I have a 1985 T5 transmission and it needs to be replaced. On Craigslist a guy has a T5 from a 2004 V6 mustang with low miles. Can I swap the input shafts? So I can install it in my mustang?
You will need to find a older T5 that has the same gear ratios as the 2004 T5 in order to swap the input shaft. Otherwise the number of gear teeth on the input shaft will be different.
When you swap the input shaft, you should plan on checking the clearances and preload on the input shaft and bearings. See the Tremec Site to download a T5 service manual.
T5 identifier information.
On the tail shaft of the transmission, there will be a stamped aluminum tag. The tag will have a number on it that you can cross reference to the chart below. There is no other way to find out what type of T5 it is without disassembling it. All the rest of the numbers on the outside of the T5 case are part numbers which are not unique to any particular T5 model.
Remember that 94 - 97 T5's have a longer input shaft (about 11/16” longer) and can only be used with a 94-95 bell housing unless you modify or replace the input shaft.
T5's used with a 4 cylinder have a 3.93 first gear, reduced torque ratings and an input shaft pilot diameter that is smaller that the T5 used for V6 & V8 engines. The pilot diameter is .59" compared to the .668" used on V6 & V8 T5's. It requires a different pilot bearing to be used with a V6 or V8. The pilot bearing you need is for a Ford Ranger diesel from AutoZone part #14672
I don't know how you feel about the DYI thing when it comes to gears, some people don't like the idea of working on transmissions. If the DYI transmission fix idea isn't something that you would rather leave to someone else, here are some resources:
A T5 rebuild kit with syncros, bearings and other small parts costs about $160. It does not include any gears or shafts.
http://www.hanlonmotorsports.com/ also has a video on how to rebuild your T5 or Tremec. It costs about $20, and is worth every penny of it.
I did a Tremec 3550 rebuild, and it wasn't that difficult. The video was an immense help, and I would recommend viewing it. At $20, it will give you an opportunity to look and decide for yourself if you think that it is something you want to try to do.
T5 Shim kits – best product I have seen in a while… http://www.5speeds.com/t5/shims.html
“The Peel ‘n Place T5 World Class shim kit makes shimming T5 counter gear and main drive gears very easy.”
Is your T-5 original to 1985? IIRC, the countergear changes in 1990 meaning the input shaft for the 1990-later T-5's is different thatn the pre 1990 T-5. You really need to confirm what gearset you have in your trans now.
Question is can you swap the input shaft and tailhousing? There is spec on preload and such so that when you assemble it with the correct input shaft, you will need to measure and shim it properly.
If not, perhaps you should focus on finding a Fox 90-93 T-5 in good shape.