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Parking Brake issue after replacement

Posted: Fri Aug 07, 2020 4:12 pm
by Derrickbwg
I bought a 710m with a parking brake that did not operate. I put off the repair for a long time but got around to it this week. The job of getting everything off was a lot easier than I thought it would be and it revealed the issue. The pull arms and the pull fork were fused together and it was full of old, asbestos I'm sure, brake dust.

After removing the pull arms, I could not budge them with a vice and a big hammer to free them up so I could punch out the retainer pin. The pin wouldn't move even after grinding one end off.

I ordered new discs(already riveted to the plate), all the pull arm parts and the rubber boot and its plate. cleaned up everything and media blasted the parts. The rotor faces were all cleaned w a scotchbrite pad and looked good as did the balls etc. I lubed everything up that was required (not the ball bearings) and it worked smooth as could be. I reassembled and set everything up but the brake dragged...a lot! I readjusted and even unhooked the cable and couldn't improve the drag.

The lever arm moves the 100mm
The pull arms work freely when I push on the arms with my hand and can feel the free play then the expanding of the plates

I let it cool off and removed everything again. Noticing that the plates expanded as they should when I tested after removing the rear pad. I double checked everything but the only thing I saw was that the disc pads were a very tight fit on the splined output shaft. I test fit an old one on it and the tolerance wasn't as tight but I expected that after years of use. So i ever so lightly greased the shaft and that appeared to help the fitment. Put everything back together and it still drags. Unhooked cable and it still drags. Adjuster bolt loose and it drags.

What exactly is going on in there when the pads are spinning with the shaft when the brake is completely disengaged? What pulls them away from the rotor faces once the parking brake is released?

I'm not sure if the pads are new and super thick and will break in w use, but a 5mph run down my short driveway and back didn't do it and the truck stops suddenly when you let up on the accelerator ( as well as really heating up the assembly).

Or if the plates are expanding the pads outwards and the pads are binding up on the splined shaft and not releasing as they should.

Hopefully someone has an idea or can verify those pre riveted plates work fine so I can cross that off my list of culprits.

Re: Parking Brake issue after replacement

Posted: Sat Aug 08, 2020 6:10 am
by Joeri
Only thing i can think of is that the steel disc( s) are or wobbled ( not flat like a discbrake) or are to wide from each other ?

Re: Parking Brake issue after replacement

Posted: Sun Aug 09, 2020 12:01 pm
by Derrickbwg
I took it apart again and measured the pre-lined pads and they came out at 13mm. The replacement pads only that you rivet to the plate measures the same 13mm (with plate) so its not the width of the pre-lined pads.

I took an old disc that was quite worn that measured 9.4mm and installed it closest to the diff, reassembled with one new pad on the end and it works perfect. I cant imagine that 3.6mm took it from totally engaged to slack enough. that it needed to be adjusted at the nut. I'm leaning toward the tight fit of pads over the output shaft splines, where the old one was loose in comparison.

I'm going to run it some (took it on the trails today) and then take it down again to see if the new pad loosened up with use and see if I cant get the other new one in at that point.

Removing is pretty simple. As you can see in the pic below I only needed to loosen the left and right rear body mounts to get the clearance to remove the tail cone (notice limit straps). 19mm box end wrench, 24mm socket and 24mm open end wrench and a 10mm allen are all that's required.

Still interested to hear an explanation of how the parts interact in the parking brake when disengaged.
Inkedold parking brake_LI 2mb.jpg
Inkedold parking brake_LI 2mb.jpg (336.18 KiB) Viewed 616 times