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Nigel

Yet another rear drum to disk conversion option!

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As a design challenge, I decided to come up with my own rear drum to disk conversion kit that meets my standards (I'm a controls designer for the Nuclear Power industry) for a bolt on kit. I wanted to design something that:

  1. Uses OEM parts where possible for ease of service and availability of parts.
  2. Has an integrated parking brake oriented such that it will not interfere with CV axles.
  3. Is capable of providing adequate brake torque to balance even the big Wilwood style front brake kits.There has been a long standing myth that rear brakes don't really matter that much. But upgrading the front brakes without a proportional increase in rear braking will actually result in longer stopping distances. There are very few OEM rear calipers with an integrated parking brake capable of providing adequate torque for much more than stock Z front brakes.
  4. Has a wide variety of pad compounds available from multiple manufacturers.
  5. Is modular to allow the use of a 300mm (11.81") OEM rotor, or a two piece 310mm (12.2") rotor for reduced weight and increased brake torque.
  6. Is as light weight as possible.
  7. Does not require removal of the caliper to bleed the brakes.
  8. The parking brake cable does not rub anywhere, and is not forced to bend at extreme angles through the entire stroke of the suspension.
So, I've spent the past several months educating myself on brake physics, crunching brake torque numbers, poring through brake part catalogs, designing brackets, and machining prototype parts to come up with the best solution to all of the requirements I've listed. I'm at a point now where I'm curious to see if there is enough interest to warrant a production run. For US customers (I'm in Canada, BTW), I would supply brackets, fasteners, a custom parking brake cable, brake lines and brake hats if a two piece rotor is desired. I can supply calipers, rotors and pads, but it's unlikely I can compete with US prices for those items. I have a connection for good prices on those parts for Canadian customers.
 
There are two caliper options depending on the wheel clearance you have. One is aluminum, which saves a few pounds, but has a much thicker bridge and so requires more wheel clearance. The other is steel, and will fit inside a smaller wheel. As a quick reference, I have 17" Rota wheels, and with the aluminum caliper positioned to fit a 310mm (12.2") rotor, the caliper just clears by a few mm. Both calipers use the same pads. I'll provide a chart of required wheel clearance shortly.
 
For the OEM rotor, there is next to nothing readily available in the Datsun 4 bolt pattern that is of sufficient diameter. This means re-drilling OEM 5 bolt rotors with the Datsun 4 bolt pattern. I can have this done, but it probably wont be all that cost effective. So, as an alternative, I'm looking into supplying centering rings and a drill template. If you're reasonably adept at using a drill press, you can drill the rotor bolt holes yourself with the template. The centering rings will ensure that even if your holes are out by a bit, the rotor won't be off center.
 
I'm still working on final pricing, but ballpark for the 300mm OEM rotor option will be around $350US + shipping. This would include brackets, plated grade 10.9 fasteners, parking brake cable and DOT brake lines. I've seen the calipers listed on Rock Auto for just over $150 each. Rotor price starts at $40 each and goes up from there depending on quality. For the 310mm two piece rotor option, the hats will add an additional cost that I'm still waiting for info on. The rotors are Wilwood items that can be had for a similar price to the OEM rotors.
 
I do work full time, and this is a side project for me on top of renovating my house and working on my Z, so I can't guarantee immediate action on everything. But I do have manufacturers already lined up, and once the go-ahead is given, it should only take a couple of weeks for production. As per hybridz rules, payment would only be required when the parts are ready to ship.
 
Now for the pictures!
 
Assembled kit with aluminum caliper and 300mm OEM rotor:
tn_full_20130525_180432.jpg
 
Custom parking brake cable with stainless inner cable. No modifications required to cable sleeve mounting brackets under the car.
tn_full_20130513_183755.jpg
 
Caliper attached to prototype aluminum bracket and parking brake cable attached to caliper. Note: production bracket will be anodized.
tn_full_20130513_182625.jpg
 
Routing of parking brake cable. The cable does require small holes to be drilled in the control arms for a clamp to hold the cable to the arm. I'm looking into options that won't require drilling.
tn_full_20130525_180216.jpg
 
Finite element analysis of 1/2" thick, 6061 aluminum bracket.
tn_full_Stress_Plot_-_50_6061.jpg
 
 
So, is anyone interested?  :icon7:
 
Nigel White

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Wow, great work! I wouldn't be ready to commit now, but would definitely be interested in the future. It's nice to have something that was actually engineered rather than haphazardly pieced together. I can appreciate the effort you went through. You may already have it, but Fred Puhn's Brake Handbook is a worthwhile read.

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Very nice. Quite impressed by the engineering. Even the two part caliper bracket that is likely cheaper to make in two parts than one.  Nothing wrong with that. 

 

Love the e-brake system too. No comprimise, all new, and simple. I also like the idea of letting people supply their own rotors and calipers. You don't need to be involved in supplying and moving heavy commonly available parts. I just want the hose, brackets and cable and PN's for the expendables. Fantastic!

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Thanks for the positive feedback everyone!

 

Very nice. Quite impressed by the engineering. Even the two part caliper bracket that is likely cheaper to make in two parts than one.  Nothing wrong with that. 

 

Love the e-brake system too. No comprimise, all new, and simple. I also like the idea of letting people supply their own rotors and calipers. You don't need to be involved in supplying and moving heavy commonly available parts. I just want the hose, brackets and cable and PN's for the expendables. Fantastic!

 

 
The two piece bracket allows for the parts to be waterjet cut. This significantly reduces machining costs and allows me to offset some of the cost of including a parking brake cable with the kit. Surprisingly, the parking brake cable was the most difficult item to source.

 

Hey Nigel,

 

I'm definitely interested, and the cost is good.  I see rear disc conversion go for upwards of the 600+.

 

May I ask why you didn't want to use the 240SX units?

 

Keep in mind that by the time you buy calipers, rotors and pads, you will be looking at $800+. Good brakes aren't cheap!

 

Regarding the use of 240SX brakes, for the short answer, skip to the second last paragraph below.

 

For the long answer... :-)

 

Braking is a dynamic process. While braking, there is load transfer on to the front axle and off of the rear axle. This is due to the forces applied to the chassis by the torque of the braking wheels, and happens even in a car with no suspension. The harder the braking the greater the load transfer. As the load increases on the front axle, the friction between the front tires and the road increases. Consequently, the front brakes can do more and more of the work to slow the car. The inverse happens at the rear axle.
 
This unfortunately leads people to believe that the rear brakes don't really matter much. However, you need the maximum combination of front AND rear brake torque to get that load transfer to the front in the first place. Undersized rear brakes are unable to generate adequate brake torque for sufficient load transfer to the front axle. Therefore, there is less friction between the front tires and the road, and the front brakes will more easily overpower the traction available from the front tires. This is of course safer than having the rear wheels lock first. But if you swing the balance too far to the front, the front wheels will lock up far too easily and braking distance is made significantly worse.
 
Calculating brake torque is relatively straightforward. It's a function of hydraulic pressure, caliper piston surface area, rotor diameter, and pad coefficient of friction. 240SX brakes have tiny, 34mm pistons that just aren't capable of applying the clamping force needed to generate the brake torque required to match much more than stock front Z brakes. Keep in mind that 240SX front brakes are no more "powerful" than stock Z front brakes. Even larger diameter rotors and high friction pads used with the SX calipers aren't enough to offset the disadvantage of the small piston when trying to balance upgraded front brakes.
 
The rear calipers I've sourced use a 43mm piston, and the 310mm rotor option is the largest I could fit for those that have 17" rims and want aluminum calipers. The calipers also have good selection of high friction, but still streetable pads. But, there are probably enough options available with this kit to find the right balance for everything from stock front brakes to even the big Wilwood front brake kits.
 
Nigel

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Good explanation!

 

What about guys who have stock brakes up front?  Wouldn't using a bigger cause lock in the rear first (what you're trying to avoid).  Or maybe a portioning valve will help with that?

 

SOrry for my ignorance, I'm a noob all around

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Good explanation!

 

What about guys who have stock brakes up front?  Wouldn't using a bigger cause lock in the rear first (what you're trying to avoid).  Or maybe a portioning valve will help with that?

 

SOrry for my ignorance, I'm a noob all around

Yes, that's what the proportioning valve is for.

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Pad compound also makes a significant difference. Pad selection can seem like an arbitrary and subjective process, but pad manufacturers for OEM calipers are required to classify the friction range of the pads. It's actually printed as a code right on the pad. If you google it you can find a description of the code. But for stock front brakes, an "EE" friction range for rear pads would likely be best. This is the lowest friction rating.

 

Unfortuantely, some pad manufacturers make it difficult to find that code short of actually buying the part. They instead rely on flowery descriptions of how wonderful their pads are. :iospalo:

 

Nigel

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What do I think? I think you shoudlve made this kit a few months ago when I went ahead with the 240sx change :\

 

Sorry about that. Believe me, I wanted to do this years ago, but never had the resourses needed to make it happen. I also didn't wan't to be one of those guys that gets people's hopes up but then takes forever to deliver.

 

I'm interested. Are you going to reveal what the calipers are sourced from? Also I'm guessing a 300mm rotor setup won't clear 15" wheels? Any chance of a kit being made with a smaller rotor for those of us wanting to keep our 15" wheels?

 

Steel calipers are from a 2004 Lincoln LS. Aluminum calipers are from a 2004 Jaguar Vanden Plas. Internally, they are the same caliper. In fact, there's a Sport edition of the Lincoln LS that also uses the aluminum caliper. They're the same internally as the 2005+ Mustang GT, so rebuild kits will be plentiful in the future. You can even use Mustang GT pads. The Lincoln and Jag specific pads look slightly different, but the Mustang pads fit just fine.

 

As an interesting side note, this series of caliper got it's start in the 2001 Dodge Viper to replace the pathetically undersized 36mm piston rear caliper that came with earlier models.  To emphasize the importance of rear brakes, a rear piston upgrade mod to 40mm that was developed for the earlier Vipers resulted in a braking force increase from 0.8G's to 1G with no other changes.

 

I'll post a chart of wheel clearance required this weekend. But with the steel caliper and 300mm rotor, you need ~13.5" inside diameter on the rim. That may fit a 15" rim? Clearance to the spokes from the hub faces required is about 20mm.

 

Nigel

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Haha no worries.  It sounds like it has the potential to be an awesome kit.  I may end up getting this just yet down the line if I decide my 240sx kit isnt adequate.  I was worried about the bias of the set up (Im using the toyota calipers up front with vented rotors as well) and went with staggered pads (more aggressive pads out back) to see if i could get a feel i like.  If not your kit sounds like it might be a good way to go.  I like the idea of being able to make use of a proportioning valve to dial back the rear because theres too much bite, instead of just having too much stopping up front at all times.

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Sorry for the delay in posting the clearance numbers. I've been scrambling to get my Z ready for the drag strip next Saturday, and getting another prototype brake kit together for EF Ian, who can't wait for the production run. 

 

Here's the measurement to the outer surface of the caliper for each of the combinations. You'll need that distance listed plus a few millimeters clearance.

Aluminum caliper, 310mm 2 piece rotor = 380mm dia, 190mm radius

Aluminum caliper, 300mm rotor = 370mm dia, 185mm radius

Steel caliper, 310mm 2 piece rotor = 360mm dia, 180mm radius

Steel caliper, 300mm rotor = 350mm dia, 175mm radius

 

You also need approximately 20mm clearance from the plane of the hub face to the wheel spokes.

 

Hopefully that will give people a starting point.

 

The only thing holding me up at the moment from taking orders is getting a manufacturer lined up for the brake hats. I was going to share a design, but there's been a delay getting that going with the person I was working with. I drew up my own design on Friday, and I've just started getting quotes in. Best so far is in the $250/pair range for 5 sets. I'd like to see if I can find something better.

 

Nigel

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Picked up the rotor centering ring prototypes today. Looks like a perfect fit! So, this should allow those with a drill press, or access to one, to drill their own wheel lug hole pattern with a template, and not have to go to a machinist every time they need to replace their rotors.

 

tn_full_20130619_164923.jpg

 

tn_full_20130619_165131.jpg

 

Nigel

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Centreing rings look good. Would be easy to loose those, will need to be carefull.

 

That's why I deliberately sized the ring to be a light press fit on the hub, so it doesn't fall off and get lost. A few taps with a hammer against a sturdy straightedge to seat the ring flush with the face of the boss on the hub is all it takes. That leaves enough of a gap around the back side so you can still pry the ring off should you ever need to in the future. It's a good idea to take a wire wheel on a drill to the circumference of the boss to clean off any rust, and then apply a light coat of anti-seize before the ring is driven on.

 

Nigel

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Hey Nigel,

 

How is your setup coming along?

 

I pm'd you a while back regarding that modern motorsports kit you purchased. I started to piece together the OE parts from it to build a set myself. I was hoping to get some dimensions from you to complete it, but if your working on a more modern variant that works better, for the prices you listed above I may be in for a set as well!

 

Keep us updated.

 

Ray

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Hey Guys!

 

I haven't given up on this. I've just run into a delay with the two piece brake rotor option, and I really wanted to offer both it and the OEM 1 piece rotor option at the same time. I've had the prototype hats and Wilwood 12.2" rotors sitting on a shelf for a couple of months now. But in that time, my Z has been plagued with a seemly never ending series of issues, which I've had to fix first. The water pump went, then the rear transmission seal, followed by the alternator. While I was repairing those things, a terrible misfire under load showed up out of the blue that I've yet to be able to solve. So my Z is more or less undriveable at the moment. In the mean time, my garage is now out of commission while I have a new floor installed, so I've had to put any work on the Z on hold. 

 

However! Before my Z decided it was going to be so uncooperative, I was able to put >1500 miles on my rear brake setup with the OEM rotors, including a trip to the New Hampshire Speedway for the track day during the convention. I'm happy to report that they performed flawlessly! The cables and brake hoses don't rub, pinch or bind anywhere. The parking brake actuation is tight and doesn't require excessive travel of the handle. I now have the TTT rear control arms, and I was able to find a perfect mounting point for the parking brake cable clamp. So, this setup will work for sure with the TTT and OEM control arms. I suspect they'll work just as well with other control arm options though.

 

For some actual quantitative performance numbers, I downloaded the Trackmaster app for my phone and did some G force measurements under braking. This is where things really get interesting. I have the AZC Wilwood front brake kit, with Wilwood street pads, and I did some brake tests with EE friction rated pads in the rear on the 11.8" one piece rotors. Even with full rear line pressure, I couldn't get the rear brakes to lock up, and I was only seeing about 0.75G's under deceleration. I then switched to EBC Yellowstuff rear pads which have a GG friction rating. I immediately had to dial down pressure to the rear brakes a few turns to keep the rears from locking up first. Once I got that set up, I did some more brake force measurements, and saw brake force climb to over 1G! This verifies what I've been saying all along about having a properly balanced brake setup.

 

Since it's likely still going to be weeks before I can try out the two piece rotor option, I may just go ahead with production of the one piece OEM rotor version. I did sell a prototype kit to EF Ian back at the beginning of July, and I was also really hoping for some feedback from him before doing a production run. But he's run into his own delays with his project, and has yet to fit my brake kit. So that hasn't quite worked out yet.

 

That's where things are at the moment.

 

Nigel

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Where are you in Toronto? I would love to come by and check this out. Is the bolt pattern a 114.3x5?

I'm in Brampton, just north of the airport. You're more than welcome to come by and check things out in person. PM me if you're interested.

 

If you have 114.3x5, then you can use the OEM rotor without modifications. 114.3x4 requires drilling new holes in the OEM rotor, or going with the 2 piece rotor option.

 

Nigel

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My replacement shock arrived this week so I should be able to finish off my rear suspension, brake and cv shaft setup late this week or early next week. I'll get some photos to you once I can of the setup fitted. I'll only be home for about two days now for the rest of the year and I don't drive my car in winter but I'm hoping to have it out again in February so I'll get a review to you then, sorry its a lot later than I had originally planned.

 

 

Interesting what you say about pads, I've only got cheap pads in at the moment, look like I may have to change them to better ones, possibly Hawk HP+ to match the pads in the front.

 

Do both Lincoln LS and Mustang GT pads fit equally as well?

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