Tutorial: R31 Skyline Rear Disc Conversion For 240/260Z. New 300Mm Rotor Conversion Sep/2016

[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 new design bracket uses standard R31 brake hoses.
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.

Edited September 1, 2016 by Scoota G

[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.

 

 

 

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.

 

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 the 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)

[Scoota G]

Update on a revised handbrake setup. I was thinking about this since i did the conversion and have since done the same rear upgrade on my 2+2.

 

First cut the R31 handbrake bracket as pictured.

 

Then take the stock Zed handbrake bracket and trim it to the first bolt hole as shown. Then cut angles on it to suit either left of right caliper.

 

Line up the Zed bracket on the R31 stalk and and plug weld the bolt holes.

 

Then turn over and weld the other side (two decent tack welds will be heaps). Then squeeze the Zed handbrake cable at the end bracket and fit the R31 washer (perhaps a small amount of grease too) and a new split pin. You will need to bend the caliper handbrake arm to suit but it's very easy to do.

 

After you fit the clip to hold the handbrake cable in place you will notice that the bracket point the cable away from the half shaft on a slight angle which helps with clear it much better than the previous modified R31 bracket. I have tested this setup and it works very well. This saves you grinding down the R31 bracket and reducing strength.

 

[C.A.R.]

10 Brownie points to you Mark!

[Scoota G]

10 Brownie points to you Mark!

Thanks Chief. Here's the cable installed.

[260Coupe]

Guys-

Question

I certainly appreciate the enginnering skills that go into such a conversion however Not withstanding big HP track cars that require long time fade free stopping power:-

 

For a road going Zed- Is there a definite and measured advantage over the standard braking system and has this been tested ? (using brake performance testing equipment).

I have driven many Zeds with rear disc conversions and without an adjustable bias valve and major upgrades to the master cylinder and front brakes - the brakes are always compromised including rear brake lock ups, long pedal travel and ineffective hand brakes etc.

 

Why I ask is that there seems to be this "misnomer" that the standard Zed brakes are rubbish however standard brakes can be made to perform exceptionally well and far beyond that would be required by the most spirited of road drivers. With nothing more that braided lines, rekitted calipers and wheel cylinders and the correct pad/shoe compound.(and a set of DBA slotted rotors to negate the effects of pad glazing) the standard brakes are more than adequate for road use (ask any Group Sc Zed driver who has to race on them)

Apart fron the shiny disc behind the rear wheels I'm at a loss to understand why this is necessary for a road car .

 

At risk of being flamed

 

Alan

[Scoota G]

Apart fron the shiny disc behind the rear wheels I'm at a loss to understand why this is necessary for a road car .

Awww, but that's my fav bit. 

 

Here's a pic of Bozo's full kit. Ain't they preddy??

 

Oh and the first word in this thread is tutor..... arr you know what it's here for, perhaps a discussion thread is needed. I have mine tweaked in the 2 seater and they rock. Can't wait to try them in the V8 2+2. By the way a disc conversion per side weighs 7.2 Kilos and the drums weigh 5.4 kilos.

[C.A.R.]

Depends on how hard you drive your road car Alan...

As with any brake conversion, it should be part of a carefully considered package by the vehicle owner.

 

Also, locating suitable drum brake components is getting difficult...

 

 

[260Coupe]

Depends on how hard you drive your road car Alan...

As with any brake conversion, it should be part of a carefully considered package by the vehicle owner.

 

Also, locating suitable drum brake components is getting difficult...

 

Lochy -yes rear wheel cylinders are getting pricy and drums and shoes can be relined

 

On the subject of hard driving-  my old Group Sc 240z was running standard brakes (as required in Sc)  turning 118 rwkw on 240 carbs (135kw on tripple 44 Mikuni's) and was good for at least ten hard laps around P.I averaging 2.01s....jason Lea did 15 flat out laps around Winton long track (notorious for cooking brakes) at the last Historic round and still had working stoppers..... ...not sure how much harder one could drive on the road.

 

Ahhh well each to there own..........I am just a little perplexed as to why some would take a step backward instead of just getting the stock brakes working as intended.

As I have advised many Zed owners............drive a good Zed with brakes that work and use that as a yardstick before thinking that rear discs are the answer.

Spend your money on getting the stock brakes woring properly and on decent tyres instead

 

My 2c

 

 

Al.

 

 

 

[Agno]

With R31 rear calipers and S12 solid rotor 4 pots my brakes are very much forward biased. When I get around to it I'm going to suss out XF rear brakes to see if that brings the bias rearwards a bit more.

[53-681]

With R31 rear calipers and S12 solid rotor 4 pots my brakes are very much forward biased. When I get around to it I'm going to suss out XF rear brakes to see if that brings the bias rearwards a bit more.

 

I thought you had adjust a valve or something of that sort to modify bias?

[Agno]

You can fit a brake bias/proportioning valve if you want, but I haven't done that yet

[red76z]

Here are a few pictures of my R31 conversion by modifying  the rear struts/hub to suit the complete bracket.

I ground the bottom corner and took a bit off each other corner witch allows you to pivot the bracket between 2-5 o'clock . The best angle for the hand brake cable I found is about 3 o'clock.

as they say (a picture says a thousand words).

I hope this helps in future mods.

[red76z]

The finished Look.

P.S If you are replacing the rear hub bearings before you try to press them back into position or bash them in with a hammer and punch, Just put them in your freezer overnight and if they are like mine you can push them into place by hand. It works a treat..

[red76z]

A few more photos to help you with your project.

[zed4ps]

I also have done this mod but my hand brake lever has to be fully engaged before the park brake applies. Would this mean that the cable is stretched and needs to be replaced, as i have adjusted it a fair bit. Cheers peter

[YosemiteZed]

Try this as it could be the answer you seek to fix the h/brake and is a simple mod

Follow link for details

http://www.nyzcc.org/viewtopic.php?f=7&t=297

Cheers

[zed4ps]

Thanks i`ll give it a try. peter

[zed4ps]

Thanks Guys, this mod works a treat. Cheers Peter