Tutorial: R31 Skyline Rear Disc Brake Conversion for 240/260Z.

[Scoota G]

This article is a step-by-step guide to mounting the rear calipers & rotors from a R31 Skyline onto the rear of your 240/260Z.
The key to to this conversion is the correct preparation of the mounting brackets as this will take the most time.
It is also recommended that you recondition the calipers prior to use, fit new pads & rotors.
I would prefer to remove the hubs as cutting off the backing plates is tedious but can be done.

Items you’ll need:

R31 Skyline rear calipers and mounting brackets
(I purchased mine on ebay for $90)
R31 Skyline discs and brake pads
(New would be good)
Custom brake lines with a male fitting at one end and a female fitting at the other.
(These will need to be around 260mm long which is the same diameter as the disc)
The mounting bolts from your rear drum plates (3 of for each side)
The caliper mounting bolts from the R31.

I'll assume that you have a workshop that is equipped with drill, grinder, welder and hand tools and a level area of ground to work on.



Before you start:
You will need to weld up the original bolt holes in the R31 Mounting Brackets and have the centre machined out to 86mm.
Also have your custom brake lines made up (or you could take your Zed to have them fitted after but that may be a PITA)


You can see the complete kit below with the Brackets already customised ready for drilling and cutting.

[Scoota G]

Step 1: Modify the brackets

Now if you have already jacked the car up taken off the wheels and removed the brakes that's fine as you will need the rear drum plates to use as a template for drilling the Modified R31 brackets to correct spec but if you have a spare set better to leave the Zed alone as it takes a while to modify them both correctly.

As i have stated before choose your method to remove the backing plates, i don't think it's necessary to go into the process as it is well documented in the thread below.

http://www.viczcar.com/forum/index.php/topic,2304.0.html

But there's a couple of pictures at the bottom anyway.

So back to the modification, the calipers are mounted facing the front of your Zed. Mounting them at 12 O'clock will cause them to foul on the strut (many thanks to simon for spotting that one) so clamp the calipers onto the old backing plate in the proper position (slightly less than 90 degrees from 12 o'clock will give better clearance for the handbrake cable) and then drill your holes.
If you decided to take off the hubs you won't have to cut the bracket further as we did which is shown it the photo below.

Please be aware that these brackets may need a tweak as in elongated holes or further grinding to make them fit properly.

[Scoota G]

Step 2: Modifying the rear strut and handbrake mounting

Now is the time you should get to Your Zed and remove the rear brakes and backing plates as described by Lurch in that now infamous thread.
http://www.viczcar.com/forum/index.php/topic,2304.0.html
Either that or remove the stubaxles (personally i've never had a problem getting them out).

Now if you have gotten this far and tried to offer up the Modified R31 bracket to the strut you will notice that it will not sit correctly on the bottom rear (in the case of our cut bracket, the other version may need more adjustment) so grab that saftey gear and grinder and carefully grind away the part of the strut it is hitting.
There's plenty of metal there and i chose to do this rather than weaken the bracket. Take your time with this to make sure the bracket fits flush.

After this you will need to unbolt the R31 Caliper handbrake mounting bracket bolt from the caliper with a 6mm allen key.
You'll need to resize the hole that the handbrake cable slides into to suit the Zed handbrake and then shorten the mounting bracket shaft by about 50%. Then tap out the bolt hole deeper and shorten the allen key bolt to suit (or just buy two shorter bolts).
With this modification the stock Zed hand brake cable will fit the R31 Calipers, another way to do this would be to use the stock Zed Brackets and weld them to the shaft of thr R31 Bracket (after you lop off the top).

[Scoota G]

Step 3: Assembly

Well if you have arrived at this point without pulling all your hair out (that's what happened to me ) all you have to do is mount all the gear.

Mounting bracket first.
The disc just slides on.
Then fit the new brake line to the caliper and your Zed trying to avoid fluid loss.
Bolt up the caliper with the stock bolts and connect your handbrake.

You will probably now see that the handbrake cable is close to the rear half shaft and will need to be suspended from the body, it's close but it works.

I would recommend that you upgrade your Master Cylinder to 15/16 or 1 Inch.

Anything i miss lurch? Check it over and see what you think!!

[.]

Thats great Scoota. I'm wondering if the bolt patern for the R31 brakes are the same as the series 2 280zx? Anybody checked? Anybody know the distance between the centres of the bolts on the R31 rear calipers? If its the same I won't need new brakets.

[Scoota G]

Here's a picture of a stock set and machining them to 86mm takes them about 1.5mm past the inner edge of the stock bolt holes (R31).

[Gyra]

I've done this conversion, but I'm getting some disturbing squeeking noises from the brakes - as if the calipers are under pressure.
After a 20 minute drive the left rear disc was hot to touch (other was warm).

At first I thought I had left the handbrake brackets too long which caused the handbrake levers on each caliper to be slightly engaged.
I've trimmed them back another 4mm with no real difference.

Is there another residual pressure valve in the brake line distribution block at the back of the car that could be causing this?

I have upgraded the master cylinder to a 1" JB1419 unit - I don't believe this has the internal valve as it's for an all-disc config.
The calipers are mounted up top and bled properly, and there isn't anything fouling the suspension (handbrake cable clears the drive shafts by at least 10mm). The calipers slide back and forth OK without sticking.

Any other ideas?

Thanks!
G

[Scoota G]

I've done this conversion, but I'm getting some disturbing squeeking noises from the brakes - as if the calipers are under pressure.
After a 20 minute drive the left rear disc was hot to touch (other was warm).

At first I thought I had left the handbrake brackets too long which caused the handbrake levers on each caliper to be slightly engaged.
I've trimmed them back another 4mm with no real difference.

Is there another residual pressure valve in the brake line distribution block at the back of the car that could be causing this?

I have upgraded the master cylinder to a 1" JB1419 unit - I don't believe this has the internal valve as it's for an all-disc config.
The calipers are mounted up top and bled properly, and there isn't anything fouling the suspension (handbrake cable clears the drive shafts by at least 10mm). The calipers slide back and forth OK without sticking.

Any other ideas?

Thanks!
G

If inside the piston and bore are dirty it will not allow the piston to return to it's seated position because of the way the piston twists as brake pad wear occurs. Disassemble, clean and rekit. I had the same problem.

Scoota (Oh and yay me for 2000+ posts)