OD or 5 speed
Post Fiend
Joined: Feb 2008
Posts: 5,831
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From: St Albert, Alberta
Ya except, page one of the Ford engineering M5OD overhaul manual.
Post Fiend
Joined: Feb 2008
Posts: 5,831
Likes: 121
From: St Albert, Alberta
I guess "complaint" was a little strong.
I see with the 3.08 gear and the OD your final ratio is 2.46:1and little over 2000 RPM@70 MPH
With 3.55 gear and OD the final is 2.84:1and a little under 2400 RPM@70 MPH
Do they make a 3.25 for your axle?
I wonder if the motor was to spin a little more to get into the power band more if that would help MPG?
If I remember you have not had a chance to get a good drive to check MPG have you?
Aint playing with number fun
Dave ----
I see with the 3.08 gear and the OD your final ratio is 2.46:1and little over 2000 RPM@70 MPH
With 3.55 gear and OD the final is 2.84:1and a little under 2400 RPM@70 MPH
Do they make a 3.25 for your axle?
I wonder if the motor was to spin a little more to get into the power band more if that would help MPG?
If I remember you have not had a chance to get a good drive to check MPG have you?
Aint playing with number fun
Dave ----
There is a 3.23 ratio available for the 8.8 most commonly used on Mustangs and Panthers with tow or the PI's
FTE Legend
Joined: Nov 2015
Posts: 30,912
Likes: 4,123
From: Angier, NC
Part of the issue I see with going to high a rear ratio besides the final RPM is on take off from a stop.
With a stick you would have to slip the clutch more but if auto you would be adding more heat from the converter needing to "slip" more to get going.
They do say the converter multiply the TQ so that can help on take off with a high gear.
And as you pointed out tire size will also play a roll so going from a normal street size of say 28" (in my case) to a 31" will also make a gear ratio change and not even know it other than the speedo being off.
There is a lot to think about when changing tire sizes, rear gear ratios, and even transmissions from auto to stick and adding over drive.
You can go over all the numbers and hope it works out but it is nice to see if others have done what you want to do and what their out come was.
Dave ----
With a stick you would have to slip the clutch more but if auto you would be adding more heat from the converter needing to "slip" more to get going.
They do say the converter multiply the TQ so that can help on take off with a high gear.
And as you pointed out tire size will also play a roll so going from a normal street size of say 28" (in my case) to a 31" will also make a gear ratio change and not even know it other than the speedo being off.
There is a lot to think about when changing tire sizes, rear gear ratios, and even transmissions from auto to stick and adding over drive.
You can go over all the numbers and hope it works out but it is nice to see if others have done what you want to do and what their out come was.
Dave ----
FTE Legend
Joined: Nov 2015
Posts: 30,912
Likes: 4,123
From: Angier, NC
Dave ----
Post Fiend
Joined: Feb 2008
Posts: 5,831
Likes: 121
From: St Albert, Alberta
Ya the 8.8 and other random pattern diffs always use an oddish ratio. The 9" had a 3.25 ratio available that was quite common in the cars.
For non-sevre service non-tow applications that see hyway use the 3.20 ish ratio is where I like to stick stuff. (especially with 3 speed autos)
Lead Driver
Joined: Feb 2013
Posts: 5,006
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From: Roseville, MN
Well that's pretty clear! I wonder why Ford recycled the nomenclature so my "ZF6" was an "M6OD"?
FTE Legend
Joined: Nov 2015
Posts: 30,912
Likes: 4,123
From: Angier, NC
Each one of us has his way to get the RPM lower at high way speeds and get better MPG but it also has to do with how the truck will be used and what motor it has.
My with the 300 six pulls from like 800 RPM up to 3000 RPM not that I spin it that high.
I also want it to pull my 5000 lb car trailer so it needs a low first gear like the granny in the T18 / NP435 transmissions and an add on OD unit.
Other wise the M5OD-R2 I think would be a good fit.
So what was your question?
Dave ----
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Thread Starter
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Senior User
Joined: Feb 2020
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Likes: 3
LOL!!!! Here's what opened up the can of worms....who knew there were so many choices... Anyway, I was curious as it seems that at 55-60, I'm turning around 2500-3000 rpm...(no tach, but good ear)....Would like to get that down to around 2000-2500...But isn't at the top of the list of chit to do to this project... As for the tranny options that are originally from flatheads...the 6.9 may be a bit much for them...old flatheads are putting out what 80-90hp and 170 ftlbs of torque...the 6.9 puts out what 170hp and 300 ftlbs of torque...
[Ok, '84 F250, 6.9idi, T18/19 BW...which is better....5 speed conversion, or an OD unit?]
[Ok, '84 F250, 6.9idi, T18/19 BW...which is better....5 speed conversion, or an OD unit?]
Posting Guru
Joined: Jun 2012
Posts: 1,061
Likes: 9
From: Mims, FL
I'm late to this party, but wanted to say, I look for ZFs somewhat often, and see the diesel versions fairly often. Those and the BBF are easier to find vs the SBF version.
Personally, I like the extra stick for the add on before the trans OD from Advance Adapters over the GV unit, esp if a 4x4. You'd need new driveshafts either way, but the pre-unit aux gearbox would work with 4x2 or 4x4, where the GV would be 4x2 only as I understand it. Please, correct me if I'm wrong on this.
Now, if it was me, would have the AA OD before (2) granny low 4 sps (NP435, T18/19) and a 203/205 transfer case (NP203/NP205) with as many shifters as possible. You'd have to do some head scratching to figure out optimal differential ratios, but dang that would be a cool set up and thieves would play hell figuring out how to get that thing out of the driveway. Maybe instead of having the 2nd granny low 4 sp, have a 3 sp with a column shift instead for one of 'em; that would really throw folks for a loop.
OK, back to your regularly scheduled programming. Maybe I shouldn't have drank that tumbler full of coffee this morning...
Personally, I like the extra stick for the add on before the trans OD from Advance Adapters over the GV unit, esp if a 4x4. You'd need new driveshafts either way, but the pre-unit aux gearbox would work with 4x2 or 4x4, where the GV would be 4x2 only as I understand it. Please, correct me if I'm wrong on this.
Now, if it was me, would have the AA OD before (2) granny low 4 sps (NP435, T18/19) and a 203/205 transfer case (NP203/NP205) with as many shifters as possible. You'd have to do some head scratching to figure out optimal differential ratios, but dang that would be a cool set up and thieves would play hell figuring out how to get that thing out of the driveway. Maybe instead of having the 2nd granny low 4 sp, have a 3 sp with a column shift instead for one of 'em; that would really throw folks for a loop.
OK, back to your regularly scheduled programming. Maybe I shouldn't have drank that tumbler full of coffee this morning...
Lead Driver
Joined: Apr 2007
Posts: 5,958
Likes: 105
From: Houston
Each one of us has his way to get the RPM lower at high way speeds and get better MPG but it also has to do with how the truck will be used and what motor it has.
My with the 300 six pulls from like 800 RPM up to 3000 RPM not that I spin it that high.
I also want it to pull my 5000 lb car trailer so it needs a low first gear like the granny in the T18 / NP435 transmissions and an add on OD unit.
Other wise the M5OD-R2 I think would be a good fit.
So what was your question?
Dave ----
Moderator
Joined: Jan 2001
Posts: 56,984
Likes: 2,738
From: Virginia
Gear spread is everything with a diesel. That 6.9 is governed to 3300 rpm. That is better than a larger cummins which redlines at 2000 rpm, but it is still a limitation. If you can keep it right below the governor at all times, it pulls a lot better. That is why the big trucks have 10, 15, 18 speeds. They keep that engine right at 2000 rpm for the best power from it.
Mountain Pass
Joined: May 2020
Posts: 142
Likes: 9
Do you have any photos of where the speedo goes into the S5-42? I'm swapping a ZF5 from a 1994 Power Stroke into my 1986 IDI and everything is going swimmingly but I can not find where to attach the cable. The transmission I have definitely states that it's a S5-42 and both trucks are 2WD. So if what you say is correct then there should be a hole for the speedo somewhere on the transmission.
FTE Legend
Joined: Nov 2015
Posts: 30,912
Likes: 4,123
From: Angier, NC
Do you have any photos of where the speedo goes into the S5-42? I'm swapping a ZF5 from a 1994 Power Stroke into my 1986 IDI and everything is going swimmingly but I can not find where to attach the cable. The transmission I have definitely states that it's a S5-42 and both trucks are 2WD. So if what you say is correct then there should be a hole for the speedo somewhere on the transmission.
Dave ----
Mountain Pass
Joined: May 2020
Posts: 142
Likes: 9
Do you know of any kind of conversion kit? Or will I need to get a rear diff from a newer F250 sometime in the future?