FWIW, I had a T5 from an '85 GT in my old '65 GT coupe behind 300 hp. When I sold the car the transmission had probably 200K miles on it. The only problem I ever had with it was prior to adding an aftermarket shifter with the positive stops. During a hard shift, the mechanism broke inside. Oh yeah, it used ATF in the transmission and it is a "World Class" transmission, though their were stronger ones produced later.

 

Although it's not the original topic of discussion, I do believe they did. I was just looking at one a few weeks back on cars.com (it's been sold so I can't link the page or check the year) that I believe was an 84 or 85 5.0 w/4 speed.

 

I was wrong. I was thinking that tremec started making the WC T5 in 86 but it came out in 85. Here is a little history of the T5

World Class & Non-World Class
There are two basic kinds of T-5's, Non World Class (NWC) and World Class (WC). The first T-5 was non-world class. In 1983 and 84 Ford used the Non-World Class T-5 to improve the Mustangs performance and gas mileage. All the V8 NWC boxes had 2.95 first gear set with .68 overdrive. All the main output shaft gears and 1st, 2nd, 3rd, gears riding on a solid output shaft with deep oil grooves to provide lubrication. The lower counter gears spin on straight cylindrical bearings with a thrust washer in front to provide support when under load. All the synchronizer rings are made of solid bronze which are of different size than those found in a would-class T-5. It is because there is no bearing under each gear and the bronze synchro rings that the NWC use the heavy 70w gear oil. Torque rating for the NWC was 265ft/lbs.

1985, Ford introduced the World Class T-5 installed with 3.35 first gear set with a .68od behind the 5.OL. T-5 was also used behind both the standard 2.3L with a 3.97 first gearset and the SVO Mustang. SVO received a one year only 3.50 first gear ratio as the 3.97 gear ratio was too low for the added power of the turbo charged 2.3L. No longer were 1st, 2nd, and 3rd gears spinning on a solid output shaft as needle bearings were installed under each gear to reduce drag. The lower counter gears saw tapered bearings to replace the bronze thrust washer. All main shaft synchro's were fiber lined steel rings to improve rings friction surface while 5th remains bronze. By improving the surface friction the synchro slows the gear faster making for smoother shifts. The design remained the same until 1989. Torque rating remained the same at 265ft/lbs.

1990 to 1993 the stock Ford production V-8 WC T-5 was upgraded with stronger 3.35 gear set by increasing the nickel content to produce a harder, stronger gear. 2nd and 3rd gear ratios were decreased slightly tp provide more torque to the rear wheels. Synchro linings on 3rd, 4th were improved by changing from fiber linings to carbon fiber to further improve the friction surface resulting in better high rpm shifts. A longer throw shifter was installed to "make shifting easier". The speedo drive gear was changed from 7 tooth to 8 tooth. The 8 tooth was a step backwards when installing lower rear axle ratio greater than 3.55 as the driven gear is limited to 21tooth count. Yes, 23 tooth gears are available but do not last long as the teeth are thin and do not mesh correctly. Torque rating jumped to 300ft/lbs.

When the 93 Cobra was introduced, so was the "Cobra Spec" T-5. It was the first T-5 with a front tapered output bearing and steel front bearing retainer. The Cobra boxes also received a reverse gear brake and synchro assembly where there was none before. Just about everything else remained the same. Torque rating was increased to 310ft/lbs.

 

Yeah, but I think the 4 speeds in early 80's Stangs were 3+OD, not really a 4 speed. I could be wrong though.

 

Yeah, I believe the 80's 4 speeds were 3+OD rather than a true 4 speed. As far as the T5's, we talked about this in the 5.0 forum the other day I think? Around like 96 or 98 I think someone said, Tremec bought out BW

 

http://www.coolcats.net/tech/advanced/t5_data.html
here is a link to check the no on the tranny