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  • .838 overdrive

    I finally got to try my transmission with the truck overdrive. I was turning about 6800 off the hill at Road Atlanta. It doesn't have as much drop between 4th to 5th as before. I believe I was at 6500 before. It pulls much better then before. Everybody needs to change to the .838.
    I also ran the new radiator without a thermostat. It was only in the 50's Friday morning. I let it warm up to about 160 before going to the grid, when on track for a pace lap it backed up to 105 and then under power only back up to 150. The afternoon practice temps were in the mid 70's. It ran 180 most of the session. Saturday feature race about the same 180-185. I think I will put a thermostat back in. I will put a temp probe to check oil temps next.

  • #2
    Did ya take any pics? I wonder if the SR trans is the same. But the .838 and the 4.636 gives a pretty low top speed in 5th even with more revs.
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    • #3
      Yes, I believe the SR is the same trans inside. It does pull a little rpm from the top. My motor didn't seem to pull as well up the back stretch with the .759.

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      • #4
        What Truck trans? Cause I believe the Hardbody trans had a .821 5th.

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        • #5
          I think the 4WD and 2WD D21's had different 5th gears.
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          • #6
            I have the 0.838 5th gear. It's from a '97 Hardbody 2WD. The 4x4 has a 0.821. The main thing I found out about the install is it will not work with transmissions w/o syncro reverse. Nissan switched to the syncro reverse in mid 1994. My trans is a 1992. I used the syncro reverse parts out of a donor trans I had from a 1995 S14.

            As far as rpm drop. I shift at 7500 and the drop went from 5700 to 6300rpm and and the whp from 180 to 200. But yes the top speed goes down quite a bit. With the 4.90 FD, the top speed went from 147 to 133mph. Again my car is NA and set up for Mid-OH.
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            • #7
              I did not have much luck running my race car w/o a thermostat. I tried using an orifice in in place of the thermostat, but could not regulate my temps well enough. I went back to a regular t-stat with an couple of extra holes drilled in it, the same diameter as the jiggle pin hole. that worked best for me.

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              • #8
                JRS, that's the thermostat setup I've been running for years. Seems to work very well.

                I think the .838 was in the S14-SR transmissions if you believe some of the write ups online about Nissan gear ratios.
                '95 240sx

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                • #9
                  Yes,I am golng back to a t-stat. I feel good about the o/d change.

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                  • #10
                    The shorter 5th gear is WAAAAY better. Listen when I shift into 5th on the back straight. It actually keeps accelerating!

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                    • #11
                      I know Jeff (240sx Motoring) has been using the .83 gear in his s14 now for quite sometime...and he's got a low to mid (maybe higher with more boost) 300 whp car. He swears by it.
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                      • #12
                        Originally posted by CodyAce View Post
                        I know Jeff (240sx Motoring) has been using the .83 gear in his s14 now for quite sometime...and he's got a low to mid (maybe higher with more boost) 300 whp car. He swears by it.
                        I was actually the one that told Jeff about it last yr.
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                        • #13
                          So what gear do we need to put in an SR trans? Source to buy it?
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                          DefSport Koni Sleeve and Spring Perch Buy!!!
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                          • #14
                            Gear is the same as the KA. '97 Hardbody 2WD - your favorite Nissan parts source
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                            BTW I work for Garrett

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                            • #15
                              But we need a synchro reverse gear as well?

                              I'm guessing once you separate the case it's easy to get at 5th gear right? Do you have to take the whole gear stack out?

                              Just trying to determine if I want to add another project to the list before getting this thing back together. It looks like I can hit just a hair over 160 with the .838. I'm guessing that's ok, but power peak will likely be around 145-150 mph. Seems fast enough, but ya know how that is... The .821 gives me 3-4 mph at the same RPM up top. But it might be a little too close to the .757 to make it worth the PITA to toss it in.

                              I only really get into 5th gear for TWS, but damn does it suck when I do toss it in there. It'll be a little better with the 4.636, but the 4.363 had me basically stuck at ~133-134 mph at 14 psi and pretty low RPM, like < 6k RPM (obviously needed to lose some drag there...). But still, I could probably chop off 10% drag and the situation wouldn't improve much with that gearing.

                              4.636 and .757 gear with 8500 RPM gives me 180 mph, which is ridiculous and 170 at 8000 RPM. Never going to hit that. .838 gives 153 mph, .821 gives 157 mph. I'd probably be fine with the .838, but I'd hate to go too short on it if I add a bunch of power and then run out of gear when it can stretch its legs.


                              So how about the install? Fairly easy once you get the rear case off?
                              '18 Chevrolet Volt - Electric fun hatch for DD duty!


                              DefSport Koni Sleeve and Spring Perch Buy!!!
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