5-lug Front Hubs?

[roverman]

Story I heard is Miata is SLA. vs. strut ? I don't suspect many of us would convert from short/long a-arms to struts, maybe hard core drag racing.  roverman.

[MGBV8]

Correct, all Miatas are SLA.

[mgb260]

A bump for those interested in Chevy bolt pattern Big  Brakes.

[BlownMGB-V8]

So is there a car that uses an aluminum hub with a 5 lug 4.750" bolt circle (Chevy and Jaguar) pattern?

JB

[roverman]

Jim B., Yes C5 Corvette, for sure. Don't know about C4 . I've used "larger shoulder" studs, in off-set boring operation, to move the BC.  Good Luck, roverman.

[BlownMGB-V8]

Sounds interesting Art, I wonder if they used the same bearings as the rest of the Chevy line. What did they use for brake rotors?

JB

[roverman]

Jim and clan, big gnarly ones, like used on a serious, 3k lb. GT machine. 1.25x 12-13" ? I'm going with Wilwood, 2" dropped , Mustang II, forged spindles,(3x on strength), and bolt-on steering arms,(front/rear steer).Aftermarket crossmember for coil-overs,(QA-1/remote control).  Cheers, roverman.

[mgb260]

Jim, Picture of Camaro LS brakes:

[BlownMGB-V8]

Those certainly look like they'd work, but after a bit of reading it looks like C4 brakes might be the way to go. About a 7/8" (.81") thick rotor instead of 1-1/4" (lighter) 12" diameter instead of 13" (lighter, and still larger than stock) but it uses a single pot sliding caliper which is OK, but not great. I see the Mazda calipers like a .88" rotor, or .070" thicker. Might be able to mill down the mating face that much, or it might be within the minimum specified rotor thickness.

Or... Speedway has hats for $30 each, steel 2lbs (or Wilwood aluminum for $80) and rotors for $25 ea. That's an 8 lb (same weight as Wilwood) 11.75 x .81" rotor and a 3" offset on the hat. Not too shabby for new parts. Of course the hat is reusable so the extra cost to add lightness may be justified but 100 bucks for 2 to 3 lbs? That's getting pricey. Triple lug pattern which can be handy. For $60/pair the steel hats are an easy purchase and easily upgraded later if desired. So $110 for a medium-lightweight rotor set or $210 for the lightest. Or stock C4 rotors for about $80 which sounds pretty good, and available at parts stores everywhere but undoubtedly heavier, perhaps as much as nearly 16 lbs each like the Intrepid rotors on the other thread. (Are we beginning to see where the 80 lb weight loss of the Fast cars IFS comes from yet?)

The best compromise sounds like the Speedway rotors and hats with the RX7 caliper (about $65 ea reman with pads). for a total cost of around $250 plus mounting brackets. Not too shabby and also lighter than stock I'm pretty sure.

Art, those C5 hubs appear to use cartridge bearings so they won't work with MG spindles at all. Good try though. The Camaro guys are cutting down rotor/hub assemblies to work with the C4 and C5 rotors so there's no help to be found there. Jaguar apparently changed lug bolt circles when they were bought by Ford, creating a quagmire. Do any of the Japanese cars use a 4-3/4" bolt circle?

JB

[roverman]

Jim and clan, I've bushed spindle dia's-larger, and ground spindles smaller,(tool post grinder).I've welded/re-machined, Porsche 911 front hubs, for 4.75 bc.'s,(Vette turbine wheels on 914)." Dorman" makes gaggles of wheel studs, with oversize shoulders,(hint).Good Luck, roverman.

[mgb260]

Jim, Just make .035 shims for the RX7 calipers. Or even more to fine tune.My 86-91 ones had shims stock,the slot is 1" wide.They go between the pads and pistons. Use the pads for a pattern,the holes for the slider pins keep them in. You would need 7/8"-15/16" master. Would work good, very light. Did you see the 92-95 ones painted Alfa Romeo on the other thread? Also a pic on the 4 lug thread of the 86-91 Mazda caliper on hat and rotor setup(note spacer to widen it out for 1 1/4" rotor). I just ordered rebuild kit from Mazdatrix for $40 for both calipers(my junkyard jewels). Doesn't include 2 small O rings that seal the halves.Still have to buy Ceramic pads. So your price for reman is a great deal! I'm out $145 and I have to rebuild them($70-calipers,$40-kit,$35-pads)!

[mgb260]

Jim, According to Centric specs, C4 12" rotor weighs 14lb.

[BlownMGB-V8]

Chances are good it'd work just fine, the only real concern might be the pad's backing plate slipping into the rotor slot if all the pad was worn off. If you've let it go that long there's no brakes left anyway. The pins wouldn't let them go too far I guess.

On those Mazda calipers, is it possible to pull the pins and slip the pads out the back of the caliper? That is to say, would it be possible to swap the pads without unbolting the caliper from the mount? Some BMW calipers were made that way and it would be a very handy feature to have. Very nice paint work on those "Alfa" calipers btw Jim, those were right sharp.

The $65 calipers were an ebay special, no core required. Painted silver. I might just have to buy a pair of those.

JB

[mgb260]

Yes Jim, The Mazda and Toyota have a spring wire to lock the pins in. You can change the pads by pulling the pins. My Mazda calipers had 3 thin shims on each side,looked exactly like pad backing plate but thinner.They can't move because they are pinned through, just like the pads. I'll get a pic of them.You can see in the 4 lug thread picture the pad wear looked pretty even.

[mgb260]

Pics of shims, first shim toward piston stainless, angled with arrow(anti-squeal?)other 2 plain rusty steel, all about same thickness. Looks about .030. 3 on each side both calipers. Maybe to adjust to rotor after rotor is turned or these calipers were designed for  thicker rotors. The slot is exactly 1" wide where the Toyota is 7/8".

[BlownMGB-V8]

Turns out that wasn't a regular seller on the caliper and he only has the one side so the cost goes up a bit. Maybe I should look a little more closely at the Toyota calipers as they may be a better match on the rotor thickness anyway. I recall you said they are aluminum but a couple pounds heavier?

JB

[BlownMGB-V8]

OK after some review maybe not. Does the Miata use aluminum calipers? Those Lexus calipers were aluminum weren't they?  Best not forget the early GM hubs either, two spacings (drum and disc) and fairly light. Not aluminum though, I have sent an inquiry to Bill on his hubs and will report back.

I think the speedway rotors and hats are a good option if the 3" backspacing will work. Soon as the car goes back on the lift I'll look into that. A lightweight (alloy) 4 pot caliper with a 7/8" rotor slot (for .81 rotor) and pinned rectangular pads (removable without unbolting the caliper) would be optimal and we're close with the RX7 caliper. That may be as close as we can get, but maybe not. I think we still have a few options to look into.

JB

[mgb260]

RX7 calipers are most common, but also 300Z and Mitsubishi 3000(also Dodge Stealth) used aluminum 4 pot calipers. The Lexus one is huge. I think they all use a 30mm thick rotor(1 1/4").They are all rarer to find used and more expensive new. The 300Z used 3.5" mount spacing,  Mitsubishi used wide pattern like Mazda. You already know about the aluminum twin piston slider Camaro and Corvette. Newer Mustang also had a similar design. Miata is single piston slider. I think The RX7 is your best bet. The picture on the 4 lug thread shows the earlier one on a rotor/hat setup. The newer one looks a little more modern, but uses the same rebuild kit and pads. The one in the picture is spaced out for a  1.25" rotor. I don't see any problem using shims for .81 rotors.RX7 stock used 22mm(.88)rotor.Maybe they were thinking about going to 24mm and thats why the wider slot. The wider ears on the calipers actually make it easier to make an adapter bracket.Check out rockauto.com for specs on rotors and calipers. I'm not as weight conscience as you. I think the thicker heavier rotors are best for people who use their cars as every day drivers. The Toyota calipers are iron and the larger ones weigh 9-10 lbs but have excellent pads and 4 large pistons for clamping the rotor. They can also use WRX and 300Z performance pads by grinding a tab off. The small Toyota weighs about the same as stock MGB. Lighter is better for racing but I'm more concerned with stopping.

[roverman]

For those obsessed with aluminum,( count me in), said RX 7's have a very nice, forged alum. lca. Mid 80's "Supra" has a beefy, alum., uca. I suspect, both will "fudge" into Mustang II spindle.This makes front/rear steering , manual/power racks-doable. Cheers, roverman.

[mgb260]

Art, I have a picture of that setup somewhere! Might be on other computer.Found it! It is a Datsun 510 with Nissan V6. It uses the RX7 upright though.

[BlownMGB-V8]

Relative piston size is not an intuitive thing and it makes a lot more difference than you'd think whether you have 1, 2, 4 or 6 pistons. You can't just add them up because hydraulics is based on surface area of the piston, so you'll come out with square inches or square centimeters. I'm more familiar with doing these calculations in English so I start by dividing the piston diameter by 25.4  but it's not necessary. The formula is "Pie are square" (cobbler) The stock 54mm pistons then, 54 / 2 = 27 x 27{squaring} x 3.14{pi} = 2289 sq mm X 2 pistons = 4578 sq mm or 45.78 sq cm.

Here's why I like working in inches. 54 / 25.4 = 2.126... / 2 = 1.06... x 1.06 = 1.13...x 3.14 = 3.55... x 2 pistons = 7.1 sq in. You can almost estimate it in your head. To me they are just easier numbers to work with and to visualize. But there is an extra operation.

So the twin piston 54mm caliper has about 46 sq cm of area. Working backwards for a 4 pot caliper we get a 38.18 mm piston, nearly the same size as the RX7 caliper, only .18 mm or about .007" smaller. So the stock master cylinder and rear brakes should work fine with this one. If anything the pedal may be a smidgen firmer though in reality you'll never even feel it.

What about  1 piston calipers? Those used to be sized in inches and it would take a 3" piston to match the stock area or about 76mm. That's fairly big. My Mach 1 Mustang brakes had a 2.38" piston or 28.7 sq cm which explains why the balance bar had to be adjusted almost all the way to the front to get balanced braking. (don't forget when you are converting area the conversion factor has to go through twice)

You can calculate the increase you need in the MC and rear slave sizes too, although converting from drum to disc is not as straightforward because drum brakes are self-actuating among other things. Still, a 10% size increase at one end, coupled with a 10% increase at the other and a 10% increase at the MC will work out just fine. Where you get into trouble is when the percentages quit matching, you go to rear disc, or something along that line.

My next task it to determine the piston size of the Jaguar XJ6 rear brake caliper and the piston size of the XJ6  front brake caliper piston. With those dimensions in hand I can determine the appropriate piston surface area for the 4 pot front calipers, and the balance for that system in an MGB should not be much different than what is used in the stock XJ6. Any error can be easily taken out by the balance bar.

The 1-1/4" thick Speedway rotor is the same price as the .81" version and 8.7 lbs vs 8 lbs so not a real severe weight penalty. With the steel hat that's 10-11 lbs each. This opens a wider range of calipers as usable.

JB

[mgb260]

Very scientific , Jim!  I based my estimates on master cylinder size on what was used in the stock vehicles.RX7 used 15/16",small Toyota used 7/8" and large Toyota used 1". MGB stock 3/4". The Nissan Z guys like the 15/16" 79-81 ZX master with the small Toyota calipers,probably for a firmer pedal. They also go to 1" master when using the large Toyota calipers because excessive pedal travel. Jim, check out the 90-92 Nissan Z calipers for 1 1/4" rotor or Mitsubishi 3000 GT (Dodge Stealth)  or Lexus LS400. Rockauto.com has caliper specs. Not as common but meant for thicker rotor.You can always use a spacer in the more common Mazda RX7 caliper.

[mgb260]

Jim, I did some research for you, all these calipers are meant for 30mm thick rotors except the Lexus LS400 which is 32mm.  91-93 Mitsubishi 3000 GT VR4 and Dodge Stealth Turbo have huge 2.25" pistons. The 95-2000 Lexus LS400 has 1.68" pistons, 90-92 Nissan 300ZX Turbo have the smallest pisons at 1.59".

[BlownMGB-V8]

I got the piston sizes for the XJ6, 48mm front and 43 for the rear. Front is 4 pot, rear is 2. The area of the front pistons is 11.2 sq in (72.26 sq cm) and the rear is 4.5 sq in (29 sq cm). The area in metric in this case gives a near perfect snapshot of the front/rear proportionality at about 70/30 give or take a point or two. Weight distribution is identical to the MGB. Readily available big piston aftermarket calipers max out at about 1-3/4" or 44.5 mm which would shift the balance towards the rear a bit, 68/32. Use of the RX7 calipers would give 60/40 which I've seen quoted as generically ideal.

So there's the range. Anything between the RX7 caliper and the big piston aftermarket units is going to work, and any of those should be within the range of adjustment and use of my balance bar/dual 3/4" MC setup. (Roughly equivalent to a 1-1/16" single cylinder except in total volume as that is evenly split front to rear.) In all probability the smaller one will have to be balanced towards the front and the larger towards the rear but in either case probably not as drastically as it is now as both those proportions should be within a workable range. My gut tells me to go for the higher distribution to the front. Time to shop for calipers.

JB

[mgb260]

picture of caliper spacers: