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Replacing brake discs


Les Henson
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Vehicle shown is a 200TDi Disco (front axle). Replacing discs is much the same - regardless of model. The main differences being the caliper and on a TD5 - the nut that retains the wheel bearing/hub assembly. Slacken the wheel nuts, raise and support the vehicle and remove the road wheel.

Get someone to press the brake pedal while you slacken the 5 x drive member bolts.

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With a little persuasion the drive member will come out (there may be a small amount of axle oil come out, so be prepared for this). Check the splined end for wear or a step and consider replacement if it's worn.

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Bend the locking tab away from the outer nut and remove it. The damage to the nut faces was cause by someone in the past using a chisel to undo/do up the nut. The proper hub nut box spanner is only about £7.

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Remove the tab washer and either replace it or straighten it and use a different part for re-locking the nuts. Undo the second nut, then the seal/thrust washer.

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Some vehicles don't have an outer seal - if this is the case then there's the possibility that the outer wheel bearing race will fall out.

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The caliper now needs to be moved out of the way. If the brake pipe/s are in good condition, then you may be able to unbolt the caliper and carefully move it off the disc without disconnecting the brake pipe/s.

Undo the two bolts that hold the caliper in place (there are different bolts for some vehicles)

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The caliper bolts should be thread-locked, do not use grease on them.

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Carefully lever the brake pads back into the caliper body to release them from the brake disc and to enable it to fit over the new one.

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The caliper - still attached to the brake pipes and resting on the drag link.

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The disc/hub will now slide off the stub axle. Lay the road wheel on it's face and place the disc/hub inside the wheel in the same way as it is when fitted to the vehicle.

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There are 5 x 14mm spline head bolts that hold the disc to the hub. Theses are quite tight, so you may need a breaker bar to undo them. Again - these bolts should be thread locked.

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You might be able to use a normal hex socket on the bolts if it's a tight fit - this is correct socket to use.

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The disc will then come off the hub - you will most likely have to clout the disc with a mallet to get it to release as they are usually stuck in place by rust.

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Clean the stub axle and grease it - including the oil seal land.

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Make sure the mating face of the hub is clean, remove the oily coating on the new disc with WD40 or brake cleaner, apply threadlock to the bolts, and attach the new disc to the hub. Apply some grease to the lip of the oil seal.

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Replace the disc/hub assembly - taking care not to damage the inner oil seal, replace the spacer, then the first nut. Tighten the nut progressively until you can feel some resistance and then slacken a small amount until the disc turns freely, but with no bearing play.

Replace the tab washer and then the outer nut and tighten it. Bend the tab washer inwards to lock the first nut and then outwards to lock the outer nut. Clean the old gasket off the drive flange and fit a new one. Replace the drive member and turn the disc until the holes line up and replace the bolts (check the spring washers are in good condition and replace them if they've flattened out).

Replace the caliper and apply threadlock to the two bolts. Make sure that the pipes haven't been damaged by bending them. Press the brake pedal repeatedly until it feels solid - it will go to the floor a couple of times as it takes up the gap between the pads and disc. Replace the road wheel and lower the vehicle back to the ground.

A few things -

Brake discs can be bought seperately, but should always be replaced as an axle set.

The brake pads should really be replaced at the same time - the contact area of the pad will be different from the contact face of the disc, so braking performance will be reduced until the two faces are the same.

Bending brake pipes is not good practice unless you are extremely careful. Old or rusty steel pipes may well break and then need replacing.

You should also consider replacing or at least re-greasing the wheel bearings and replacing the inner hub seal.

Keep an eye on the brake fluid level in the reservoir - if you have kept it topped up, then the level will rise as you push the piston back into the caliper, so it might overflow. Brake fluid will strip paint off if it isn't cleaned off quickly.

Les.

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Did mine on the 90 for the MOT this year.

Only difference was I released the torque from the drivemember bolts (same as the roadwheel) prior to raising the vehicle.

Oh.. and one of the drivemember bolt heads sheared off :angry:

The "obvious" use of the wheel as a holder for the Hub/brake assembly took me a few minutes to spot!

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Some more pointers to consider

  • While the hub & disc are in the back of the wheel (and spline bolts removed), get hold of the old disc and rotate it around the hub - this frees it from the hub and it should lift off easily.
  • It is worth re-packing the wheel bearings with grease (if they are the grease filled type).
  • Spin the hub assembly after setting the wheel bearings to check for lateral run out. Excessive run out will knock back the pads, giving long pedal travel before the brakes work.

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sgnas - The wheels were alloy, so there is no access to the drive member bolts with it on.

Les.

Good point :rolleyes:

For a DIYer the most worrying bit is resetting the bearings. Too tight/too loose.

Time consuming with a full clean and regrease but satisfying.

DaveS11A - My 90 is 19 years old. I would have had to refit the hubs/discs (minus the bolts) and gone for a drive and a brake in order to twist the pair apart.

(oddly, that now sounds like a good idea for a really stubborn combo)

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