T85 c trans question


New member
This is a follow up question to my earlier R&P ratio query. Thank to you all for the responses as they each were well said and quality help, I appreciate it . I pulled the diff cover tonight, cleaned and counted teeth on both ring and pinion to verify I indeed have 4.10 gearset . I also verified the trans has t85c cast into the case. My question now is did the t85c ever cone with a lower than standard gearset in it. not a 1 to 1 high gear raito? I cant find a lot of info out there but did run across a post saying a t85 with the overdrive in trucks had a numerically higher gearset in it . To clarify this truck has not had an overdrive in it when dad bought it in 1976. And he got it from the original owner. Was this ever a thing?
Could be I need a different t85 or a different trans to replace the t85c to fix my issues. It just doesn't make sense to anyone i talk with why it will only run 45 to 50 mph and be wound tight.
I am going to buy a tach as it will hook to the msd 6al box quick to verify the rpm. Everyone i speak with thinks this set bp should cruse 60 with no issues. 31x10.50x 15 tires by the way,
Thoughts?? Im very confused. Trans options to replace the t85? I don't think the 3.54 R&P is going to make that big of difference. mabey 300 rpm's.
Thank you in advance for all the help.


Top Poster
Staff member
Supporter 2021
Supporter 2019
These are the T85 Ford ratios used in the C and the N Trans, maybe GM and Mopar applications were similar or even identical but I don't know that.
The T85C R10 and R11 Overdrive Units
The Borg Warner R10 OD came out in 1934 and was used up through 67. R10s were made to adapt to other manufacturer's transmissions as well as their own later model T86 which was a light to medium duty trans. They had a small planetary with only 3 planet gears. In 1948 they started making the heavy duty T85 with the heavy duty R11 OD with a much larger planetary gear with 4 planet gears. It was used in late 40s/early 50s Lincolns, 55-57 T birds, full size Fords/Mercs with FEs through 1964. All of these were the C model (at least the Ford/Merc/Lincoln ones were), and it was standard behind the 1960 360 horse 352 Hi Po, and the '61 375/401 horse 390, and optional behind 406s and 427s thru 1964, There were a number of OD tail shaft configurations, but the guts were all the same.

T85 C: info
Input shaft 19 teeth, countershaft 29 teeth. Input shaft is 1" diameter and can either be coarse or fine spline.
3rd gear is straight through, or 1 to 1 ratio
2nd = 26 teeth, countershaft = 25 teeth, ratio is 1.59 to 1
1st = 31, countershaft = 19, ratio is 2.49 to 1
OD = .72 to 1
So, in regular drive with OD locked out the ratios are 2.49, 1.59, and 1.00
In OD, the ratios are 1.79, 1.14, and .72
If you split shift it into a 6 speed it is 2.49, 1.79, 1.59, 1.14, 1.00, and .72. OD 2nd and regular 3rd are very close when you split.

The T85N was the one that was made for use in the Ford pickups from 1965 thru 1972, you could of ordered them in an F100 and up to a 3/4 ton. The N model case had both the narrow and wide bolt patterns on the mounting flange, an input shaft that was about 7/16" longer, and the input shaft cover slightly larger diameter, but with the same bolt pattern as the C model. Also there was no tail shaft behind the OD and no slip yoke on an N model. The u-joint bolted directly to the OD shaft and a double drive shaft was used with a slip yoke between the 2 driveshafts.

More Info on the T85N:
Input shaft = 17 teeth, countershaft = 31 teeth. Input shaft is 1 1/16" diameter and is coarse spline only. It is about 7/16" longer than a C. There is also a very, very rare N model with the huge 1 3/8" input spline usually found behind a 65 truck with a 292 Y block engine.

The N Trans Gear Ratios in regular drive the ratios are 2.98, 1.75, and 1.00
In OD ratios are 2.15, 1.26, and .72
6 speed split is 2.98, 2.15, 1.75, 1.26, 1.00, and .72 The N trans will spilt the gears better than the C Trans because the ratios are noticeably farther apart. 1st gear is much lower for better power multiplication.

Hope that is some help to you