Ok, '84 F250, 6.9idi, T18/19 BW...which is better....5 speed conversion, or an OD unit?

 

My vote would be a 5 speed conversion, more simple and less moving parts than adding an additional O/D unit.

 

5 speed conversion is usually cheaper. Overdrive unit is more expensive, but can give you interesting options like splitting gears for 8 forward speeds. The overdrive unit itself is very expensive and the driveshafts must be modified. Depending on what model you get, the overdrive unit may not work in 4x4 mode.

 

Ja, that's what I figured...so, is the 5 speed basically a bolt on proposition? Any mods to the driveshaft? Clutch? (Probably will replace it as a matter of course...in there already, why not,) And I have 2wd, so 4x4 issues don't apply.... BUT...that splitting for 8 forward gears does intrigue me... beings I have been a truck driver...(Freight since '78)

 

Forget the drive shaft(s) because he would need to change them any way he goes.
Same may go for the cross members depending on how he goes, GV he would not need to deal with them.

Now if I understand him right he has a T18 or T18 in his truck now.
There is only 1 OD unit that will work with them, the AA range splitter. http://www.advanceadapters.com/categ...lete-units/91/ at about $1700 +s/h
I take that back GV I think makes one http://www.gearvendors.com/f2wdt.html at about $3100 +s/h

Where can you find a known good ZF for a diesel with a warranty for under $1700?
Any used one will be a crap shoot if good or not so may need to pull it, pay to send it back if they will take it back and hope they have another to try.
Could buy a used one and have it rebuilt what would that run $$$ ? Would we be up to the cost of the GV unit now?
Guess you could go for a new / rebuilt ZF if you go with the $3100 of the GV unit.

I have kind of run the numbers for a ZF for my F100 with T18 / NP435 and finding a ZF for a small block with speedo cable is a needle in a hay stack but a diesel may be easier?
How much time do you have looking for one? I don't during the week when everything is open. Then again what shape is a used one in?
I cant swing $3100 past the banker (wife) but I might be able to do $1700 and I can split ALL GEARS, the GV you have to be going faster than (think) 30 MPH before the unit will let it shift.

The T18 / T19 have pretty low granny gears what is the ZF have for its first gear as you are driving it as a 5sp not a 3sp like the T18 / T19 till you need the granny gear.
Just something else to think of.
Just my .02
Dave ----

 

The ZF's for the diesels are out there, I have an S5-42 sitting under the workbench just taking up space for instance. The ZF for the diesel is pretty bulletproof especially if it was a 2WD unit.
The Later S5-47's are a bit stronger but were only used 95-97. The S5-42 is a bit taller in the gearing compared to the T19, the S5-47, on the other hand, is pretty close. Forget about the wide-ratio units they were only used behind gasoline engines.

 

From what I have seen posted mostly yes a bolt in.
I am not up on when the diesels and larger (250/350) trucks went to a juice clutch but if your truck has one then you are good on the clutch as all ZF's use juice to work the throw out bearing.
My truck (81 F100) uses linkage so I would have more work for swapping pedals drilling holes in the firewall locating the master firewall brace, if you don't have one now would be the time to add it, and bolt all that in place.

If you can get the ZF cross members then that will bolt in if not you will need to move yours back and drill holes.
You would need to do this with the AA RS OD unit and your trans as it moves the transmission back 7.5"
Drive shaft would also need 7.5" taken out for the AA RS OD unit, don't know on the GV OD unit as I did not look that close after the price.
On the ZF if you find the same wheel base as your truck then that will bolt in.

As for splitting gears. only 1 you can split all gear the other only after 30 MPH. So not the granny gear.
Also note that some of the ratios will be so close it may not be worth splitting all gears all the time but could have times you could split and be ok it is close.
Say normally splitting 2> 2od> 3 is too close but stuck in slow moving traffic 3rd lugs the motor but 2nd the RPM is to high so 2od might work for you.
I had a Toyota L/C that had an OD unit with twin sticks and I did find some of the gears close it was not worth splitting but it was cool to throw 6 gears (3sp toy trans) with the header & glass pack.

I wish the AA unit had a electric shift like the GV unit so you could use a Hi / Low button on the side of the shift lever like for 2 speed rear axles.
The AA unit uses a shift lever so you have to "twin stick" it but that should not be to hard for an old(er) trucker LOL
Got to ask after driving a truck all day for work and jump into the PU do you find yourself starting to float the gears?
Dave ----

 

When it comes to a OD unit like GV, it is best with a wide ratio like you said. C6 is a good option with the GV as they have a wide ratio between 1st, 2nd, and 3rd. I also believe my conversion with a wider ratio planetary gear set with 1st gear being 15% lower than stock ratio and second being 5% slower than stock would work even better with a GV unit for gear splitting.

I just don't know how good they are so I cant recommend them. Everyone online seems to praise them but Ive never met one in person that has used them that praised them. They have all said how bad they are and how they don't work right. Could simply be user installation error for all I know but for the cost of a GV unit I don't think I would want to take that risk to see. But nice thing with the GV unit is you don't have to change anything but your drive shaft length as the GV unit replaces your tail shaft piece from your transmission.

 

Given the choice, I would just opt for a ZF swap.

I'm Not fan of the GV in any application that sees any sort of heavy use. And the split shifting is not as easy as they make it sound yes it can be done but practically only on the up ****s. The reverse clutch in the GV also has the issue that in reverse the torque "pulls" it's clutch away from the drum. If the GV is in "Manual" mode, and you are reversing at more than say 20 mph, which is easy to do with wheel spin, the unit will grenade.
Ask me how I know.... This is not an uncommon occurrence either. If it is going in a pavement queen that is never ever going to be abused the GV Overdrive is fine, otherwise, pass...

 

Interesting comments...will look for a 5 speed and see what a reman/rebuilt will set me back...the OD looks to be too much $$..and I'm not looking to spend a whole lot on this project... Will let you all know how it all works out. For now, the 4 speed is working fine...just wish I had a taller gear in 4th. And the "granny...well, if I start in 2nd, that poor clutch really gets a work out...so "granny" is what I start out in.

 

Fuzzface...no, I find myself looking for the clutch in the schoolbus I'm driving now...LOL!!!! And in the past, I've been known to reach for some gears in the Rolls and Benzs I've had...LOL!!! Wife gets a kick outta that... And then there was the K5 Blazer...had a 5 speed manual...occasionally, I'd try and get another 8 out of that one... But, floating the gears in ol Brown Bess can be done, but I usually use the clutch...I'm in 4th by 20-25mph...lots of miles on her...gotta treat her gently.

 

Which is funny cause Jay Leno swears by the GV Unit and he even has one behind the greyhound transmission for his patton tank powered hotrod. They brag about how much power it can handle. Me personally if I was going OD after I started looking into it, the AOD is a lot better for me as the OD is so steep I could run a 4.11:1 axle ratio and be around 3.00:1 final drive in OD.

 

Since you are doing swap you will need the shift tower as they generally do not come with the remans. You are better off finding a complete unit. If you do a wrecker seach pretty sure you will turn up a pile of them. (Edit did a quick search and there are piles of them ) Search your local wreckers here Car-Part.com--Used Auto Parts Market

 

Hey Matthew,

Did the ZF5 lose the speedo cable drive in 1992 like the M5OD did? I know that is an issue with the 4x2 F150 swaps. The M5OD 5spd only had speedo cable drive between 1988-1991, as I believe the speedo output switched to the rearend in 1992. Not an issue for the 4x4 guys, but curious about the 4x2 ZF5. Of course the 1992-1996 transmissions fit and function fine, and some guys don't care about the speedo, so there is that.

 

Do you know what rear gear ratio you have in the truck? Yea 2nd gear starts with the T18 in mine is also ruff on the clutch. Because the trans needs a rebuild with some gears replaced and finding a NP435 for just the rebuild kit (less gears) I went with the 435 and it also has a lower 2nd gear so should be easier on the clutch .... I hope.

A 3.00:1 might be good for a 302 on the high way but I can tell you even with 2.75:1 at 70 MPH the 300 six is turning 2500 RPM.
I want to get down to 1500 to 1800 RPM at 70 MPH, right now I am 2300 at 65 MPH
If I figured the math right with my 2.75 rear gear and the AA OD unit I should end up with a 2.01 rear gear and that should put my RPM at 1650 at 70 MPH

That was the other thing I had to over come in that hay stack for a ZF swap, small block bell & need a speedo cable hook up on a 4x2 trans.
And then you have like what you found, someone calling the M5OD a ZF transmission.

From what I hear the ZF & M5OD shift really nice compared to the T18 / T19 / NP435 truck transmission but with the wide power band of the 300 it is not bad as you don't have to shift a lot.
Because you also can not shift them fast you get to take your time and enjoy the drive at a slower pace

I think anyone wanting to go with over drive transmission needs to do there home work on all the options out there and what they want to use the truck for.
If stick and street truck the M5OD might be the way to go.
Work truck then the ZF might be the way to go.
Auto then the AOD transmission might be the way to go.
Or either of the add on OD units (GV or AA) might be the way to go.
Just my .02
Dave ----