hey i looked everywhere through the forum and in the tech section but it was all mumbo jumbo ...... all i want to do is get some discs up the front of my car and get some extra stopping power....i heard that u can just get a 120y front end and bolt everything including the discs striaght up..is this an unboosted setup and do u use stock master cylinder or 120y
whats the easiest way to do all this

thanks heaps for ur help

Hi Fat, what you have said is correct 120Y or 1200 coupe discs will bolt straight on.
coups were unboosted and 120y"s had a booster.
I replaced the drums on my old sedan with discs and had no need for a booster
Ade

By all means, use the struts & brakes from a 120Y, but re-use the 1200 springs, top mount & possibly even the shocks [if they are replacement type] as the 120Y setup is longer in this area & your car will sit up higher in the front if you use the whole thing.

Also. Don't use the Australian built parts from a sedan that was made from July "76 onward. There is nothing wrong with these parts, but the diameter of the pistons in the calipers, the master cylinder & the rear wheel cylinders are all diferent from the Japanese parts & if you mix & match, you will have problems.

Make sure that you remove the residual pressure check valve from the front brake circuit of your drum brake model master cylinder. While you have it all apart, now would be the time to overhaul it too. Your workshop manual will show you how it's all done.

Now,.. here's the important bit. Either get [& overhaul] the rear wheel cylinders from the same car that donated its original disc brake front end, or go buy some new ones.
The rear wheel cylinders from disc braked cars have a smaller diameter piston. The disc brakes need a higher line pressure to make them work & this higher pressure leads to rear wheel lockup at the most inconvenient time,.. like in the wet.
These cylinders correctly balance out the brake forces & remove the lockup problem.

If the factory could have gotten away with the standard drum brake cylinders, they would have, but they didn't. They changed them for a very good reason,... so should you.

Dodgeman

I'm just about to perform this very upgrade to my 1985 Ute, using the front struts off a 1975 120Y (Aussie). So I'm assuming I'll need the rear wheel cylinders as well to stop the rear locking up. Does this cylinder size change mean that I won't need a metering valve?

Thanx

Andrew

also do we need to steal the booster from the donor car or what do these bolt straight up with the donor master cylinder

and do we use donor brake lines or stocko brake lines

cheers

Vaztr
Basicly you need to replicate what the donor car had.
If your master cylinder bore is the same size as the donor, then use the original, but overhaul it to ensure that it is in top condition.

I don't know what rear brakes were used on these late model utes, but if they are the same as the earlier ones, then use the donors cylinders as well. If the donor didn't have a proportioning valve, then it's unlikeley that you will need one either. That's why the wheel cylinder bore was reduced, to balance out braking forces without the need for additional parts.

It's always a good idea to overhaul any used brake parts before installing them. That way you will KNOW that they are in good servicable condition & will perform as advertised.
Install them unchecked & you may well be taking your life into your hands every time you drive.

BOOSTER?
With this particular conversion,... generally no. When a booster is fitted to the donor car, you will find that the master cylinder often has a smaller bore size, so check this when contemplating booster useage. Boosters also need a vacuum supply, but if you run Webbers, or similar, particularly with a sporty cam profile, then you may not have much vacuum anyway. Sometimes less is more.

Whenever in doubt, re-read line one of this post.