13" Wheel Rear Disc Brake Discussion

[Byron510]

Good day all,
So the simple question is, what have you guys done to make rear disc brakes work under 13” wheels. And more importantly, what rotors and calipers made the combination work?
More specifically, what ideas - or even packages - are available out there to build (or buy) a rear brake set up that will fit under 13x7 - Zero offset wheels utilizing the Wilwood Dynalite caliper – if possible?

I would like to utilize the Wilwood Dynalite caliper as this is what I am using up front, mostly so that I can keep the same pad and compound on both ends of the car. This is my biggest struggle at the moment – maintaining compound balance through the heat ranges.

Recently I have been looking at this, and found through a friend (JasonLee) that the 200SX (82-84 S110) rotor and the Dynalite caliper is just a hair to large in radius to fit under the 13x5.5 12mm offset Libre wheel that we tried – assuming the 13x7 wheel is the same ID. In fact Jason told me he felt a tiny bit of filing on the caliper likely would have done the trick and daylight could be made visible easily enough. The limiting factor in making the caliper mounting radius smaller to clear the inside of the wheel is the caliper actually coming in contact with the hat “hub” OD section.

Personally, I was hoping that a solid rotor hat from an OEM application would be available to make this work with a Dynalite caliper. I really don’t think the weight of a vented disc is necessary in the rear – they hardly get that hot as it is compared to the ZX rotors up front. And with the pad compounds today, heat hasn’t been a limiting factor (maybe I need more power, but that’s another discussion).

The alternative is to make my own hat and utilize an available racing type rotor. The only issue here is that available racing rotors seem to be 10.5” or larger. The 200SX rotor is 10.156”, so design around a 10.125 or 257mm OD disc would be ideal.

The second thing that I would like to add here is that I will be utilizing 2 calipers per side on this set up – to make the separate E brake system, keeping the set up road legal. So on one hand I talk weight, and on the second I talk about adding a second caliper – I know these two ideas don’t meet, but we are required to have a hand brake system legally, and I should engineer this into the whole package.

So to the few that have retained the aging 13” wheels for Vintage Racing or similar categories, what have you done to make rear disc brakes work on your 510? Love to hear from you.

Byron

[bertvorgon]

I believe I have the 200 sx rotor and of course used the BMW 2002 FRONT caliper on the rear of mine.

They cleared my 13" x 8" zero offset PANASPORT wheels no problem. Now that being said, my Panasports in the day were like TODAY'S Race only Panasports, so were quite thin. Wish I had made note of how much clearance I had rotor to rim.

There is a TON of pad choice due to the vintage racing of the 2002 BMW crowd. That is a 4 piston caliper and with my
front BrakeMan/Wilwood/JFZ/DYNALITE size caliper, I have had no issue with brake bias balancing, more than enough latitude front to rear with my old Direct Connection bias adjuster.

[icehouse]

Me and Sam are working on a disk conversion for the rear of our Eunduro car. The Drums needed to be adjusted way to often and made the pedal feel yucky much to quick after re adjusted and sent back onto the track. We have a set of Z32 rear calipers and z31 rear solid rotors. Which are bigger then the S11 or S12 rears. The model will be easy to adjust though if needed. I would like to run them under 13's with a non vented rotor.

[JordanTr]

Infiniti M30 may be a good option since I think they had high offset rotors and are 4 lug out of the box. They may be the same as z31 4 lug but can’t say for sure at the moment.

[JasonLee]

Hi Byron,

I understand you wanting to use a matching set of calipers, front and back, so that you can match brake pad compounds to get consistent 4 corner brake fade. You already have the fronts, so why change all four if you can get Wilwood Dynalite rears to work? I am going through this exact project right now. My car came with Dynalites all the way around, and the rears are the ones with the 3.75" bolt spacing. Dynalite also makes a caliper with 3.25" bolt spacing, and the smaller of the two is the ideal size to use if the plan is to install two rear calipers per side. Twisted Image builds a dual rear caliper bracket that accommodates the 3.25" caliper.

http://www.twistedimages.com/Twisted-Im ... p_154.html

But my car came with the 3.75 ones, and I didn't want to go backwards, so I acquired a matching set of 3.75" calipers. There is still plenty of room to mount the wider caliper but you do lose an inch of flexibility. Again, the motivation is to reintroduce a E-brake system back into the car and to make it street legal again. And to maintain the option of using 13" wheels. When I test fit one of your rims, the inside of the wheel grinded on the two caliper mounting ears when I tried to turn it, which would be the same regardless if using the 3.25 or 3.75. But I could still turn it by hand, so the smallest amount of material removed from the wheel or caliper mounting ears would solve that problem.

Back the bracket. I referred to the Wilwood instructions and was quite literal in my interpretation. It states that with the 3.75" caliper and a 10" diameter disc. the bolt circle should be 91.7 mm. If the disc is 10.25" diameter, then the bolt circle should be 94.2mm. The 200sx disc is 10.156" I believe, so I extrapolated to get a bolt circle of 93.37mm. But this doesn't take into consideration the diameter of the hub hat, which would appear to be the critical variable when fitting these calipers, yet the Wilwood instructions treat this variable like it doesn't matter and don't comment on it. Now unfortunately I am not quite operating at Jordan's level, so I made a paper model with a steel ruler and a student compass, and then transferred this on to 3/8" aluminum plate. My error was proceeding with the project to completion before verifying that the mounted caliper would clear the hub. I checked the fitment of everything but this and then completed the brackets including installing steel threaded inserts (Time Sert) and polishing the perimeter. They don't fit! The issue is that I should have gone with a slightly larger bolt circle. But how large? Should I use the stated bold circle assuming the disc was 10.25? I want to use the smallest bolt circle as possible so that I don't use up precious room that 13" wheels need, but don't know how to figure that dimension out. I am not interested in expanding the bracket mounting holes to get this all to fit, as it would be sloppy and end up in different position every time I installed it. The best option is to simply make another bracket, but only after I know what the ideal bolt circle should be. The other is to create some clearance by machining the hub hat a bit smaller (1-2mm?) and filing down the lowest portion of the caliper. As it is now, I would have to remove too much material off of the caliper to make it fit if this was the only variable that I could adjust. I am tempted to create the room I need by clearancing the hub hat with a 1" wide band that is 2mm deep, and fine tune the fit by removing material from the caliper. The rotor hub is over engineered and wouldn't lose enough strength to matter in my opinion. The brackets are done after all, with the minor exception of them not fitting.

[JasonLee]

Cant figure out how to get multiple pictures up in one post.

[JasonLee]

I just had an ideal. I had slightly less than the required room to spin a 13" rim with my calipers mounted onto the original bracket, before I tore things apart. Now I have a bracket that will require the hub hat to be turned down 1-2mm to make fit. Which is the same thing as using a smaller bolt circle than it should have had, which means that I have come a lot closer to being able to spin a 13" rim without any further modification. Byron, this might be the formula you are looking for.

[JordanTr]

Why not shave a caliper once and then you're good to go for off the shelf calipers?

Confirmed M30 rotors are indeed a taller hat to accommodate internal ebrake drum. Perhaps that will help free up some space on the OD so that the caliper can be pushed off the hat hub? Would require a large offset bracket to make it work. The height of the rotor may even interfere with the control arm?

No definitive solutions but some ideas to spitball anyways!

Unfortunately, I couldn't easily find numbers below to compare to S110 or S12 200sx rear rotors.

M30 rotors (Centric 121.42013) compared to Z31NA rotor (121.42021):
M30 '84 Z31 NA
OD: 265.9 290
Height: 69.4 47
Thick: 10 10
Hub: 68.1 68
Pattern: 4x114.3 "
Wt: 11.5lbs 10.75

The brackets are done after all, with the minor exception of them not fitting.

Doh! Hate it when that happens!! We've all been there.

Would agree that the hub is likely quite over-engineered but that also makes it nice and safe! Perhaps a combo of slotted mounting ears and machined hub hat if you have the room? At least the bracket will see much less thermal cycling.

[Byron510]

Very interesting input gentlemen - thank you very much.

Jason, what is the hub OD and offset on the S110 rotors by chance - larger or smaller than the 68.2 and 69.4mm and overall OD at 265.9mm that Jordan measured of the M30 rotors?

It may be time to get on this project after all.

On the flip side... I had Jordan, Jason and Mr Vorgon chime in - anyone else out there have a Wilwood Dynalite brake caliper under a 13" wheel?

Byron

[JasonLee]

Byron, the OD of the rotor hub is 170mm, and as far as offset is concerned, all that is required to get the caliper lined up with the rotor is a 1mm shim against a flat bracket. There is no requirement to make a complex offset bracket with the Wilwood caliper. Just a piece of 3/8" aluminum (or 3/16" steel) and a 1mm shim. Can't beat that in terms of simplicity.

[GREG510]

Hi Byron, I have dynalites with the the 200sx rotor. My caliber brackets are very similar to Jason's.
Will post more pics when I can find them.
They are Under my 13'' Carol Shelby libras as well

[JordanTr]

The condemning ID for Q45/Z32 internal drum ebrake is 173mm and I'm 99% sure M30 would be the same which puts the hat OD certainly larger than the S12 and similar rotors. Perhaps 182-184mm OD?

[510rob]

I vaguely remember that the larger Superlite calipers can be fit within a smaller radius than the Dynalite calipers can. Something to consider.

Compare spec "E" in the two charts, for the same sized rotor...

https://www.wilwood.com/Images/Caliper/ ... -cm-lg.jpg

https://www.wilwood.com/Images/Caliper/ ... -cm-lg.jpg

maybe there is another spec I am overlooking elsewhere that would make them unsuitable though...

[JasonLee]

I just looked at those links, and the second one looks like it could fit under a 13" rim. But only one will fit. Both of these rotors are too large to be able to fit two in side by side, with one to be used as the E-brake. In the Wilwood lineup, the Dynalite 3.25" of 3.75" seems to be the only reasonable option. With the 3.75" that I am using, I have less than an inch of room on each side before they contact with control arm, and have an inch separating them as well.

[cartel]

Dp racing makes a bracket- i have more parts coming up in a few weeks if you want a set of the brackets be about $120 landed here

Part Number: 401-9510 is the kit





Rear brake kit, Datsun 510. Includes 10.25” dia. x .39” thk. solid rotor, (2) piston Wilwood Dynalite Single calipers, brackets, brake pads, and hardware except for the brake line. Fits 13” diameter wheel.