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Info needed about Ring and Pinion

Discussion in '1973-1991 K5 Blazer | Truck | Suburban' started by BigCUCV, Jul 15, 2003.

  1. BigCUCV

    BigCUCV Registered Member

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    Hi guys,
    I still have my original 3.08 Ratio Ring/Pinions for the 31inch Tires in my Differentials, but driving 38.5SuperSwampers.
    I figured out that with 38.5 tires I would need a 3.77 ratio, does that sound ok??? (i'm driving 95% highway, very little off-road)
    where is a good place to buy Ring and Pinion Kits???
    thanks for your help!!!
     
  2. BlazerGuy

    BlazerGuy 3/4 ton status

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    3.77 is too high, I would say that you need at least 4.56-4.88s more like 5.13s...
     
  3. Jonny-K5

    Jonny-K5 1/2 ton status

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    if you drive 95% on streets and with no overdrive you probubly want 4.10's or 4.56 gears. 4.10 will be a big improvement over your current gears but wont provide the power that 4.56 or bigger will. all depends on how fast you drive on the freeway. at 65mph with 4.10 youll be turning about2350 rpms. with 4.56 it'll be around 2600. the 3.73's that you were thinking of will put you at about 2100, but would give you much of a performance increase. i dont remember what the redline is on your diesel, but its not much over 3000. So if you like going 75+ down the highway, 4.10 would be better, if not i think 4.56 will make you happy.
     
  4. MTBLAZER89

    MTBLAZER89 3/4 ton status GMOTM Winner

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    Try here they have a lot of formulas.
     
  5. Jonny-K5

    Jonny-K5 1/2 ton status

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    i just used a formula in one of my catalogs to calculate gear change

    new tire divided by stock tire = % of change x original gear ratio= new gear ratio

    it came up with 3.825 .. closer to 3.73 but i'd still recommend the 4.10 because of heavier tires and increased drag from the lift (wind drag)
     
  6. BigCUCV

    BigCUCV Registered Member

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    at 4Lo I've calculated that with 31" tires the motor makes 2170/min at 65mph
    with 38.5 tires at same speed and same revs it comes up with 3.83 ratio
    with the 4.10 ratio it would make about 2325/min
    but remember: there is no speed limit on German Freeways!!! /forums/images/graemlins/grin.gif
    so I've thought I'd rather go a little bit down with the revs instead of letting the motor rev to death.......
    the next available ratio from 3.73 up, would be a 3.90, would that be a good compromise????
    I mean its between 3.73 and 4.10 and the revs would be at around 2210/min
    and yes you're right: the 38.5 are a lot heavier and have more drag so I think I should go with 3.90.........
     
  7. rjfguitar

    rjfguitar 3/4 ton status GMOTM Winner

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    One question, what the heck are you doing with 38" swampers if you don't go offroad and do mostly highway driving? Highway driving is very hard on those tires especially at 75mph, they will probably seperate on you. If they don't you are very lucky. I would first go to 3/4ton or 1ton running gear then probably 4.88's and keep it around 55mph.

    85K5 3/4ton 14bolt/10 bolt, 9"lift,35" boggers 16.5x14welds, big horse 406SBC/700r4 /forums/images/graemlins/k5.gif
     
  8. BigCUCV

    BigCUCV Registered Member

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    actually the 38"s are doing very well at 65, haven't been driving them over a long distance at speeds of 75 or more though,
    but I just like the looks of a lifted truck and I think you agree that it would look very funny with an overall lift of 9" and 31" tires.......
     
  9. rjfguitar

    rjfguitar 3/4 ton status GMOTM Winner

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    yeah I agree on the looks, although I like 35's with 9" much better, 38's look stuffed in the fender wells to me. I would go with a super lift 12" with 38's /forums/images/graemlins/thumb.gif It still is hard on them at any freeway speed especially 60mph and above.

    85K5 3/4 ton 14 bolt/10bolt,9"lift,35" boggers,16.5X14 welds, big horse 406SBC/700r4 /forums/images/graemlins/k5.gif
     
  10. RootBreaker

    RootBreaker 3/4 ton status Premium Member

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    i know a guy that has a ferd f250... 12" leafs and 44's... ran 5.13 gears.... great off road truck and perfect gearing offroad... he also has an automatic....

    now he has always kept the truck nj legal... his daily driver... so now we are allowed only 38's... he left the lift on but took the 3" body lift off and put 38's on. he told me that the 5.13's were killin him... he went with 4.56's and said that is perfect.....

    you can look at gear ratio and tire charts all you want.. they are to give you ideas... sometimes unrealistic too....
    you will only learn by experience and the expensive part is if you dont get it right the first time....


    good luck. /forums/images/graemlins/thinking.gif
     
  11. BigCUCV

    BigCUCV Registered Member

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    thanks for all your ideas guys
    now, where is a good place to get the stuff????
    I was thinking of Summit, they take around $570 for two sets with Installation Kits...........
     
  12. wrathORC

    wrathORC 1/2 ton status

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    OK, my truck came with a 305, 700R4, NP208, and 2.73 gears. It turned around 1400rpm at 60mph in overdrive with 235x75r15 rubber. Throw on the 33s and overdrive is useless. Put it in overdrive and it feels like someone threw out a parachute.

    I now have a very healthy 305. It has a lot more top end than the 350 I had in it until I had a pump failure but it is kind of girly on the bottom end.

    Recently I lifted my truck 4" and stuck 3.42 axles under my truck on the same 33" rubber. We're talking about a world of difference. I can easily hold AND accelerate in overdrive up a hill. At 70mph I'm cruising at 2000rpm and it takes a pretty steep grade for me to have the torque converter unlock or drop a gear.

    I used to get 505 miles out of 40 gallons of gas with the old gears and no lift. I now get 505 miles out of 31 gallons of gas.

    More importantly, it is now driveable in the city and overdrive is now usable. I still don't run fourth gear if I'm not on the highway but I also don't find myself leaving it in second gear until 45mph like I used to. I used to have to try to get a tire to smoke without the brake and my 2.73s. I can now easily roast a tire with the 3.42s by merely stabbing the throttle. If I roll on the throttle I can make the tires chirp at every seam in the asphalt up to 40mph. That is one heck of an improvement.

    Since your 6.2 oil burner makes its torque a boatload sooner than my 315 gasser you can easily get away with only turning 2000rpm at 70mph. If you do as much driving on asphalt as you say then don't overgear it. Some people might like listening to a motor sing 2500-3000rpm at expressway speeds but I don't.
     
  13. rjfguitar

    rjfguitar 3/4 ton status GMOTM Winner

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    There's one thing that everyone is forgetting and that is that big tires are hard on automatic transmissions. Add the stock gears with a set of large tires and it's only a matter of time until that tranny gives out. I was told to do something right away when I had 3.08's and 33"'s and now I hear about guys running 2.73's and big tires. That is equivelent to pulling a medium sized trailer around all the time. Tranny and rear end shops including offroad stores(ex. 4wheelparts) recommend 3.73's and 4.10's with 33", 4.10 and 4.56 with 35", and 4.88's and lower for anything bigger than that. These recommendations are for good all around performance.Just tryin' to save some trannys out there. /forums/images/graemlins/cool.gif

    85K5 3/4 ton,14bolt,10bolt,9"lift,35"boggers,16.5x14welds,big horse 406SBC/700r4 /forums/images/graemlins/k5.gif
     
  14. wrathORC

    wrathORC 1/2 ton status

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    Yeah, I be guilty of that, mon. I've beat my truck with 31s or larger for 20,000 miles with 2.73s. My 305 scares most 350s in the process. I've been waiting for my 700R4 to bite the dust. It's one of the "early" ones anyway with almost 85,000 miles on it now.

    But I keep it out of overdrive if the torque converter unlocks. I have the large stock fluid cooler and that keeps things pretty cool. I don't know many people that'll drive their vehicle around in second gear because the "stoopid" 2.73s and 33s will make the torque converter unlock like I do. The first time I replaced the filter (just after I got it) it was relatively clean for a plow truck even though the magnet had about a teaspoon of metal on it.

    I think if you keep the heat at bay, the torque converter locked, and keep it from searching through the gears it'll last a long time.

    I know I've run mine through the gears manually quite a few times with a great many 6,000rpm shifts and it is still going relatively strong. If I do it too many times in a row there will be a slight bobble going into third gear because she's getting toasty.


    I've got 3.42s now and let me tell you they're great. I can hold overdrive easy on the highway and even accelerate up moderate hills. I can easily hold 70 on the expressway in overdrive (around 2,000rpm) and go up decent hills as long as I don't have a headwind. I get a hundred more rpm at 75mph and she does even better there. My speedo is way off though. It used to be with the 2.73s and 33s I was going 70mph when my speedo showed sixty and now to go sixty my speedo shows 68mph.

    If I run in third gear I have plenty of power to tow. I don't think 3.73s or 4.10s are necessary as far as highway and expressway speeds are concerned unless you've got a really girly motor. 3.73s would probably be ideal but I don't think it is necessary to overgear to 4.10s for 33" rubber. You'd be going deaf at 70mph in third gear and you don't need that to be able to hold fourth without a trailer.
     
  15. rjfguitar

    rjfguitar 3/4 ton status GMOTM Winner

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    sounds like you know how to listen and feel your tranny's converter, that probably is what will save it. Some guys like those higher gears and thats ok with me but I've had both high and low gears and there's no comparison. The higher ratios are more sluggish no matter how much power you have. Question why did you build a 305? I had 3.73's with 33" and a 406 SBC that puts out way more horsepower and torque than any smaller cubed V-8 and I couldn't wait to get my 4.10's. I can light up my 35" boggers with 4.10's no problem but I know I couldn't with any gear higher than that. It's all about putting your speed in your power band of the motor. I'm very suprised you like 3.42's with a 305 because that is not generally a torquey motor but if your rig is somewhat light than it wouldn't be to bad. My guess is your K5 is still a 1/2ton and that makes a difference, when I went 3/4ton I could feel the weight difference. As far as the noise It's not that bad because overdrive quiets the motor way down no matter with 3.42's or 4.10's, besides whats wrong with listening to a big cammed 406 wound up through long tube headers, dual 2 chamber flowmasters, and dual 5" tips. /forums/images/graemlins/cool.gif

    85K5 3/4ton 14bolt/10bolt,9"lift,35"boggers,16.5x14welds,big horse 406SBC/700r4 /forums/images/graemlins/k5.gif /forums/images/graemlins/angryfire.gif
     
  16. wrathORC

    wrathORC 1/2 ton status

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    I've seen the inside of a 700R4 and I can't believe they survive as well as they do. There are a great many things that I see in the world that I can't believe can handle the abuse they get served. Therefore I usually try to maximize the maintenance so I can still beat on them without breaking.

    I rebuilt the 305 because I had it at my parents' (they could take it to a respectable machine shop--Reichert Racing engines--Bill is on TV once in a while) and needed a motor. The only other motor we had there that was a Chevy was a 327 besides two 305s. It is morally wrong to put a 327 in anything but a musclecar. I broke an oil pump input shaft on my 350 so it needed to be tore down even though I replaced all the main bearings. I could get another 350 where I'm at but not where my parents were at.

    It ended up being a budget rebuild. It was meant to be a "backup" motor and was going to be replaced by a 350 this summer. However, I ran out of money in April so no 350. I'll probably end up swapping engines for the third time in a row during spring break.

    I ported the heads, had the valves done by a friend who has an old stone-type machine and then shimmed the springs, bored it .060" over, new Speed Pro hyp flat tops and moly rings, emery-clothed the crank, new timing set, 262H cam and lifters, ARP main studs and oil pump shaft, stocker non-EGR intake, and an oil pump. It moves pretty good, probably as good or better than the 350.

    The last time I weighed my truck was last fall which was before the lift and the truck box I have with a bunch more tools than I normally carry. At that time it weighed 4400lbs with everything in it including 40 gallons of gas. The truck box probably added 100lbs but the conversion to rear disc and the removal of my interior probably got rid of 50lbs. I did add a receiver on the back and the front lift springs actually weigh the same amount as my stockers (weird, eh?). I'd say it weighs around 4500lbs now. I scrapped the 14FF idea because it weighs 180lbs more than a 10 bolt and deprives me of case clearance. I have faith in my 10 bolt that it won't break again even with 33s. I don't plan on going bigger because the vehicle gets to wishy-washy for my liking.

    I think I'm getting old. I don't like noise anymore. I have some cheap mufflers under my truck right now that are kind of noisey. They now dump under the bed because in late April I backed over my driver's side tailpipe so I cut them off after getting mangled. At idle the noise is so bad you can't talk over it. If I bump the rpms up to 1200 it goes away. It sounds awesome a parking lot away with the goofy exhaust and mild cam but it sucks in the cab.

    I'd go for deep gears in a trail vehicle but not in a daily driver. Especially since I run pizza cutters in the winter (235x75r15). It's too easy to spit teeth off a ring gear with 4.10s on a axle with a ring gear smaller than 9.5". 4.56s and you're down to 1 tooth contact patch. 4.88s if you breathe on them wrong they're going to give up the ghost.
     
  17. rjfguitar

    rjfguitar 3/4 ton status GMOTM Winner

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    Yep I agree about the teeth that is a problem but with the lower gears it is easier on everything else. I know what yer saying about the budget buildup, been ther done that, I think a stroked 327 would be pretty cool though, something different. Do you like that comp 262H? I have the 268H in my 406( check out my profile for engine specs. if interested)and it delivers a nice lobey sound at idle an lots of torque. I'm thinking of going 1:6 roller rockers for a little bit more lift but if I do that than I think I'm going to go with a 4" stroke crank to make it a 434ci.What do you think? As for the gears again, I am looking for a dana 60 front(9.75RG) like everyone else and if I find one than I'm going to change to 4.56. There is a serious weight gain with 1ton gear I'm weighing around 5,000 plus pounds with a 10 bolt front, drums still on my 14bolt,35"boggers,etc. P.S. how big of a difference did your rear disks make? /forums/images/graemlins/ears.gif
     
  18. wrathORC

    wrathORC 1/2 ton status

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    Well, I've always wondered about how much easier on things it is. I know it's easier on a transmission but you'd think it'd be harder on the motor. I know if I run third gear at 70mph my motor isn't working at all, there is no load on it. That can't be good. I don't know, I just figure the torque multiplication from the gears has got to be harder on everything else further down the line.

    Well, 327s are those rare critters that you don't let out of your site. Sure, they're essentially just a 350 with a 3.25" stroke but it is hard to find an original 327. We've got one with a forged crank from 1968.

    The camshaft is alright. The duration is a little high for such a small motor but it helps the pathetic heads breathe and fill the abnormally long stroke to small bore ratio at high rpm. It has around 13" of vacuum at 850rpm with 6° of advance. It prefers 12° but 91 octane is $1.88/gallon here so I run it a little late so I can get by with 89 with my 9.44:1 pistons. At about 475 (the lowest it'll idle with foot on the brake in gear) it is down to just under 11". With my exhaust that gives you the headache at idle (it reverberates in the cab, actually making the inner shell of the cab vibrate) it sounds pretty lopey and cool. It doesn't "churn" like the 272H that is in my 350. That cam only put out 11" of vacuum at 750rpm with 13° advance.


    I've always had a theory about smallblocks. Why try to make bigblock power with a smallblock? Those 4" cranks are $600 for a cheap one. You're going to need either long rods with pistons with the wrist pin in the "wrong" spot or run really low RPM with a short rod. For that kind of money you can start spending some money on a bigblock and be happier. I know that's what I'd do. I mean, once you get past the $1500-2000 TCO mark you might as well go with a bigblock.

    Then again, I'm the kind of person that is happy with "enough" low end but I like to hear it scream at six grand. A 350 gives me enough idle and off-idle performance for the woods. The 315 doesn't quite hack it. The 350 gives me enough for cruising too. However, it never gives me enough ricestomping WOT fun.

    My goal is to buy a cast 3.75" crank and have a 383. It'll give me enough low-end to make me happy and if I run 5.7" rods with an ARPed bottom end she'll stick together at six grand. It'll still be cheap if I run cast or hyp flat tops with a cam. I'll do my normal porting. I should be able to get around 400ponies and about the same amount of torque with a 272 cam. It'll be a cheap motor and money can be saved for a bigblock.


    As far as a Dana 60, I'd like to have one. There was one in the paper in downstate Michigan for $500 a month ago. I would've liked to have it but I don't need it. It'd be something that got set on the shelf for the future. In my opinion it isn't needed unless you wheel really hard with 36x14.50 or bigger rubber. After that, it's pretty much a trail only rig because it isn't much fun to drive on the expressway. I don't know, some people like barreling down the expressway on 38s with 6" of lift or so it seems.

    A 14FF and a Dana 60 is a waste on 33s though. I'd lose ground clearance and gain about 450lbs. I always used to have problems getting hung up on my NP208 before my lift, now it is my differential cases dragging. If I gained that extra weight it'd be even more of a dog in acceleration and more unsprung weight is bad for handling. Yeah, I expect my truck to handle well (read: not ride well, just handle well).



    I like the rear discs. Took me a while to figure out but it was the best $130 I've spent thus far as far as offroading goes. It is so nice not to have to pull the tires off and hose out the drums. It is really nice to know that I'm not going to lose an axle shaft if a c-clip breaks.

    However, now that I don't have to pull the tires off I'm less inclined to switch back to my street tires. They don't lock up like the drums did when I stomped on the brakes even though I'm not running an adjustable proportioning valve. The drums used to lock up then slowly release. The drums worked fine as long as they weren't full of mud, sand, and sticks when I rolled the brakes on slow. They'd still lock up before the fronts though. Now all four lock up at the same time. There's a definite improvement in stopping distance because I don't have to let off the pedal waiting for the rear tires to start spinning again before I get back on the pedal. I haven't had to use my brakes in an emergency situation yet but I'm willing to bet it'll be much nicer than just staying on the brake and letting the rear tires stay locked up and just stop the truck with the front tires while trying to keep it pointed straight. It's weird how that worked because I could brake the truck hard and as long as I rolled them on they wouldn't lock up until the last 10-12 feet.

    It's pretty cool to have the brakes recessed deep into the wheel and not see any parking brake lines hanging way down like my old previous owner disconnected ones did. Plus, it has the bling factor. "Dude, not only does your Honda have Wrong Wheel Drive but it's got rear drums" is my favorite line.
     
  19. 87BrnRsd

    87BrnRsd 1/2 ton status

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    I dont know about in Germany, but if I was you, I would buy some 1 ton stuff, like a 14ff rear at least. A front 10B should be able to hold up to the the 38.5's since you dont offroad, and the axle wont be engaged. You can get a 14ff and a front 10B with matched gears (3.73, or 4.10) from a junkyard for cheaper than the price of re-gearing. It is also easier to swap in new axles than it is to re-gear. Plus, you will have a 14ff to push those 38.5's since a 10B rear like you have now wont hold up to them, and WILL eventually break, even on the street! My brother has a rear 12B with 35's and 3.08's, and he has only had the 35's on there for about 7 months now, and the is already chips and burn marks in the ring and pinion. /forums/images/graemlins/eek.gif Given he does offroad, but it is stronger than a 10B. Luckily for him, I sold him a 14ff which he is putting in soon, so he can really wheel and not have to worry about breaking an axle.
    -Harrison
     
  20. R72K5

    R72K5 Banned

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    finally, a thread that shows that there are soem individuals out there who understand differences between high and low gear ratios and understand what is better for highway or for acceleration and also understand effects each has on drivetrain and drivelines, my stepdad pisse me off cuz he is ignorant o the fact that his 2.73 are killing his 208 and th350 in his 81 K-10 shorty, he rails that thing all the time like its 3.73 and yanks boats ourt of water with it revving the hell out of the engine and then a neighbor of his likes to throw a ton or ton and a half of rock in it all the time and lug it around and says "oh its ifne it will haul it fine"

    plus the junk POS original autolock hubs, he says "oh i dont want to get out of the truck int he mud to lock them"
    they have slipped and grinded in the past, im waiting any day now for them to lock or explode on him,
    the oriignal tranny was a 700r4 and 82 was first year and they were junk when they were brand new, now its th350 and he had to have it rebuilt once already.
    he doesnt understand why and he is mechanically inclined and 44 years old,

    choose gear ratios in axles carefully.. base it all on use you plan to get from the truck, and how often too.


    good luck
     

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