Thread: Gear ratios??

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Here's a question somebody should be able to answer.

How can a person find out what the rear end gear ratio is on a 1980 Chev Malibu?
Is there a tag on the rear axle, or can it be broken down from the VIN# somehow? Perhaps a GM site that has info??

Thanks, Bill

On some rearends, if you pull th cover off and spin the ring you can find a number over another number, like a fraction. Divide the top number by the bottom. That will give you your ratio.

I thought everybody used a peice of chalk and a jack ? ......

Originally posted by techinspector1
Place wheel chocks under the front tires, place the trans in neutral and jack up 1 rear wheel off the ground so you can spin the tire. Have a buddy slip under and make a chalk mark on the driveshaft. Leave him under there to count revolutions of the shaft. Turn the tire exactly 10 revolutions while he counts revolutions of the shaft. Now, divide the shaft revolutions by the tire revolutions. 35 1/2 revs on the shaft (35.5/10) = 3.55:1, 38 1/4 revs on the shaft (38.25/10) = 3.83:1, etc., etc. I have no idea what the actual ratio might be. I'm just using these numbers for example.

ya ! ....... thats what I said .......





T L

Thanks fellows. I have to admit the inspector made the chalk bit a lot clearer... Now if I can just find a friend who wants to lie under my car I hope that jack isn't still leaking....

I admit I had thought of something along the same line, but it seemed too simple..I always thought they tagged rear ends in the old days. My other newer Chevy still has the build specs on the glove box door, which is real handy!

now go on the net and find out what the options were on a 1980 Chev Malibu, and your half way there .......


and ya.. .. tech is better at Splan'N then me .......



T L

There is something I don't understand here. In trying to figure out whether I have a 3.50 or a 3.55 ratio rear (probably a 3.55 since it is an 8" Ford rear, but the shop guy insisted it is a 3.50) my son and I tried the chalk mark trick. We jacked up the right rear wheel and the left rear stayed fixed. We counted 35.5 shaft rotations for 20 rotations of the right rear tire and 71 rotations of the shaft for 40 rotations of the right rear tire. Thus the procedure given by Tech1 gives us 1.775 which is unlikely. I think the problem is that you have to know if you have a positraction rear or an open-differential. I agree that the method Tech1 gave is correct for a positraction rear, but in my case I think the factor of 2 is caused by the differential spider gears?? With that factor of 2 included we get 3.55 and give the warning that one needs to know if you have a positraction rear or and open differential.

Don Shillady
Retired Scientist/teen rodder

On an open rear end, you have to multply the results by 2 because the differential will cut the ratio in half if only one wheel is turning. In Don's case 1.775 x 2 = 3.55. This may not be exact, but will give an approximatation that you can relate to available ratios. Hence the difference your shop guy claims.

If the rear end is a positraction/limited slip/traction loc/spooled or whatever then your count will be the actual number of turns, but you are not going to be able to turn one wheel easily with the other wheel on the ground.

If you have the rear end apart, divide the number of teeth on the ring gear by the number of teeth on the pinion to get your ratio.

Pat

Originally posted by Don Shillady
There is something I don't understand here. In trying to figure out whether I have a 3.50 or a 3.55 ratio rear (probably a 3.55 since it is an 8" Ford rear, but the shop guy insisted it is a 3.50) my son and I tried the chalk mark trick. We jacked up the right rear wheel and the left rear stayed fixed. We counted 35.5 shaft rotations for 20 rotations of the right rear tire and 71 rotations of the shaft for 40 rotations of the right rear tire. Thus the procedure given by Tech1 gives us 1.775 which is unlikely. I think the problem is that you have to know if you have a positraction rear or an open-differential. I agree that the method Tech1 gave is correct for a positraction rear, but in my case I think the factor of 2 is caused by the differential spider gears?? With that factor of 2 included we get 3.55 and give the warning that one needs to know if you have a positraction rear or and open differential.

Don Shillady
Retired Scientist/teen rodder

ive been wrong before but i dont think anybody makes a 3:50 ratio. if you get that close it will be a 3:55.

lt1s10, I agree, there is a 3.50 gear set for the 9" Ford rear but I have only noted a 3.55 ratio for the 8" Ford Rear and the ratio we got with the tire rotation method gives 3.55 for both 20 and 40 tire rotations so I am pretty sure the ratio is 3.55:1. It only matters for the mechanical speedometer gears and I have already obtained a set for my tire size and 3.55 rear. I may/may not use an electronic speedometer, but I want to retain the option for a mechanical speedometer. DennyW the second site you list also shows only a 3.00, 3.55 and 3.80 ratios for 8" rears in that range. The only logical (lawyer talk, math-speak) question is whether I actually have an 8" Ford rear. I saw the '74 Maverick it came out of which had a 302-V8 and five lug bolts so I believe it is what is called an 8" Ford rear and the 3.55 ratio seems right.

Don Shillady
Retired Scientist/teen rodder

OK, so how can I be sure it is an 8" Ford rear?

Don Shillady
Retired Scientist/teen rodder

Richard/Tech1, Thanks. By that check it is indeed an 8" and one more indication that the ratio is 3.55:1, so I have the right set of speedometer gears. Thanks. (The unheated garage was OK for a quick check on the rear bolts, but it seems that the warm weather is gone for now and too cold to work in the garage even with a small heater. Anyway I think I made a good move to get the engine, trans and rear upgrade done by a shop. and I will assume I have a 3.55 rear gear.)

Don Shillady
Retired Scientist/teen rodder

As they say a picture is worth a thousand words!

Now how about a pic of the malibu's rear end differences...

I tried a web search for options for the malibu that year...no luck so far...Anybody have a web site they know of?

what motor? is it stock? if not what was stock,,,,,,,?

3.8L
4.4L
5.0L
5.7L

At this point it is totally stock with the 4.4 mill. I have been reading my butt off trying to get ideas on how I can turn this inherited (late Father's) Malibu, into a nice looking street machine, with a little rumble.

I am currently trying to decide on what engine may do me best, 327,350 seem to be the best choices so far. I did read one thread on a fellow who put a few mods on a 267, and it sounded quite impressive, but I don't know if he was joking or not...? I suspect the stock tranny may not have the gumption for more power, (although I am still trying to find out more about it.) so I suspect the 350TH will end up in it, when I do an engine swap.

I have about 2000 questions, but am fairly new to the forum, and don't want to overrun it with my concerns..8>) I thought I would work into it slowly...