R34 Gtt Brake Improvement Without Breaking The Bank

[V28VX37]

I've been having some vibration under braking so I went and measured the runout at the very edge of the rotor (just at the outermost end of the slots):

• Left: outside face 0.10mm / inside face 0.08mm
• Right: outside face 0.04mm / inside face 0.04mm

That's a lot of runout on the LH rotor, and quite a big difference between LH/RH. Since this is measured at the very edge I don't think it's due to uneven pad material deposits.

Can I get away by machining the rotors once more (they've been skimmed once) or is it new rotor time? There's no cracking or any visible heat stress on the rotor surface.

Also, what's the recommended runout on Skylines? DBA suggests the following as a general guideline:

Type of vehicle           Typical Run-out value
Small family car         100 microns (0.10 mm)
Medium family car    80 microns (0.08 mm)
Luxury car                 50 microns (0.05 mm)

[GTSBoy]

The only way to know whether they can be machined is to measure them with a micrometer in a few places and have a guess how much material would need to be taken off to straighten them up and smooth them out.  If it's going to require going down to or past the min thickness, then new rotors is the better option.

As to the question of how much runout is acceptable....about as much as you have.  If it was more than that you should start to feel it.

[V28VX37]

2 hours ago, GTSBoy said:

The only way to know whether they can be machined is to measure them with a micrometer in a few places and have a guess how much material would need to be taken off to straighten them up and smooth them out.  If it's going to require going down to or past the min thickness, then new rotors is the better option.

As to the question of how much runout is acceptable....about as much as you have.  If it was more than that you should start to feel it.

Thanks. Both rotors are currently about 29.1mm at the thinnest point, measured at three spots through the wheel using a basic digital caliper. There's a bit more variance between the thinnest and the thickest spot on the LH side.

Given that these rotors are 30mm thick new and have minimum thickness of 28mm according to the DBA catalogue, looks like they are at about halfway through their useful life so might try one more skim.

Also I've just replaced outer tie rod ends and also checked for wheel bearing play (all good) so I'm pretty sure any braking vibration is likely to be rotors...

[V28VX37]

Rotors were taken off to the machine shop today but they wouldn't skim them, combination of runout & not enough meat left. Sounds like this may be the end of tracking these rotors, sucks as they're only halfway worn and they don't look too bad but then again they did last a couple of years. They're fine for the street though.

In terms of replacements, can RDA blanks be tracked safely, or am I better off getting the same DBA T3's again? Or is there another budget option?

[admS15]

Get the rda's. They're cheap and they've held up well for me. 2 sandown track days done and they're not showing any signs of fatigue or warping and still braking without any shudder. For the average track hack like ourselves they can't be beat for bang for buck.

[V28VX37]

13 minutes ago, admS15 said:

Get the rda's. They're cheap and they've held up well for me. 2 sandown track days done and they're not showing any signs of fatigue or warping and still braking without any shudder. For the average track hack like ourselves they can't be beat for bang for buck.

Thanks mate. I might even check my old plain rotors, if there's enough meat left might give them a go.
Currently aiming for the 20 Jan MX5 day at Sandown, keen to check out them go karts too    

[Dose Pipe Sutututu]

Hit me up for rotors, I'll try to give you the best possible price

[V28VX37]

22 hours ago, V28VX37 said:

Thanks mate. I might even check my old plain rotors, if there's enough meat left might give them a go.

Nah 28.9mm of thickness left on the old ones, I don't think so. Also they've got Nissan castings so they may in fact be the original rotors from 1998 (!).

Options are RDA at about $200/pair or slotted DBA T3's for about $400/pair. I'm not convinced that the DBA's are twice as good, it's really just a glorified heat sink right?  

[niZmO_Man]

I've had zero issues with RDA plain rotors

[V28VX37]

Ok the RDAs are in. The first impressions are that (unsurprisingly) they feel exactly the same as the DBAs, minus the vibration under heavy braking. My Intima SRs are still squealy, perhaps a touch quieter but now it's noisy on both sides, not just on the right. Also these pads like a bit of heat to start working properly.

Pro tip: Get a dial indicator before swapping rotors! Here's the cheapo one I got, it comes with the base and holder, works a treat: http://www.ebay.com.au/itm/0-10mm-Dial-Indicator-Gauge-Magnetic-Base-Holder-0-01mm-Resolution-/262248550292

I didn't do this when slapping on the DBAs, and whilst I've had a myriad of other issues along the way (factory backing plates roasting rotors on the inside, stuck caliper pistons, overheating LH brake line due to lack of turbo heat shield, lack of brake cooling etc.) I'm pretty sure not checking runout and oscillation originally has contributed to the reduced useful life of the rotors.

I spent fair while cleaning the hubs and spacers, here's the final measurements:

• Left: runout 0.03mm, oscillation 0.075mm
• Right: runout 0.025mm, oscillation 0.07mm

Note that the minute gap between the hub centre and the rotor contributes to oscillation and can be adjusted under some circumstances. For instance on my car the LH oscillation was 0.12mm if I just sat the rotor on the hub and tightened it where it naturally sat. Pulling the rotor upwards whilst tightening reduced oscillation by two thirds, down to 0.075mm, meaning that the rotor is centred on the hub better.

I was worried about my wheel bearing(s) being buggered because of track work and using spacers but luckily they seem ok, it was good to have the measurements to confirm.

Two good brake instalation threads for reference:

• https://www.sau.com.au/forums/topic/362526-diy-skyline-front-big-brake-install/
• https://www.sau.com.au/forums/topic/414681-diy-replacing-pads-and-rotors-on-d2g4attkd-etc-8-piston-brakes/

Here's a great summary form the first one on what you should be checking and why by Checkbuzz:

On 01/06/2011 at 4:13 PM, Checkbuzz said:

Hi Guys

I have been installing a K Sport 330mm 8 pot kit on my ECR33 and I would like to add a couple of points that may save you money and headaches down the road:

1. Buy yourself a dial indicator with a magnetic base stand ($90 Repco) and check the new disk rotor for run out (should be <0.05mm) and oscillation (should be <0.15) once you have cleaned the hub and fitted it to the car using wheels nuts and about 30NM of torque (Google anything you don't know here)

2. If run out is out of tolerance rotate the disk by one wheel stud, refit and measure (mark original position first) often run out can be brought into tolerance by simply rotating the disk until you find the spot where run out is at it's lowest.

3. To fix any remaining excessive run out you must clean the hub face up until it is shiny using a wire brush (preferably pneumatic) and fine emery paper. The hub cannot be too clean; as you can imagine it only takes a tiny bit of rust scale to put the edge of the disk out by 50 microns!!! (i.e. 0.05mm)

4. If you can't get it within tolerance check hub play (<0.05mm) and run out (<0.02mm) replace hub or wheel bearing if out of tolerance

5. If you do not do this be prepared to replace your disks after about 5000kms due to DVT caused by the excessive run out (symptom = pulsating brake pedal and/or brake shudder)

6. Both of these measurements if not within tolerance can also cause brake shudder and/or vibration at high speed

7. Excessive oscillation can be sometimes brought within tolerance by wrapping plumbers tape around the centre of the hub and refitting the disk

These tolerances, tests and remedies are documented in the Nissan work shop manual and/or K Sport supporting doco.

The tolerances are tiny but quite critical to on going good brake performance

Also here's the key torque specs and runout numbers from the R34 workshop manual for future reference:

• Wheel nut torque: 103 - 122 Nm
• Front caliper mounting bolt: 152 - 154 Nm
• The runout limit is 0.07mm. Oscillation limit is not specified.

R34 workshop manual page SD-27:

R34 workshop manual page SD-28: