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1975 Cj5 - Build Guidance Needed

Discussion in 'Intermediate CJ-5/6/7/8' started by David Shackelford, May 19, 2022.

  1. May 19, 2022
    David Shackelford

    David Shackelford New Member

    Simi Valley, CA, USA
    Joined:
    Sep 6, 2021
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    Sooo... finally getting close to solving all my "immediate" driving issues. This jeep was a mess when I bought it... but she is now freeway stable at about 75mph (bursts) cruises at 65 with one hand and has minimal to no clenching :). Solved steering (gears/tierods/caster).. solved driveshaft (cv).. replaced rear Dana 44 (bearing blown out and ruined shaft/housing). Radiator woes to fix.. then winch and armor annnnnd...

    My build:
    SBC swap (healthy/mild build/lopey cam)
    wide track Dana 30 Front, wide track Dana 44 Rear, both "e" lockers
    3:73 gears
    T10 4 spd (came with jeep, works very well on street)
    Dana 20 tc with herms terra low 3.13 low gear
    33 TSL 12.50's (soon to be general grabber x3, maybe 35X10.50)

    This will be a fun weekend light trail jeep long-term and she is currently GREAT at that... BUT I have the bucket list Rubicon trip to do with my kids and a group of friends in a few years. I know my crawl ratio sucks (28.9), but 99.999% of this jeep's life will be street driving and I don't want to sacrifice all of that. Looking for a compromise that will get me through the rubicon 1-time (minimal damage) while keeping the street manners, such as they are for a cj5.

    I throw myself on the mercy of the court... can't make up my mind between transmission/diff gears or run it like it is and hope). Any and all suggestions would be welcome short of going buy a new jeep. There are many like it but this one is mine and it's special :).

    What would you guys&gals do?...
    Thanks
     
  2. May 19, 2022
    sterlclan

    sterlclan Member 2022 Sponsor 2021 Sponsor

    exploring the...
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    not run 35s , definitely not with 3.73 gears
     
  3. May 20, 2022
    David Shackelford

    David Shackelford New Member

    Simi Valley, CA, USA
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    Sep 6, 2021
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    Thanks... so you think 33's are tall enough for the rubicon?

    I'm actually looking for options to improve the gearing anyways... I'm not certain where my money would be best spent (trans/diff come to mind). The SBC I've swapped in has no issue pushing 33's with 3.73 gearing and I've run 35s with less power in other machines... just not sure how that plays with rocks.
     
    Last edited: May 20, 2022
  4. May 20, 2022
    Buildflycrash

    Buildflycrash The pride of Cucamonga 2022 Sponsor 2020 Sponsor

    Gulf Breeze FL...
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    I think everyone of us on the Rubicon last year ran 33” tires.
    [​IMG]
     
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  5. May 20, 2022
    sterlclan

    sterlclan Member 2022 Sponsor 2021 Sponsor

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    no idea but out east with the tight rocky trails yup and 35s break other parts. i run a 32 x 9.5 ish tire
     
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  6. May 21, 2022
    dvader

    dvader Member

    Northern Nevada
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    Jul 20, 2006
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    205
    How about swapping in a SM420 transmission? It would be easy because a GM pattern bell housing bolts right up to both your SBC and the SM420.
    It would solve your gearing with a crawl ratio of 82.7. I think the lowest 1st gear offered in a T10 was 2.65. That would fall between 2nd and 3rd in the SM420.
    NP435, SM465, and T18 would also be good choices, but the SM420 has the lowest 1st and 2nd gears at 7.0 and 3.6.
     
    Last edited: May 21, 2022
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  7. May 21, 2022
    timgr

    timgr We stand on the shoulders of giants. 2022 Sponsor 2021 Sponsor 2020 Sponsor

    Medford Mass USA
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    What's the T-10 first gear like from a stop? They were popular in Jeeps in California that ran dunes a lot, back in the day. Today, it seems like more owners want the deep 1st gear of a truck 4-speed, for technical trails like the Rubicon.

    I think with 33s, 4.10 or 4.27 axle gears would be fine, especially with a modern V8. Check the numbers ... According to internet sources, your T-10 has a first gear ratio of 2.43:1, giving you a crawl ratio of ca 28. This is ok, not great for technical trails. My KL Cherokee has a 60:1 ratio, and my J10 pickup is about 21:1, for example. You could change the axle gearing to 4.10 or 4.27 and improve a few points to about 32.

    The main downside to the truck transmissions is the shifting. Their throws are long and the gates are wide, and the gears are heavy. They shift like a truck. You never use 1st around town. And, they tend to be noisier than a passenger car transmission (gear whine). A SM420 is a really old transmission, and parts may be an issue if the transmission has a lot of miles. In a Jeep, the truck transmissions are under-stressed and will last a long time, but who knows the history of these old transmissions.

    Another possibility is an automatic - the TH350 fits ok in a CJ, and would be easy to mate to your SBC. You'd need an adapter kit. The overdrive automatics might appeal, but but I suspect they are too long for a CJ with a V8. This might be an opportunity to swap in the 4.3L V6 and move the transmission forward, but that does not use much of what you have now. The TH350 won't gain much in crawl ratio, but driving an automatic in the rocks is different from a manual. You use the brake and throttle together to limit forward speed, and the torque multiplication of the automatic helps.
     
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  8. May 21, 2022
    David Shackelford

    David Shackelford New Member

    Simi Valley, CA, USA
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    Sep 6, 2021
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    Preciate the info... thanks guys

    The t10 first gear isn't great...but the sbc kinda covers that up a bit. I could see this being a good setup for the dunes (like mentioned above)... i seriously doubt it would allow for decent control on a technical trail.

    I would like to avoid a sloppy shifting truck transmission if possible. no experience with a T18, sm420/425, or the like but guessing it won't feel very precise. I could prob live with that, but essentially I'll end up with a 3-speed on the street that feels like a compromise that might bother me even more.

    I like the th350 idea...but only if I can't find a manual trans that lives between the extremes of the T10 and truck transmissions that I've looked into.

    anything in between? :). I've been looking into tc gearing (tera low)/tc swaps (Atlas) which seem expensive at first, but kinda looking like the same price after i factor in adapters and parts.

    Maybe super low diff gearing/tc geering and a overdrive?
     
    Last edited: May 21, 2022
  9. May 21, 2022
    dvader

    dvader Member

    Northern Nevada
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    Jul 20, 2006
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    On the street with a truck four speed, you start out in second. It is just about right! You drive it on the street as a 3 speed. It will still be much wider than your T10 and start out easily in 2nd. Top speed will be the same. If you start changing axle ratios, you will lose your top speed.
     
    Last edited: May 21, 2022
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  10. May 21, 2022
    David Shackelford

    David Shackelford New Member

    Simi Valley, CA, USA
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    I really have no experience with these trans... prob should go see if I can drive one from someone else before deciding. As awesome as those gear ratios sound like they would be for a full-time rock crawler, I'm not sure driving that on a street every weekend would be a lot of fun. I am taking this thing through the rubicon once or twice ...but mostly it's going to be an occasional camping/trail/beach duty rig. I have plenty of time and I'm not in a hurry, feels like there is a better compromise out there ... maybe
     
  11. May 21, 2022
    timgr

    timgr We stand on the shoulders of giants. 2022 Sponsor 2021 Sponsor 2020 Sponsor

    Medford Mass USA
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    There's no place to put an overdrive behind a Dana 20 in a CJ-5. Overdrives are popular for the Dana 18 used before 1972, but the rear output of an 18 is offset more than a foot, leaving a place for an added planetary transmission inline with the engine.

    The T-176 used in CJs from 1980-on is an easy shifter, and has a 3.52:1 first. This would give you a crawl ratio of about 41 with current axle ratio. This is an aluminum case version of the Ford Top Loader 4-speed, made on contract by Tremec for Jeep. I think their main problem - they are considered "medium duty" and not bulletproof like the truck 4-speeds. The shift tops wear out too, and jam. Replacement shift tops are available, but they aren't durable like the truck 4-speeds. They also have a round New Process transfer case pattern, paired with the Dana 300 in CJs or the NP208 in J10s and wagons.

    The Borg-Warner T-19 is another possibility. It comes in three ratio versions, with a 4:1, 5:1, or 6.32:1 first. It's the same overall size and weight as the T-18, but has a synchromesh 1st gear. There's also a close ratio (4:1) T-18 used in CJs 1972-76, which shifts like any other T-18 and has the non-synchro 1st.

    Personally, I don't think the T-18 is such a burden to shift, but it's not like a passenger car 4-speed.
     
    Last edited: May 21, 2022
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  12. May 21, 2022
    Norcal69

    Norcal69 Out of the box thinker 2022 Sponsor 2021 Sponsor 2020 Sponsor

    Northern California
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    There's a few things to consider.
    Most of our group runs 33's on the Rubicon.
    35's with spring under suspension will most likely require fender clearance cutting if you wheel it very hard. Do you plan to go to spring over?

    28:1 crawl ratio is going to be pretty rough on the Rubicon even with a high grunt engine. I'm not saying its impossible to do...... but your going to be attacking obstacles with much greater speed than others. If your new to Rubicon its going to be a steep learning curve with that crawl ratio. Your more likely to incur body damage and find yourself in precarious situations.

    If your going to highway drive I would stick with 3.73 gears if you run 33's and make the crawl ratio up with the transmission. If you go to 35's I would go with 4.10.
    There is no better feeling than cruising at 65-70 mph on the freeway and the engine only turning 2,200 rpm.
    A T18 in good shape shifts from 2nd to 4th no worse than that Hurst t-10 shifter once you get a little sand in it. Ive been told that the NP435 transmissions are the best shifting of the HD 4 speeds. There is a Native GM option for the 435 that would mate easily to your SBC. The T18 is by far the easiest transmission to come by. Herm and Novak offer turn key units.

    E lockers, some people love them..... it seems like lots of people say "is the locker working?" My local gear guy has replaced allot of E lockers with ARB and OX units after the owners had problems. YMMV
    Have you considered ARB? With ARB you get the benefit of the air compressor for inflating tires, water toys, blowing dust off... ect. Just a thought.

    Everyone has their own magic combination that makes their jeep tick and only you can decide what your recipe will be.
     
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  13. May 21, 2022
    David Shackelford

    David Shackelford New Member

    Simi Valley, CA, USA
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    killer advice... thank you guys!
    I'm going to look into a few clubs around me and see if I can get some experience with the Transmissions mentioned above. I may need to rethink my stance on the "truck" trans. The T10 just isn't going to be the one methinks.
     
  14. May 21, 2022
    David Shackelford

    David Shackelford New Member

    Simi Valley, CA, USA
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    I'm going to stay spring under, and likely will stick with my 33's. the current set is fairly new and I have other issues to root out for now. I've never been on the Rubicon, but have decent experience with other locals (enough to know I need to worry about the current crawl ratio). I think you are spot on with the trans gearing recommendation as well. After playing with a few crawl ratio calc... the diff/tc doesn't make the needle move the same as the trans 1st gear does. So now I'm thinking I need the first-hand experience with the various transmissions you guys have pointed out and then maybe look into a tera low. Keeping the 3.73s for now.

    So far I am a fan of the e locker, but that choice was made for me by the PO. Going to run them until they break then re-eval if that happens. I've had ARBs before and agree those are prob the top of the line though/air compressor is nice to have as well.
     
  15. May 21, 2022
    dvader

    dvader Member

    Northern Nevada
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    If you end up going with a tranny swap, one factor in deciding the transmission is if you can find a transmission/TC adapter combination that is the same length as you T10 and TC adapter That would make it a lot easier.
     
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  16. May 21, 2022
    boopiejones

    boopiejones I can’t drive 55

    California east bay
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    I have an SM420 in my 56 cj. I don’t find the throw of the shifter to be too long. It’s definitely not short, but I wouldn’t call it obnoxiously long either. In my particular case, it’s coupled with 5.38 gears and tires that are about 32” tall. So 55mph is about as fast as it likes to go - which is fine by me as i have no desire to be going any faster in an old Jeep.

    If you’re ever in the Bay Area and want to give the sm420 a test spin, let me know.
     
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  17. May 22, 2022
    rejeep

    rejeep Well-Known Member 2022 Sponsor 2021 Sponsor 2020 Sponsor

    Rochester, NY
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    building a jeep with 1 goal in mind, that’s counter to the life it will live is a recipe for problems.

    Don’t try and reinvent the wheel.. it’s all been done before and if it’s it’s not common there is a reason for that as well..

    my CJ will do 90 mph all day long with one finger on the wheel drinking a cup of coffee, but also has 100:1 crawl ratio…. So it can be done.
     
  18. May 24, 2022
    cj2atruck

    cj2atruck Member

    Spokane, WA
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    Dec 12, 2020
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    I run an sm420 in my cj2a truck conversion, and it's a solid transmission...no slop. That first gear is so low it's unreal. I have a 93:1 crawl ratio in first gear, and agree with others, your 3.73 gearing is a problem without the right tranny. The sm420 is getting harder to find, but may allow you to run 35s with the low first gear. An automatic will help some, but I'm personally not a fan of automatic transmissions...
     
  19. May 24, 2022
    johneyboy03

    johneyboy03 The green beast

    Quebec, Canada
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    Th350 with a sbc with an adapter to the th350 and dana 20 is about 1" longer than an amc v8 t18 and dana 20 transfert case. Transmission is longer by around 5" but engine is shorter for about 5", you need to put engine as close as possible to the forn radiator.
     
  20. Jun 18, 2022
    David Shackelford

    David Shackelford New Member

    Simi Valley, CA, USA
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    just to wrap this up... met up with a few "new" friends and test-drove a few of these suggestions... I can see the pros and cons of each transmission recommended here as well as a few that weren't on the list. My first choice likely would have been the TH350, but I don't think my engine is far enough forward to work with the lift I have, and ultimately I'd still like to keep this rig a stick.

    For a hard-core rock crawler, all the suggestions above felt similar to me. There are differences in shift feel/throw and gearing, but the street driving felt very "truck" like, and that feeling is a bit too amplified for me in a small cj5 given that 99% of this rig's life will be light duty. I went down the rabbit hole of wheelbase stretches and all the mods required to make that work. Ultimately I decided to stay closer to the stock look, but I do need to get a better crawl ratio.

    Given that I have time to plan and a functioning jeep at the moment... I'm thinking that I'm going with a T177 and a dana300 teralow kit (4.1), 3/73 diff ratio, and staying with my 33's... should get me at or near a 60 crawl ratio. I may change the 3.73s (locked front and rear) to a lower ratio depending upon how she drives but this feels like a good enough compromise to get me through the rubicon 1X and then light duty street/trails afterward if I don't try to drag race her. Seems like I should be able to sell my T10 and dana 20 for a bit of change as well that might make that hit easier to save up for.

    Thank you for all the great suggestions, really helped me research and I learned a ton. Feel free to tear apart my logic here if you see fault in it. Hope this thread is useful to others researching the same stuff.
     
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