overdrive compatible?

[DonD]

Hello folks, I have a 68 f100 with 240, three speed, and 3.70 rearend. I'm getting really good mileage as it is, 19 mpg, but I am wondering if an overdrive would help or would the final drive be to high, and lug the engine? Thanks for any input.
Don

[Donnie]

Don, I think it may be a bit much unless you live in Kansas or other flatland areas....You could install an overdrive & just run direct when you need it...What were you considering? You are pretty close to your peak with this engine/ trans set up...Other's may have different opinions..Donnie

[guhfluh]

Louisiana is pretty flat. I see that's where you are, from you're post in the welcome mat. Fill out your profile and people can help you easier when they know where you're from and everything about your truck. What part of LA are you in? I'm in south LA.

If you are on the interstate a lot and traveling 70mph quite a bit, the engine is really turning some rpm with a 1:1 top gear and 3.70 rear end. An overdrive should help mileage a little, but help the drivability and your sanity the most. A M5R2 swap is probably the most common and "easiest" five speed swap into the truck. There are a couple other overdrive options, but that one(or a ZF 5-speed) is the most appealing to me from a price point and amount of work involved. The gear splits aren't as wide as your 3-speed also, which will help with around town drivability too, and *might* help a little bit with fuel mileage if driven right.

The 5-speed swap is something I want to do to my truck in the future for the creature comfort and slight fuel mileage help. I also would like to perform an intake, exhaust and carb upgrade to help with mileage and power, but I'm torn between keeping the stock look and any drivability or mileage hits the upgrades can have.

[eggman918]

The M5ODR2 is the most bang for the buck and ease of install as well as drive ability

[KnockKnock]

M5R2 is a Mazda trans & doesn't hold up well if you use your truck to haul &/or tow anything (I've read a lot of failure threads on this trans from other forums). I'd say the ZF is the way to go for practicality & longevity.

[DonD]

Hi fellas, thanks for the input, been gone a few days.
I'm located in the Northern Part of Louisiana, just north of Winnfield, its pretty much flat, nothing that would cause problems anyway.
I have a line on a B/W T85 that I was considering. I would really like to keep it generally stock.
I do occasionally pull a 16' trailer with tractor/bushhog but not far and not fast. Most of my driving is two lane, but when I hit the Interstate it really winds up higher than I like.
With the T85 am I correct in thinking I can still operate it as a regular 3 speed?
Thanks again
Don

[guhfluh]

I don't know anything about the T85, but I thought it was the predecessor of the T18 and not an overdrive, just a granny low 4 speed and 1:1 4th gear?

Average250 seems to think the m5r2 is failure prone only when run low on fluid from the top plugs leaking. I tend to agree, as that's all the issues I've personally seen with them. The ZF is reported to be stronger, but I have seen plenty of them break also, though its been behind more power than the m5r2's and beat hard. I wouldn't sweat it if I could only find a m5r2 and couldn't find a ZF or the ZF was more expensive; I don't think you're ever going to overpower either of them with a 240. Just keep them full of fluid.

[KnockKnock]

You can use brass plugs to keep the fluid from leaking from where the plastic caps dry-rot, crack & break away on the M5R2 (I used to have the PN handy when I considered this swap for my '07, but got rid of it since I decided not to try the M5R2). There is a guy on my old forum with a 4.6 that has gone through (at least) FIVE of these M5ODR2 transmissions. Look at the design spec-sheet on the M5ODR2 - tiny needle bearings = junk. Google it.

[motzingg]

is there a good way to tell if a junkyard m5 has been run dry or otherwise torn up? this thread really has me thinking i'll hold out to find a ZF... the junkyard by me charges $125 flat for any transmission.

[guhfluh]

Not that I know of. Check for fluid in it. Fluid condition and leaks from top plugs. That's all I know of.

For a flat rate price like that, I'd get a ZF for sure, unless you have to wait a few months or year for one, then it may be worth it to get the M5 unit and swap in a ZF down the road. A Mazda to ZF should be a direct swap as far as I know.

[eggman918]

If you do go the ZF route you will need to find one from a small block F-250 for it to fit your motor,they are not all that common.
I have been looking for over a year,hitting the 2 local self serve boneyards every 2 weeks I've seen quite a few diesel and 460 zf's but no small blocks
I hope you have better luck than I'v had

One more thought ..when I found my M5ODR2 I paid about what you plan to pay and for that price I budgeted the cost of an overhaul kit and rebuilt it,
it was not difficult or too costly. When I had it apart and saw how it was built I had much more confidence in it it has big bearings both shafts are well supported and their are steel/iron inserts
cast into the case where the bearings fit it does have small dia. needle bearings but the bores and shafts that they run on are hardened so I don't think that is a weak point
The M5 has been in my truck for aprox 6,000 miles and made 3 trips to the High Sierras on Forest service roads and 4x4 trails as well as hotroding around town and is functioning flawlessly,my '68 CrewCab with the Cummins 4BT weighs 7,7000 empty and over 11,000 with the trailer and gear in/on it. Feelings regarding this trans are VERY strong people either like it or hate it,
a lot of the negative reports I'v read are from people that admit to flogging there trucks and as a machinist in the repair field I'v learned over the years that you cannot build something
that some fool cant destroy


here are some pics of the M5's guts

[Nitekruizer]

Hi fellas, thanks for the input, been gone a few days.
I'm located in the Northern Part of Louisiana, just north of Winnfield, its pretty much flat, nothing that would cause problems anyway.
I have a line on a B/W T85 that I was considering. I would really like to keep it generally stock.
I do occasionally pull a 16' trailer with tractor/bushhog but not far and not fast. Most of my driving is two lane, but when I hit the Interstate it really winds up higher than I like.
With the T85 am I correct in thinking I can still operate it as a regular 3 speed?
Thanks again
Don

The T-85N is a tough tranny. Yes, you can operate it as an ordinary three speed if you pull the overdrive cable to the full out position.

[motzingg]

"If you do go the ZF route you will need to find one from a small block F-250 for it to fit your motor,they are not all that common."

oh dear, i thought all the 5 speed/4.9 f150 up to '94 were mazda, and 94-96 were ZF? I guess that's too good to be true, huh?

With a 240 i'm not too scared of overloading much of anything, and I have plenty of other vehicles to hot-rod... the truck is there to get them home. I'm just gun shy from the last mazda 5 speed i owned in an 89 ranger. Synchros in 2 and 3 kept going. I prefer manual transmissions because there is less in there to let go, its something I'd like to install and never think about again...


I would KILL for a T85, but so far all the local junkyards, including one that specializes in pre-1970's stuff, just laugh at me when i ask about it. I've seen the long shaft chrysler ones but nothing with the short shaft for a truck.

[eggman918]

The mazda trans in the ranger is the M5ODR1 and is a much lighter duty unit then the R2

[motzingg]

i knew they were different, figured the ranger one was a punk! to be honest, it wasn't that bad, it survived my high school driving habits and towing countless cars (many of them heavier than the truck itself) a boat, and full time duty with a lawnmowing trailer. Even hauled my dad's 4500 lb farmall M! Never dropped a gear, although third gear was pretty noisy when i sold it.

just hearing 'mazda five speed' and 'problems' in the same sentence gave me chills!