Front brakes for a Harrison

[sambo]

I'll soon have a Harrison with the Nissan IRS and I've been looking at brake options for the Commodore hubs on the front. A lot of the stuff coming out of HSV (eg, ex Commodore stock prior to the HSV brake upgrades) is making it onto the internet and the prices seem reasonable.

A few questions to the Harrison owners out there: what have you used for the front discs and calipers and how effective has it been? What would you consider "too big" on the fronts when matched with the stock Nissan brakes on the rear? Has anyone used proportioning valves and to what effect?

I'm looking at these items on ebay:

VT 296mm TWIN PISTON FRONT BRAKE UPGRADE FOR VR-VS

VT COMMODORE BIG BRAKE CONVERSION VR VS V6 V8 PBR HSV

330mm twin piston brake upgrade for VR-VZ Commodores

If you search that particular ebay store you'll see that the kits go even bigger and so do the prices. I'm already thinking a 330mm rotor will be enough for an 1100kg Cobra.

Paul

[Rebel1]

Sambo, you gonna track ya car?

[sambo]

Most definitely Les.

[Rebel1]

Then Warwick would be the best to ask.

He raced that red one now owned by Wazza and what appears in the center on the front page of the Queensland web site.: http://www.cobracarclubqld.org.au/

Maybe even ask Wazza if he will talk to you. You being a Victorian and all.

[sambo]

Hey I was born in Brisbane, that has to count for something!

I asked Warwick about this and he reckons the std VT Commodore brakes are fine. What I'm trying to decide is whether more is better, for only a few dollars extra.

[400TT]

Best bang for buck is Warwick's(or other supplier) pbr twin piston calipers & 300mm rotor. Seems to be a very popular option with Harrisons of late.

If you want to get serious the next best value for money is 330mm 1-piece rotors and 4 piston Skyline calipers. Warwick is doing a turn-key at the moment and he has gone that way as that Cobra has an owner who has a lot of track experience.

After that the sky is the limit.

Warwick is probably right as you can dial in the right pads, slotted rotors and get some serious track performance out of those VT brakes in something the weight of a Harrison Cobra.

[Rebel1]

Originally Posted by sambo

Hey I was born in Brisbane, that has to count for something!

Yeah Ok...but also cuz you purchased a Queensland based kit.

[sambo]

Thanks Craig. It sounds like the VT brakes have a fair bit of headroom.

[400TT]

Originally Posted by sambo

Thanks Craig. It sounds like the VT brakes have a fair bit of headroom.

Next step would be to duct some air to them if you start getting serious.

As they say, the less unspring weight the better. I bet this is what Warwick is thinking about also.

My brother is about as quick as they come on the track and is only now thinking about moving to a larger than 300mm rotor. Already running Nissan 4 piston calipers but that's because we used the Skyline front alloy uprights instead.

[sambo]

How hard was that conversion Craig (Skyline front uprights). I was thinking of redrilling the front or rear to get matching stud patterns but since the wheels are different widths front to rear it doesn't really achieve much.

[400TT]

We did it because Warwick was using HQ stub axles on the earlier cars(ours), it wasn't that easy. With the move to Commodore, there is a lot less reason for it. Skyline uprights have their hassles, like difficulty in obtaining the lower ball joints and wheel bearings. Actually buy 2nd hand replacement uprights to get replacement wheel bearings.

The car actually runs R32 GTR front uprights, rotors & calipers. Also complete R32 GTR rear. It's hard to find genuine GTR stuff, I just found a replacement GTR diff centre a few weeks back as the current one seems to be now starting to suffer from years of abuse on the track.

Yeah, I would stick with Commodore pattern on the front as it will make rotor changes/replacements so much cheaper and easier.

[sambo]

Interesting about the GTR stuff Craig. Not sure what mine is but I believe the S15 200SX helical diff centres can be retro fitted to the Skyline as the housings are very similar. I hear they can be sourced new from Japan for "around a grand" which might be an option if/when the centre needs replacing.

Have you looked into setting up ABS with the Skyline brakes? Warwick suggested fitting a sensor to the tailshaft if the sensors were not fitted standard to the Nissan brakes on my diff. By fitting a sensor to the tailshaft I imagine it is not possible to brake individual left/right rear wheels, since the computer does not have feedback on the rotation speed of each wheel.

[400TT]

The GTR centre has different drive flanges, actually just about everything is different. Just about all Harrisons with Skyline rears have R32 GTS-T diffs fitted, certainly a more than capable rear-end.

We use one of the rear(diff) speed sensors for speedo etc. Not all diffs have the sensors as the sensors only exist if the vehicle was fitted originally with ABS. All GTR's had ABS. Even the mounting flanges are removed on non-ABS vehicles.

We also have a front wheel speed sensor fitted. Originally fitted for traction control.

Can't you just fit ABS Commodore hubs to the front?

[schipps]

Sambo,

I got a set of unused VZ SS discs for my front end with PBR twin pot calipers and new pads for $180.

Mick

[WKB]

Sambo,

You can use the S15 diff in the GTST K frame by changing the back cover and swapping the drive shafts over. The holes in the front of the diff will line up with the holes in the K frame, but will need a plug in them as the holes are bigger than the original diff. If you are going to fit one do it before you get the tailshaft made as the S15 diff has a ABS speed sensor behind the the drive flange which makes it longer than the standard GTST diff. The S15 ratio is 3.69 to 1 which is a good replacement for the GTST diff if you want a higher diff ratio. S15 diffs come up a ebay every now and then. I bought one for $250 recently.

Warren

[400TT]

If you want a taller ratio you should be asking Warwick now as I'm pretty sure he has done the swap a few times and might work out to be priced well. e.g. Dru's Daytona has the taller 3.7 ratio.

[sambo]

Thanks for the info Warren, that's a real help. Would you say the S15 diff conversion is worth the effort? How does it change the handling?

[WKB]

Sambo,
Havn't fitted the diff to the car yet as I am waiting to get it registered(August 24th trip to the transport dept for the final inspection). I want to feel what it is like before I decide wheter I will change the ratio. Most of the Jap cars that use the 1uz V8's use diff ratios around 3.9 to 4.1 so the 4.1 I am using will suit the motor I am using but I will be 500 - 600kgs lighter.With yours the taller diff ratio might be an advantage as 3.7 would be arounnd the ratio the performance holdens would be using.
If your are after a replacement then the diffs Warwick uses are from nissan silvas. All you do is replace the back cover and drive shafts and it bolt straight in.
One was on Ebay that didn't sell in melbourne for $200 a couple of days ago.

Warren

[Merv and Sharon]

Warren, I am also getting the Nissan R32 diff that Warwick fits. More than pleased with its reputation. It seems to have 4.1 ratio. Using a calculator and planning to use the T56 6 speed gearbox (and 17" wheels, etc) I have been working out that I seem to do OK at the rpm @ 100km/h 'test'. This is mainly because the T56 6th speed is supposed to be about 0.5. Does this make sense or should the Nissan rear end be reduced?

[400TT]

You will also need to see how suitable 1st gear is, i.e. whether it is too low. Also whether 2nd gear is suitable for low speed corners etc etc.

Then as you mentioned above, is overdrive(5th or 6th) suitable for cruising, can you get into it at suitable speed and not be running too many revs at cruising speeds. You also find there is always a sweet spot for cruising revs where the engine/exhaust is quietest.

For track use, then correct gearing makes a huge difference, different tracks favour different gearing both for corners and top speed down the straights.

Like most things, it's all a compromise and personal preference comes into it as well. So it might be something you need to road/track test yourself first.