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There have been a few on here that have mentioned that they would like me to do a write up on building a doubler. Now keep in mind that I only have experience with two doublers, one being a 203/241 in which I used an adapter that WMS made for my application, and the one that I built to replace it, which is a 241/241 setup, so I have very limited experience with these. I'll tell what I did and if anyone has anything to add then feel free.
Having never been into an aluminum transfer case before, the first thing that I did was tear it down to familiarize myself with the internals. It didn't take long at all to realize how easy it would be to pull this off. After spliting the case I removed everything from the front section ot the case where the gear reduction planetary is located. Then, after marking it where it needed to be cut off, I placed the front section on a band saw and removed the section that goes out towards the front output just past the range selector lever. After getting it cut off and ground square, I took a piece of aluminum and cut it so that it could be welded into the area that I had just removed so that it could be sealed up with a single flat plate/adapter that will be made later. Then, not being set up to weld aluminum at the time, I took the case and the piece of aluminum that I had cut to fit to a local welding shop and had it welded in place. Here are some pics of it at that point.
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From there I had to figure out how to build the adapter plate that would bolt to the section pictured above to the second case. Not having a lathe large enough to machine the area to accept the second case (that would look just like the rear of the transmission) I decided to go a different route. I took a factory adapter that was located between the 4L60e transmission and the second transfer case that I used and cut it off, just in front of the flange where it bolted to the transfer case, with a sawzall. After doing that it would fit on my lathe. Then I machined it down untill it looked like a 1/2" thick plate.
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Then I found a piece of 1/2" plate steel laying in the shop so I used it to build the adapter plate. All I did was lay the front section that was in the first pic down on the 1/2" plate and scribed it with an awl. After that I took the time to cut it out with the band saw so that it wouldn't require much grinding, then I marked all of the holes that would bolt it to the section in the first pic and drilled them including two extra holes that I drilled and tapped into the new section of aluminum that I had welded into it. At this point I marked center on the plate where the output shaft would go through it and to locate where the plate in the last pic would be welded on. This is a VERY important step because that is what centers the second case to align where the shaft will exit the first. To do this, I found center and drilled an 1/8" hole through the plate and from there I measured out to where the ring in the last pic would EXACTLY center, this can't be wrong. After marking where the ring would weld on, I cut out the larger hole where the shaft would go through. and welded the ring in the last pic to the plate and drilled the holes that were in the ring through the larger plate. Something else to consider before welding the plate is how you want the second case clocked. My second case was already used in the truck behind the 203 in the factory clocked position and worked fine there, so that is what I set it at. Here is what it looked like at this point.
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Something else I didn't mention earlier is the squared off section in the lower left hand corner of the adapter. Before I cut the adapter plate out I decided to leave that section so that it would hang down below the rear transfer case so that I could modify it later for a mount to support them with a cross member.
At this point it was time to "build" the shaft that would go from the first case to the second. Before I start, it would probably be better in every way to have a custom shaft built and sumner machine works sells them for around $225, but I'm to cheap and prefer to figure out my own method. To do this, I re-installed the planetary and everything related to it and the range selector lever so that it wouldn't have to come back apart and bolted the adapter plate to the rear of the first case and measured the depth from the planetary to the back of the adapter, then I measured how far the input shaft goes into the second case. That determined how long the shaft needed to be. Then I took the original output shaft from the front case and cut it off just behind where it exits the platery. It is hollow and has about a 1/2" hole through it. Then I went to a local transmission shop and bought an old output shaft from a 4l60 since the front 241 had a 32 spline output shaft and the rear 241 had a 27 spline (4L60) input. Then I cut it off 1" longer than it needed to be measuring from the rear of it and placed it in the lathe and turned that extra inch that I left on it down to where it would fit very snug into the 1/2" hole in the first shaft. Then I "pressed" the second section where it was turned down into the hole in the original shaft and chucked it up in the lathe and turned it to verify that it was straight and welded the two together with my mig. I know that isn't the best method, but it has held up to over 400lb/ft of torque and 38" tires pulling combined truck & trailer weights reaching over 18,000 lbs, so I doubt anyone with an S10 will cause a shaft built this way to fail.
At this point it was time to unbolt the adapter from the first case and bolt it to the second case since those bolts come from the front side of it and will be located inside the rear of the first case, then I slide the shaft in and bolted it back to the first case. For gaskets I just cleaned the sufaces and applied RTV. To fill the front case I just removed the VSS in the top of the front case and added fluid until it was over the planetary. The "proper" way to do it would be to add a fill plug to the adapter plate at the proper fill level and also to drill and tap the adapter plate near the top and bottom and add 90* pipe fitting with a section of clear tubing clamped between them so that you could monitor the fluid level. I will do that at a later date.
Here are some pics of all of it assembled.
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Anyway, that's my story, hope it will help someone and if I wasn't clear on anything or if anyone has any questions or anything to had just feel free.
Having never been into an aluminum transfer case before, the first thing that I did was tear it down to familiarize myself with the internals. It didn't take long at all to realize how easy it would be to pull this off. After spliting the case I removed everything from the front section ot the case where the gear reduction planetary is located. Then, after marking it where it needed to be cut off, I placed the front section on a band saw and removed the section that goes out towards the front output just past the range selector lever. After getting it cut off and ground square, I took a piece of aluminum and cut it so that it could be welded into the area that I had just removed so that it could be sealed up with a single flat plate/adapter that will be made later. Then, not being set up to weld aluminum at the time, I took the case and the piece of aluminum that I had cut to fit to a local welding shop and had it welded in place. Here are some pics of it at that point.
From there I had to figure out how to build the adapter plate that would bolt to the section pictured above to the second case. Not having a lathe large enough to machine the area to accept the second case (that would look just like the rear of the transmission) I decided to go a different route. I took a factory adapter that was located between the 4L60e transmission and the second transfer case that I used and cut it off, just in front of the flange where it bolted to the transfer case, with a sawzall. After doing that it would fit on my lathe. Then I machined it down untill it looked like a 1/2" thick plate.
Then I found a piece of 1/2" plate steel laying in the shop so I used it to build the adapter plate. All I did was lay the front section that was in the first pic down on the 1/2" plate and scribed it with an awl. After that I took the time to cut it out with the band saw so that it wouldn't require much grinding, then I marked all of the holes that would bolt it to the section in the first pic and drilled them including two extra holes that I drilled and tapped into the new section of aluminum that I had welded into it. At this point I marked center on the plate where the output shaft would go through it and to locate where the plate in the last pic would be welded on. This is a VERY important step because that is what centers the second case to align where the shaft will exit the first. To do this, I found center and drilled an 1/8" hole through the plate and from there I measured out to where the ring in the last pic would EXACTLY center, this can't be wrong. After marking where the ring would weld on, I cut out the larger hole where the shaft would go through. and welded the ring in the last pic to the plate and drilled the holes that were in the ring through the larger plate. Something else to consider before welding the plate is how you want the second case clocked. My second case was already used in the truck behind the 203 in the factory clocked position and worked fine there, so that is what I set it at. Here is what it looked like at this point.
Something else I didn't mention earlier is the squared off section in the lower left hand corner of the adapter. Before I cut the adapter plate out I decided to leave that section so that it would hang down below the rear transfer case so that I could modify it later for a mount to support them with a cross member.
At this point it was time to "build" the shaft that would go from the first case to the second. Before I start, it would probably be better in every way to have a custom shaft built and sumner machine works sells them for around $225, but I'm to cheap and prefer to figure out my own method. To do this, I re-installed the planetary and everything related to it and the range selector lever so that it wouldn't have to come back apart and bolted the adapter plate to the rear of the first case and measured the depth from the planetary to the back of the adapter, then I measured how far the input shaft goes into the second case. That determined how long the shaft needed to be. Then I took the original output shaft from the front case and cut it off just behind where it exits the platery. It is hollow and has about a 1/2" hole through it. Then I went to a local transmission shop and bought an old output shaft from a 4l60 since the front 241 had a 32 spline output shaft and the rear 241 had a 27 spline (4L60) input. Then I cut it off 1" longer than it needed to be measuring from the rear of it and placed it in the lathe and turned that extra inch that I left on it down to where it would fit very snug into the 1/2" hole in the first shaft. Then I "pressed" the second section where it was turned down into the hole in the original shaft and chucked it up in the lathe and turned it to verify that it was straight and welded the two together with my mig. I know that isn't the best method, but it has held up to over 400lb/ft of torque and 38" tires pulling combined truck & trailer weights reaching over 18,000 lbs, so I doubt anyone with an S10 will cause a shaft built this way to fail.
At this point it was time to unbolt the adapter from the first case and bolt it to the second case since those bolts come from the front side of it and will be located inside the rear of the first case, then I slide the shaft in and bolted it back to the first case. For gaskets I just cleaned the sufaces and applied RTV. To fill the front case I just removed the VSS in the top of the front case and added fluid until it was over the planetary. The "proper" way to do it would be to add a fill plug to the adapter plate at the proper fill level and also to drill and tap the adapter plate near the top and bottom and add 90* pipe fitting with a section of clear tubing clamped between them so that you could monitor the fluid level. I will do that at a later date.
Here are some pics of all of it assembled.
Anyway, that's my story, hope it will help someone and if I wasn't clear on anything or if anyone has any questions or anything to had just feel free.
