Tranny Transformation

[frankendat]

In the early steps of rebuilding a 71B, I admitted "more than I could chew". I might revisit the project,  as I have two 71B's and a rebuild kit, but I am looking for a 71C in the meantime. (If I can a deal on one in good shape, the rebuild could be avoided)

 

From what I have learned on Ratsun, only specific 71C transmissions will interchange, with a 71B from a 1985 4wd 720: A 71C from a 2wd pickup with a KA24E or a 71C from a 240Z with a KA24E.

 

However, the 71C transmission was available in both previously mentioned vehicles, mated to a KA24DE, a Z31 mated to a VG30 and an S12 (There might be more)

 

I phrase this next question as "Is it possible?", but I define "possible", as neither excessively costly or difficult and define costly, as more than $100 above the cost without and difficult, as not requiring specialized tooling or more than a weekend, e.g. if swapping a 71C from a 2wd D21 into my 720 would cost $400, then swapping a 71C including swapping the bell housing from a 71B would not be more than $500. (Since I have the 71B, the bell housing swap could be only a investment in time)

 

Give the above parameters, Is it possible to swap a 71B housing onto a 71C transmission? Allowing me to re-purpose a 71C from a KA24DE or VG30?

 

The more options for donors the more opportunities for success, and I will accept a 71C that identifies as a 71B as long as it kept the stronger internals.

[datzenmike]

There were two different length 71C transmissions that fit the KA engines KA24E or KA24DE The S13/14 240sx was 34-35" and the truck 2wd was around 30". I've never measured one so??? this is approximate. The truck 2wd 5 speeds are the closet to the L series 71B.

 

There were no 71C transmissions with an L series front case. (bell) However with some machine work an L series 71B front case can be mated to a 71C of either length. 

 

Counter bearing...

The L series 71B used a 56mm counter bearing. In '85 all 71B were changed to the better stronger 62mm counter bearing and this was continued into the 71C transmissions.

 

Front case...

 

1/ First/second shift rod hole in the 71B is only 14mm. The 71C shift rod is 16mm so this will have to be drilled out larger to accept it. Electric hand drill will work for this.

 

2/ If you install a 71B front case onto a 71C transmission it will bind and not turn. This is because the 71C gears are wider and space is tight right behind the counter bearing. A machine shop will have to mill the inside face of the transmission around the counter bearing for clearance. While at it get them to open the counter bearing hole from 56mm to 62mm so you can take advantage of the important bearing up grade.

 

 

Finished L series with 16mm shift rod hole and counter bearing hole widened to 62mm. Plus the case thickness thinned to just under 1/2" around the counter bearing out to at least 3 1/2"

 

New Nachi 62mm counter bearing is under $15 and there's the machining maybe $150 to $200???   (i have no idea on co$t)

[frankendat]

29 minutes ago, datzenmike said:

There were two different length 71C transmissions that fit the KA engines KA24E or KA24DE The S13/14 240sx was 34-35" and the truck 2wd was around 30". I've never measured one so??? this is approximate. The truck 2wd 5 speeds are the closet to the L series 71B.

 

There were no 71C transmissions with an L series front case. (bell) However with some machine work an L series 71B front case can be mated to a 71C of either length. 

 

Counter bearing...

The L series 71B used a 56mm counter bearing. In '85 all 71B were changed to the better stronger 62mm counter bearing and this was continued into the 71C transmissions.

 

Front case...

 

1/ First/second shift rod hole in the 71B is only 14mm. The 71C shift rod is 16mm so this will have to be drilled out larger to accept it. Electric hand drill will work for this.

 

2/ If you install a 71B front case onto a 71C transmission it will bind and not turn. This is because the 71C gears are wider and space is tight right behind the counter bearing. A machine shop will have to mill the inside face of the transmission around the counter bearing for clearance. While at it get them to open the counter bearing hole from 56mm to 62mm so you can take advantage of the important bearing up grade.

 

 

Finished L series with 16mm shift rod hole and counter bearing hole widened to 62mm. Plus the case thickness thinned to just under 1/2" around the counter bearing out to at least 3 1/2"

 

New Nachi 62mm counter bearing is under $15 and there's the machining maybe $150 to $200???   (i have no idea on co$t)

Fantastic information! Do you know any shop or Ratsuner that has accomplished this modification? It likely requires a special jig, but you never know. It does raise the price I am willing to pay for a right one

[datzenmike]

You could probably drill out the shift rod hole and grind down the area around the counter bearing but can't see making the counter bearing hole larger. What's an hour of machine shop worth??? They do this for a living can't be an hour's worth of work.

[frankendat]

The old story of $1.00 to drill the hole $1000 to know how/where to drill it. Since, I am not exactly sure what I am talking about, unless the shop has preformed this procedure, the likely will not choose to attempt it and/or it will be costly.

Is that your work in the pictures or do you know who has accomplished this task?

 

[bottomwatcher]

I wouldn't mess with any of that when the factory produced thousands ready to go. This isn't some rare exotic car you are trying to keep on the road. Just need a 2wd 4 cylinder hardbody from 86 through KADe frontiers. I have seen them up to 2003 and maybe they went longer. 

[datzenmike]

71C won't fit an L series engine and I think that is the intent. Swapping a KA and transmission is going to be way more work and costly... and yes this is a rare exotic car that is being kept on the road, so to speak.

[datzenmike]

8 hours ago, frankendat said:

The old story of $1.00 to drill the hole $1000 to know how/where to drill it. Since, I am not exactly sure what I am talking about, unless the shop has preformed this procedure, the likely will not choose to attempt it and/or it will be costly.

Is that your work in the pictures or do you know who has accomplished this task?

 

 

All you are doing is enlarging the shift rod hole from roughly 1/2" to 5/8". Not rocket science, put drill in hole and pull the trigger. Any competent shop can mill the front case. Once done it will transfer to any other 71C.

 

Not my work just found it while exploring transmission options. The 71B is used on the 280zx and will handle about 180-200 engine hp, what ever the non turbo made but ithad been upgraded to it's limit. The 71C is about twice as strong.

[bottomwatcher]

7 hours ago, datzenmike said:

71C won't fit an L series engine and I think that is the intent. Swapping a KA and transmission is going to be way more work and costly... and yes this is a rare exotic car that is being kept on the road, so to speak.

Not sure where the L came in. Unless I am reading it wrong it is going in a 1985 4x4 720.

[frankendat]

7 hours ago, bottomwatcher said:

I wouldn't mess with any of that when the factory produced thousands ready to go. This isn't some rare exotic car you are trying to keep on the road. Just need a 2wd 4 cylinder hardbody from 86 through KADe frontiers. I have seen them up to 2003 and maybe they went longer. 

 

7 hours ago, datzenmike said:

71C won't fit an L series engine and I think that is the intent. Swapping a KA and transmission is going to be way more work and costly... and yes this is a rare exotic car that is being kept on the road, so to speak.

Gentlemen, Thank you for your continued guidance and patience. I continue to question to increase knowledge and confidence, it is a great benefit when dealing with mechanics/machinists.

 

The 71C in question is sought to attach to a Z24. It is my understanding the bell-housing for the  Z24 and the L-series are the same.

The Z24 that I own came attached to a 71B transmission. It lived in a 1985 4wd 720 with a divorced transfer case.

It is my understanding that the stronger 71C transmission from a 1986+ D21 will fit without modification to the bell housing, (driveline modifications are likely) if the 71C transmission is pulled from a 2wd 1986+ D21 with a KA24E engine or a 71C transmission from a 240Z with a KA24E.

 

Opportunities for well cared for 71C transmissions from 2wd 1986+ D21 pickups have been absent from the local second hand market and to widen the number of potential candidates, I sought information on other vehicles that came with a 71C transmission.

It is my understanding that the same 71C transmission found in 1986+ D21 pickups with a KA24E is found in D21 pickups with a KA24DE, VG30 and 300ZX. The 5 speed 71C is the same but the bell housings are different and not compatible.

 

My question was the possibility to obtain a 71C transmission from any of the aforementioned donors with different and not compatible ("wrong") bell housings, remove the "wrong" bell housing and employ the bell housing from a 71B.

 

The information provided by DatzenMike are the steps necessary to fit the internals of a 71C transmission into a 71B bell housing. The only reason to perform this operation is to open up the field of potential donors and locate a local 71C. Current shipping costs make shipping heavy second hand items impractical and 2wd trucks are rare in my area.

 

If any of my understanding is incorrect then please correct

[bottomwatcher]

No. L bellhousing is different. The bolts fit but the housing is clocked like 12 degrees putting the trans at an angle if bolted up. 240z had B series. 240sx had a long version of C series not good for 4wd truck. V6 used 30A transmission not compatible. You are looking for 2wd 4 cylinder nissan truck from 86 to at least 2003. They are out there.

[frankendat]

2 hours ago, bottomwatcher said:

No. L bellhousing is different. The bolts fit but the housing is clocked like 12 degrees putting the trans at an angle if bolted up. 240z had B series. 240sx had a long version of C series not good for 4wd truck. V6 used 30A transmission not compatible. You are looking for 2wd 4 cylinder nissan truck from 86 to at least 2003. They are out there.

Thank you. I will continue to search, maybe I'll start hollering about a "shortage", as that seems the standard go to when something of a sufficient quality isn't offered at a desired price point.

 

[datzenmike]

22 hours ago, frankendat said:

In the early steps of rebuilding a 71B, I admitted "more than I could chew". I might revisit the project,  as I have two 71B's and a rebuild kit, but I am looking for a 71C in the meantime. (If I can a deal on one in good shape, the rebuild could be avoided)

 

From what I have learned on Ratsun, only specific 71C transmissions will interchange, with a 71B from a 1985 4wd 720: A 71C from a 2wd pickup with a KA24E or a 71C from a 240Z with a KA24E.

 

However, the 71C transmission was available in both previously mentioned vehicles, mated to a KA24DE, a Z31 mated to a VG30 and an S12 (There might be more)

 

I phrase this next question as "Is it possible?", but I define "possible", as neither excessively costly or difficult and define costly, as more than $100 above the cost without and difficult, as not requiring specialized tooling or more than a weekend, e.g. if swapping a 71C from a 2wd D21 into my 720 would cost $400, then swapping a 71C including swapping the bell housing from a 71B would not be more than $500. (Since I have the 71B, the bell housing swap could be only a investment in time)

 

Give the above parameters, Is it possible to swap a 71B housing onto a 71C transmission? Allowing me to re-purpose a 71C from a KA24DE or VG30?

 

The more options for donors the more opportunities for success, and I will accept a 71C that identifies as a 71B as long as it kept the stronger internals.

 

The question was about swapping a 71B front case onto a later 71C...... and I got lost thinking this was the usual swap to an L series.

 

If this is a X series engine the Later 71C form a KA engine just simply bolts up. Release collar should be the same as both Z24 and truck KA engines used a 240mm clutch, not so on the Car KA which were 225mm.

 

I'll add that the '86-'89 D21 Hardbody used a Z24i but the 71C in it is the same as the '89  and on KA engines. Just sayin' the early Hardbody didn't have KA engines. Z series and KA series transmissions have the same bolt pattern and 'lean'. VG are totally different.

[frankendat]

7 minutes ago, datzenmike said:

 

The question was about swapping a 71B front case onto a later 71C...... and I got lost thinking this was the usual swap to an L series.

 

If this is a X series engine the Later 71C form a KA engine just simply bolts up. Release collar should be the same as both Z24 and truck KA engines used a 240mm clutch, not so on the Car KA which were 225mm.

 

I'll add that the '86-'89 D21 Hardbody used a Z24i but the 71C in it is the same as the '89  and on KA engines. Just sayin' the early Hardbody didn't have KA engines. Z series and KA series transmissions have the same bolt pattern and 'lean'. VG are totally different.

Thank you DatzenMike, I thought a KA24DE transmission from a 2wd D21 was also a no go, is that not the case?

[datzenmike]

The '86-'89 D21 with Z24i and the '90 and up 2wd D21 with KA engines use the same 71C transmission. It will fit and replace the earlier 720 with Z series engines. The length is not the exact same so you'll need to mod the drive shaft length and maybe where the transmission mount is on the cross member.

 

Through '93 a regular speedometer pinion sleeve was used in the 71C, and after '93 an electric speed sensor was used. I'm almost positive you can pull the electric speed sensor out and replace it with your '85 speedometer pinion sleeve.

[bottomwatcher]

He has a 4wd. The speed sensor is in the transfer case so the speed is correct either in 4 high or low. All the speed sensor does in is plug the hole in a 2wd trans. You are good with any kae or kade 2wd trans. The 4wd trans bolts directly to the newer transfer case is why it is a no go.

[frankendat]

6 minutes ago, bottomwatcher said:

He has a 4wd. The speed sensor is in the transfer case so the speed is correct either in 4 high or low. All the speed sensor does in is plug the hole in a 2wd trans. You are good with any kae or kade 2wd trans. The 4wd trans bolts directly to the newer transfer case is why it is a no go.

Do 86-89 D21's with the Z24i have the divorced transfer case or the newer one?

[bottomwatcher]

4wd have the integrated transfer case. This is why you are looking for a 2wd transmission.

[frankendat]

5 minutes ago, bottomwatcher said:

4wd have the integrated transfer case. This is why you are looking for a 2wd transmission.

Understood. I wasn't sure about the cutoff dated from divorced to integrated transfer case.

[datzenmike]

1 hour ago, bottomwatcher said:

He has a 4wd. The speed sensor is in the transfer case so the speed is correct either in 4 high or low. All the speed sensor does in is plug the hole in a 2wd trans. You are good with any kae or kade 2wd trans. The 4wd trans bolts directly to the newer transfer case is why it is a no go.

 

Can only go by what's in his profile. Didn't see 4x4. It's been a long day too....

[Jesse C.]

On 3/28/2023 at 8:04 PM, datzenmike said:

 

Can only go by what's in his profile. Didn't see 4x4. It's been a long day too....

 

[frankendat]

On 3/28/2023 at 8:08 PM, bottomwatcher said:

4wd have the integrated transfer case. This is why you are looking for a 2wd transmission.

 

On 3/28/2023 at 9:04 PM, datzenmike said:

 

Can only go by what's in his profile. Didn't see 4x4. It's been a long day too....

It took a few months, but I am now in possession of a 2004 2wd 5 speed that was in Frontier and previously mated to a KA24DE. To recap the knowledge graciously shared on employing this transmission in a 84/85 720 4wd with a Z24:

1. KA24DE bell housing will bolt up to the Z24 without modification.
a. Speed sensor will attach to transfer case
2. Installing the KA24DE transmission will require driveshaft and/or center console customization

It is that easy.
(or did I miss some steps)
___________________________________________________________________________________________________
Question: A fellow long term Ratsun member sells transmission mounts/brackets (IXYDe...or something). Would one of his brackets be beneficial in this swap?

[datzenmike]

39 minutes ago, frankendat said:

 

Iemploying this transmission in a 84/85 720 4wd with a Z24:

 

1. KA24DE bell housing will bolt up to the Z24 without modification....... YES keep your current release bearing collar even if the Frontier comes with one. Use a new bearing though.

a. Speed sensor will attach to transfer case. Just to be clear leave your speedometer as is, driven from the transfer case. The Frontier likely does have an electrical speed 'sensor'. Just leave it to keep the oil in. You can't use it on the 720 anyway.

2. Installing the KA24DE transmission will require driveshaft and/or center console customization. The Frontier is likely about 30" give or take so slightly shorter than the 71B it replaces. Length is one thing shifter location is another. It may be close enough to fit the hole.

___________________________________________________________________________________________________
Question: A fellow long term Ratsun member sells transmission mounts/brackets (IXYDe...or something). Would one of his brackets be beneficial in this swap? ]2eDeYe makes transmission mounts for KA conversions. I think the mount is slightly different than the 71B it replaces so an already made one will simplify things. Contact Steve by private message at   https://ratsun.net/profile/38-2edeye/ 

 

[frankendat]

4 hours ago, datzenmike said:

 

EXCELLENT! That is GREAT news, one step closer, thank you for all your help

[bottomwatcher]

Nobody makes the trans mount. The adapter is a simple piece of plate. I made mine from steel. Madcaw made his from aluminum which is plenty strong. Covered in the 720 forum.