Mechanical overide brakes - pads rubbing on disk

Submitted: Wednesday, Jan 23, 2008 at 13:10
ThreadID: 53830 Views:5021 Replies:6 FollowUps:2
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Hi all

I have just checked and repacked the wheel bearings on my camper trailer after about 2000km from new. It has a treg hitch with mechanical override disk brakes. On one side of the camper, the outside pad (the one that does not have the brake lever attached) is always in contact with the disk and therefore the wheel does not spin all that freely. The other side has no problem, with the pad just kissing the disk at one point in the revolution. Is this normal? It is like the pad is too thick. I assume that eventually the pads will wear down to create clearance. There are three raised lumps on the inside of the calliper that the pad sits on; can these be filed down a bit instead of waiting for the pad to wear? The edge of the pad also sits slightly outside the disk and I can see that there has been some pad wear (perhaps 0.5mm). The handbrake lever sits at 5 notches when fully on.

Any thoughts?

Thanks in advance

Tim
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Reply By: PradOz - Wednesday, Jan 23, 2008 at 14:13

Wednesday, Jan 23, 2008 at 14:13
Not sure if these people can help, but I have some terrific information on the workings of electric brakes supplied by them. The bottom of their infomation sheet says:

For further information, spares and service, please contact:
Vehicle Components Pty Ltd
352B Bilsen Road, Geebung, Qld 4034
Phone: (07) 3624 3800 Fax: (07) 3624 3888
www.vehiclecomponents.com.au
AnswerID: 283329

Reply By: Gerhardp1 - Wednesday, Jan 23, 2008 at 15:03

Wednesday, Jan 23, 2008 at 15:03
The pad operation should be the same as on cars - ie, when the brake is applied, the piston moves and applies pressure to the pads which in turn press against the rotors. When released the internal cup rubber tension pulls the piston back a tiny distance, enough to just be free of the rotor.

If your piston/pad starting position is wrong, which it is based on your report, you will have erratic operation until the "tight" pad wears down enough. It sounds like the caliper position is out on one side of the trailer, relative to the rotor. This is probably due to manufacturing error.

You should return the trailer for a warranty fix, since you also say the pad is not in full contact with the rotor.

failing that, I wouldn't relieve the lumps on the caliper, but it's remarkably easy to grind/file/sand the friction material of the pad.

I'd take enough off the pad itself until it spinds freely at rest..
AnswerID: 283341

Reply By: 96 GXL 80 series - Wednesday, Jan 23, 2008 at 15:28

Wednesday, Jan 23, 2008 at 15:28
Check the guide pins on the callipers and make sure there is nothing interfering with them, and maybe lubricate the guide pins.

Have you applied the brakes since adjusting the wheel bearings as they might just need centring up on the disc.

Cheers
96
AnswerID: 283346

Reply By: Scoof - Wednesday, Jan 23, 2008 at 16:58

Wednesday, Jan 23, 2008 at 16:58
tim-s

From memory mine was the same we filed the pad were it missed the disc by a smidgen.

Haven't had any problems it doesn't get any hotter one side to other side.(RH to LH)

So all good done about 6000 km since last time we had it all apart.

So should be OK just go for a test run and check the heat build up from one side to the other.

Cheers Scoof .. :-)
AnswerID: 283360

Reply By: Shaker - Wednesday, Jan 23, 2008 at 17:51

Wednesday, Jan 23, 2008 at 17:51
There is nothing that pulls the pad away from the disc as shown below, some vehicles actually have slight 'runout' machined into the disc to knock the pad away .....

>>>A disc brake comprises a disc which rotates with a hub, two brake pads positioned on opposite sides of the disc, and pad moving means operable to cause the pads to be urged against the disc into a"brakes on"condition in which they apply significant braking forces to the disc.

The pad moving means is often a calliper mechanism which often comprises a hydraulically-operated piston and cylinder assembly. Disc brakes normally do not provide for the pads to be pulled fully away from the disc after a brake application. Instead, when the pad moving means ceases to urge the pads against the disc, the pads are "knocked"away by the disc into a"brakes off"condition in which the pads are close to the disc but out of contact therewith. <<<

AnswerID: 283370

Follow Up By: Member - Barnray (NSW) - Wednesday, Jan 23, 2008 at 20:05

Wednesday, Jan 23, 2008 at 20:05
Sorry but when I machined brake disc's in the past I had a lot of trouble trying to get a rhythm to get the run-out just right so in the end they all got machined flat.Barnray
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FollowupID: 548003

Follow Up By: Shaker - Wednesday, Jan 23, 2008 at 20:31

Wednesday, Jan 23, 2008 at 20:31
It would be impossible to machine the factory runout with a normal brake lathe.
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FollowupID: 548011

Reply By: kiwicol - Friday, Jan 25, 2008 at 19:02

Friday, Jan 25, 2008 at 19:02
have a look at where the cable runs behind the hitch i had problems like yours and put it down to the way the cable is pulled resulting in uneven braking, solved the problem by fitting a stainless yaught pully wheel, which gave an even pull on each wheel. Col
AnswerID: 283786

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