I have a 65 f100 with a 390 in it with stock 3 speed manual is there a replacement 4 speed that will fit wth out a lot of modifacations. please help need more gear for the freeway in cali

 

Welcome, The 4sp that came in these trucks will have the same 1-1 ratio as the 3sp. They would have a lower 1st gear. For more hiway gear, you would have to go with a OverDrive.

 

As the previous post said, a four speed won't lower your highway revs more than you have now because 3rd gear on the 3 speed and 4th gear on the 4 speed are both the same 1:1 ratios. As he also pointed out, overdrive is a good way to achieve your goal. Another possibility is changing your rear axle ratio - however this may also hurt your ability to get away from stopped. Do you know what your axle ratio is? The warranty plate on the driver's door will have a code on it which will tell you - if you have one of the books/manuals with the decoding information. Axle ratios in the 2's or low 3's (for example, 3.00 or 3.25) will be better for highway mileage. High 3's and higher (for example, 3.73 or 4.11) will be worse for highway mileage.

 

Checking the ID plate for ratio is a good start, but if your truck has been modified as mine had, that will serve no purpose, another route is to see if the rear axle has a ratio plate attached to it.. Mine has a tag showing that it has a 4.10 ratio, and when I checked that against rpm per mile, it checked out to be correct. at 65 mph, I am turning just under 3000 rpm. There are a few web sites that will calculate your rear end ratio by mph versus rpm... if all is correct and working properly, it is an easy way to go. Others will suggest jacking up your truck spinning a rear wheel, and comparing the wheel revs to the drive shaft revs, kind of pain in the **** IMO, the web site calc is much easier in my opinion... Chances are good that you might also have a 4.10 rear end as I do.. It seems it was a popular gear back then. I see that you live in OC, as I do. There is a shop in Anaheim that does very good reasonable work, on rear axles, and at a reasonable price... Much cheaper to swap a ring and pinion, over a transmission. Another point, the 4 speed that i have is the granny 4 speed, so in reality it is a usuable 3 speed, with granny low. Very common in the trucks. While there are quite a few trans that will mate to your 390, the automobile trans such as the T5 cannot usually handle the torque versus weight of your truck, in other words you would be spending a lot of money to install a trans that would fail pretty quickly. I was surprised myself at how little the torque capacity is on those. Just food for thought! Good luck

 

My trans was not set for od. I was hunting around a little on line and found some info abount a borg warner t 19 trans thats a four speed and has a taller than 1-1 raito it came stander in a lot of trucks and van any ideas on that.

 

The Novak conversion guide list the T19 with a 1:1 top gear, but lower 1st gear and it is for the small block (302) engine group primarily I do believe that Speedway motors has an adapter that would work though

The Borg-Warner T18 & T19 Transmissions - Novak Conversions

 

It seems to me, about the only two things you can do to get the revs down is change axle ratio or find an overdrive transmission. If you get lucky, there is a "three on the tree" manual with overdrive that was an option on these trucks back in the day - whose name escapes me for the moment, but ND or Garbz or Jowilker or someone will have it - but finding one available in good working order might be difficult. The other overdrive options are pretty pricey: Gear Vendors have a unit that bolts on to the transmission, I believe, and then there are the Tremec TKO 500 and 600 whose top gears are overdriven, and who will have no problems living with the torque of your engine, but require an expensive adapter bell housing to bolt up to the FE engine. So it would appear your least expensive option would be a ring and pinion gear change.

 

What kind of 3 speed do you have? All synchro?

Ford put OD's on the tail of BW T85 (& similar) 3 speeds. Finding one that works with all the parts and electrical wiring would be a good trick.

There is a 4 speed OD trans from the late '70s to mid '80s that would stand up to a gently driven 390. First up here:

Domestic Truck Tranny Guide

The iron cased version would the one to go with.

As per prior posts, a taller axle could be an answer, depending on what the OP has now.

But figure out what your savings will be. 10%? 20% with a tailwind?

If you are getting 10 mpg now, is 11 or 12 going to pay back the expenses here?

 

That is part of the quandary that I faced, I have researched, and come up with 3 basic choices in this dilemna,

1) a trans swap to a Tremec T500 or T600 very pricey between the cost of the trans, and any mods or adaptation.

2) A Gear Vendors under/overdrive unit, still pricey not as bad, but keeps the truck the same, just with an over drive added to the trans, 2 friends have done this and love it, but it is pricey.

3) Ring and pinion swap... this is my choice , it is a very reasonable price, it will increase the freeway capability of the truck, but the lower gears will also be higher too. I have a 4.10 Dana 60, and all of the gears seem low to me. I found a shop locally that comes highly recomended, that will swap in 3.54 gears and rebuild the rear end for about $700 complete. I am going to go this route, and if I am not happy with it, I will look at the other choices, most likely the T600.

My concern is not so much the Mileage concern where it does play into the picture, as much as getting the engine turning a lower RPM at 65-70 mph to prolong engine life.

 

It sounds like you won't be towing. If so inclined, a T5 will do just fine in that case. Hauling something now and then shouldn't hurt it either. The strongest one is rated at about 330ft/lbs. Assuming an as assembled from Ford 390, it won't be producing a whole lot more than that. It will be cheaper than a TKO.

I've had one behind my Y, which should be producing around 340 ftlbs, for several years now and so far it's doing great. I've even hauled several loads with no trouble at all. I have a friend running a 4cyl T5 behind a built Y and he hauls a camper around for half the year. It's doing great, with no signs of eminent failure and I guarantee he works his harder than I work mine which is a Motorsport Z-spec, the strongest one. And, I have yet another friend with a T5 behind a turbo charged Y and it, too is doing fine. These guys have '57-'60 F100s.

So, if it comes down to it, you can get overdrive without having to fork out the cash for a TKO and that right there will probably save you at least $1000.00. If you drive like a maniac or are planning significant future upgrades for the 390, the stronger trans is probably the way you want to go.