-ft which worked fine since I recently did the brakes on the Alero.

Best part was figuring out how to adjust the parking brakes with the hidden adjuster.

[jr6078]

Originally Posted by xeroinfinity

One way to verify would be to set your torq wrench to the 23-24 Ft Lbs and try loosening the caliper bolts.
If it loosens them then that is the torq value, iF it just clicks try raising the torq wrench values.

No disrespect intended here, because I highly respect your knowledge and experience, but from an engineering standpoint and having been exposed to having to check breakaway torque values to prove fastener integrity...

This isn't an accurate way to measure applied torque without applying several different aspects of the fastener's physically properties and its operating environment to the equation. Breakaway torque values are typically much higher than applied torque values, especially on fasteners that have been subject to numerous alternating heating and cooling processes or that may be subject to rust or corrosion.

[BNaylor]

Originally Posted by jr6078

No disrespect intended here, because I highly respect your knowledge and experience, but from an engineering standpoint and having been exposed to having to check breakaway torque values to prove fastener integrity...

This isn't an accurate way to measure applied torque without applying several different aspects of the fastener's physically properties and its operating environment to the equation. Breakaway torque values are typically much higher than applied torque values, especially on fasteners that have been subject to numerous alternating heating and cooling processes or that may be subject to rust or corrosion.

Interesting and good point. Also, you could consider whether there is any threadlocker applied and add that variable to the equation. I recall seeing old threadlocker applied by GM on the original bolts. I cleaned it all off and applied new low-med strength threadlocker (Permatex brand).

[xeroinfinity]

Originally Posted by jr6078

No disrespect intended here, because I highly respect your knowledge and experience, but from an engineering standpoint and having been exposed to having to check breakaway torque values to prove fastener integrity...

This isn't an accurate way to measure applied torque without applying several different aspects of the fastener's physically properties and its operating environment to the equation. Breakaway torque values are typically much higher than applied torque values, especially on fasteners that have been subject to numerous alternating heating and cooling processes or that may be subject to rust or corrosion.

True !
I didnt even think of the heat factor , not something I practice all the time but has resolved some issues quickly.

I'd hate to even try the math on that one.

[oldmike]

Thank you guys for all the input. I'll put it all to use when I pull the rears and give a followup report.
Mike

[oldmike]

Bob, I wondered what the phrase "rear disc/top hat rotor" meant until last night when I pulled the rear wheel. Funny looking thing. So will the rotor just pull off after I remove the caliper and caliper mounting bracket? Also, on the backside outer edge of the rotor, there is a thin piece of metal circling nearly the whole rotor. What is this?
Thanks Again
Mike

[BNaylor]

The rear rotor will pull off after you remove the caliper and caliper bracket but you may have to use PB Blaster or WD40 at the point where it meets up with the hub. Also, above the wheel studs you can tap very lightly with a mallet or hammer to loosen it up, grip with both hands and rock back 'n forth to pull rotor off. That thin piece of metal (plate) is the just a backing plate and is technically part of the rear hub since it seems to have a press fit and it has the mounting points for the parking brake mechanism. Good luck.