I have finished my 62 and put on 1777 miles. It's got a 700R4 with a low enough 1st gear so I want to change the ring and pinion but cant find ant. Has anyone else ever have this problem? I have a 305 and with the tire size I got about 12 to 13 mpg. I am looking for a ratio between 250 and 275.Don't know exactly what the differential is but here are some pictures and #s. Would appreciate any help.
You will probably have to change the whole rear end to get the gear ratio that you want. Those old trucks didn't come with gears past 3.73 as far as I know. Most were in the 4.11 to 4.56 range. The low powered 235 6 cylinder engines didn't have enough power to pull higher gears with a load and the roads were not really good enough to go very fast anyway. Most people swap in a first gen Camaro or a late '60s or '70s Nova rear end. If you wanted to keep it looking somewhat original then you could use a '57 Chevy car rear end and put a early '60s car chunk in it with a 3.08 gear.
The only common place you will find that ratio is from a 70s cadilliac. Measure your rear track width it may be close. Unsure of the bolt pattern off the top of my head.
Another option is a brownie with .8 or .7 overdrive and your current gears. Let you slap it in high or direct from a craw for the conditions and leave it in there. No need to cut up your floor. Most have the direct and high on a single lever letting you cable or silionoid operate it. If you wanted low then you need a shifter.
I would like to get a overdrive but as you can see the truck is lowered and I had to cut holes in frame for pipes. It probably will be a rear swap and to save a lot of time looking does any one know one that will work with minor adjustments.
The rear ends that I listed above are pretty close to the correct width. The bolt pattern will be different. A later '60s GM 1/2 ton 12 bolt might be a better choice because of the 6 lug axles. They will be about the same width too. There are 3.07 gears available for that rear end.
GM used SWING arm Rear suspensions up thru 1972 as i recall... i would bet you can get a later rear end with different ratios that may bolt up.. somebody will know.. that is an EATON rear end.. probably 11,000 GVWR rated..
i don't like the color of the gear lube.. it looks like it has been contamintated with WATER.. please check the vent tube.. that is has a piece of HOSE that go up and over.. or long enough to go up between the truck bed and cab somehow.. so driving thru deep water does not cause the hot housing to get cold and suck water into it.
if you plan on keeping that rear end.. you might want to change the oil 2 or 3 times in the next few weeks.. or until it comes out just as clean as when you put it in.. ps you have to drive it and get it up to operating temp for a while to blow the moisture trapped in there
thanks waynep712 . That picture was taken 3 years ago and has been cleaned and new oiled. This rear does not have a vent on the axle that I remember and I was worried that I would blow a seal. I am going to change it out but if for some reason I don't I will drill and tap one in.
With the overdrive tranny, I suspect your main problem is the tune and/or build of the engine... what year engine? Is it stock? May have a surprisingly low compression ratio... Should get better MPG than that in easy driving...
Can put rear end on jackstands and count the driveshaft turns to rotate both rear tires one complete turn... i.e. 3 1/3 turns = ~3.33 rear gears...
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Head on over to JalopyJournal.Com, and in the classifieds, is a vendor selling 3.38:1 gears for 55-62 Chev/GMC trucks for $310.00. That seems like the BEST way to me. junior stocker.
with a 700r4 and a 305 (in the first post), maybe the answer isn't in the rear gear, but in the engine tune. Also, is the lockup converter functioning properly?
Most carbed engines aren't very efficient below 2200rpm.
2wd truck up to (iirc) 69 are 6 lug..
12 bolt rear ends, should bolt in.. chevy had long arms the gmc didn't
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