I'm in the process of purchasing a 1981 F100 shorbed with a 300 six and 4 speed trans. The owner says the truck shifts fine through all 4 gears except if you try to shift fast from 1st to 2nd it sometimes grind's a little going into 2nd. He thinks it's an issue with the synchro's. My question is, I'd like to have that fixed if I make the purchase but have no idea who works on these older transmissions anymore. Any suggestions? I haven't driven the truck yet so I can't offer any other information.
Thanks,
Glenn

 

I does help if we knew what 4 speed it has. And I dont think I would not buy it because of the transmission issue even after test driving it and the price is right.
If it is the SROD, 3sp with 4th an over drive that some call a speed. It has synchro for all gears.

If it is a T18 like mine had and the 81's would of had, or a NP435 like mine has now, they are have a granny first gear, (non-synchro) 4sp but you drive it as a 3sp when not loaded.
2nd to 4th are synchro, this is a truck transmission read shifts slowly and if you try shifting fast can lead to issues.
Even with 2nd synchro in my truck you have to be going pretty slow to get it in gear when down shifting but no issues when up shifting going from granny 1st to 2nd.

Now being my NP435 was used when I bought it, 3rd gear has some issues going up & down so I double clutch going into 3rd and it helps.
It also shifts easier after the gear oil warms up some and talking gear oil I am one for only running GL-4 or older lube that we know is safe for yellow metal (synchros) in the transmission.

Now your question has a lot to do with what transmission the truck has and what your plan is to use the truck for.
I hear the over drive transmission can have problems finding parts then someone to rebuild it if you cant. I also dont know how much info is out there for this transmission if you wanted to rebuild it yourself?
The T18 / NP435 is not hard to find parts for as lot were used not only in Fords but others and I hear not hard to rebuild yourself as there is info on the web on how to do it.
If you dont want to give a rebuild a try look up local transmission shops and see if they will rebuild it or know of someone.

If you dont want to or cant find someone to rebuild the transmission you have you can hope for the best and install a used one like I did and this can give you some options depending on what the plans are for the truck. If you have the granny 4sp and want or need the granny gear either rebuild yours or find a good used one.

But if you have the over drive transmission I would not even think about rebuilding it and look for a M5OD from a 87> small block truck.
It is a 5 speed with over drive and will bolt to your motor and with a few other parts from the truck the transmission came from it is a bolt in.
You will need to replace the clutch pedal and install a hydraulic assy. as the M5OD uses a hydraulic clutch and the pedal is different than yours.
There is a little bit more to this and if you do a search in here you will find info as others have done this.
Hope that helps
Dave ----

 

its a 4 speed with overdrive. I had hoped it was a 4 speed with the granny gear but it's not. If it isn't too bad and only happens if you try to shift quickly from 1st to 2nd as the owner described, I probably won't mess with it. The truck is in excellent condition so the trans issue isn't a game changer. How is the trans with the granny gear cruising at 60 or 65?

 

Not too good. It's only 1 to 1 in 4th. If you get this truck, then go down the highway but leave it in 3rd. 3rd gear is 1 to 1 like 4th gear is in the granny transmission. That will give you an idea what it would be like. If you are set on changing transmissions, I would get a 5 speed and put in it.

 

That's kind of what I thought. Well hopefully it will be fine as is. If not I might try finding someone who can fix it and if not I'll look into the 5 speed option. Thanks for your help and suggestions.

 

As DaveF said on the transmission but a lot depends on the rear axle ratio.
My 81 Flare Side short bed with a 300 six and the granny first and 2.75 ratio runs 2100 @ 60 MPH / 2250 @ 65 MPH
Now my parts truck, 81 style side long bed, 300 six had the 4sp over drive transmission with a 2.47 ratio both had Ford 9" axles.
I dont have the speed / RPM for the parts truck it did not have a motor and was a roll over but you can find math on line to run the number for the ratio you have or post it and we can.

The sweet spot for the 300 motor is about 1800 RPM and when our trucks were built the MAX speed limit was 55 MPH and my truck was 1800 RPM @ 55 MPH.
I added a over drive unit, no longer made , and I turn 1800 RPM @ 70 MPH the speed limit here.
Oh in direct drive I have 2500 RPM @ 70 MPH it is not as bad as it sounds, we are so use to everything having over drive and low RPM when driving is all.

I also said about the M5OD as it is a stronger transmission then what you have and with the 5 sp has better gear ratio spread and over drive.
Dave ----

 

It may be the nature of the beast. The problem they had with this transmission, is cramming all those gear ratios into just 4 speeds. Some of the rpm jumps are dramatic. If you get a dramatic jump in ratios from one gear to the next, it can be difficult for the synchronizers to get the speeds matched. If you rush things, they may not be able to do it at all.

I have a zf 5 speed in my truck, and 1st gear is pretty low, but not quite a granny gear. But it's a large ratio spread between 1st and 2nd gear. If I rev it up and rush the shift, it will scrape also.

 

Isn't it possible for these earlier trucks to be a RUG 4 speed over drive or a SROD. I think the RUG is more well regarded and might share the synchro's as the non overdrive 3 and 4 speed top loaders. Don't quote me on that but it might be worth rebuilding if it is the RUG. I rebuilt my top loader and it wasn't too bad a job with the ford shop book from GarysGarageMahal.

 

Well if it was me I would want a better, stronger modern trans and that would be the M5OD.
It had better gear spacing, over drive and was used with 300 / 302 / 351 SB motors the 3sp were used with 200 and 302 and not for many years because of the issues it had.
But that is just me.
Dave ----

 

OP probably has an RTS or SROD version.

2nd gear takes a beating as it's giving the synchro work out on the up shift and down shift pretty regularly.

All things considered, including the fact that you may have an aluminum case, just slow your shift down and take it easy on the transmission.

Mine was the RUG, the one with the external shift linkage and an iron case. It would take the faster shift but the clutch didn't like it much.

2nd to 3rd was miserable with 3.50 gears and 31-10.50x15s.

 

Lots of great suggestions and much appreciated. I won't be able to complete the purchase until the end of the month. The owner wants to fix a few minor things before I come for a test ride like the turn signals and gas gage is a "bit wonky" according to him. He thinks it's the sending unit in the gas tank. I don't plan on doing any power shifting from 1st to 2nd so hopefully it's a minor issue and the guy says it doesn't happen all the time. it has 78K miles and was well maintained so I'm not concerned about the engine. No leaks according to the owner. New interior but has a really bad dash pad. I'm curious about what you guys might think it's worth, although the best answer I ever heard on value is "It's worth whatever you're willing to pay."

 

A word never so true "It's worth whatever you're willing to pay" LOL

This side looks pretty good take it the other side is just as good?
If you pull the rubber mat back the floor and cab mounts in good shape?
1 tank or dual tanks? If dual it has the easy tanks switching set up of all the trucks like I installed on my flare side.
As a guess a high of maybe 5K if everything is in good shape and working. I am cheap and would not pay that much
Dave ----

 

[QUOTE As a guess a high of maybe 5K if everything is in good shape and working. [/QUOTE]

$5K? Wow, if you know anyone selling an 81 shortbed professionally repainted a few years ago please let me know, I'll buy 2 of them. The paint job would cost $5K at a minimum..

 

Well maybe for you for me it is the cost of the paint and my time
I can tell you a gallon of red paint for my truck 5 years ago was $1000.
I had more red for the inside of cab and under hood + the white.
Yea paint is not cheap and labor is crazy!

From pictures it is always hard to tell just what anything cost or if just painted or not.
Then again rust and dirt could have been painted over and someone was learning how to paint and got runs all over the floor
Dave ----

 

[QUOTE From pictures it is always hard to tell just what anything cost or if just painted or not.
Then again rust and dirt could have been painted over and someone was learning how to paint and got runs all over the floor
Dave ----[/QUOTE]
He sent a lot of pictures of the paint preparation, there were only a few small surface rust spots, all nicks and chips were properly repaired, no dents anywhere, no need for bondo. When I wanted to get my 68 repainted by a shop that I do business with he quoted $6 to 7K minimum. However, I'll take my refrigerator magnet with me and check all the typical areas that usually rust through.