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Thread: rear disk brake conversion

  1. #51
    Join Date
    Jan 2004
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    Michigan
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    70 '02 / 85 557e
    VW rabbit rotors, the hub needs to be turned/machined down some.
    www.classicdaily.net
    1970 m42 swapped 2002
    1985 LS1/T56 Swapped e28 (557e)

    Follow me on Instagram for constant build updates @classicdaily

  2. #52
    Join Date
    Aug 2001
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    NC
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    E30M3,318is,318i,E21320
    Quote Originally Posted by captain awesome View Post
    What rotor are the people using with your bracket and does it require any machining? Rabbit MK1 front rotors like mentioned above?
    Yes MK1 rabbit front rotors (solid ones) are what I used also. Calipers I chose are light weight MK4 aluminum rears off a 95 GTI.

    I dropped the hubs to the machinist with a mk1 rotor and let them turn to exact fit inside the hat.
    Last edited by autox320; 01-08-2019 at 12:29 PM.
    88 M3
    91 318is
    91 318i
    83 320is
    08 X3 3.0si

    "If it flys, floats, or f*cks, rent it!"

  3. #53
    Join Date
    Feb 2019
    Location
    Finland
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    1
    My Cars
    BMW e21 m30b28
    JakeB do you still have brackets left? I would like to buy one set

  4. #54
    Join Date
    Mar 2016
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    Bentonville, AR USA
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    91 318is - 83 320is
    Does anyone have the dimensions of what the 320i rear hub will need machined to? I'm assuming 65mm to fit the VW rotor, but what is the e21 hub dimension before hand?
    91 318is
    83 320is

  5. #55
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    Michigan
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    70 '02 / 85 557e
    Quote Originally Posted by Hunnari View Post
    JakeB do you still have brackets left? I would like to buy one set
    yes here they are. https://www.classicdaily.net/product...rake-brackets/

    I also make a bracket that allows the stock ebrake cable to attach. Those are not on the site yet but are $40 for a pair.
    ALSO I will be offering the service to turn down your hubs very soon. Just got my lathe working.
    www.classicdaily.net
    1970 m42 swapped 2002
    1985 LS1/T56 Swapped e28 (557e)

    Follow me on Instagram for constant build updates @classicdaily

  6. #56
    Join Date
    Aug 2001
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    NC
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    E30M3,318is,318i,E21320
    Quote Originally Posted by JakeB View Post
    yes here they are. https://www.classicdaily.net/product...rake-brackets/

    I also make a bracket that allows the stock ebrake cable to attach. Those are not on the site yet but are $40 for a pair.
    ALSO I will be offering the service to turn down your hubs very soon. Just got my lathe working.
    Hey Jake what bias valve do most use with this conversion? Currently I've a wilwood, but testing a stock e30 dynamic valve. Street use I can easily get away with the fixed knob wilwood, but for track the rears can still lock after hot brakes and hot tires. Do most use the stock bias valve?

    Another point brought up is piston displacement. These vw calipers are 38mm. Rear wheel uprated cylinders are 19mmx2 so again same 38mm. In theory should be the same and I believe the proportioning valve is the X factor in these setups.

    Much like the Brembo fronts, the VW aluminum mk4 rears are super lightweight.
    88 M3
    91 318is
    91 318i
    83 320is
    08 X3 3.0si

    "If it flys, floats, or f*cks, rent it!"

  7. #57
    Join Date
    Mar 2016
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    Bentonville, AR USA
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    91 318is - 83 320is
    Ditto on the bias stuff. The factory rear calipers for 323 or 320/6 are either 27mm in the early years or 33mm in the later. I'm probably going to ditch my mk4 calipers (41mm) and try to fit some from an early Hyundai Elantra/Tiburon to get a near factory brake bias. I don't think they are as light as mk4 stuff, but at least they are 34mm vs 38/41 and there are tons of pads available. They also have an integrated parking brake like the VW but have a different bolt spacing, 100mm for the Hyundai and 90mm for the VW bracket. The offset looks the same as an mk3 bracket setup, but until I get one in my hands not sure. Once I get one here I can measure to see what rotor will work best, but I'm betting the VW Rabbit will do just fine.

    Also to answer my question earlier the e21 rear hub is ~141.5mm outside diameter and the VW rotor is ~135mm on the inside diameter of the hat. I was unsure what needed machining earlier, but now I see it's not the center bore that's an issue, but the inner hat of the rotor. There are plenty of other rotors that will fit over with similar offsets, so we will see what works best for these.


    Edit: After a bunch more eyeball and internet measuring I'm pretty sure the mx5/miata rear caliper may work as well. It's 32mm, cable operated parking brake, about the same weight if not a fraction less than the vw mk4 stuff, and I "think" the same bolt spacing as the VW stuff. I got a cheap one on ebay to test fit on the way now and will post up when I figure out if it will work. The pads are super inexpensive for performance stuff, and the pad area is still larger than the 323 or 320/6 stuff.

    95 miata vs e21 rear pads by hatchethairy, on Flickr

    95 rear mazda caliper 32mm b by hatchethairy, on Flickr

    95 rear mazda caliper 32mm d by hatchethairy, on Flickr

    95 rear mazda caliper 32mm a by hatchethairy, on Flickr

    95 rear mazda caliper 32mm c by hatchethairy, on Flickr
    Last edited by captain awesome; 02-20-2019 at 05:02 PM.
    91 318is
    83 320is

  8. #58
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    Mar 2016
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    Got the Miata caliper in a while back, but haven't had a ton of time to mess with it yet. I need to get my hubs machined before I can fit up the rotor to check if the Miata offset will work or if spacers/shims could correct any misalignment. The Miata caliper does bolt up to the VW brackets I have, and appear to be in the proper position. I am going to get some measurements to post up soon with comparisons to the mk4 calipers. I don't have mk3 brackets in hand so I don't have them to compare with.
    91 318is
    83 320is

  9. #59
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    NC
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    E30M3,318is,318i,E21320
    Quote Originally Posted by captain awesome View Post
    Got the Miata caliper in a while back, but haven't had a ton of time to mess with it yet. I need to get my hubs machined before I can fit up the rotor to check if the Miata offset will work or if spacers/shims could correct any misalignment. The Miata caliper does bolt up to the VW brackets I have, and appear to be in the proper position. I am going to get some measurements to post up soon with comparisons to the mk4 calipers. I don't have mk3 brackets in hand so I don't have them to compare with.
    What year miata? I'm looking at 1995 cause can get race pads for them. Appears early years don't have as many options for compounds.

    Hey man thanks for the info. I'm guessing some run the VW 38mm and 41mm rears without issues, but I'm at the edge of bias. My bias valve is all out (57%) and it's not enough with race pads and dotR tires. After crunching numbers in a bias calculator I'm swapping to E30 33mm calipers. The miata will work but the pad area is a bit much(larger area seen by the rotor rotation) which will make them less effective. They would still be able to dial in with a bias valve though only being 32mm (-more for pad) so probably few turns extra on the knob for rear increase of bias. I'm working my way toward this part of the car so not 100% settled on the e30/miata. I could go either way. Liking that its a VW bolt on

    Why is this a deal for our rig setup? Well when start chopping a car for weight the rear always ends up lighter than the front. Moving the engine back and everything inside the axle centerlines helps. You'll still get lots of weight transfer when under the most load ie braking hard from triple digits in a straight line (end of front and back straightaways). A bias of 55 front 45 rear can dip below 40 for the rear needing less bias at extremes due to the rear tires are unloaded more. Some set at slow speed like a trailer brake and ok for street. Street driving most can set and probably will never notice unless panic braked on the interstate . When on the track and the rears slightly lock before the fronts, it gets very hairy. The back end will try to snake around stepping out on you. Which is the last thing you need slowing from buck20's into a downhill off camber turn.

    If running stock sized 48mm pistons up front the vw 38mm (and probably the mk3 36mm; definitely the 41mm) are just a bit too much in the rear IMO. So avoiding a wilw$$d setup I'll use another stock caliper. Only downside is i'll have to give up the FEATHER weight 1.5 lbea vw mk4 aluminum calipers

    PFC11 race pads for the e30 rears are $130
    miata $160

    centric calipers; 91 e30 $61.79ea including core charge (if have core they are only 36.79ea)
    centric calipers; 95 miata $117.79ea including core charge (if have core they are only 47.79ea)
    Last edited by autox320; 03-14-2019 at 12:05 PM.
    88 M3
    91 318is
    91 318i
    83 320is
    08 X3 3.0si

    "If it flys, floats, or f*cks, rent it!"

  10. #60
    Join Date
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    NC
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    E30M3,318is,318i,E21320
    Quote Originally Posted by captain awesome View Post
    Got the Miata caliper in a while back, but haven't had a ton of time to mess with it yet. I need to get my hubs machined before I can fit up the rotor to check if the Miata offset will work or if spacers/shims could correct any misalignment. The Miata caliper does bolt up to the VW brackets I have, and appear to be in the proper position. I am going to get some measurements to post up soon with comparisons to the mk4 calipers. I don't have mk3 brackets in hand so I don't have them to compare with.
    Can you weigh for giggles one of the miata calipers and oh what year it is? thx
    88 M3
    91 318is
    91 318i
    83 320is
    08 X3 3.0si

    "If it flys, floats, or f*cks, rent it!"

  11. #61
    Join Date
    Mar 2016
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    Bentonville, AR USA
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    91 318is - 83 320is
    I'll have to check weight this evening, but with it being Miata based it's fairly light. They don't feel heavier than the VW mk4 ones I have which are aluminum.

    Are you sure they are 1.5 lbs? Mine were around 5 with bracket, I can't imagine the weight between the 41mm and the 38mm being that drastic in difference. I have used Autozone to compare weights to them before with decent accuracy and here's what they have listed.

    MK4 ~5.3 lbs
    02 Miata ~5.0 lbs
    e30 ~5.5 lbs

    The year Miata I purchased is 99 through 03 I believe. I would probably go e30 if e-brake wasn't an issue when running in SCCA events.
    Last edited by captain awesome; 03-14-2019 at 12:32 PM.
    91 318is
    83 320is

  12. #62
    Join Date
    Mar 2016
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    Bentonville, AR USA
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    91 318is - 83 320is
    Also, I just realized the Miata calipers are typically positioned at the ~10 o'clock position not ~2 o'clock. I'm trying to visualize whether this would cause clearance issues on an e21 arm, but can't think of anything that would be in the way.
    91 318is
    83 320is

  13. #63
    Join Date
    Mar 2016
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    Bentonville, AR USA
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    91 318is - 83 320is
    So I weighed the VW calipers and they are around 4 lbs without pads. The Miata ones are roughly a pound heavier, so there would be a weight gain. I snapped some pics of both side by side, and I "believe" the VW calipers are with the mk4 sliders. If I understand correctly the mk3 sliders are the ones to use. I installed the adapter brackets to both for comparison of where it would locate them.

    Untitled by hatchethairy, on Flickr

    Untitled by hatchethairy, on Flickr

    Untitled by hatchethairy, on Flickr

    Untitled by hatchethairy, on Flickr
    91 318is
    83 320is

  14. #64
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    NC
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    Decided. . . I'm moving to the e30 calipers. One side is almost finished today. I remeasured the veedubs, your right man. I don't know how I had 1.5, weighed mine at 3 lbs even each. Brackets were 1.3 lbs so 4.3 lbs total for the aluminum ones. I have deleted my ebrake hardware on them so probably the slight difference.

    I just weighed the steel E30 33mm caliper with bracket slider, pins, and full hardware. . . 4.6 lbs ea Damn whatever lol

    I'll be sure to post in the build thread when get a chance.
    88 M3
    91 318is
    91 318i
    83 320is
    08 X3 3.0si

    "If it flys, floats, or f*cks, rent it!"

  15. #65
    Join Date
    Aug 2001
    Location
    NC
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    E30M3,318is,318i,E21320
    Yo Derrick. Man run some exact figures in this calculator and see what you come up with. For a car with more rear weight the miata calipers may work. I'm not sure they'd work for me or would be on edge using the bias valve(most way in adding rear brake). Miata just may be a bit small?, and pad a bit large (less effective). My bias knob is now over half way in to start locking the rears with e30 calipers 33mm piston and smaller pad. Food for thought. Made some test runs and posted this in my build thread.

    Shot some carb cleaner through the jets of the carb. Fired up, warmed up, made a few test runs to adjust the brakes. Much much better. Car seems to stop better and the bias valve is over half way in to start locking the rears now. Our car weight distribution is 55% front 45% rear on the scales. Under hard braking it's probably dipping below 40% in the rear easy. The e30 rear 33mm calipers and pads seem to be within range of the bias knob doing something now. Fronts are 48mm just like factory 320 calipers.

    A basic bias calculator lets you see what changes affect what for an idea what to do. I plugged in figures into this calculator. http://www.tceperformanceproducts.com/bias-calculator/
    88 M3
    91 318is
    91 318i
    83 320is
    08 X3 3.0si

    "If it flys, floats, or f*cks, rent it!"

  16. #66
    Join Date
    Mar 2016
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    Bentonville, AR USA
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    91 318is - 83 320is
    I’m out of town in Texas for a few more days but when I roll back in there are some goodies for me to test fit. I’ll post up when that happens because I’m unsure how it all will work at the moment. A different rotor than the usual VW and a set of Miata pads. I’ll try to spend a few minutes punching the data in the calculator and see what it says. I still need to get the car to my buddy’s scales to see how my balance ends up.
    91 318is
    83 320is

  17. #67
    Join Date
    Oct 2005
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    It's probably cold here.
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    ‘76 2002, ‘1
    The easiest way to do the conversion is to locate the rear bits from a euro car, such as an 83 - which I happen to have for sale amazingly, both parking brake cables are included and in pristine shape. Nothing against the VW parts/fabrication methods, but this is available and I need my shop space back so hit me up if you’re interested

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