Hello all!

So I have been looking into an overdrive option on my 1979 f150 4x4. Gear vendor is just stupid expensive with an new driveshaft and the gearbox its self.

A newer overdrive 5 speed from say a mid 90's f350 (I have a 400 and a FE bell housing) seems like an option. When doing this though I think I would need a new cross member and drive shaft? Also the T-case would need to be moved back.

I think the easiest route would be to have the existing NP435 regeared to a more modern ratio. I never use the granny gear, so in theory I could move all of the gears down one and put an overdrive gear in the place of 4th.

I called the local AAMCO and the guy didn't seem to know much about my transmission and was not sure if bigger gears would even fit in the case.

Currently I am running 4.56 gears, and a brand new set at that. I would like to keep these gears since 35 to 38 inch tires are in the near future. It doesn't seem to like going more than 60. I wont even attempt going on the interstate. Kind of off topic here but.. What is a reasonable redline rpm for a 400? The PO has the tach redline set at a rather low 3500.

 

The ZF5 is a good transmission, still a compound low gear, but it's not quite as low as the NP435 1st.

One of the things to consider, is the transfer case. Because you have a married t-case setup, you'd most likely have to use the case from whatever truck the transmission comes out of. So in addition to the custom length front and rear shafts, you'd have different yoke sizes. And possibly custom linkage

I think the stock transmission x-member can be used, but you may need an adapter plate.

The other thing to consider on the ZF5 is the hydro clutch. You would need to find a way to mount the clutch master cylinder and get linkage attached to it.

I've never heard of anyone re-gearing a NP435, but I think it might be more of a hassle than it's worth. Both your main and countershafts would change.


-Jameson

 

A zf5 trans would work 'but you would have to go hydro clutch .Also note a Zf5 Trans would be a one piece unit trans and bell housing .Personally I would have stuck with a 4.10 gear ratio with what your running and 35 inch tires.If your going to 38 inch tires 4.56 would be fine .And have you verified your speedo is right? Your speedo could be reading 10 to 15 Mph slower than what your really going .I got 4.10 gear ratio in my 78F250 running33 inch tires when my speedo reads 50mph I'm really going 60 mph

 

Maybe you should look into a Ranger Overdrive Splitter. It seems like it would be a decent option to me. But then again, I like shifting.

 

MeanGreen- I know for a fact the speedo is off haha! I use rpm and gear to determine relative speed.

1979RedNeck- I have never heard of that before. I will do a bit of google work and see what I think. Do you know anyone who has run one?

Edit!

So from what I understand the ranger system fits between the trans and the bell housing- forcing the trans and transfer case to be moved back 7 1/2". But I gain effectively twice the gears and a 27% overdrive. I would have 8 forward gears, 2 reverse gears, and 18 gear combinations in 4wd. That sounds like a TON of shifting! As far as I understand the shift process would be much like a big rig. The unit retails for about $1,400 after shipping.

With this unit it would also require fabrication of the trans tunnel, trans crossmember and I think a new mount for the T-case. This would also require modified drive shafts.

2nd
clutch
2 1/2
clutch
3rd
clutch
3 1/2
clutch
4th
clutch
4 1/2

OR could I run through the gears like normal, clutch and go into 4th and a half?

At a .77 final drive with 33" tires and 4.56 gears, I can cruise 70mph at 2,500rpm. Is this an acceptable engine speed for hour plus drives?

 

Yep. You only have to use it when you want. I have read that they are a little noisy.

 

I put a ZF in dads 79 F350 last year and it was no problem. Had to cut a notch in the mounting flange (to match the one on the original t18) on the tranny. After that the 205 transfer mounts right up. No need to modify or move the mounts. As far as the clutch goes, modify the old clutch linkage and it works great, no hydraulic clutch needed.

 

^Now that sounds like a good plan! So you didn't have to move any cross-members? How much did the T-Case move? What engine did you use?


However a rebuilt zf5 costs as nearly much as a T56 magnum 6 speed with a reallllyyy nice overdrive gear. If I could find a junk yard zf that would make it a lot easier.

 

None of the cross-members had to be moved. The ZF5 came out of a truck that he bought for parts. He paid $750 for the truck, pulled the tranny, Reese hitch, and a few other parts then off to the scrapper it went (along with some parts that he had laying around and didnt want). Made his money back and pretty much got the tranny and other parts for free. The truck is a 79 F350 SC 4wd w/ a 429 (had a 400). As far as finding a junk yard ZF5, around here if you want one you pretty much have to buy a truck with one and pull it. All of the junk yards in this area only go back to maybe 2000 with a few hangers on from the 90's.

 

That's one sweet looking dent you have there. I will prowl craigslist and junk yards for a parts truck. Im sure I will find someone with one for cheap.

How does the ZF5 shift compared to say a tranny intended for a mustang? The NP435 is not what I would consider smooth.

Did you need to shorten or lengthen either driveshaft?

 

It was about as close to a direct bolt in as you're probably going to get. Shifts like a newer truck, nothing like the T18's or NP435's

 

Thanks for the help! I think the ZF5 trans sounds like the best option with the least fabrication. Now for finding one sub $1,000..

 

The zf5 is a good transmission. Shifts real nice. Had one in a 87 diesel that I had for a while

 

Oh one more quick question about them.. Are the bellhousings different between gas and diesel engines?

 

Yes. You'll need a transmission out of a truck that had a 460