Hi Harley.
I just went through the same exercise myself on a HT, laid up for 20 years.
First, the bundy tube hard lines. Mine were fairly rusty inside, and from your description of clogged flexible hoses and your inspection you are in the same boat. You will probably flush the loose stuff out with metho but under hydraulic pressure, which will be much higher than anything you can create with a vacuum bleed setup, more junk will be dislodged from the inside walls of the bundy tubing. These abrasive rusty particles will eventually find their way into, and damage, all the seals in the system and promote cylinder bore corrosion.
I've replaced all the hard lines, and I suggest you replace them if you can afford it. If not, bleed a full master cylinder of fluid through the system at frequent intervals, at least for the first few thousand kms. That should help flush any loosened rubbish out of the bleeders. When you do bleed it, don't use a full stroke of the brake pedal. That bottoms the master cylinder pistons, which is where all the rubbish lives, and if you use a full pedal stroke it will chop out the seals.

On the subject of the calipers, I had the same issues. There was some corrosion around the fluid ports at the bottom of the bores. I cleaned it up with Grade 0, and then polished it with Grade 0000 steel wool using brake fluid as a lubricant. I'd keep clear of the wet and dry if you can. You will feel ridges in the bores, which create multiple fluid seals against the piston, along with the main rubber seal. What you do not want to do is rub them smooth!
Corrosion at the bottom of the bores doesn't matter too much, as long as you stop it spreading, as the piston doesn't touch it, but how far up the walls of the bores do you have the corrosion? That, and how deep it is, will determine if the calipers can be saved.
How is the piston surface? It should be uniformly polished without any scuffing, dings or corrosion.
They seem to go for around $120 for a set of four, so relatively cheap to replace.
I assume you are replacing the hydraulic seals as well as the boots. Try and go for PBR/Bosch if you can, as I've heard some of the other brands are not very good. Don't be tempted to split the caliper halves to replace the O rings which live inside, unless they are leaking between the halves.

If everything else about the pistons is OK, a ding or two in the pad backing plate face is no big drama.(assuming it is not huge ding, that is). Just get a flat plate of thick glass or similar, wet it, slap some 600 or 1200 wet and dry in the puddle and lap the face flat. A small low spot or two wont matter, but you definitely don't want high spots, which will tend to cock the pistons in the bores. Perhaps mark the face with a texta and lap until the texta is all gone. (Except for the low spots, obviously)
I hope that helps.

Hi John.
Perhaps my choice of wording wasn't the best, and "ridge" is too strong a word to use.
Call it machining marks, if you will. On the ones I've seen the bores of these particular calipers are not dead smooth from the factory.
You would be reaching for your hone, or even a boring bar if you saw the same finish in an engine cylinder.
The operating conditions for a caliper bore/piston and an engine bore/piston are, however, completely different.
The caliper piston is driven by an incompressible medium (brake fluid), has a very short stroke, and has very low piston velocity.
An engine cylinder is obviously almost totally the reverse with compressible gasses, relatively long stroke and very high piston speeds, hence the need for multiple piston rings, different sealing and different surface finish.

The point I was trying to make was that the surface finish should be left as it was ex factory, and not honed smooth, which may create excessive clearance between the bore and the piston and cause leaks.
In any case, getting a hone in there would require splitting the caliper halves, which is specifically not recommended in the factory shop manual.
I believe the HG would have the thicker brake discs (0.625") and the calipers would have a spacer plate between the halves, which makes it even less of a good idea to split them.

Yes, I agree, replacing all the hard lines is the best choice, but not everyone can afford it, hence my alternative suggestion.

Regards,
Geoff

No problem Harley. The copper lines may give you a roadworthy issue if you get someone picky inspecting it, as copper is not OEM specification.
Try Bunnings for your 0000 steel wool, in the sandpaper section. They have so much they will actually sell some of it.

Oops, double post.

Happy New Year, Geoff.

I'm spending time in Thailand as we speak. great weather & great food !!

As far as DIY goes, I think that splitting the caliper halves is probably less risky than the piston R & R job itself.

Having said that, even the best mechanics or fitters learned by DIY, initially any way. There are many areas of a car where caution is required. Power steering, auto transmissions & brakes are probably top of that list.

I've always used the same torque specs for all 4 of the UNF caliper housing bolts, with or without spacers. The big trick is be careful not to over-tighten, otherwise the calipers are 'toast'.

The UNC mounting bolts (to the stub axle) have different specs, however.

Dr Terry

There are 3 different locations for the brake pipe junction block on HK/T/G rear axle housings, but it's not clear cut on the model break. What you probably need is the 'correct' housing to suit your car. There is more than a fair chance it has been swapped in the past, only to find out too late that the junction location was incorrect for that body.

I make a sell 3 different rear brake houses for this purpose, all to factory specs & checking with the catalogues are per model application only confuses the issue further.

Get new brake pipes made, they are quite cheap. I do them for $50 the pair, in new bundy with new tube nuts. I just need the length specs for your model.

Dr Terry

quote:

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Originally posted by Dr Terry

As far as DIY goes, I think that splitting the caliper halves is probably less risky than the piston R & R job itself.

Having said that, even the best mechanics or fitters learned by DIY, initially any way. There are many areas of a car where caution is required. Power steering, auto transmissions & brakes are probably top of that list.

I've always used the same torque specs for all 4 of the UNF caliper housing bolts, with or without spacers. The big trick is be careful not to over-tighten, otherwise the calipers are 'toast'.

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Well, the rubber kit finally arrived (10 day's postage? I think the seller forgot to post it!) comes with new internal caliper rubber, so now it's a do I/don't I question. I have a proper ratchet torque wrench and I'm not afraid to use it. What torque is right here? It has ft/lbs and NM scales iirc.

And Geoff, it wasn't the regulations I was questioning in the ACT, it was the quality of the inspectors.