Axle help...Please....

[LuvMy86Camaro]

Please help anyone for I am at my wits end....
When I bought my 1986 camaro its speedometer was not displaying accurately (I think it was about 10 under what it should have been at 60 mph). The vehicle was equipped with a 2.8L (yuck!) with a five speed. The RPO says that the axle is a 3.42 (GU6). As soon as I got the car home, I pulled the engine and transmission and I replaced them with an L69 HO and 700R transmission from an 84 Z28. I also grabbed the instrument cluster because I knew I needed the V8 tach and the speedometer. I removed the computer and emmission controls, and replaced the distributer with non-computer contolled Accel, the carb with a holly 750 double pumper with vacuum secondarys (overkill I know but I had the carb), the manifold I replaced with an edelbrock rpm air-gap. Now after driving down the road it is still about the same mph off of what it should be. I checked the 84 camaro and it was supposed to be equipt with the same axle gear ratio of 3.42. I tried to varify my axle code on my 86 but mother nature has rendered it unfindable where it is supposed to be. I lifted the back wheels off the ground and put the tranny in nuetral to spin the axle by hand and see the ratio of the axle and tires but got wierd results. It only took 13 turns of the axle before the tire turned 10 times!!! Is this suspect and could this be what is causeing the speed to be off on both combinations? Any help would be most welcome.....

[ridge_runner]

its not your axle that determines the speed its the tranny..... the speedo cable goes right into the transmission

[LuvMy86Camaro]

Also my start offs are slower that what I would have imagined they should be with the rpms that are being produced.

[ridge_runner]

mine was the same way, i jus lived with it, mine came with a 2.8 5 speed, its got a 700r4 in it now, but i have an autometer speedo, havent drivin the car with it hooked up, but id say your gonna have to get it calibrated?? or maybe a new speedo cable for the 700r4 will fix it im not sure..

[LuvMy86Camaro]

I used the cable that came with the 700r and speedometer.. wierd though.

[ridge_runner]

hmm, the 84 prolly had a different gear ratio

[68chevelle]

all you have to do is change the gear in the trany.

[LuvMy86Camaro]

i thought about that but i used everything from the 84 but the axle and rive shaft. The tranny, the cable, the engine, the gage cluster with speedo and tach, it all came from the 84. When I checked with a speed program it says that with 3.42 axle and at 1600 rpms with the tranny in od at .7 I should be traveling at 52mph. But I've clocked it and I am actually traveling at 62mph. Only with the 2.73 axle should I be traveling at 62mph in .7 gear.

[LuvMy86Camaro]

Or with the 3.08 axle. Any way it's just wierd that in both cases...the 2.8L with 5 speed and the 305HO with 700r that both were off.

[68chevelle]

all GM mechanical speedo's are calibrated at 1000RPM's at 60MPH. so that means that you would not have needed to change the guage because of that. that also means that the car you took eveything from came with a different rear gear than you have. thats whats causing your speedo to read incorectly. now like i said above, all you have to do is change the gear in the trans. you will need to find out what gear you have in there, that means removing it and looking at what color it is( they are color coded for the most part but that can not be the only thing you go by) and count the actaul teath on the gear. then you will need to get a gear with a higher number of teath so that it lowers what your speedo reads.

[LuvMy86Camaro]

Ok. thank you. I will do that. You say that I should get a gear with more teeth or less? My speedo actually reads 50 when I am going 60.

[LuvMy86Camaro]

Also you don't think it was weird that even bore I changed everything over to the 86 that my 86 speedo was off almost the exact amount?

[LuvMy86Camaro]

The reason I ask is because my original concern wasn't really with the speed being off but with the possability that I might not have the original axle. 13 turns to 10 is rather odd. To my understanding, a 3.43 means that I should be able to spin the axle by hand 34.3 times for every ten turns of the tire.

[68chevelle]

umm ok, now just to clarify, cuz now your saying the reverse. your speedo reads 50 when the car is going 60, then you will need to decrease the number of teath on the gear. but like i said thats backwards from what you said a few minutes ago. no i dont really find that weird. out of everything you changed only one thing makes a difference in what the speedo reads, and thats the trany itself. there are two gears(that control the speedo reading), a drive and a driven. somewhere along the lines something had been changed in your car to make your speedo not read corectly, it could have been the rear, because i think you probably have something like a 2.73 or a 3.08 as oposed to the 3.43 you are talking about. im not sure cuz i dont feel like running the numbers to find out for sure, but i would almost be willing to bet it. now if you want to check, the easies way to do it if you have no idea what rear you have like posi or open and the one way to be sure is to...
1. jack the car up and put axle stande under the rear
2. take off the rear cover
3. look at the ring gear and find the numbers stamped into it. on the outer edge facing you somewhere it should have the number of the pinion and the ring gear stamped in it.
4. devide one number by the other, example=(33/11. thats just an example, but the big number devided by the little number)

then you will know your rear end ratio. dont forget to put the cover back on and put new gear oil in, and then you will know for sure if you have a posi or not, and you will probably have to turn the rearend when your trying to find the numbers stamped on the rig because you cant see all of it at once.

[68chevelle]

umm ok you probably dont have the original ratio like i said above, but if you want to do it that way, if you dont have a posi rear then jack up the passengers side tire only. then you really need to people because it is easy to count incorectly. now have someone under the car looking at the drive shaft, mark it some how so you know for sure ever turn, now have someone at the pass. tire. now kinad slowly rotate the tire 2 turns, and have the person under the car cound the rotations of the drive shaft. you need to be precise in your turning of the tire, (the valve stem works pretty good as a referance), and of the counting of the drive shaft. now you take the number of turns that the drive shaft turned and guess what, thats your rearend ration. so there ya go.