5spd to 6spd conversion
New User
Joined: Feb 2001
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5spd to 6spd conversion
Will a 6spd tranny from a new F350 fit as a replacement for the 5spd tranny in my '89 F350 diesel crew cab? If it won't exactly fit, what would be involved in the conversion. I'm looking for a tougher transmission with which to tow my 26 ft trailer. Current 5 spd is showing signs of stress after only 55k miles.
Senior User
Joined: Jun 2003
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5spd to 6spd conversion
Hi jeronimo, same thing crossed my mind, only I have a 97 7.5 with the zf 5 spd, what do you mean by signs of stress?. I tried talking to auto wreckers about converting (no straight answers) Are the 6 spd stronger? there has to sombody out there who has tried this. Or have you found any info? regards domenico
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Joined: May 2003
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From: Joliet, Illinois
5spd to 6spd conversion
Does anybody know the ratios of the ZF and the 6 speed?
These are the ones I have so far.
NP435==6.69 3.34 1.79 1.00
T18====6.32 3.09 1.69 1.00
T19====5.11 3.03 1.79 1.00
T19 optional 1st: 6.32 and 4.02
Z.F=====???
6 speed=???
These are the ones I have so far.
NP435==6.69 3.34 1.79 1.00
T18====6.32 3.09 1.69 1.00
T19====5.11 3.03 1.79 1.00
T19 optional 1st: 6.32 and 4.02
Z.F=====???
6 speed=???
Last edited by archangel; Aug 17, 2003 at 02:26 AM.
Posting Guru
Joined: Dec 1999
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From: Copley, OH
5spd to 6spd conversion
For the ZF S6-650:
5.79 3.30 2.10 1.30 1.00 0.72
For the ZF S5-47
5.72 2.94 1.61 1.00 0.76
Both of these trannies have an integral bellhousing, so the question you need to be asking is whether the bolt pattern on your block matches a Powerstroke or a mod motor. In the case of the 300 it does not, but you can upgrade to the 5 speed ZF from a 97 down F250/350 with a 300 of a SBF
5.79 3.30 2.10 1.30 1.00 0.72
For the ZF S5-47
5.72 2.94 1.61 1.00 0.76
Both of these trannies have an integral bellhousing, so the question you need to be asking is whether the bolt pattern on your block matches a Powerstroke or a mod motor. In the case of the 300 it does not, but you can upgrade to the 5 speed ZF from a 97 down F250/350 with a 300 of a SBF
Freshman User
Joined: Jun 2003
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From: Southern In, close to Lou
5spd to 6spd conversion
I have been doing some research on this exact thing. I have a 95' f-350 5.8 and from what I have found on Ebay there is a rebuilder that sales 5 and 6 spds. They list that the 6 spd fit the 1999 5.4. Also the 5 spd fits the 5.4. So unless there is a bellhousing change in certain years they both 5 and 6 spds fit 5.4 and 7.3. Now here where it gets a little confusing. They also show the 5 spd on 5.8, 5.4 through 2002. So that tells me that the 5.8 and 5.4 should have the same bellhousing again unless there is a year change that is not mention. I am doing more research and will keep you updated if I find out anything else. 
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Posting Guru
Joined: Dec 1999
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From: Copley, OH
5spd to 6spd conversion
The Windsor and the Triton have different bolt patterns. The trannies for them will not interchange.
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Posting Guru
Joined: Apr 2002
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From: CT
5spd to 6spd conversion
The ZF 6 speed is a beast of a manual trans and would be an awesome swap, the 5spd hold 420ft-lbs while the 6 is able to hold 650ft-lbs, and starngeranger is right, it will not bolt up to the 5.8.
Senior User
Joined: Jun 2003
Posts: 139
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5spd to 6spd conversion
hey guy's so from what your saying the 7.5 wont bolt up to the 6 spd (correct me if I am wrong, the 7.3 power stroke came with a 5 spd pre 99 and with the 6 spd post 99 , so they made a different transmission for the power stroke than gas engines or did they use an adapter plate?) "I'm so confused" Has anybody tried these places that make transmission adapter plates, I tried surfing the net but I couldn't find anything. I can't remember the name of the company (I thought it was transdapt or somthing?) From what I read on this side we got a lot of smart cookies here and if we put are heads together we should come with a solution to this. (It might be expensive but it will be a solution) regards Domenico
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Joined: Aug 2002
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From: Laveen
5spd to 6spd conversion
I'm trying to sort out the trannys, from what I was told the earlier diesels used the same transmissions but had their own bell housings and the transmissions were interchangable but somewhere along the line they came out with a new transmission, one of the ZFs for the diesels, and there is no bell housing to fit it to the ford SBs or BBs and the six speed ZF is the same, I am still trying to find out for sure. If not McLeod makes modular bell housings and blank tranny adapter plates.
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Joined: Dec 1999
Posts: 1,903
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From: Copley, OH
5spd to 6spd conversion
The ZF trannies have integral bellhousings. The 5 speed is machined in at least 3 different patterns: Windsor/BB6, 385 and PSD. The 6 speed is machined to fit the Triton or the PSD.
An adaptor plate is the only possibility. Be careful about input shaft length though, the plate may require a longer shaft to get into the pilot bearing
An adaptor plate is the only possibility. Be careful about input shaft length though, the plate may require a longer shaft to get into the pilot bearing