O/T Chev truck rear ends

old · Nov 3, 2009

Ok so I think I found where the piece came from which is bad news since they are part of the pinion gear. So is there any way to know the gear ratio of a rear end with out opening it up and counting teeth?? I have 1 half ton rear end from a 1969 but know I would need to use my housing with the ring and pinion from it. I also have 2 3/4 ton rear ends and if one of them would be the same gear ratio as my 1/2 ton one I would just swap the whole rear ends if they will bolt in that is. I figure if I can put the 3/4 one in that would give me better/bigger brakes and also a heavier rear end.
Thank for any help you can give me

glennster · Nov 3, 2009

there may still be a tag on the rear end, bolted to the pumpkin, either on the fill plug or the rear cover bolts. if not, kind of a down and dirty way, but if you put a mark on the axle flange, then spin the yoke where the driveshaft hooks up, count the revolutions of the yoke to get one full revolution of the axle. say you turn the yoke 3 and 3/4 turns to get one revolution out of the axle, its about a 3.75 ratio. not real exact, but its a ball park.

old · Nov 3, 2009

Ops I left out the fact this is a 4X4 truck so the 2 axles have to match or I could end up with a truck that would tear its self apart if put in 4 wheel drive.
And no tag on my bad rear end and sure wish I knew what the numbers I see on the ring gear mean

rustyfarmall · Nov 3, 2009

Rich, the V.I.N. plate on the dash, or maybe it's on the door jamb, will tell you exactly which axle you have, but it is in code, and you will need to decipher that code somehow. Also, sometimes you can find a "build" sheet tucked into the back of the seat, but yours is probably gone by now.

Bill in IL · Nov 3, 2009

Chevy used to put the options on a sticker in the glovebox if its still in there. Sometimes in code sometimes not. May have to web search to find the codes meanings.

bradk · Nov 3, 2009

Count the ring gear teeth,then the pinion teeth.Divide the ring number by the pinion number and you have your ratio.

Example.37 ring teeth 9 pinion teeth.37 divided by 9 equals 4.11

chevytaHOE5674 · Nov 3, 2009

Look in the glovebox for the RPO code sticker. If its still legible there should be some that start with Gxx, Like G80(posi traction), or GU6 (3.42 ratio) etc. Post up what you find.

trucker40 · Nov 3, 2009

Well on the 3/4 ton you would need to put the master cylinder and rod that pushes it off of the 3/4 ton to get the better brakes maybe.To get an idea of what a ratio is mark a wheel,turn it all the way around and count how many time the yoke turns.If it turns a little over 4 turns thats a 4.11.A little less than 4 turns is 3.90 or 3 and a half would be 3.50 3 and a third 3.30.Cars would be higher except maybe a station wagon.Just about any ratio could have been ordered or changed.3/4 would probably be lower than 1/2 ton,especially if it came out with a 6 cylinder engine.If it came with a v8 it might be higher than a 6 cylinder but still lower than your 1/2 ton.There might not be an exact match between 3/4 ton and half ton,but I think I read somewhere that you want the faster or higher rear end on the front of a 4 wheel drive.I dont know how much difference you can get away with,not much probably.Like 4.10 on the front and 4.11 on the back.

dlplost · Nov 3, 2009

"And no tag on my bad rear end"

How about a tag on the front?

BCnT · Nov 3, 2009

your local dealer can tell you from the vin #

carman870ky · Nov 3, 2009

There should be an 8 or 9 digit part # then something like a 41 followed by, say a 16. Divide the 16 into 41 and you get the ratio. In this case a 2.56 Your #s WILL be different. This is just an example.

JDemaris · Nov 3, 2009

Just jack one wheel off the ground, put the trans or transfercase in neutral, and turn the one wheel - and see how many turns it goes to make the driveshaft turn once. Very easy to do.

If the wheel turns 1.8 revs to the driveshat turning once - it's a 3.73 ratio.

It if the wheel turns 1 3/4, it's a 3.42 ratio.

If the wheel turns 1 1/2 turns, it's a 3.08 ratio.

Note that if one wheel won't turn on it's own, you've probably got a posi-rear and you'll have to get both in the air. Also the math is different.

If both rear wheels turn together:
Wheel turns 3.7 turns to the driveshaft once - 3.73 ratio.

Wheel turns 3.4 turns - 3.32 ratio.

Wheel turns 3 turns - 3.08 ratio.

old · Nov 3, 2009

I didn't think about that. Of course I still have to figure out the gear ratio on the donor

PJH · Nov 3, 2009

Isn't it the other way around JD? I think the driveshaft makes several revs to one wheel rev - or am I confused???

Paul

rustyfarmall · Nov 3, 2009

Yes, the driveshaft will make more revolutions than the axle.

JDemaris · Nov 3, 2009

Yes, I was in a hurry and stated all backwards.
Not an uncommon event for me.

E.g. a 3.73 ratio is 3.73 turns of the driveshaft to one turn of both back wheels (if turning together . . . or 1/2 that if an open differential with only one wheel turning.

old · Nov 3, 2009

Well other then the fact the smaller number is first then the bigger one you are right. My ring gear has on it 13:40 which as per the Chev dealer makes it a 3:08 rear end so at least I know why I get so good on gas for what the old truck is

rustyfarmall · Nov 3, 2009

There should be a bunch of those 3:08s out there somewhere.

old · Nov 3, 2009

Ya local salvage yard has one for $350 but then a new one is also at least that much and that is just for the ring and pinion set so guess no matter which way I go it is going to cost about the same

Jeff B. · Nov 3, 2009

Usually they will stamp the ratio or tooth counts of the ring & pinion right on the side of the ring gear. Spin it around while it's still in the housing and you will find a GM part number followed by the ratio or tooth counts, and then the date of manufacture.
If the cover bolt counts are the same e.g. 10 bolt or 12 bolt rear end, then the stuff will swap.

schmuck · Nov 4, 2009

Keep one tire on the ground so that it cannot spin. Mark the pinion and housing with chalk or a paint stick. Turn the tire that has been raised TWO full turns and count the pinion revolutions. This DOES work.

schmuck · Nov 4, 2009

I forgot to say, if the differential is a limited slip or posi-trac, this WON'T work.

schmuck · Nov 4, 2009

I had a 3.08 rear end in a 2-wheel drive 1/2 ton. Pulled it out and put a 3.73 in it. HOLY CRAP! You would think I just pulled out the small block and put in a big block. Course, it wouldn't run 55 MPH in first gear anymore either ...

JDemaris · Nov 4, 2009

1/2 ton 3.08s are all over the place. I have over two dozen sitting out in my field, in 4WD Blazers, trucks, and Suburbans. A few older 12 bolts in late 70s stuff, but mostly 10 bolt from the 80s.

I've never come across any 3.08s heavier axles, 14 bolt and up. All mine are 3.73 and 4.10.

Clefus · Nov 4, 2009

If you swap a heavier rear in you may need an adaper u-joint for your driveshaft...
As long as you get the same ratio, you could get a rear from another make as long as the spring perches are the same width....different mfgs used Dana over the years also....
Still trying to find a reasonable Dana 60 or GM 14 for my mudbog truck...have a Dana 44 for the front...

steve n carol · Nov 4, 2009

(reply to post at 09:50:24 11/03/09)

Okay,

here's a story,... Kid at work had a ramcharger (4WD). He only had the front drive shaft on it. When asked about it, he told me that the rear diff went out and he was waiting for $ to fix it. Meanwhile, he was driving on the front drive axle..... For 3 1/2 years!!!

This was in the 70's. Front wheel drive was available but a bit unheard of...

Now, Old, read up on how to "set-up" the gears on your new 'ring and pinion', if you go that route. It's not rocket science. AND, if you buy used, open it up at the junkyard and inspect the unit BEFORE you buy it!!!!!! EVEN if it's gaurrantied javascript:emoticon(':lol:')
Make sure that there isn't too much slop in it also. Have fun, get someone to give you a hand installing it. Yes, you can do this by yourself, but why?

case in point....
:
:

I had a shop in Central Lousy-ana (a long time ago), my father decided to come by and use the concrete slab (as the lift was in use, to change the rear axle. The truck dropped on him while he was underneath on his side.
Well, being the hic that he was, he chose to use some (2) chunks of Cypress logs as jackstands. Oh Yeah, he was as strong as he was stubborn too. Good thing. We all heard the truck go down. The axle was out from underneath it, but he wasn't. I looked out there and the look on his face was something to remember!! I could see that he was okay. I should have got a pointed stick and poked him a few times while the pokin' was good :lol:

Be careful...sl

O/T Chev truck rear ends

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