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Straight cut synchronized gear box!

Posted by keltalon, Jun 22, 2018

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  1. iugrad92turbo

    iugrad92turbo Supporting Member

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    Im happy with my set up its a street car, but jon will hook me up with next rebuild lots if choices.
     

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    1992 Eagle Talon TSi
    awd · manual · 1G DSM
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  2. keltalon

    keltalon Supporting VIP

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    You know Jon is a cool dude!
     

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    1998 Mitsubishi Eclipse GSX
    manual · 2G DSM

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    1998 Mitsubishi Eclipse GST
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  3. mavericktsi83

    mavericktsi83 Proven Member

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    IMO to complete a high end build like this I think getting a hold of the forged Evo III hub/slider(s), used if need be, is prudent. In this context, the trans failure point would likely shift from gear teeth to the 3/4 hub/slider. A big increase in safe torque capacity via stronger gears would be significantly diminished without addressing this key area and worse yet a failure would likely destroy the whole gearset investment. IIRC, keltalons car puts down ~600+ WTQ. IIRC, TMZ blew up a H/S at around 600 whp trashing the old PAR set. Usually I strip teeth but Ive had a OEM 3/4 small “HD” H/S explode on me destroying a new professionally assembled OEM gearset w/treatments in ~3k miles at ~500TQ, no missed shifts. Is this H/S reliable at 500ft/lbs and street use? Maybe it was a fluke but it gives me pause and similar failures have been documented on the various forums. I deduce this would likely be more pronounced and therefore crucial especially as gear strength and TQ increases.

    Now there are three hub/slider versions worth discussing—as there is already a consensus with the fragile large hub failing around 350 Tq. This leaves; OEM small H/S, OEM small H/S modified for double synchros and the Evo III H/S. The only variant I have never seen broken is the Evo III H/S which happens to be forged—maybe because it is much stronger or rare or both. I presume there may be some advantage in cast metal generally having less thermal expansion than forged as it relates to keeping its shape/clearances more as it gets hot. Alloy comes into play here but some alluded to heat being a failure mode and I’m not sure what to make of that. Considering this part transfers the torque supplied by the engine from the shaft to say either 3 or 4th gear, it is plainly under a lot of stress when meshed together. I have heard that machining down the small H/S weakens it, but by a noteworthy amount that shows up in rate of recurrence when compared to std. OEM I am left to wonder. The PAR synchro set will surely be limited by these particular H/S combinations and understanding their respective limits would better avoid a ticking time bomb scenario.

    @twicks69 and anyone else that may have insight; what is your thought/experience on the safe (and differing) TQ capacity on these three H/S variants? At what TQ do failures (non driver error related) start showing up? Any other relevant info is appreciated.
     
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  4. Canadian_CD9A

    Canadian_CD9A Proven Member

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    There is technically a 4th variant - the Evo 1 uses the large diameter hub, but is forged/broached. It might buy some safety over the 93-99 DSM unit, but not much. Also curious to hear about some failures.
     
  5. twicks69

    twicks69 Supporting Vendor

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    Regarding the hub and sliders,

    For hubs,
    I typically see the stock 1990-1992.5 style small synchro hub break/crack around 600ft/lb tq or with excessive abuse at a little lower power levels. The stock 1992.6-1999 style large synchro hub typically would break around 350-450ft/lb tq on the street / track or dyno. I have broken several personally.

    The Evo 1 and Evo 2/3 forged / broached hubs are considerably stronger than any of the cheap powdered metal DSM hubs. I would assume that an accountant with Plymouth/Eagle/Chrysler was pinching savings on material costs when you are manufacturing a few million of the parts for the entire DSM platform in comparison to the Japanese making a high quality product for their Mitsubishi Evo 1/2/3 platforms. That is the most realistic answer why we have crappy material used for the DSM components. It came down to cost.

    Of course, the Evo 1 and Evo 2/3 3rd/4th forged / broached hub and sliders are completely discontinued.

    I have not seen any failures personally of an Evo 1 or Evo 2/3 HUB. Sure, I have seen sliders fail or overheat / bind, but not the hub failing.

    As for the MD747646 OEM "HD" 1991.6-1992.5 thick flanged powdered metal DSM 3rd/4th hub and slider that accepts the small diameter synchros or the Evo 2/3 double synchros when modified, well, I have seen numerous failures at high power levels. With modification to the hub for accepting double synchros, you have to machine down a little spot for additional clearance so you don't jam the double synchros in them, and the key importance is put in to machining the radius, and then shot peening and surface treating the hub after machinework. I have seen several from Jack that were done and there was no chamfer left on the clearanced area and it would be exactly where the hub would fail, splitting the interior splined portion of the hub that presses onto the input shaft clean off from the rest of the hub. Jon @ TRE does a great job with his machining and shot peening of the hub and there is still a decent chamfer on the machined spot and it clears the Evo 2/3 double synchros properly. He also uses nice and strong hub and slider springs that have a different tang style than the DSM OEM spring tang design. It results in a much lower likelyhood of it popping out of the key, and pretty much stops the spring from breaking off the tang.

    For sliders,

    There are like 5 designs of sliders used. The thicker flange 1990-1991.5 style with the square face side on 3rd gear side which uses the MD742777 large face keys and small diameter springs (MD738050 or MD742441), and then the 1991.6-1992.5 style with tapered faces on both sides and uses smaller MD748663 keys, and same springs as above -- MD747646; then the MD746826 which is a thick flange hub with the MD742777 large face keys and same springs as above. Those are all the small diameter style sliders. For the large diameter sliders, there were a few part numbers that were used, all used the MD748663 small face keys and large diameter MD742445 springs (same style as 1st/2nd hub and slider). The flange on the MD747647 slider is a bit beefier than the later MD749416 hub and slider; I have seen and used both in the past, and the MD747647 slider does a bit better with surviving under power before it breaks / overheats and jams on the hub or breaks into pieces. The MD749416 typically broke in the 350-450ft/lb torque range, and I pushed them up to around 550tq on the dyno and have broken them on the dyno too LOL.

    The sliders for the Evo 1 and Evo 2/3 hub and slider assemblies are very similar in slider construction. The Evo 1 MD747651 3rd/4th large diameter synchro assembly has one identification mark on the slider OD, and a thick/ squared edge flange face on one side, and it uses shallow face MD742419 style synchros with small face MD748663 keys. I have never seen the hub fail, and I think I have only seen 1 slider bind up from super overheating it (3rd/4th gear pulls without cool down). The Evo 2/3 MD747378 hub and slider is designed to be used with MD742777 large face keys, MD738050 or MD742441 springs, and then either MD744782 single synchros or MD747255 Evo 2/3 double synchros. It has a thick/ squared edge flange face on one side with two identification marks on the slider OD. The slider is the same style as the MD746826 DSM hub and slider; difference is the DSM version has one identification mark on it.

    The DSM 3rd/4th hub and slider is the biggest weakness in a high power application when we are discussing gearsets in general. They like to break the hub or crack the hub from abuse or power levels, and the slider likes to break from abuse or power levels, or warp and bind up on the slider from heat.

    Best way to keep the part alive the longest? Dyno at low boost and power levels, do not do a ton of street pulls, don't shift like a gorilla. Having a good gear oil will help, having an oil cooler and high capacity pump with a well designed spray bar or inlet/outlets on the transmission will definitely help.

    The new version PAR gearset is a very nice piece, but we are still relying on the OEM Mitsubishi hub and slider which will be the failure point from heat or abuse. This is the reason why I prefer face plated gearsets or dogbox gearsets. More durable sliders and much thicker hubs. The Liberty face plated hub and slider is easily double the thickness hub and a very durable slider. The PPG hub and slider is also extremely durable and well made. The PAR old version was not so strong; I don't know if Haysam has changed the 3/4 slider design since 2014 which is the last time we ran their dogbox in Andrew's WTAC car. We exploded the slider and it killed our entire gearset.

    I think that's enough time touching on that topic.
     

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    1999 Mitsubishi Eclipse GSX
    9.499 @ 155.00 · 2G DSM
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  6. ViciousLord

    ViciousLord Proven Member

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    Checkmate. LoL
     

    Street Build 823  1

    1997 Mitsubishi Eclipse GSX
    awd · manual · 2G DSM
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  7. Lou98GSX

    Lou98GSX Proven Member

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    My trans was done by t.r.e and it's still going with no problems .
     
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  8. keltalon

    keltalon Supporting VIP

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    We'll I beat the crap out the fwd it was running strong when I decided to swap to awd. I built the awd myself using the small 3/4 hub slider wpc treatment and all . The awd trans I built is good as far as gears and hub slider but I started feeling some vibration that I couldn't get rid of so I broke the tranny down . For Two reasons I got tired of the 3.909 very quickly and second the vibration. Come to find out after Jon tore down the center diff the cross shaft was galled pretty badly causing the vibration. Never broke a gear or hub. I had the Center diff machined locally to accept the 4 spider Jon said it was machined wrong causing the damages. I'll post a video later. I am very confident in the buikb and cant wait to beat on it.
     
    Last edited: Jun 30, 2018

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    1998 Mitsubishi Eclipse GSX
    manual · 2G DSM

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    1998 Mitsubishi Eclipse GST
    11.1 @ 137.3 · 2G DSM
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  9. keltalon

    keltalon Supporting VIP

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    manual · 2G DSM

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    1998 Mitsubishi Eclipse GST
    11.1 @ 137.3 · 2G DSM
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  10. bastarddsm

    bastarddsm Proven Member

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    It wasn't a machining issue. Its a bullshit factory design with bandaid fixes
     

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  11. bastarddsm

    bastarddsm Proven Member

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    There is no might. I am 100% correct. It's a f***ed design.
     

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  12. twicks69

    twicks69 Supporting Vendor

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    Well, if it's a bullshit design, and to my knowledge it has had 4 damaged shafts including both of yours, out of like 600 or 700 or so that have worked just fine with no issues, I would say it works pretty good.

    It does come down to machining in alot of cases.

    The 4-post ones get issues too, even when you use a factory rear pinion shaft machined to fit, like the shaft TRE does. The speed design ones failed regularly.

    Jack's and Shep used stock cross shafts machined down without a heat treatment and it failed quickly.

    If you want to make a better part and sell it, go right ahead Kurt. It doesn't bother me. I only was trying to make a good product for the community when it was designed about 14 years ago.
     

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    1999 Mitsubishi Eclipse GSX
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  13. keltalon

    keltalon Supporting VIP

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    Yeah I had no problem with the shaft untill I changed my gearing from dsm 1990 to the Evo gearing which required a different center diff to match the later tooth cut. This guy locally swore he could machine the housing by copying the old one. Well in very short mileage it failed. I don't believe it's the shaft design at all for John pointed out to me the reason for the failure. The machinist machined the housing well into the gear area. So this time I let Jon machine the housing the right way with another cross shaft from twick. So this failure was my fault for not sending the housing in to be machined the right way like my first housing!
     

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    1998 Mitsubishi Eclipse GSX
    manual · 2G DSM

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    1998 Mitsubishi Eclipse GST
    11.1 @ 137.3 · 2G DSM
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  14. twicks69

    twicks69 Supporting Vendor

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    Jon sent me a video showing that the diff housing was not machined square, and that was the reason for Kelvins damage to the cross shaft and spider gears.
     

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    1999 Mitsubishi Eclipse GSX
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  15. keltalon

    keltalon Supporting VIP

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    I saw the one you designed looks pretty good!
     

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    1998 Mitsubishi Eclipse GSX
    manual · 2G DSM

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    1998 Mitsubishi Eclipse GST
    11.1 @ 137.3 · 2G DSM
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  16. donk

    donk Proven Member

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    Looking forward to see what this trans could DO ! / A
     
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  17. iugrad92turbo

    iugrad92turbo Supporting Member

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    A lot of us are curious.
     

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  18. dragonov_elite

    dragonov_elite Proven Member

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    Can't wait to see progress on this and longevity of the units being thought up.
     

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    awd · manual · 2G DSM

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  19. mavericktsi83

    mavericktsi83 Proven Member

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    @twicks69 thank you for taking the time to write such an amazing post and sharing your knowledge on this subject!!
     
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  20. keltalon

    keltalon Supporting VIP

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    Me too illI definitely keep the thread updated. I am waiting on replacement 8 leg disc for larger shaft so I can get the transmission back in the car.
     

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    1998 Mitsubishi Eclipse GSX
    manual · 2G DSM

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    1998 Mitsubishi Eclipse GST
    11.1 @ 137.3 · 2G DSM
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  21. donk

    donk Proven Member

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    Any progress ? /A
     
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  22. keltalon

    keltalon Supporting VIP

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    I've been crazy busy with my company but plan on taking some time soon to install the transmission.
     

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    manual · 2G DSM

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    1998 Mitsubishi Eclipse GST
    11.1 @ 137.3 · 2G DSM
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  23. keltalon

    keltalon Supporting VIP

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    Finally got the trans in and man!!! Speechless! I switch back to the stock gear ratio and love it. Interior shot feels aoo good....... 20181024_204638.jpg
     

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    1998 Mitsubishi Eclipse GSX
    manual · 2G DSM

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    1998 Mitsubishi Eclipse GST
    11.1 @ 137.3 · 2G DSM
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  24. bastarddsm

    bastarddsm Proven Member

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    Go beat on it so we can see how it lasts, but I don't know if it matters. Day 180 of waiting for a response from TRE.

    btw, want to part with the 3.909 finals?
     

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  25. donk

    donk Proven Member

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    Well i am a greedy swedish and everything costs more for me since customs and shipping , so a picture of your custom floormat wont make me buy the gearset. haha waiting for moore input as soonn as you have it.

    /A
     
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