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Discussion Starter · #1 ·
Hey everyone, I have an 88 F250 and a 12v out of a school bus that i want to marry :) The 250 has a 351 so a SB zf5 and I have a lead on a rebuilt diesel zf5 but i haven't committed to it yet, so i am open to other options. I was thinking of trying to use a zf5 just so i could keep easier but i dont mind a bit of fabrication :)
Does anyone here know where i can get an adapter for a zf5 or another transmission i can use? I would like to stay with a manual ( i like to shift) and the 3rd pedal is a very good theft deterrent this day and age ;) I am in NC and will be traveling to NH soon so i can pick up anywhere sort of on the way, so if you have anything or know of anything please LMK, thanks-Bill Tire Automotive parking light Wheel Land vehicle Vehicle
 

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Glad to see another NC guy. First off, I wouldn't recommend the SB ZF for a couple reasons. #1, it has an internal slave cylinder which means you have to pull the transmission to change it. Second, you have a limit on clutch size which can be a problem. The better transmission would be one that came behind the 7.3 diesel. It has better gear ratios and is the same strength. The SB ZF can use the Cummins factory adapter and flywheel which can be found on the used market. The 7.3 will require an aftermarket adapter setup which tends to be more expensive. I looked at all this planning to install a Cummins in my '90 F250. Same body style as yours. Mine is white where yours is tan. Destroked makes the adapter. It requires a slight amount of grinding on the block skirt for starter clearance but that does not affect anything on the engine. Quick Draw Bands has the Ford adapter kit for $995 plus shipping. The Destroked setup plus a clutch and starter costs around $1600 to $1800. I bought one and I've never used them. All but the adapter are in the original boxes. I may or may not have the bolts. Had a break in at my house and not sure what the thieves took along that line. The base parts were all locked in my garage they didn't bother as far as I know. This setup has a flywheel and 13" clutch from Valair and a Ford 6.0 diesel starter, and if it wasn't stolen I have a barring tool and adapter which was about another $100. I'm in rehab right now so I'd have to get someone to check on the bolts and get the parts out of the garage. Wouldn't want to ship them. That stuff is heavy. What part of NC do you live in?
 

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Glad to see another NC guy. First off, I wouldn't recommend the SB ZF for a couple reasons. #1, it has an internal slave cylinder which means you have to pull the transmission to change it....
Amen
 

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Discussion Starter · #4 ·
Thanks for the info, I am in the winston-salem area of NC but I can drive. I am planning on heading to NH soon but am definitely interested. Let me know where you located are and we can go from there
 

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Another thing to add is the ratios are different. Stole this from the internet.
Gas version (wide ratio)
1st 5.72:1
2nd 2.94:1
3rd 1.61:1
4th 1.00:1
5th 0.76:1

Diesel version (close ratio)
1st 4.14:1
2nd 2.37:1
3rd 1.42:1
4th 1.00:1
5th 0.76:1

Since I am cheap, I would just use the SBF ZF if it was me. I used an M5OD-R2 that came in my F-150 and bought the truck with a Cummins swap intended. Yeah, the internal slave sucks. But, it is LOADS easier to remove a truck transmission than say the ZF in my BMW 540i. I don't think the ZF5 is significantly larger than the M5OD but either way, work is work.
 

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Discussion Starter · #6 ·
I was thinking of trying to use the SB ZF that is in there, it seems to be fine. The problem is that a stock 6bt is 400ft/lb and that will be difficult to constrain with an 11" clutch....but it does seem that the cummins to SB ZF adapters are easier to com by....
 

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The clutch will be the limiting factor. 11" will hold 400 lb/ft, but most 12 valves make significantly more than 400 lb/ft. Bone stock the earliest were supposedly 400, but I haven't seen a stock 12 valve in over a decade.
 

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Discussion Starter · #8 ·
This one is bone stock, got it from a school bus. great deal with only ~120k on it and fleet maintenance. As of right now i plan on keeping it stock, but i also know that i like to modify things (gt35 audi 200 20v, diesel swapped nissan wd21, soon MTDI vw eurovan) This truck is for towing a car trailer back and forth from NC to NH......i am really considering leaving my transmission in.....much more cost effective....and time effective..... The truck is fairly clean but at some point i would like to pull the body/bed and clean up/coat the frame and perhaps then ill upgrade to a better transmission. Where is the best place to source a good 11" clutch/FW and adapter plate?
 

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Discussion Starter · #10 · (Edited)
Like i said, i will probably upgrade transmissions in a few years, but for now if i get a good clutch, dont turn up the fuel and drive it nice it still wont last? the total rolling weight (truck,trailer,car) should be ~around 11k or so.... I know if i floor it while going uphill i would eat the clutch, but if i hold it steady and possibly downshift ( I want it to hold up till i have time to swap transmissions) would it hold up? swapping transmissions add around $4k plus a bunch of time

here is part of a post over on ford truck enthusiast....

The only significant difference between a SB ZF and a BB/diesel ZF is the bellhousing and input shaft diameter. Are the 6bt boys saying the smaller input shafts on the SB trans fail? They hold up to built 408s just fine, so I'm guessing you'd have to crank a 6BT up pretty good to get to the level of breaking an input. That said, the output shaft sees approx 6x (5.72 to be exact) the torque the input sees and while bigger, it's not 6x bigger. From what I read on really pushing the limits of the ZF (never actually had one fail myself), the limit is the case itself, which will stretch and lose preload on the bearings, allowing the shafts to move, eventually leading to grenading. That's why the biggest difference between the S5-42 and the S5-47 is more webbing on the exterior of the case and then the S6-650 got a center support for the main shaft.

And then the variable nobody talks about with strength of a manual trans is the loose nut behind the steering wheel. Rolling into and out of the throttle gently and not doing stuff like going full send on the skinny pedal in 1st gear goes a ways to making a trans last. Alternatively, it doesn't take an enormous engine break stuff (including everything after the trans) if the driver is doing 1st gear burnouts over pot holes.
 

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I have run the M5od and the SBF ZF5 42 with a LUK gold clutch and fresh flywheel surface behind a 4BT at the 200hp prolonged level excessive CGVW removed the teeth at the input shaft/countershaft junction, the ZF5 served well and the as did the clutch. After a engine rebuild which included compounds it's at the 300hp level the ZF was still up to the task but at 10K GVW on level ground with any real application of throttle in direct or over the clutch tapped out.
As far as the smaller input shaft IMHO it's shock loading that will be what kills it not the thru put loading, hell NP435's and ZF's both have served well in medium duty trucks.
Ford issued a TSB regarding ZF's that changed the lube requirements to synthetic and reduced the change interval from 60K to 30K that makes me think that heat is your #1 enemy.
I now have the Diesel ZF s42 so I can run the 13" clutch it was a LOT of $$ that I would rather have spent elsewhere and in hindsight I should have listened to that voice in the back of my mind 10 years ago and started with the Diesel ZF seeing as I'd be ahead ~ $2,500 easily but the 4BT came with the SBF adapter........$.02
 
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So much of how a transmission holds up is how you treat it. If you shift gears normally and aren't trying to do burn outs to impress people, most manual transmissions will survive. Steve literally put his M5R2-OD through hell before it finally gave up the ghost. Audios, you mention your 6bt came from a bus. What HP is it? Bus engines often range from 170-230 HP. The 160 HP and 400 lb ft torque were mostly the Dodge use engines which were detuned from the commercial engines. The ZF S5-42 is rated at 420 lb ft but will stand a bit above that. Ford changed to the S5-47 for the last few years of the 5 speeds and it was rated at 470 lb ft. With the 7.3 Powerstokes they went to the S6-650 six speed which handles 650 lb ft and when the 6.0 came out they used the S6-750 which was 750 lb ft. All of these can be a adapted to a B series Cummins. As Eggman pointed out, the limiting factor is usually the clutch unless you do something stupid. If your HP is in the 200 area or less then the small block clutch will generally hold. After that you generally want something bigger. For example, the CPL 1553 6bt that came in buses and trucks was 230 HP and 605 lb ft torque. No small clutch is going to hold that. And at the same time that much torque is just overloading a ZF 5 speed.

PS. I live in Newton NC which is 65 miles west of you.
 

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Discussion Starter · #13 ·
So much of how a transmission holds up is how you treat it. If you shift gears normally and aren't trying to do burn outs to impress people, most manual transmissions will survive. Steve literally put his M5R2-OD through hell before it finally gave up the ghost. Audios, you mention your 6bt came from a bus. What HP is it? Bus engines often range from 170-230 HP. The 160 HP and 400 lb ft torque were mostly the Dodge use engines which were detuned from the commercial engines. The ZF S5-42 is rated at 420 lb ft but will stand a bit above that. Ford changed to the S5-47 for the last few years of the 5 speeds and it was rated at 470 lb ft. With the 7.3 Powerstokes they went to the S6-650 six speed which handles 650 lb ft and when the 6.0 came out they used the S6-750 which was 750 lb ft. All of these can be a adapted to a B series Cummins. As Eggman pointed out, the limiting factor is usually the clutch unless you do something stupid. If your HP is in the 200 area or less then the small block clutch will generally hold. After that you generally want something bigger. For example, the CPL 1553 6bt that came in buses and trucks was 230 HP and 605 lb ft torque. No small clutch is going to hold that. And at the same time that much torque is just overloading a ZF 5 speed.

PS. I live in Newton NC which is 65 miles west of you.
Awesome, it looks like its around 1.25 hrs from me (approx.) My 6bt is rated at 190hp according to the plate on the side. Send me a message if you want to sell your adapter / etc.
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Discussion Starter · #14 ·
Just an update, I found someone that is going to help me put The Cummins in my truck. I think I'm going to try to use my stock transmission just for getting it in there fairly quickly. Later I will try to find a transmission that will take some more power but for now I will try to find a good clutch, perhaps dual disc, to put on the 11-in flywheel and just try to be nice with it.
 

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I have run the M5od and the SBF ZF5 42 with a LUK gold clutch and fresh flywheel surface behind a 4BT at the 200hp prolonged level excessive CGVW removed the teeth at the input shaft/countershaft junction, the ZF5 served well and the as did the clutch. After a engine rebuild which included compounds it's at the 300hp level the ZF was still up to the task but at 10K GVW on level ground with any real application of throttle in direct or over the clutch tapped out.
As far as the smaller input shaft IMHO it's shock loading that will be what kills it not the thru put loading, hell NP435's and ZF's both have served well in medium duty trucks.
Ford issued a TSB regarding ZF's that changed the lube requirements to synthetic and reduced the change interval from 60K to 30K that makes me think that heat is your #1 enemy.
I now have the Diesel ZF s42 so I can run the 13" clutch it was a LOT of $$ that I would rather have spent elsewhere and in hindsight I should have listened to that voice in the back of my mind 10 years ago and started with the Diesel ZF seeing as I'd be ahead ~ $2,500 easily but the 4BT came with the SBF adapter........$.02
I had a similar experience. I had a zf5 sbf and it was fine at 208 whp and 478 wtq. I ran a centerforce clutch. Never slipped one bit. But I didn't tow any more than about 3k lbs and the truck was just over 5k lbs.
I stepped up to compounds and if I rolled on boost it would slip right away.
Like eggman said, in hind sight I should have ran a bigger trans to start with cause I then spent 2500 on a new nv4500, 1000 on another clutch kit, 250 on new hydraulics...ect ect. You get the point.
I wouldn't run a zf5 sbf with a 6bt unless you were gonna keep the 6bt at stock power lvl and not tow.
 

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Discussion Starter · #16 ·
The motor will stay stock, and I'll be towing one vehicle at a time probably around 5,000 lb or so. I'll just be careful with the skinny pedal to not get the clutch to slip. I did get an organic dual disc clutch and I will have to just be careful for any slippage, thank you for all the information everyone
 

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The motor will stay stock, and I'll be towing one vehicle at a time probably around 5,000 lb or so. I'll just be careful with the skinny pedal to not get the clutch to slip. I did get an organic dual disc clutch and I will have to just be careful for any slippage, thank you for all the information everyone

I was looking into the dual disc clutch and was told that the input shaft is the next weakest link once you beef up the clutch. so I went with the nv4500. guess your gonna find out!! good luck
 

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Yeah, in racing, it is good practice to let the clutch be a "fuse" of sorts. It is cheaper to fry a clutch than snap an input shaft.
 
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