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How-to: Probe RWD Conversion

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  • How-to: Probe RWD Conversion












    Notes:

    *this is to be used for entertainment ONLY – it is not intended to be or replace sound engineering advice, and any parts of it used are done at your peril, loss of vehicle and/or sanity. Its value lies in entertainment only. You are responsible for securing proper structural advice in the modification of your vehicles.
    *These modifications are difficult and should only be undertaken by qualified (or mentally insane) persons. I claim to be neither (or both, depending on whom you speak to). I claim neither accuracy nor completeness in the following narrative, and any omission is deemed either legitimate (like a lot of the material stock dimensions) or is purely accidental on account of my advanced age and forgetfulness.
    *If in doubt, overbuild. If you attempt something as ridiculously dumb as this, you do so at your own express risk.

    Alright so here’s a brief “how-to” in converting your Probe/MX6 to RWD, since there are several threads each year asking how to do it, or promising to do it but asking for advice. So, let’s jump right in!



    Purpose

    This is intended to be a daily driven car. As such, it must have fairly compliant suspension, not be too loud, be easy to repair/upgrade, have a large aftermarket upgrade pool, and be safe enough for public roads and the occasional accidental drift. By occasional I mean all the time, and by accidental I mean whenever I mash the pedal on the right in a corner.



    Background
    First, we want a RWD vehicle to supply the parts. It’s easier than fabricating your own suspension. It’s also been tested by competent engineers. I chose the 1994+ Mazda MX5 Miata for the following reasons:
    *double unequal length a-arms on all 4 corners – the multitude of benefits of this system has been discussed extensively, and its dissemination is beyond the scope of this thread – but feel free to educate yourself in the process. Grab a suspension book or spend some time googling.
    *4-wheel disc brakes. It’s not Vietnam, nor the 50s. Drum brakes are so last century.
    *massive aftermarket suspension possibilities, from the Ebay springs to full blown $25,000 remote reservoir competition shocks.
    *narrower track will allow the use of wide wheels with near-zero offset (think massive lip) without fender flares or modifying the body in any way (ok, maybe rolling the fender lips, but nothing beyond that).
    *available 6-speed transmission stock
    *available Torsen rear differential stock
    *manual steering rack (I still hate the extra weight and leakiness of power steering).



    Process
    It’s really not that complicated, really – take the stuff out of the Miata, put it in the Probe. This sentence, right there, is the entire “how-to”, in a nutshell. It really is that easy. But that may appear vague, so let’s highlight a few steps (since it is a process, after all):
    *since I want to use the Miata subframes, it would be swell if they could just bolt up to the Probe body………(1)
    *since I want bolt-on subframes, I should move the Miata frame rails & strut towers to the Probe……………….(2)
    From Equations 1 and 2 above, we then deduce that I should cut out the Probe bits, cut out the Miata bits, and weld in the Miata bits in the Probe body, therefore allowing me to bolt in the Miata subframes, and omitting some details, VOILA – RWD Probe.
    Hope that answers all the questions. If there are any specific questions, ask away. I might get to them, I might not.



    Tools
    Before this process begins, you should have the minimum required tools. First, the minimally necessary devices:
    • Sawzall with variety of metal blade lengths
    • 2, preferably 3 angle grinders with 1) cutoff wheel, 2) wire wheel, and 3) sanding disc. You need 3 if you don’t want to constantly change the wheels as you perform various operations
    • Metal cutting shears or pneumatic shears
    • Welder – MIG welder with argon/CO2 shielding gas
    • Cordless drill with good power
    • Drill press
    • Cutoff saw with good blade
    • Variety of metal hand/pneumatic tools, clamps, vice, metal shaping hammers,
    • Typical toolbox for removal/assembly of parts
    • Transmission jack for test fitting subframes (motorcycle jack would also work)
    • Furniture dollies for easily moving subframes/engines in/out
    • Jackstands on custom adjustable plates for easy vehicle leveling
    • Spot-weld drill bit (8 mm preferred) - you will use this. A lot.


    And it’d be nice to have the following:
    • Sheet metal brake
    • Sheet metal shear table
    • Bead roller
    • Tube bender
    Last edited by Dan [Sac]; August 16, 2013, 01:12 PM.
    90 Mazda 323 - KLZE, fender-flared, right hand drive, 2350 lb fully loaded sex machine. || Pic Thread ||- SOLD
    93 PGT FRANKENPROBE - 10.24 @ 139.9 mph ||545 whp @ 20 psi || Timeslip || Dyno slip|| Build Thread - GONE
    97 GTS - Rear Wheel Drive KLZE, 6-speed, 3.90 Torsen LSD, 2650 lb, daily driver! - Build Thread - GONE
    90 Ghettocet KLiata - forever WIP

  • #2
    Details

    So here we go, let’s jump right in the deep end. I will list the steps chronologically here (all together), then insert them in the photo displays. These are ONLY the MAJOR steps. There are many many intermediary ones that I am omitting because otherwise I turn into Dostoyevsky, and I have neither the time nor the talent to write a 1,200 page paper here. Honestly, if you do not understand or deduce the intermediary steps, you are not fit to undertake this project. I beg pardon for the bluntness.

    Step 1 – Strip the Probe

    Step 2 – Strip the Miata

    Step 3 – Cut out the Probe front firewall and stock exhaust tunnel

    Step 4 – Cut out the Miata transmission tunnel

    Step 5– Weld in the Miata tunnel in the Probe

    Step 6 – Fabricate a strut tower bar for the Miata front strut towers – the reason for this will be apparent later

    Step 7 – Cut out the Miata and Probe front strut towers. Before you cut out the Miata ones, securely bolt in (and mark the location of) your neatly fabricated sturdy strut tower bar to keep the struts at the correct factory spacing.

    Step 8 – Locate the Miata strut towers in the Probe. Make sure you select the proper X, Y, and Z coordinates (or, for those with simpler lives, the height, side-to-side, and front-to-back locations). Test fit the fenders to make sure you are locating the wheels in the center of the wheel arch.

    Step 9 – Weld the Miata front strut towers in the Probe after checking and mocking up their position at least 850 times. Do not unbolt the strut tower bar at any point as doing so will change your dimensions and you’ll make a ton of new work for yourself.

    Step 10 – Complete sheetmetal welding to fill in gaps, provide structural support/stiffness. Mind any brackets that need to be attached and tire clearance underneath.

    Step 11 – Curse your luck that the subframe is now banging in the Probe front floor panels and footwell panels. Rejoice when you realize you have devices that cut metal, and proceed to cut out notches for the rear mounting bolts of the subframes. Once you box the rear mounting points, weld in the mounting nut. Alternatively, you may weld in a downward-facing stud. Make sure you additionally notch the frame for lower a-arm clearance.

    Step 12 – cut out humongous hole in the rear of the car. Flintstone that thing like it’s not even yours. This will be to make room for the Miata rear frame rails and fuel tank firewall. The Probe rear strut towers will likely have to be removed – how much, depends on step 13.

    Step 13 – cut out the Miata rear frame rails and fuel tank firewall. Enjoy copious amounts of swearing at this stage. The actual dimensions of this step are arbitrary and you may use as much, or as little as you dare. It’s up to you at this point.

    Step 14 – Test fit the newly liberated Miata frame rail segment in the Probe. Note how much you have to trim off before final location.

    Step 15 – clean up and prep Miata frame rail section. Cap all frame rails, and use the wire wheel to clean ALL edges where other pieces will be welded to it. You will be well served to take this advice, as swearing will be abundant if you do not and then have to pre-weld clean while this thing is in the car and you’ll be upside down wire-wheeling blind and with your limbs resembling pretzels.

    Step 16- Weld the Miata rear frame rail segment in the Probe after checking and mocking up its position at least 850 times. Make sure you select the proper X, Y, and Z coordinates (or, for those with simpler lives, the height, side-to-side, and front-to-back locations). Test fit the fenders to make sure you are locating the wheels in the center of the wheel arch.

    Step 17 – Once you’ve consulted a structural engineer in the method of securing the Miata frame rails to the Probe, proceed to construct the wheel arches (this will take a while) and fill in the rear floors. All flooring should be stiff and sturdy, with no “oil-can” effect. Add support struts as needed or recommended by your engineer. Again, this will take a while – make liberal use of manila folders to construct your templates as it will reduce the amount of cursing and you won’t have to resort to domestic violence to let off steam.
    90 Mazda 323 - KLZE, fender-flared, right hand drive, 2350 lb fully loaded sex machine. || Pic Thread ||- SOLD
    93 PGT FRANKENPROBE - 10.24 @ 139.9 mph ||545 whp @ 20 psi || Timeslip || Dyno slip|| Build Thread - GONE
    97 GTS - Rear Wheel Drive KLZE, 6-speed, 3.90 Torsen LSD, 2650 lb, daily driver! - Build Thread - GONE
    90 Ghettocet KLiata - forever WIP

    Comment


    • #3
      Step 18 – Add rear floor extensions. You might have noticed by now that the Probe is a just a bit longer than a Miata (by about 2 feet). You’ll have to construct a transmission/driveshaft/exhaust tunnel extension and add the rear floors. Enjoy the time you spend here, doing the same bits as in step 17 over, and over, and over, and over, and over. And then repeat for the other side.

      Step 19 – The Pedals and choice of hydraulics. You pick what you want as long as it all fits and provides enough room between the pedals. Ideally go with aftermarket race pedal set, but this is a daily driver so I chose Probe throttle pedal, Probe brake pedal, and Probe clutch pedal. I chose the Miata booster & master cylinder because it’s already ideal for the brake system (subframes are already complete with all Miata braking) and is a bit smaller. Miata master clutch cylinder was picked for same reason – plus it has its own dedicated reservoir. Mixing and matching the adjustable activating rods is also necessary. Much, much cursing will ensue at every part of this step. Get used to it, buy your toddler and dog ear plugs, and tell your wife to stay at her sisters this week.

      Step 20 – seats – use whatever you want, except Probe seats – they won’t fit now unless you really smush them up against the transmission tunnel. I chose Miata seats so I had to make all new mounting brackets for them. Remember, these bolts keep you inside the car in a wreck (assuming you aren’t mentally retarded and are actually wearing a seat belt). So, overbuild if in doubt and consult your engineer friend
      .
      Step 21 – Steering column – it can be routed between throttle and brake, or brake and clutch pedals. Your choice depending on your preference. You may have to use a few different u-joints to make it work. The junk yard is your friend, but always keep in mind # of splines and diameter. Everything should fit like OEM, otherwise you will take out Ms. Wilson’s tree on your first test drive and become a neighborhood pariah to the end of your days. You don’t really want that, do you? No, you don’t – so do the steering properly. Notice the bracket that I made that simultaneously lowers the column and moves it 1” to the right to provide the proper angles and clearances. The column will have to be secured at both ends since it is pinned on the driver end and will pivot about that pin if the firewall side is not secure.

      Step 22 – Dashboard – this actually, should be before Step 19, but I’m sure you’ll have figured it out by now. The lower mounting legs will have to be shortened since the Miata tunnel is so much taller.

      Step 23 – finish all the welding you’ve put off so far because it’s “hard”. Also, stop whining. You signed up for this, so finish it. Make an extension or fabricate a new filler neck for the fuel tank. Be smart, use OEM mounting and keep the anti-spill/reversion floaty ball in there.

      Step 24 – Use automotive-grade seam sealer to seal ALL edges where you welded. On BOTH sides. Don’t be lazy and cheap out now. Water doesn’t care for your feelings, and you’ll be crying bitter tears if you skimp on this step and it starts raining in your car. You’ll unnecessarily beat your dog for the wet spots on the carpet when in fact you’re the one who caused them by not sealing all the welded seams. Animal cruelty is a felony. Don’t beat your dog – seam seal your car properly.

      Step 25 – use self-etching primer (or regular automotive bare metal primer if you’re a cheap bastard or broke) on all exposed metal parts. Again, on BOTH sides. Rust comes after water or water vapor, and it also doesn’t care for your feelings.

      Step 26 – on the underside, use heavy duty rubberized undercoat spray, or if you’re rolling in dough, truck bed spray liner. This will keep some noise out and help further seal the areas you missed because you’re probably lazy and/or incompetent.

      Step 27 – use paint of your choice to color the inside. Bright pink is popular now.

      Step 28 – use Miata/Probe carpets to Frankenstein an interior rug (but install your chassis wiring before you do this)

      Step 29 – Run your hydraulic and fuel lines. I used the Miata lines. I extended the rear single brake line (yay MX-5!) with a braided SS brake-spec line. Used Miata fuel lines/filter and extended fuel lines using fuel-spec rubber lines.

      Step 30 – install dash and seats and audio

      Step 31 – Install engine and gearbox of your choice along with computer

      Step 32 – have a professional shop fashion you a proper length driveshaft. Remember, the Probe is a bit longer than a Miata. That’s probably the only time you can actually truthfully say the words “My probe is longer than ____________”. It’s ok, no one really is looking down upon you for being short in that department.

      Step 33 – put fluids in the car and drive it.

      Step 34 – send me loads of money, or buy my car.



      Conclusion
      Congratulations, you have a RWD Probe. You now have a decent looking car (if you pick the right wheel/tire combo) that can be oodles of fun. Twin turbo KL using inexpensive 16G turbos? Piece of cake. Supercharged KL with an M90 sitting between the heads? Easy peasy. 5.0 Mustang engine or 4.6? Done. LS1/T56 6-speed gearbox? Done. Rolling in money? Then go 3-rotor 20B. Or Renesis RX8, or 350/370Z, or 2JZ, or just about any combination you can conjure up.
      90 Mazda 323 - KLZE, fender-flared, right hand drive, 2350 lb fully loaded sex machine. || Pic Thread ||- SOLD
      93 PGT FRANKENPROBE - 10.24 @ 139.9 mph ||545 whp @ 20 psi || Timeslip || Dyno slip|| Build Thread - GONE
      97 GTS - Rear Wheel Drive KLZE, 6-speed, 3.90 Torsen LSD, 2650 lb, daily driver! - Build Thread - GONE
      90 Ghettocet KLiata - forever WIP

      Comment


      • #4
        Step 1 – Strip the Probe




















        Last edited by Dan [Sac]; August 16, 2013, 01:24 PM.
        90 Mazda 323 - KLZE, fender-flared, right hand drive, 2350 lb fully loaded sex machine. || Pic Thread ||- SOLD
        93 PGT FRANKENPROBE - 10.24 @ 139.9 mph ||545 whp @ 20 psi || Timeslip || Dyno slip|| Build Thread - GONE
        97 GTS - Rear Wheel Drive KLZE, 6-speed, 3.90 Torsen LSD, 2650 lb, daily driver! - Build Thread - GONE
        90 Ghettocet KLiata - forever WIP

        Comment


        • #5








          Last edited by Dan [Sac]; August 16, 2013, 01:36 PM.
          90 Mazda 323 - KLZE, fender-flared, right hand drive, 2350 lb fully loaded sex machine. || Pic Thread ||- SOLD
          93 PGT FRANKENPROBE - 10.24 @ 139.9 mph ||545 whp @ 20 psi || Timeslip || Dyno slip|| Build Thread - GONE
          97 GTS - Rear Wheel Drive KLZE, 6-speed, 3.90 Torsen LSD, 2650 lb, daily driver! - Build Thread - GONE
          90 Ghettocet KLiata - forever WIP

          Comment


          • #6
            Step 2 – Strip the Miata






























            Last edited by Dan [Sac]; August 16, 2013, 01:41 PM.
            90 Mazda 323 - KLZE, fender-flared, right hand drive, 2350 lb fully loaded sex machine. || Pic Thread ||- SOLD
            93 PGT FRANKENPROBE - 10.24 @ 139.9 mph ||545 whp @ 20 psi || Timeslip || Dyno slip|| Build Thread - GONE
            97 GTS - Rear Wheel Drive KLZE, 6-speed, 3.90 Torsen LSD, 2650 lb, daily driver! - Build Thread - GONE
            90 Ghettocet KLiata - forever WIP

            Comment


            • #7
              Step 3 – Probe cutting
              Cut out the Probe front firewall and stock exhaust tunnel





              Last edited by Dan [Sac]; August 16, 2013, 01:50 PM.
              90 Mazda 323 - KLZE, fender-flared, right hand drive, 2350 lb fully loaded sex machine. || Pic Thread ||- SOLD
              93 PGT FRANKENPROBE - 10.24 @ 139.9 mph ||545 whp @ 20 psi || Timeslip || Dyno slip|| Build Thread - GONE
              97 GTS - Rear Wheel Drive KLZE, 6-speed, 3.90 Torsen LSD, 2650 lb, daily driver! - Build Thread - GONE
              90 Ghettocet KLiata - forever WIP

              Comment


              • #8
                Step 4 – Tunnel Prep
                Cut out the Miata transmission tunnel

                Last edited by Dan [Sac]; August 16, 2013, 01:51 PM.
                90 Mazda 323 - KLZE, fender-flared, right hand drive, 2350 lb fully loaded sex machine. || Pic Thread ||- SOLD
                93 PGT FRANKENPROBE - 10.24 @ 139.9 mph ||545 whp @ 20 psi || Timeslip || Dyno slip|| Build Thread - GONE
                97 GTS - Rear Wheel Drive KLZE, 6-speed, 3.90 Torsen LSD, 2650 lb, daily driver! - Build Thread - GONE
                90 Ghettocet KLiata - forever WIP

                Comment


                • #9
                  Step 5 – Welding
                  Weld in the Miata tunnel in the Probe













                  Last edited by Dan [Sac]; August 16, 2013, 02:51 PM.
                  90 Mazda 323 - KLZE, fender-flared, right hand drive, 2350 lb fully loaded sex machine. || Pic Thread ||- SOLD
                  93 PGT FRANKENPROBE - 10.24 @ 139.9 mph ||545 whp @ 20 psi || Timeslip || Dyno slip|| Build Thread - GONE
                  97 GTS - Rear Wheel Drive KLZE, 6-speed, 3.90 Torsen LSD, 2650 lb, daily driver! - Build Thread - GONE
                  90 Ghettocet KLiata - forever WIP

                  Comment


                  • #10
                    Step 6 – Jigging
                    Fabricate a strut tower bar for the Miata front strut towers – the reason for this will be apparent later


























                    Last edited by Dan [Sac]; August 16, 2013, 02:54 PM.
                    90 Mazda 323 - KLZE, fender-flared, right hand drive, 2350 lb fully loaded sex machine. || Pic Thread ||- SOLD
                    93 PGT FRANKENPROBE - 10.24 @ 139.9 mph ||545 whp @ 20 psi || Timeslip || Dyno slip|| Build Thread - GONE
                    97 GTS - Rear Wheel Drive KLZE, 6-speed, 3.90 Torsen LSD, 2650 lb, daily driver! - Build Thread - GONE
                    90 Ghettocet KLiata - forever WIP

                    Comment


                    • #11
















                      Last edited by Dan [Sac]; August 16, 2013, 02:55 PM.
                      90 Mazda 323 - KLZE, fender-flared, right hand drive, 2350 lb fully loaded sex machine. || Pic Thread ||- SOLD
                      93 PGT FRANKENPROBE - 10.24 @ 139.9 mph ||545 whp @ 20 psi || Timeslip || Dyno slip|| Build Thread - GONE
                      97 GTS - Rear Wheel Drive KLZE, 6-speed, 3.90 Torsen LSD, 2650 lb, daily driver! - Build Thread - GONE
                      90 Ghettocet KLiata - forever WIP

                      Comment


                      • #12
                        Step 8 – Mock-up, Front
                        Locate the Miata strut towers in the Probe. Make sure you select the proper X, Y, and Z coordinates (or, for those with simpler lives, the height, side-to-side, and front-to-back locations). Test fit the fenders to make sure you are locating the wheels in the center of the wheel arch.


                        Last edited by Dan [Sac]; August 16, 2013, 02:55 PM.
                        90 Mazda 323 - KLZE, fender-flared, right hand drive, 2350 lb fully loaded sex machine. || Pic Thread ||- SOLD
                        93 PGT FRANKENPROBE - 10.24 @ 139.9 mph ||545 whp @ 20 psi || Timeslip || Dyno slip|| Build Thread - GONE
                        97 GTS - Rear Wheel Drive KLZE, 6-speed, 3.90 Torsen LSD, 2650 lb, daily driver! - Build Thread - GONE
                        90 Ghettocet KLiata - forever WIP

                        Comment


                        • #13
                          Step 9 – Front Structural
                          Weld the Miata front strut towers in the Probe after checking and mocking up their position at least 850 times. Do not unbolt the strut tower bar at any point as doing so will change your dimensions and you’ll make a ton of new work for yourself.







































                          Last edited by Dan [Sac]; August 16, 2013, 02:57 PM.
                          90 Mazda 323 - KLZE, fender-flared, right hand drive, 2350 lb fully loaded sex machine. || Pic Thread ||- SOLD
                          93 PGT FRANKENPROBE - 10.24 @ 139.9 mph ||545 whp @ 20 psi || Timeslip || Dyno slip|| Build Thread - GONE
                          97 GTS - Rear Wheel Drive KLZE, 6-speed, 3.90 Torsen LSD, 2650 lb, daily driver! - Build Thread - GONE
                          90 Ghettocet KLiata - forever WIP

                          Comment


                          • #14
                            Step 10 – Welding
                            Complete sheetmetal welding to fill in gaps, provide structural support/stiffness. Mind any brackets that need to be attached and tire clearance underneath.


























                            Last edited by Dan [Sac]; August 16, 2013, 02:59 PM.
                            90 Mazda 323 - KLZE, fender-flared, right hand drive, 2350 lb fully loaded sex machine. || Pic Thread ||- SOLD
                            93 PGT FRANKENPROBE - 10.24 @ 139.9 mph ||545 whp @ 20 psi || Timeslip || Dyno slip|| Build Thread - GONE
                            97 GTS - Rear Wheel Drive KLZE, 6-speed, 3.90 Torsen LSD, 2650 lb, daily driver! - Build Thread - GONE
                            90 Ghettocet KLiata - forever WIP

                            Comment


                            • #15
                              Step 11 – Fix things
                              Curse your luck that the subframe is now banging in the Probe front floor panels and footwell panels. Rejoice when you realize you have devices that cut metal, and proceed to cut out notches for the rear mounting bolts of the subframes. Once you box the rear mounting points, weld in the mounting nut. Alternatively, you may weld in a downward-facing stud. Make sure you additionally notch the frame for lower a-arm clearance.





















                              Last edited by Dan [Sac]; August 16, 2013, 03:01 PM.
                              90 Mazda 323 - KLZE, fender-flared, right hand drive, 2350 lb fully loaded sex machine. || Pic Thread ||- SOLD
                              93 PGT FRANKENPROBE - 10.24 @ 139.9 mph ||545 whp @ 20 psi || Timeslip || Dyno slip|| Build Thread - GONE
                              97 GTS - Rear Wheel Drive KLZE, 6-speed, 3.90 Torsen LSD, 2650 lb, daily driver! - Build Thread - GONE
                              90 Ghettocet KLiata - forever WIP

                              Comment

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