Brake fade when off roading - Defender Source
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  #1  
Old July 30th, 2013, 02:51 PM
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Chris Davis
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Brake fade when off roading

This only happens to me when offloading: when going down rough, rocky terrain, 4-LOW range, crawling along and not touching the brake for a while I notice that the pedal goes way down on first press-- I pump a couple times and they are fine. The brakes work great and no fade when holding down. Only issue is that first press on brake has a long travel. At first, I thought maybe a bearing race was loose and the added force of hitting rocks made the rotor wiggle around and push out the calipers a bit (hence the initial brake fade), but I have double checked them all and all bearings and everything are good, tight, properly adjusted. This has been happening for a decade, through more than 1 rotor change and I've even changed the master cylinder within this time frame without a change.. I've never figured it out. Anyone have is happen to them? Wondering what to else it may be? Brakes are bled great-- I have no breaking issues other than when rough wheeling. Going down steep rocky slopes seem to be the worst case scenario and I have triple checked the front suspension.

Only thing that makes sense to me is I am somehow compressing the brake pistons. Which makes me think the rotor must be causing this by slipping-- which makes me think either bearing or race wiggle-- but things seem golden when I have checked them-- races properly seated, no play in preload... Hmmmm. I'm used to it, but my druthers would be to eliminate this issue...
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  #2  
Old July 30th, 2013, 03:16 PM
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John B.
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Rear drums behind not adjusted can cause this.
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  #3  
Old July 30th, 2013, 03:34 PM
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steve
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This happens to me also... I always thought it was slightly loose wheel bearings making the rotor push the pads back.
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  #4  
Old July 30th, 2013, 03:45 PM
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J. Michael McCaig
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If you don't have rear brakes as was suggested then look for play in your wheel bearings. The rotors moving back and forth can indeed push the pistons back in the calipers which will give you that "scary" first pump of the brake pedal.
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  #5  
Old July 30th, 2013, 04:00 PM
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Todd Kendrick
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This has been happening to me for years; I would love to find the answer.............On the road brakes are always on top but soon as off road the pistons get pushed back. Hell my Series w/ drums is better braking off road than the D90 but so were the door tops. D90 door tops suck compared to Series trucks so I switched to SW doors and that made a huge difference.
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  #6  
Old July 30th, 2013, 09:08 PM
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Chris Davis
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reassuring that others too experience this. As for adjusting the wheel bearings, I have done this over a dozen times in the last 10 years---never could get rid of it....
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Old July 30th, 2013, 09:31 PM
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Jason Lavender
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Happens here too...I always figured that the brake fluid sloshing around in the reservoir just lets a little air in the breather hole in the top of the cap, and you need to double-pump once in awhile to push the air out and build up the pressure. Nothing concrete to base this on, just my hunch.
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  #8  
Old July 31st, 2013, 09:31 AM
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Happens to me also, only when offroading. I fix it by reajusting the front wheel bearings hand tight on the box socket, firmly locking the tab washer with the rotational slack taken up, tourqing down the locknut and firmly locking the tab on the locknut.

IMHO, any play in the bearing allows the disks to push the pistons back with the side forces of crawling. The manual calls for slack of course.
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  #9  
Old July 31st, 2013, 10:36 AM
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Todd Kendrick
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Yes I too have tightened down wheel bearings many times over the years w/ little to no improvement. I had Rob in ABQ look at it a few years ago; he could not really find the problem. He told me his does the same thing.........Fine line between too tight and too loose I guess.
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  #10  
Old May 29th, 2014, 09:33 AM
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Chris Davis
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Resurrecting this thread---It still happens to me and I could swear I have always had my bearings adjusted correctly, no slop, and I have really torqued down initially on tightening things down before properly adjusting the hub/bearing slack. I still live with it, but would love to know if anyone has figured this one out...
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  #11  
Old May 29th, 2014, 09:44 AM
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Are you crossing streams? The first brake application after submerging the rotors will do this.
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  #12  
Old May 29th, 2014, 10:53 AM
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The most recent experience was a few days ago at Lake Mac in NE---I went through a lake runoff, down a steep bank and into the runoff--about 1-2' deep. So in this case, yes, but most the time it happens rock crawling in CO, so I don't think it is limited to that...
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  #13  
Old May 29th, 2014, 11:14 AM
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Maybe this just isn't happening with the Tdi's. On the face of the brake servo booster, check for a hairline crack just outside the mounting bolts on the front side. The most common place is next to the bolt on the left (as from the front of the vehicle), next to the brake fluid reservoir, it is very faint. If you have a crack, you're loosing vacuum. It can be siliconed over for a quick fix, but you have to let it cure too. Duct tape might work on the trail. The servo unit's part # was STC442 but is now LR013844.

Another option if you find the crack is not the problem, is go to a recycler and get one of those vacuum reservoirs, white plastic bubble things, out of a wrecked car. This will increase your vacuum reserve.

To test your servo you'll have to get a Miti Vac and test it to see if it holds vacuum, 18" of mercury is the standard.
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  #14  
Old May 30th, 2014, 07:36 AM
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This happens to my NAS90 as well but not in my ROW110. It has not always happened though. I've owned my 90 for almost 10 years and I've only experienced this over the past couple of years. I've recently replaced rotors, pads, seals and bearings on all corners. First time, other than front pads once, in ten years. The firmness in braking on road is much better but I've not had a chance to do any serious off roading yet. On my last trip off road in April I was following someone down a steep steep drop and I thought at one point I wasn't going to be able to hold. But when I got level and could afford to pump the pedal it was back to normal. Very unnerving so I decided to replace everything even though I still had visible life left on the pads and rotors.

Good Luck!
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  #15  
Old May 30th, 2014, 07:51 AM
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Any chance you guys are boiling old brake fluid? As brake fluid ages it absorbs moisture from the air that lowers the boiling point of the brake fluid. I saw this happen to a D1 at Wintergreen.
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  #16  
Old May 30th, 2014, 08:05 AM
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That's a possibility. I've not flushed my brake fluid in a few years. The level has held well and when I check it it is clean to the eye.

Good suggestion.
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Old May 30th, 2014, 08:13 AM
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Chris Davis
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No chance here. Good fluid, no leaks, brake system is solid. I swear it the only thing that makes sense to me, regardless of how much I have tried and inspected, is that somehow the bearing/race is shifting. Thing is, I have even inspected the races. Even did this when the bearings/races were replaced, so it isn't wear. And, if it was "shifting" then you would think that it may introduce some play into the system--it doesn't. It is about time I regrease the front (back are wet hubs) and I am nearly positive it is a front-end condition due to when it happens, so I am about to check everything again. I don't expect to find a thing--I have looked 4 or 5 times...
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Old May 30th, 2014, 08:23 AM
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Well I wish you all the luck. I've started driving off road differently. Hand in parking brake when my nose is pointing south. It sux. I forgot to mention earlier that I've talked to a couple others about this as well and 9/10 other NAS owners are experiencing this as well. One particular guy I met recently has the same set up as I and I know he is very astute re maintenance and he's very experienced off road. He said he's experiencing the same thing and can't figure it out either.

Clay
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  #19  
Old May 30th, 2014, 11:30 AM
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Brake servo history 101.

I've read the reason vehicles with drum brakes don't experience the fade is because they don't have power brake assist. There was a period when there was a mix of disc's on front & drums to the rear though.

Power assist came about because of disc brakes. Disc brakes needed more "push" pressure on the discs because of the lesser brake material surface area actually touching metal disc than the old shoe brakes which had gobs of stopping surface contact area. So since human legs were not getting more muscular to activate disc brakes, they came up with the power brake servo to "assist" those long slender legs you see in LR extending from short dresses
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  #20  
Old May 30th, 2014, 11:49 AM
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Ive noticed on both trucks generally when backing down obstacles.
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