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3 speed to 4 speed conversion?

RPM289

Sr. Member
Joined
Jan 4, 2008
Messages
835
I HAVE A 69 WITH A 3 SPEED IN IT AND WANT TO UPGRADE TO A 4 SPEED OD OUT OF A 81 2WD FORD TRUCK WHAT DO iIHAVE TO HAVE TO MAKE THE SWAP?

THANLS,
MIKE
 

fordtrucks4ever

Bronco Guru
Joined
Oct 8, 2006
Messages
1,280
Loc.
DFW
First thing is to find a trnasmission that will swap in. Unless the 82 has a NP435, or castiron 4speed OD, not much else will work from that donor. The lighter duty F100-150 trucks had an aluminum SROD tranny that wont work. Later models(85-89), had the aluminum RTS thats a good choice if not planning any hardcore serious offroading. Unless it has the NP435, you will have to change out the mainshaft for it to work.

DO you know what tranny the truck has?
 
OP
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RPM289

Sr. Member
Joined
Jan 4, 2008
Messages
835
First thing is to find a trnasmission that will swap in. Unless the 82 has a NP435, or castiron 4speed OD, not much else will work from that donor. The lighter duty F100-150 trucks had an aluminum SROD tranny that wont work. Later models(85-89), had the aluminum RTS thats a good choice if not planning any hardcore serious offroading. Unless it has the NP435, you will have to change out the mainshaft for it to work.

DO you know what tranny the truck has?

It is a cast iron 4 speed. Is all I need to do is modify the tail cone and shaft from the 3 speed to fit the 4 speed? I was told that the output shaft is the same legnth as the 3 speed from the 69 bronco don't think he is correct but not sure. What t-case came on the 3 speed in the 69?

Thanks for all tha help everyone!

Mike
 

Lumpy

Newbie
Joined
May 15, 2005
Messages
33
dana 20 t-style shifter in the 69's. Boy those 3speeds suck for offroading. I'm suprised you even get offroad with that tire-tranny-gear combo. With those gears and those tires wouldn't you be alright without an overdrive? I put an NP435 in mine and all I had to do is buy an adaptor, no mods to the bronco except for the floor. There's a lot of good info on this site about tranny swaps.
 

fordtrucks4ever

Bronco Guru
Joined
Oct 8, 2006
Messages
1,280
Loc.
DFW
It is a cast iron 4 speed. Is all I need to do is modify the tail cone and shaft from the 3 speed to fit the 4 speed? I was told that the output shaft is the same legnth as the 3 speed from the 69 bronco don't think he is correct but not sure. What t-case came on the 3 speed in the 69?

Thanks for all tha help everyone!

Mike

The cast iron 4 speed shoud be an OD version. A little weaker than the famous Ford toploader. But just strong as stock 3 speed. This tranny needs a new mainshaft from Advance Adapter. Its the only way you will get one to work. Fortunately, only slight machine work is needed to Bronco tailhousing(transfer case adapter) for everything to bolt right in. The 4 speed is 1" longer than stock 3 speed, so a little slotting or redrilling for new location of tranny crossmember. You will also need a floor shifter. Its basically the 3 speed Duff kit with a 4 speed shifter. I dont think the stock one from donor truck will work. You may not need to modify driveshaft lengths if adding a small lift. Now for the bad news. The gear spacing is not that great for offroading. It has a wide gap between 2nd and 3rd. Without decent axle gears with those big tires you want, not going to be really happy offraod. Of course there is always low range. For a daily driver, with smaller tires the tranny is a good choice.
 

texaswildcat98

Sr. Member
Joined
Mar 29, 2004
Messages
401
Loc.
Wichita, KS
Thanks for the link guess I will be running the 3 speed for now any idea if I can run highway speeds with the 302 3 speed 3.55 gears and 35 to 38 in tires. This will be a on and off road toy so I want to be able to run 70mph on the highway.

I'm running a similar setup but with 33's, but I seem to run about 2800 to 3000 at 70, though my truck doesn't like it, there seems to be a sweet spot at about 60ish. Oh if your curious I used my GPS to check speeds against the tach, so it fairly close.
 

hdmc

Sr. Member
Joined
Dec 24, 2008
Messages
517
Loc.
goodyear AZ
i just did the np435 swap i've got 3:54 gears 35" tires huge difference in the way the truck drives on and off road . lots of these trannys out there. i did everything on mine for $500 bucks its a fairly simple swap .
 
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RPM289

Sr. Member
Joined
Jan 4, 2008
Messages
835
I will be changing gear ratios some time in the future so that will help off road etc. What is a good gear for the 35 38 in tires? I am installing a dana 44 with a 3-4 in suspension lift so it looks like I will avoid the drive shaft changes. What tranny is in a 70 ford f 100 with a 302 It is a granny gear? I think it is the NP435 Best of all I can get it on the get it out of my yard special I think will find out tomorrow.


Mike
 
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