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Stay with 4.10 or go with 4.56?

Discussion in '1973-1991 K5 Blazer | Truck | Suburban' started by Wheels, Jul 22, 2001.

  1. Wheels

    Wheels 1/2 ton status

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    Here's the deal. I have a Corp 12-bolt that has 4.10 gears in it now. The pinion bearing is acting like it wants to head south. The engine has plenty of torue and HP, but at 70, it wants to jump in and out of 4th when climbing hills, not sure if this is because of the pinion bearing. Since I have to change the ring and pinion, thinking I may as well go with the 4.56. This will raise the rpm up from 2046 @ 70 to 2250 @70. This is gets into the power band of the motor a little better. My only problem with 4.56 is the heat generated by the lower gears. On a 40 mile trip, the 12-bolt gets hot. Any one else running 4.56 gears in a 12-bolt and do you have any heat problems with it?
    Running 350/700R4/NP205, turning 33" tires. Thanks ahead of time.
     
  2. CaptCrunch

    CaptCrunch 1/2 ton status

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    I would think that is an excellent combo.. 4.10's and 33's I mean. I have 4.10's and 35's (they measure out at 34" though) and it is pretty good. I am debating or looking to possibly go to 4.56's because I may end up going bigger tires... But really it depends on how much freeway driving you do... I would probably stick w/ 4.10's if it is is a daily driver or mostly pavement because 4.56's are gonna suck the gas pretty good at freeway speeds. Plus one thing to keep in mind it the 700r4 has a pretty good overdrive... it drops from 1 to 1 down to .7 in forth and it really is made to downshift for hills, passing, etc. at high speeds. That is the purpose of any overdrive tranny... cruise at a lower rpm, but kick bat to 3rd for good acceleration and power.

    -Mikey
    1987 Chevy K5 Blazer- 350 TBI
    <a target="_blank" href=http://www.geocities.com/milnerlives_2000/blazer.htm>http://www.geocities.com/milnerlives_2000/blazer.htm</a>
     
  3. 1990K5

    1990K5 1/2 ton status

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    4:56's all the way, i have a 1990 w/ 4:56's and 35's and a 700r4, it is perfect, infact i was thinking of going to 4:88's and it would still be very hiway happy, im getting 15+mpg now!!
     
  4. 84_Chevy_K10

    84_Chevy_K10 Banned

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    If you're keeping 33s, go with 4.10s. If you're going bigger, go with 4.56s or 4.88s. I've got 4.10s and 35s now, and if I change my gears again, it's going to be 4.88s.

    Tim
    '84 Chevy K10, lifted, loud, fast, and 3/4 ton axles
     
  5. ftn96

    ftn96 1/2 ton status

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    IF the gears are set up right, the 4.56 shouldn't get any hotter than the 4.10's.

    I've got the 4.10 setup with 33's right now and have beend debating the same thing. I think but haven't made up my mind yet, but if you mostly drive on the highway, I'd stay with the 4.10's. But if you are going to be driving around in town alot, stop and go and wheelin every chance you get. I may lean towards the 4.56. Alot of this depends on weather your going to have to have someone else install them or not.

    Beer!!!! Its not just for breakfast anymore!!.[​IMG]
    <a target="_blank" href=http://www.nashvillek5.freeservers.com>www.nashvillek5.freeservers.com</a>
     
  6. ftn96

    ftn96 1/2 ton status

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    PS, the tranny changing gears on a hill from overdrive 2 third is normal. With a .7 drop from the 1:1, is a a big jump in my opinion. With my 4.10's adn my 32 inch 33's I run a little on the high end of my power range, but when I get on a hill it wont stay in 4th very long at all. Every 700R4 I have ever ridden with has done this. Maybe GM shoulda designed the overdrive to be a little less of a jump than .7

    Beer!!!! Its not just for breakfast anymore!!.[​IMG]
    <a target="_blank" href=http://www.nashvillek5.freeservers.com>www.nashvillek5.freeservers.com</a>
     
  7. I would go 4.56 or 4.88 with an od tranny.You still are running low rpms on the highway and you get better 4 lo power,just my opinion though.I'mm going from 3.73's to 5.13 with 36" tires and I'll still only be turning about 2300 at 70 mph.
     
  8. ftn96

    ftn96 1/2 ton status

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    Yeah, but chad your just a sick twisted ol Tn boy. LOL!!!!!!!!


    Beer!!!! Its not just for breakfast anymore!!.[​IMG]
    <a target="_blank" href=http://www.nashvillek5.freeservers.com>www.nashvillek5.freeservers.com</a>
     
  9. txbartman

    txbartman 1/2 ton status

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    A couple of things... I have 35s with a 305/700R4 and am running 3.73s. I am going with a gear swap to 4.56s shortly. While the RPM will be higher, the engine will perform better by using less throttle at higher speeds. Higher RPM but lower throttle should equal if not improve my gas mileage. I will be sure and let you guys know what I find out here. I was getting 10MPG before I added my 35s. Now I get 9.

    As far as the tranny shifting, it may not have as much to do with your gears as you think. I had 32s/3.73s with my 305/700R4 before. And my engine is tired as it has over 200,000 miles on it. It used to do a lot of the 3-4 shuffle. Even on fairly level roads at highway speeds. I serviced the tranny (new oil and filter) and it has worked perfectly ever since. My problem was that the oil level was a little low. As it would heat up, it would have problems and tended to shuffle. Even with a tranny oil cooler, the low level caused it to just get too hot. So, if you haven't serviced your tranny in a while, I recommend doing that first. It only costs about $15 and may buy you some time before getting your gears. Lower your ratio will definitely help as well, but I would still do this. In addition, if you don't have a tranny oil cooler, think about getting one. Especially if you spend much time on hills. Finally, if you are going to be in the rear end changing gears, think about a locker or a posi. The cost of labor for my gear swap is the same whether I have a locker installed at the same time or not. Hence, I have decided to go with dual lockers with my swap.

    Just my pennies...

    Brian
    Click to see <a target="_blank" href=http://tx85gmcguy.alloffroad.com> My 85 Jimmy </a>
     
  10. Leadfoot

    Leadfoot 1/2 ton status Premium Member

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    Why do you NEED to replace the ring and pinion? If the pinion bearing is going south a complete rebuild kit (less than $100 with lube) should be all you need (unless you wait for it to grenade). Yes, if you are going through the hassles of pulling the pinion out to change the bearings it would be the perfect time to change gears IF you need to, but you don't have to and could save a couple hundred bucks. Plus get ready to shell out several hundred more for doing the front end to match. Just some food for thought. 4.10's or 4.56's should be fine with 33's and a 700r4. If you are thinking bigger tires definitely go 4.56's but if not, you need to decide if the expense of changing both R&amp;P's are worth it for you. If they are, then go for it. Good luck with whatever you decide.

    If you didn't build it yourself, how can you call it yours.......?
     
  11. 6.2Blazer

    6.2Blazer 1/2 ton status

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    Most likely the heat buildup in the rear axle is due to the fact that the pinion bearing is going bad. 4.56 gears shouldn't run any hotter than 4.10's.

    The transmission shifting when going uphills is pretty much normal for an overdrive. The overdrive gear was meant to be used when cruising at highway speeds on fairly flat roads. The gearing in o/d is just too high for the engine to be able to pull up much of the slope, especially with 35's and "only" 4.10 gears, and the trans will attempt to keep the engine in the proper rpm range for best ecomony and performance. Also, keeping the trans in o/d while climbing grades can cause a lot of additional load and heat buildup. My suggestion is to manually downshift the trans out of o/d when climbing grades, driving around town, or on back roads where you really never maintain a good cruising speed. Every time the trans shifts it causes wear and heat.

    I do think that 4.56's would be better suited for 35" tires and an overdrive trans (though 4.10's are not that bad), in both performance and mileage.....I wouldn't be surprised if your mileage increased, at worst it will probably stay the same.
     
  12. I have 3.73's with 35 gumbo's right now and od is a useless!I can use it if I'm going dowm hill!LOL The tired old 305 don't help any though.I'm building a 350 for it now,I can't wait.

    FTN 96 Your just sckered to run them deep gears!LOL
     
  13. bigblue

    bigblue 1/2 ton status

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    Well I have 3.73's with OD and, yeah, Can't use OD unless going downhill. But oveall better than my 3.42's. Luckily the 208 is low geared. I plan on going with 5.13's when I re-gearr....
     
  14. Wheels

    Wheels 1/2 ton status

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    Thanks to all for the inputs. The tranny isn't the problem. Just went through it for the third time this year. (pump face was slightly warped causing pressure blow by). Finally got all the shift points right. The ring and pinion have devoloped an unusual wear patttern from the deflection of the pinion caused by the bad bearing. Backlash has opened up to .026 from .008 as originally set. Havent taken the pinion out yet to see which one of the bearings have failed, so a pinion rebuild only would work, but may be a temporary fix. Since I'll have it apart, might as well put a new set in (along with the Detroit locker sitting in the garage). Gas mileage? Not a worry here, aerodynamics of a Blazer is like driving a sheet of plywood through the wind. Thanks again.
     
  15. Executioner

    Executioner 1/2 ton status

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    Did you correct the odometer each time you chaged the gears/tire size ?
    10 miles to gradma's house is still 10 miles independent on tire size, and gears !
    +/- 10 % at 10 MPH, can be a big # for a 1000 mile trip !
     
  16. ftn96

    ftn96 1/2 ton status

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    Ok, RE-read your post again. As for the heat, the gear change will not increase your heat. The extra heat is more than likely the bearing failing.
    But none of this has to do with your transmission.
    So if you are a pavement pounder stay with the 4.10's
    If you be a wheelin, then go with the 4.56's when you go to replace the pinion bearing.................

    Better yet, just sell me that 12 bolt. As I need one with 4.10's. Seriously, call me, I'll buy it!!

    Beer!!!! Its not just for breakfast anymore!!.[​IMG]
    <a target="_blank" href=http://www.nashvillek5.freeservers.com>www.nashvillek5.freeservers.com</a>
     
  17. txbartman

    txbartman 1/2 ton status

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    I understand what you mean on the aerodynamics. Take at look at mine through my link below. Try putting a rack on top with the 8" round lights like mine has. I feel like I am driving a couple of 8' tall refrigerators into a headwind!

    Brian
    Click to see <a target="_blank" href=http://tx85gmcguy.alloffroad.com> My 85 Jimmy </a>
     
  18. Wheels

    Wheels 1/2 ton status

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    Got tired of spending 50 to 60 bucks a pop. Went to an on board GPS using 5 sec speed averaging. Right now 75 mph indicated equals 71.4 mph on GPS. Plan is to swap out entire instrument cluster with a Dakota Digital unit, right after I win the lottery...
    ftn96 - Sell the 12 bolt? sure, if you can get Gary off his butt to get the Dana 60 out from under his parts truck. Weather is too hot here to work long outside (100+)
     
  19. Leadfoot

    Leadfoot 1/2 ton status Premium Member

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    There is a valve that takes care of this. Look at <a target="_blank" href=http://www.700raptor.com>www.700raptor.com</a>.

    #20. 700R4 full throttle 3-4 up-shift sleeve. Now you can have a full throttle 3-4 shift. At 80 MPH it takes 90% throttle to make a 4-3 downshift. Can be installed without removing the valve body. The Up-shift Sleeve also eliminates part throttle 4-3 downshift for less gear searching. Cost $49.00




    If you didn't build it yourself, how can you call it yours.......?
     
  20. Wheels

    Wheels 1/2 ton status

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    Thanks. I'll add that to the parts list. I have a week and a half off from school and a ton of parts to put on. Plus some fishing, mowing what little grass has grown in this hot weather....and of course, the wife honey do's
     

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