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Opinions on gear ratio?

Discussion in 'Differential & Driveline' started by RecklessWOT, Aug 8, 2019.

  1. RecklessWOT

    RecklessWOT Full Access Member

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    I'm going to be re-gearing my truck soon and just want a little feedback on what gears y'all are using or what you would recommend.

    It's an '87 v10 Suburban with a 700r4, 10 bolts front and rear. Currently it has 3.73s which were fine with the wee little 235/75-15 tires that came on the truck and it was tolerable with the 31x10.5s also. Now that I have 33x12.5s it is completely unacceptable, I can't stand driving it the way it is. I haven't been driving it much the last couple years but now that I'm using the truck more often again enough is enough, time for new gears.

    Doing the math, a set of 4.27s will basically put it back to how it was stock, but I've been thinking of 4.56s instead. I do a decent amount of towing (not a shitload, but enough that I am taking it into consideration), and that 350tbi isn't exactly a powerhouse to begin with so a little extra torque would be appreciated. My only concern is that I do drive on the highway a lot, and I've never been one for obeying speed limits- I'd say 80-85 is my average cruising speed. I don't know if the 4.56s will be too short, I don't want to be driving around at like 4500rpm for extended periods of time. I'm aware they make gears much shorter than that and even 4.56s aren't ideal for towing with 33s, but I have a few friends that can't reasonably go more than like 70 on the highway with their trucks and I just want to make sure I won't end up in that boat. I feel like they're only a little shorter than what should be on there so it won't be a problem at all, but I barely remember what driving this thing felt like with the baby tires on it so I have no clue how my RPMs would compare.

    Long story short, to anyone else with 33s and a 700r4, what gears are you running and how are they working out for you?
     
    Last edited: Aug 8, 2019
  2. 73c20jim

    73c20jim Supporting Member Supporting Member

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  3. gmbellew

    gmbellew Junior Member

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    I have a 90 v1500 burb, 350, 700r4 with 3.73 and run 33x10.5 on the stock 15inch alloys. It is far from peppy, but gets around decent enough on road, is fine offroad, and cruises the highway at 74-75 without issue. But I'll be curious to hear other experiences on this one.
     
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  4. Arkansas_V8

    Arkansas_V8 Proud Redneck

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    I run 4.10s right now on 37s. But I have a th400. I dont find it to be any issue. I have a set of CUCV diffs waiting in the wings with 4.56.

    I had 3.73s in my old Suburban with 35s for a long time with a th350, was a 700r4(junk in my opinion). I never once found it to be an issue. Swapped to 4.10, never thought about how much better it was.

    But I think 4.56 with a 33" tire is overkill. A 4.10 would be plenty for what you want.
    (^off roader in me^)



    So just consider this whole post for naught.
    I hate your trans, ran one for less than a year. My whole post was off road biased! Lol, sorry.
     
    Last edited: Aug 8, 2019
  5. Nonstop

    Nonstop Full Access Member

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    My truck runs 4.56s with a 4 speed and 35s. My freeway driving is pretty much at 65mph. With that, I have no experience with a 700r4 and towing. From what I have HEARD (so of course take it with a grain of salt) that is not a super strong trans. The 4.56 gears would likely help take some of the stress off the trans when towing and likely prolong its life. I would likely go with the 4.56s, you should be happy with them and probably get better mileage too.
     
  6. RecklessWOT

    RecklessWOT Full Access Member

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    So we have basically the same setup. Yeah I can go fast on the highway all day at low RPMS and not burn a lot of gas, but man if I mash the thing to the floor going up a hill or something it can't get out of its own way, sometimes it won't even downshift because the 700r4 is geared so high as it is. I live in new england, there are moron drivers everywere, sometimes you gotta pick up speed to pass or merge or whatever. Towing is also a nightmare.

    Yeah the 700r4 is not a super good trans for towing. It can overheat easily, but that's why I have a B&M trans cooler and an AT temp gauge instead of a clock. It does alright I guess.
     
  7. RecklessWOT

    RecklessWOT Full Access Member

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    Hah yeah I've looked at that chart before, with 33s and 3.73s I'm below the yellow "economy" recommended, and that's for 1:1, so with the OD I'm even less than that lol.
     
  8. gmbellew

    gmbellew Junior Member

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    I definitely have to give it some advance help to cruise the ozark hills on the highway, but I dont have an issue getting it to downshift. Moderate hills it can handle on cruise control, often without a downshift. Big ozark hills, I will give it some gas coming up to the hill and usually can either keep it from having to downshift, or at least I control the downshift and keep it from hunting for gear. It doesnt perform that much worse than my 2004 z71 suburban does (it's a stock setup). But arguably, the 2004 is under powered for its weight...
     
  9. Frankenchevy

    Frankenchevy . Supporting Member

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    What is your rpm at when 4th goes into lockup?

    2500 rpm is pretty good for a average power sbc.

    I have 3.73s and 33s and I’m at that rpm on the highway. I have a th400 though at 1:1 final. If I swap a 4l80, I’m going between 4.11 and 4.56 which means a carrier swap.

    That .75 O.D. won’t cut it with 3.73s
     
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  10. RecklessWOT

    RecklessWOT Full Access Member

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    Well the 400 does not have OD whereas the 700r4 does, so yeah if I didn't have the OD I'd stay with taller gears. But 4.10 would put my gearing even lower than it was from the factory, I'd have to go with 4.27 just to get back to factory spec now that I have 33s

    (and FWIW I agree the 700r4 is junk, but that's what the truck came with and it still works so I'm not gonna fuck with it. When I finally get around to getting a 454 I will switch to a turbo 400)
     
  11. RecklessWOT

    RecklessWOT Full Access Member

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    It almost never locks in OD unless I'm going stupid fast, and even then it's only for a second, in and out cause it's so hilly around here. I'll have to pay attention to the tach next time I'm out on the highway
     
  12. gmbellew

    gmbellew Junior Member

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    If you aren't worried about the MPG, just run in D on the highway instead of OD. It will keep it in 3rd gear.

    If the issue is around town, different gears would be needed to make an improvement.
     
  13. Arkansas_V8

    Arkansas_V8 Proud Redneck

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    Yeah, I already changed the bottom of my post to address this.


    But hey, with 4.56s, you would be ready for a 37"-40"(37" max with 10 bolts) tire with that th400. Maybe meet me on the trail some day.
     
  14. RecklessWOT

    RecklessWOT Full Access Member

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    Hah it's all good. I don't wheel the burb much. I have a couple times when I was out west, and got bored and hit the power lines near my house once or twice, but it's mostly tight woods trails around here so it's just too damn big to do any real wheeling with it. When I was big time into off-roading I ran mini trucks, a lot of old Yotas and a couple s10 blazers in my past.

    I probably won't go bigger than the 33s for what I use this truck for. I talked myself out of 35s last time I bought tires and still might get some next time, but for now it's good how it sits. I had 35s on my K5 and I loved the way that thing looked, but this Suburban rarely sees more than the occasional unmaintained dirt road so I think any bigger is overkill.
     
    Last edited: Aug 8, 2019
  15. Arkansas_V8

    Arkansas_V8 Proud Redneck

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    We are nothing but woods around here. About an hour to Disney Oklahoma(great rocks). I make the Suburban fit. Closest TRUE mud pit is about 3 hours away.

    But sorry to intrude, back to original programming.
     

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