I know I ask alot of questions and i appreciate youre patience. I have another one. The first picture is of the transmision from an 82 chevy van and the second is from a 75' El Camino. Could anyone help me I.D them? Im trying to find out the gear ratio's so I can decide which one to use. Thanks again.



 

the last pict didnt work maybe this will.
engine mock-up/2 trannies  

The '57 El Camino trans is a TH350, 3-speed automatic. The trans otu of the Chevy Van is a much more valuable TH400.  

thanks i appreciate the help. Now i can try and find the gear ratio's.  

You can go to 700R4.com to look up the gear ratios, as they market the valuable O/D trannys, they use the THM-350 and THM-400 as comparisons. In fact I'll go look it up for you. Also, anytime you are unsure of part I.D, try to look for a number on it somewhere, usually a part number, or casting number. That can help ID them. If all else fails try to get a hold of some old Chilton's manuals. They have pictures to help you ID things like transmissions, engines, etc.  

Ok I did the work for ya and I'll list them starting with the THM-350 and axle for the El Camino. In 1st gear you have 2.52:1, 2nd gear is 1.52:1, 3rd is an even 1:1 ratio, and you 90% likely have a 3.08 axle in the El Camino. Your 82 Chevy Van has the coveted THM-400 correct??? This will be the transmission you wil want to use in your project. It is a MUCH stronger transmission and slightly higher gearing, which sacrifices lateral acceleration slightly, but the strength of this tranny far outweighs the gear ratio. Your first gear is 2.48:1, second is 1.48:1, and of course third is the known fact of 1:1. You axle in that van is a higher numerical(lower)ratio. Probably a 3.55:1 or something like that. I doubt they would put a 3.08 in it, and 3.73 would kill any kind of fuel economy on the freeway, but I'm not sure. You can find your ratio by pulling the pan off of the rear axle pumpkin housing. Then mark a starting point on your pinion gear and your spider gear(I think those are the names). Rotate the driveshaft or the tires, whichever is easier, and count the number of teeth on each gear. You then divide the no. of teeth on the big gear(Spider???) by the number of teeth on the litte gear(Pinion???). An example would be your 3.08 axle in your El Camino. You have 40 teeth on the big gear and 13 teeth on the little gear. 40/13 = 3.076923 or to make it simple you round up to a 3.08. This can be a messy task as you must cleanup and replace spilled gear oil, and the gear oil stinks too. It is the best way to do it if you don't have any ID tags remaining on the rear axle, or don't know what rear axle is in it.  

Hey, I think you can mark the drive shaft and then rotate the tire one complete circle. count how many times the drive shaft rotated and how far past the start point it went. A 355 gear should spin 3.55 times per one axle revolution. that is the clean and fast way  

RodBender:
Hey, I think you can mark the drive shaft and then rotate the tire one complete circle. count how many times the drive shaft rotated and how far past the start point it went. A 355 gear should spin 3.55 times per one axle revolution. that is the clean and fast way

I think you're right, but I couldn't remember. So I just went with the textbook definition. Used to work in a salvage yard years ago, and they did it your way, I think.