First off, thank you to all the members who gave me insight into how to address my transmission situation, I really appreaciate it.

I want to replace my manual 4-speed overdrive SROD transmission with a used toploader transmission.

My truck is a 2WD shortbed 1980 F100 with a 300cid 4.9L straight-six and a 9" limited-slip rear with 3.00 gears.

I want the switch to invole as little modifications as possible (driveline, etc...).

When I'm looking for a toploader, what spec's on the tranny should I be most concerned with, in order to not have to make any unnecessary modifications?

My SROD is 24" long and here are the numbers/letters that are stamped on it:

RF-D9BR-7006-AB
ACE/CO 2
C-2604194

The shifter turret mounted on the rear extension housing also had some codes:

RF-EOTR-7F306-AB
C-2604302
FA1

This turret also had a cable connected to the back of it. I don't know what it is, could it be an indicator that senses when I put the tranny in reverse? I don't think its the speedo, because there's another cable connected to the rear extension housing, right near where it connects with the main part of the tranny.

Anyway, when looking for a toploader, what is an acceptable engine size range and rear-end gear ratio range of the vehicle that the tranny came from, that would work for my application? I think I should look for a close ratio, how do I verify this? How can I be sure I won't have to make any mod's with the driveline, cable connections, clutch linkage, tranny mounts, and anything else I can't think of, for that matter?

 

I think any toploader is goin to require the same amout of work because they all have the same shifter locations and are the same tranny crossmember. I would use a wide ratio (first is 2.78) every time i can the close ratios have too high of a first (2.32:1) gear so you have to run really low rear gears. you are just goin to have to measure to find the right length, i think the fairlane/comet trannys are right in there. you could also consider a 3.03 three speed they have a 2.95:1 first gear, are esay to find, and pay for and they are every bit as strong as the four speed they are the same design minus a gear. you could get a way with the 3.00 rear gears if you had a 2.95:1 first not with the 2.32, oh yeah just thought i'd tell you they all have the same final drive 4th in the four speed and 3rd in the three speed are both 1:1.

-johnboy

 

I'm okay with the shifter location change, I'd been told that I'll have to make some mods for it. As for the crossmember, won't I be able to use the one I have now? Will I be able to reuse the support that's located between the tranny crossmember and the tranny? Do you think I'd have any problems with freeway driving (80 mph) with the 3 speed?

Thanks for you help,
Bran

 

I think 80 mph with a straight six and a 3.03 is a bit much to expect - our dear departed '80 F-100 would do well to make 65. The 300 just doesn't like to rev - Unless you're concerned about breaking the SROD, I'd be content with overdrive and a slightly steeper rear end. Or an M5OD - my 95' 300 with the 5 speed drives great towing or cruising down the highway. For good all around driveablility with an NP435 or T-19, you'd probably be happy with the a rear end in the 3.00 - 2.73 range.

 

I think your crossmember will work i didn't say any thing because i am not positive that is will and i didnt want to missinform you, i have a 82 F-150 with 3:25 rear gears a T-18 (1:1 first gear just like the toploaders) and it will do 70-75 on the highway just fine. With the three speed your final drive will be exactally the same as with the four a strait one to one out of the tranny, it makes no difference if you go three or four the three speed is just a wider ratio tranny 1st is lower and 3rd is the same as forth in the four speed.
Johnboy

 

First off, you WILL NOT have to do anything to the crossmember, as the mounts are in the same spot as the srod is (i have done this) and the mounts on the toploade to my knowlege are all in the same spot, just after the main part of the case right after where the tailhousing bolts to the main part of the case, also a wide ratio and 3.00 gears is perfect for a DD (again this is what i have), getting going is no problem, and the gears are spaced nicely as well. Also try to get a tranny from post 66, as the small blocks used a 5 bolt bellhousing verses the 6 bolt bellhousing of the post 66' (they change mid year in 66 to a 5bolt). But to make your life easier try to find one from a small block, but the bellhousings from you tranny will work on the toploader as well.

Please post any other questions you have
Really the only difference between different toploaders is the location of the shifter, as different locations were needed for different cars, and the difference is where the bolt holes were located on the tailhousing. Now you will have to reroute the speedo' cable through the clutch boot as the speedo gear is on the p-side of the tranny, and this is different verses the srod.