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Hi folks,
I am stumped. I recently installed new brake pads and rotors on the front wheels of my old, faithful '84 900S. I had never done the brake rotor job before, but had done pad replacements several times between the two '84s I've driven.
When I got it all back together, I went for a test drive. To my horror, I heard (and felt) a cyclical POPPING noise coming from the front wheels only when braking going FORWARDS (I make sure it was coming from front wheels by pulling up the parking brake, which, of course, operates the front brakes on pre-'88 900s).
Now, I am familiar with the "POP" in reverse that pre-'1988 900s can have (due to caliper yoke wear) and the fact that the U-pins which hold the pads in the calipers straighten out over time and need to be re-bent to remedy this (but preferably replaced with each pad change, along with anti-rattle springs).
I had forgotten to order this hardware (DOH!) with my pads and rotors, so I tinkered to no avail, taking off the front wheels a time or two, scratching my head, staring at the calipers. At first, I reckoned the popping to be shifting of the calipers, thinking that I didn't torque them sufficiently after re-reading the Bentley manual. So I bent back the lock-plates and torqued them up to top-end of spec at 95 ft-lbs. (Bentley lists 81-96 ft-lbs.) No dice, still had popping noise.
I gave up on this and ordered the new hardware kit (springs and U-pins).
Well, the kit (made by Scan Tech of Sweden, via eEuroparts.com) came Saturday morning. I noted that, before installation, the U-pins appeared to have zero amount of pre-bending and were as flat as a flitter, but I put the springs and U-pins on, anyway, then did a test drive. Same result: bad popping noise, slows as the vehicle slows down, heard ONLY when braking and ONLY going forwards, all same as before.
After more staring at the brake calipers, I removed the U-pins and bent them as Tom Townsend had shown me some two years ago (unless I looked at his diagram wrong, which is possible). I bent the pins so that the uprights (if viewed as a letter "U") now have an angle of about 10 degrees bend towards you in them and that the shorter end (top side, without the hole in it for the cotter/retaining pin) is bent away, towards the rear of the car (when viewed in its installed position). I hope that makes sense.
Oddly enough, as I mentioned, the popping NEVER occurs while applying the brakes in reverse, not even the "trademark" initial pop/clunk we all know and hate.
What gives? What in the world could be causing this popping? Did I bend them the wrong way?
The only other thing I notice is that top (forward) part of the friction material on the new pads (PBR Deluxe) protrudes ABOVE the top of the cut-out in the rim of the new BALO rotors, when the cut-out is rotated to align with the pads. The pads rise about 1-2mm above the cut-out, but do NOT rise above the rotor edge when cut-out is NOT adjacent to pads. Is this my problem? Is the cut-out in the rotors snagging the friction material on the pads with every half revolution of the wheels?
Any ideas or suggestions will be greatly appreciated.
Thanks,
Micah in NC
'84 900S, 249K mi.
posted by 172.133.12...
, Mon, 5 Jan 2004 21:47:42, Tue, 6 Jan 2004 17:46:46
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