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Unread 07-04-2013, 04:30 PM   #1
Hiro
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Join Date: Mar 2012
Location: Paris
Posts: 21
99 WJ 4.7 brake drag fix

OK I had severe brake drag on my 99 WJ 4.7 as most of us:
usual stuff started at the rear left brake shortly after replacing the rear pads,
then after a while vibration also started in steering & front left caliper warped its rotor,
accordingly there is almost no lash at the brake pedal so that's a straightforward case apparently.

my front calipers are ATE so I went for the usual Akebono swap,
I just thought that some additional pad clearance would not harm so I've removed the spring part from the pad locator clips.

my rear calipers were more of a headache as both did not show any sign of piston or sliding pin problem,
everything moves very easily so I've tracked other reasons why they could go wrong,
of course all the usual cleaning/deburring/greasing job has been done too.

so far I've made 3 easy mods that can help a bit:
- the inboard pad has a locator made of 3 springs; the longer spring pushes the caliper upward & this creates a small lateral drag on the sliding pins;
just collapsing this spring reduces the pin drag a tad.
- the caliper has an external spring that attaches to (& rubs on) the caliper bracket; this spring has too much load in it, thus prevents the caliper from sliding freely;
I've reworked this spring in such a way to reduce the load.

now my rear calipers both slide very easily & can be checked without removing the wheel, just by gently prying with a big screwdriver.

the last thing I did was installing drag reduction clips to my rear pads:
I could not find any for the rear calipers so I've made my own from steel wire,
not my best fabrication but you get the idea (BTW Raybestos makes some for the Akebono calipers: part # is H6038),
currently there is only one clip fitted per caliper on the leading edge of the pads.

now how is this all working?
I did a simple brake drag check by driving a couple of miles on the highway without touching the brake pedal,
then I stopped the car when going uphill only applying gently the e-brake for the last yards.

next I've measured the 4 rotor temperature with a IR pyrometer & compared the readings with ambient temperature:
front left = ambient +3C
front right = ambient +3C
rear left = ambient +12C
rear right = ambient +5C

so as of today I think both front calipers are OK as well as the rear right one,
the rear left caliper still has some minor drag but nothing severe,
probably adding a second drag reduction clip might help here.

HTH,
Hiro from Paris, France

(now trying to upload some pics...)

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Unread 07-04-2013, 04:35 PM   #2
Hiro
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Join Date: Mar 2012
Location: Paris
Posts: 21
this pic shows the mod of the Akebono pad locator clips:
truckybrakes1.jpg

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Unread 07-04-2013, 04:37 PM   #3
Hiro
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here is the rear pad locator spring I've collapsed:
truckybrakes3.jpg

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Unread 07-04-2013, 04:39 PM   #4
Hiro
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this is the rear caliper spring that needs reworking to relieve some load from:
truckybrakes4.jpg

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Unread 07-04-2013, 04:42 PM   #5
Hiro
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Join Date: Mar 2012
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Posts: 21
and here is the home made drag reduction clip for the rear pads,
with some approx. measurements & how it fits on the rear caliper:
truckybrakes5.jpg

truckybrakes9.jpg

truckybrakes7.jpg

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Unread 07-04-2013, 04:46 PM   #6
Hiro
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Join Date: Mar 2012
Location: Paris
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and this is the nice drag reduction clip sold by Raybestos (part # H6038) for our front Akebono calipers:
akebonoantidragclip.jpg

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Unread 07-16-2013, 02:10 PM   #7
Hiro
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Join Date: Mar 2012
Location: Paris
Posts: 21
tracking the last bit of residual drag from the rear left caliper:
I've made & installed a second drag reduction clip on this caliper between the pads,
test performed as above now shows identical rotor temperature left & right,
both are only 5C above ambient temp so I guess my GC will survive it,
problem solved!
HTH,
Hiro
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