I'm checking the ratio of my 71 cutlass. I turn the dirveshaft 1 turn and the wheel turns 1.75. I have tried holding the other wheel(not posi) and I get the same result. I know the is no such thing as a 1.75 to 1. So what am I doing wrong??????

 

Your numbers sound off. For non posi rears, you need to turn the tire two revolutions (keeping the other still) and count the driveshaft revolutions to determine your gear ratio. I don't see how the driveshaft revs can be less than the wheel's?

 

Ill try that thanks

 

I read somewhere that you want to rotate the tire 10 times and count drive shaft rotation to get a more accurate average. I tried it, and came up with some wild number that correlated to nothing. I eventually opened up the diff to find a pegleg 2.56 12 bolt. that will probably be changed to a 3.42 or thereabouts possi. IMHO oppening up the diff is the most accurate way to determine what you actually have.

 

OK then, for perhaps a more accurate result, turn the wheel 10 times (with the other held still) then divide the number of driveshaft rotations by 5. Easy to see chalk marks on the tire and shaft may help increase accuracy as well.

 

Sorry aliens. I wasn't trying to refute you. I cant type for doo doo and it takes me forever to post anything. I didn't even see your post. If it works great, but it didn't for me. I probably did it wrong.

 

Pull the cover and count the teeth = foolproof

-Richard

 

No need to apologize, csstrux, and if I came across as smarmy, was not my intention (even if I have been known to be so on occasion), I was just giving the conversion if you want to try the approach you suggested.

 

Here is what I was taught in High School in the horse and buggy days.

Open rear end:

Jack up one wheel make a chaulk mark on the tire that lined up with a chaulk mark on the floor. Make a chaulk mark on the drive shaft that lines up with a chaulk mark on the housing. Turn the wheel one revolution and divide by two eg: 6 turns = 3.00:Ratio. If you use the starter to turn it must be in high gear to work

 

Wow, they taught you that in high school, huh? (now I AM trying to be smarmy).

 

The problem with an open rear is that unless both wheels are turning the same amount, you run the risk of getting bad data. If one side is held firmly, then the other wheel will always turn exactly twice as many times due to the differential. The best thing to do is to block one wheel. Turn the other tire and count the driveshaft. I like to turn the tire 10 times instead of once because it can be hard to tell the difference between 3.42 turns of the driveshaft and 3.23 turns. On the other hand, the difference between 34.2 and 32.3 is pretty easy to tell. Keep in mind that if you have an open rear end and you've blocked one wheel as described above, the driveshaft will only turn half as many times. As an example, ten turns of the wheel with a 3.42 axle will produce 16.1 turns of the driveshaft.

Of course, if you have any sort of limited slip axle, you won't be able to turn one wheel if the other is blocked. In that case, jack up both and simply divide the wheel turns into the driveshaft turns.

 

Don't you mean 3.23 ratio (i.e. ~16.1 / 5, see my post #5 above) or 17.1 turns?

 

DOH!!! Yes I meant to type 17.1...

 

I had auto shop from 1962-1964 had a full machine shop in those days built everything from scratch.

The auto shop had a 1953 ford wagon that was given to it new in 1953 Every senior class took that car apart and through out the senior year we put it back together again for the next senior class. Taught us a lot about cars. Now it is just class room training. We used to go to local, State and National meets to Compete on who had the best high school auto shop teams. That was fun. So, no I have not forgot everything in my 62 years

 

My buddy (the one who took all the pictures of the project and helped me out) teaches automotive. They still have hands on training in his school district. They still get new or newer cars donated for use by the students. The last one they got was an '05 Cadillac.

 

Thanks to everyone for the help. Now I need help to get new gears.
I tried it 3 times and kept getting the same answer 2.53. Not the
answer I wanted to hear.

 

Thanks to this I found out I have a 2.56 rear. Took both kids out to help. Then explained what the different rears do. My 15 year old daughter is becoming more interested in helping. Maybe starting another car nut.

 

Wish my shop classes were like that. All the stoners and trouble makers took shop cause they knew that as long as they were there for roll call they would pass. Needless to say... I didn't learn a whole he(( of alot in shop. Most of what I learned was on the side of the road. I ran A TON of old junkers, but they were cool cars. 60's chubbies, and 70's oldses and a 70 bronko. the bronco was the only one that really was in good condition, and being a kid I destroyed it. But I can say honestly I owned a lot of classics and "cool" cars.