Nigel

I haven’t found a way to calculate brake torque for drum brakes. Apparently they have a non-linear curve in relation to hydraulic pressure. So calculating the stock bias of an S30 isn't easy. Regardless, there is no one magic ratio though because there is so much variability between our cars. However, a 280ZX has a 63.5/36.5 split. Assuming an S30 has roughly a similar CG, that’s a starting point. Just from anecdotal evidence, around 70% front bias appears to be borderline. I’d avoid anything beyond 70% front bias. There are on-line brake force calculators, or you can create a spreadsheet, so you don’t have to calculate everything out by hand. You just have to make sure you understand the parameters you’re entering. Seatlejester, I’m curious where you got your brake rotor diameters for your SX and 280ZX rear brake calculations? The data I have shows the Z31 rear rotors used with the SX swap are 290mm, and I wasn’t aware of a ZX swap that uses anything other than ZX rear rotors, which are 258mm for ’82 rotors. Earlier ZX rotors 269mm. Nigel

271mm - 27mm is the rotor diameter minus the piston radius. You want the difference of the radius of both (or diameter of both divided by two). So, 135.5mm - 27mm and 135.5mm - 21.5mm.

You forgot to show Pi in your equations, but your results look right. However, yes, you do need to take into account the leverage arm of the rotor. But, it's not as simple as using the OD of the rotor. You're not actually applying full force at the OD. You have to subtract the pad height from the OD, since the force is averaged to the middle of the pad height. Finding pad height is not easy though, so I typically assume it's the diameter of the largest piston. Nigel

I forgot to mention that there are two versions of the 240SX rear caliper as well, which adds to the confusion even more. There's an early 34mm piston version, and a later 38mm piston version. The bias ratios I gave are for the 34mm version. However, even the 38mm piston caliper is marginal with the V6 4-Runner front caliper, but would be well matched with the 4x4 caliper. V6 4-Runner: 43mm/43mm I4 4-Runner (also vented rotor): 43mm/34mm 4x4: 43mm/34mm While the difference may seem small, a 43mm piston provides substantially more clamping force than a 38mm piston. Piston surface area is one of the factors. Hydraulic pressure, rotor diameter and brake pad co-efficient of friction are the others. Brake pad surface area has nothing to do with it. Leon got the rest of it.

There's a huge difference between the non-vented 4x4 calipers and the vented V6 4-Runner calipers. The non-vented caliper piston surface area is not that much bigger than stock 240Z calipers. It's only about a 3% increase. The V6 4-Runner calipers have an almost 27% increase in piston surface area! That results in a huge difference in brake torque. So, saying your "Toyota" front brake and 240SX rear brake combo is balanced is meaningless without specifying exactly which Toyota front calipers you have. Keep in mind that stock 240SX front brakes are actually LESS "powerful" than stock Z front brakes. So, don't expect 240SX rear brakes to be suited to anything more than stock Z front brakes. An engineered solution is doable. It's just a matter of gathering the appropriate data and doing the math, which is all available on-line. It's not voodoo magic, or guess work. By crunching the numbers, I can tell you that a V6 4-Runner/240SX brake combo has approximately a 74/26 front/rear bias, assuming equal pad coefficient of friction and full line pressure to the rear brakes. Non-vented 4x4 caliper/240SX brake combo has approximately 70/30 front/rear bias. To expand on Leon's answer about excessive front brake bias, you need an adequate combination of front AND rear brake torque to transfer load to the front wheels to increase their grip to take advantage of the additional brake torque that bigger front brakes can generate. Without the rear brakes contributing enough to that load transfer, the front brakes will easily overpower the friction between the tires and the road and the front wheels will lock prematurely. Consequently, longer braking distances! And don't be misled by those "Big" front brake kits you see advertised for newer cars into thinking that excessive front bias isn't an issue. Those big front brake kits don't actually generate any more brake torque than the stock front brakes. Even though the rotors are enormous, and the calipers may look huge, the calipers actually have tiny little pistons in them to keep the brake toque in-line with stock, so as not to throw off the factory brake bias. Nigel

Not yet. Hopefully I'll have some nice outdoor pictures in few days.

Here's the finished vent with a quick coat of paint: I'll take a better picture when I get the car out of the garage. Nigel

Glad to hear it's working for you! BTW, have we met? Nigel

4mm isn't likely to be a show stopper, but it's worth another look. Now the driveshaft shop? You just can't catch a break! Unbelievable!

4mm isn't likely to be a show stopper, but it's worth another look. Now the driveshaft shop? You just can't catch a break! Unbelievable!

I measured this as 30mm. As per my write-up, I replaced these unused switches with 14mm drain plugs, avoiding any interference issues. FYI, you can swap out the 240SX electronic sending unit with a 280ZX mechanical unit and use the stock Z speedo. This is also in my writeup. Nigel

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

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. Nigel

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

That's a huge master cyclinder for rather small calipers! Have you actually tried it yet? Nigel

Great topic! I'd love to see a discussion of this too. With modern cell phones and tablets with built in G sensors, braking force datalogs should be possible too. I'm hoping to run a few tests myself this summer. Nigel

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. 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

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. Nigel

Thanks for the positive feedback everyone! 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. 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

I did read that. But thanks for the reminder not to get too focused on the diff. However, I have an RT front mount with a poly bushing, and poly bushings in the mustasche bar, so the diff itself isn't going anywhere. I have CV axles, and I've had three difference transmissions in the car, and two different driveshafts, none with any discernable play. It definitely sounds and feels like the diff teeth clacking together. The poly bushings don't help to dampen it much. Regardless, it's not a huge concern, but I thought perhaps I could remedy it somewhat by getting the backlash back in spec. It turns out that there's a driveline shop down the street from work that a coworker knows the owner of, so I'm going to bring the diff there for final setup. With 20+ year old parts, experience starts to count more than specifications and precise measurements. Nigel

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: Uses OEM parts where possible for ease of service and availability of parts. Has an integrated parking brake oriented such that it will not interfere with CV axles. 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. Has a wide variety of pad compounds available from multiple manufacturers. 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. Is as light weight as possible. Does not require removal of the caliper to bleed the brakes. 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: Custom parking brake cable with stainless inner cable. No modifications required to cable sleeve mounting brackets under the car. Caliper attached to prototype aluminum bracket and parking brake cable attached to caliper. Note: production bracket will be anodized. 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. Finite element analysis of 1/2" thick, 6061 aluminum bracket. So, is anyone interested? Nigel White

Thanks Dave! I should have the completed part back in a couple of weeks. I'll keep your delivery service in mind. Can you bring an LS1 over Nigel

Thanks for the reply Jon. I don't have the FSM in front of me, but it does state to check the pinion preload before disassembling anything and again at the very end of assembly. It does also mention checking it when setting up just the pinion, which is probably what you're thinking of. I've run the 3.7 with the LSD for years, and I could really feel that 8 to 9 thou backlash. Other people who drove my car even commented on it. I hoped to tighten it up a bit, but maybe going to 0.005" is too much? I guess it's a gamble if I throw it in the car like that though. Nigel

Does anyone bother to check this after swapping in an LSD carrier? I just transfered an LSD carrier from a 3.7 to a 3.54 diff. I tried the side shims that came with the 3.54, but the backlash was .011, so then I put in the shims that came with the 3.7 and that dropped the backlash to 0.005. Both diffs were between .008 and .009 before. With the 3.54 shims, the shims slid in easily. With the 3.7 shims, I had to give the last shim in a few taps to get it to seat. But when I measured the rotating torque on the pinion, it was only about 3 inlbs. The spec calls for somethinig like 10 to 20 inlbs. No side seals or stub axles installed yet though. I've read all of the threads I can find on swapping an LSD carrier, but no one mentions checking the preload. They only ever talk about measuring the backlash. Should I worry about this? Also, I did the math in the FSM for determining the side shims needed, assuming that the different bearings won't make a significat difference. According to the numbers, I should only need about a 0.05mm thicker shim on the left side to get the right backlash. But the left side shims from the 3.7 are actually about 0.3mm thicker. Still, like I said, this gave me a backlash of 0.005, which is within spec. The 3.7 right side shim is not quite proportionately smaller, so I get a bit more bearing preload, but judging by the input torque, it's not excessive. I'm going to try marking the teeth to see if the wear pattern is ok. Any thoughts or suggestions? Nigel

I've had the competition hood scoop on my Z for a couple of years now (here's a link to my album of the install: http://www.motortopia.com/album/28569). I mostly like the looks of it, but was never pleased with how angular the nose is. It doesn't match the contours of the hood's original power bulge at all. So, I decided to gamble and hand the vent off to a guy I know with decades of fiberglass experience (custom yacht builder) to reshape the front of the vent. I finally got a look at the progress yesterday. Overall, I think he's done a great job. The only thing I've asked him to do is add a bit of material to the very front so that it come to more of a point where it meets the hood. On a side note, he was concerned about the fact that the vent has no support through the length and believes it will sag in the middle over time. I suggested glassing in a support on the underside along the length of the vent. But he was concerned that the support will eventually distort the top. Given his experience with fiberglass, I'm sure he's right on both counts. After talking it over, I'm going to weld in a rod that goes from the front to the back of the cutout in the hood, and possibly from side to side like a + sign. In the middle of that I'll weld in a threaded block that I can put a height adjustable rubber bumper on, like the bumpers that support the rear corners of the hood. Nigel