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kuta1972 02-28-2012 11:09 PM

86 c10 gearing
hi all,i wont to change my diff gearing on my 86 c10 shortbox..gearing is standed at the moment and has no take off power at all..dont really care about highway revs but then again dont wont truck to be ringing out at 60mph...alittle lost in what rearing would suit...trucks running a 355 chev with fuelie heads and tow is a shaft kitted 350 with standed converter..i think its standed is blue but can't find any info on it.was going to go 4.11 but was told on the open road she be reving hard out.keen to find out if there any truck owners on hear that have 4.11 gearing and how it runs..cheers all

SSedan64 02-29-2012 11:18 PM

There are several rpm/speed calculators online.
Input a few Rear ratios, Tire sizes etc.. to see what the rpms will be.
Here's a few:
2nd down >>

I wouldn't go highwer than 3.73 if you plan on crusing the road. 3.42, 3.55 are good all around ratios.

American Muscle 03-01-2012 01:03 AM

I have 86 C10 with 3:42 gears and a 700r4 tranny with 255/70/15 tires(29in tall). She pures on the interstate at around 2000rpm at 70. And can burn the tires through second with a mousey 305sbc. Was thinking of going 373 or 410 but thats too much tire peeling fun for me.

75gmck25 03-01-2012 04:51 AM

My '75 GMC has a TH350, 4.11 gears and stock height 31" tires (245/75R16). When I drove it to work this week I was running about 2700 rpm at 60 mph. This is not hard on an SBC 350 engine, but it gets fairly noisy in an old truck with very minimal sound insulation. I also have an old chain-driven transfer case generating noise right under my seat, so your 2WD truck should be a little quieter.

I'm going to replace the stock hood insulation blanket (mine fell apart) and also add insulation (dynamat, etc.) to the back wall of the truck behind the seat and to the inside of the doors to see if it helps. I already have full carpet with jute backing, but there is still a lot of bare metal in these old trucks.

Bottom line answer - 4.10 gears work fine and the rpm won't hurt the engine, but the higher rpm makes more noise and the truck sounds like its working a lot harder. This noise increase makes some folks uncomfortable if they are used to modern cars where you can cruise at 60 without any obvious engine noise.


kuta1972 03-01-2012 11:07 AM

i running 325/60r/15 bfgoodrich..finding them hard to come by now so i'll be going 275 or 295 wide my next set...running 40 series flowmaster muffler with no carpet so would need ear muffs with 4.11s lol...mite go high 3s by the sounds of you guys reply...any gains in messing with the converter and putting in a higher stall..i'm getting mixed replys from people some say that the stock convertor is bogging down the truck and some say not to bother if it a mild build..thanks for replys

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