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Thread: Rear Drum to Disk Conversion

  1. #1
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    Default Rear Drum to Disk Conversion

    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. However, with the right pads and an adjustable proportioning valve, this kit should be suitable for just about any front brake setup.
    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:


    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.


    Once I have at least ten interested people, I'll do a production run. I have a few people lined up already.

    Nigel

  2. #2
    1978 280Z (stock) TomoHawk's Avatar
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    Default

    If only we could get someone like you interested in designing a beter cylinder head for the L28 engine...
    Drive Responsibly.
    enjoy classic Rock music.

  3. #3
    Registered User LeonV's Avatar
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    Default

    Quote Originally Posted by TomoHawk View Post
    If only we could get someone like you interested in designing a beter cylinder head for the L28 engine...
    What's the reasoning for this?

    To stay on topic, I already commented on HBZ but I'll say it again. I appreciate the great effort and engineering that you've put into this. When I decide to upgrade to rear disks, this sounds like a great option.
    2/74 260Z

  4. #4
    1978 280Z (stock) TomoHawk's Avatar
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    I mean some who selflessly put in his whole professional experience, talent and time to do a thorough and complete job, with some options, not just the minimum to get by.
    Drive Responsibly.
    enjoy classic Rock music.

  5. #5
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    Quote Originally Posted by TomoHawk View Post
    I mean some who selflessly put in his whole professional experience, talent and time to do a thorough and complete job, with some options, not just the minimum to get by.
    Sorry it's taken me so long to respond to these messages. I don't spend much time on classiczcars, and all of my classiczcars e-mail notices were going in my junk mail folder!

    Thanks for the postive feedback. This has been a tremendous amount of work, but I hate half-assed solutions! I've actually tried 3 other popular rear disk conversions and I wasn't happy with any of them for various reasons.

    There have been a number of developments since I first started this thread. I don't have time at the moment to summarize all of them, but I will try to do so soon. Or, you can check this thread out:

    Yet another rear drum to disk conversion option! - Vendor's Forum - HybridZ

    Nigel

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