T-case swap from 1.4 to 1.2 question - Defender Source
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  #1  
Old May 19th, 2013, 03:58 PM
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Question T-case swap from 1.4 to 1.2 question

I intend to purchase a good used 1.22 T-case to swap with my 1.4, as the research I've found shows that the 1.2s is a great match to the 2.8 TGV power, and I'm hoping to gain some economy and lower revs/noise on the highway at speed. Looks from initial research like it would be easier and more cost effective to find a good D2 locking case to swap out with mine, then the ashcroft ratio conversion. Before anyone asks, I want to keep my 1.4 case in case I don't like the 1.2, so i can go back. If I like it, I'll sell it then.

Can anyone confirm if a D2 locking t-case will be a straight fit to my R380 and shifters? I'm assuming I would have to change the prop flange, but other than that?

I'm seeing D2 t-cases on fleabay for $300ish, which sure beats the cost of the ashcroft conversion kit.
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  #2  
Old May 19th, 2013, 04:00 PM
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Do you have a 2in output on your R380 or a 3in? If you have a 2in, it will not fit. If you have a 3in, it is fine. You can also fit a DII front shaft (please fit a rebuilt one with greaseable joints) rather than swapping the flange. The last issue is the speedo drive housing is different so you need to swap that too. Oh, and pull the shift interlock solinoid.
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Old May 19th, 2013, 04:08 PM
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thanks Dr. Evil. I'm going to have to measure the output on the R380 I just swapped out to confirm. I was going with a D2 since they would likely be lower mileage than a D1, and I want to be certain I get a cross drilled shaft. If D1 t-cases were all cross drilled, I would be open to that too.

As for front shaft, I have a double cardon GBR, so that's no issue. And my speedo is a 97 electronic (thanks Pendy), so also no issue.
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Old May 19th, 2013, 04:21 PM
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here's old 380. 3 inch?
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  #5  
Old May 19th, 2013, 04:28 PM
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The D2 t-case will bolt up but you have to change a few things. The Hi/Low arm is different-swap the one from the 1.4 box. The front flange is different-swap the one from the 1.4 box. There will be a shift solenoid and a couple of switches that you won't need-remove the solenoid & ignore or plug the switches. The D2 uses the ABS for a road speed input. As a result, the rear output housing has no provision for the speedometer gear. You will need a rear output housing that has this provision. This gets a little trickier because the original NAS 110 box is older and uses gaskets to seal the case parts. The D2 box uses sealant. The gasket thickness is an integral part of the bearing preload and they made some changes to the cases when they went away from the gaskets. The rear output housing is machined with a raised area that supports the rear center diff bearing and insets it into the bore in the main case. The height of this raised area varies from just under 2mm to 2,7mm on the 5 samples I just measured with casting dates from 1983 to 2003. What this means is that if you swap rear output housings and this raised bearing support isn't the exact same dimension, you will change the bearing preload on the center diff. Generally, the later D2 housings had thicker dimensions, so swapping the rear output housing from the 1.4 onto the D2 box will likely result in substantially loose bearings. This can be corrected by fitting a thicker preload shim, but that will require dismantling the D2 box. The Last bit of the puzzle is the parking brake. The park brake linkage bracket mounts to 8x1.25mm holes drilled into bosses on the rear output housing. If you use the 1.4 output housing, no problem. If you use a later housing, you will have to drill & tap these holes or switch to a later type parking brake with the cable going directly into the backing plate with no external linkage. It would be easier to use a 1.2 box from a D1 and just take out the solenoid.

The output spline length on the transmission is a non-issue as both the LT77 and early R380 output shafts neck down forward of the splines. Manual transmission output shafts will fit either the older non-drilled or the later cross drilled input gears. It's only the automatic transmissions that have fitment issues in this regard.

I'm pretty sure your speed transducer for your electronic speedometer will be driven off of the speedometer gear just like the D1s and it will be a concern for you. All D1s from 1996 to 1999 will have a cross drilled input gear. Swapping in a cross drilled gear into a 1994-1995 LT230 that needs one is not a big deal. The machining tolerances on the gears is much tighter than on the cases. I have yet to see an LT230 require a shim change when installing a new input gear.
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Old May 19th, 2013, 04:44 PM
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Great info Rob. I'm open to going with a D1 case, if I can be assured of getting a cross drilled gears. reliability is important. Is there a particular year that would be my best bet? sounds like the speedo and parking brake rule out a D2 case for my application. I want the easiest bolt in approach, since this is a daily driver and don't want to be down messing with a t-case tear down to get this to work.
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  #7  
Old May 19th, 2013, 04:54 PM
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The 1994-1995 D1 boxes will have the coarse cut 1.2:1 gears (28tooth input) but may or may not need an updated input gear. Putting in a new input gear is no big deal...as bad as I am at typing, I could have changed one in the time it took me to type the first post. The 1996-1999 D1 boxes will be the newer fine cut gears (38 tooth input). Either should work. I'd just try and find a nice clean lowish mileage one. As far as the park brake bracket goes, you'll probably have to drill & tap holes in the rear output housing. It's no big deal & not difficult. Attach the park brake bracket to the forward holes on the side of the case. Mark the centers of the holes you need in the rear bosses, drill & tap to 8x1.25mm. The exact position isn't super critical, just get the holes generally in the center of the bosses and as square & straight as you can. If you have enough mechanical know how to get your t-box out, you can drill & tap these holes. They are just going into an external cast aluminum boss, not the case itself. You would be hard pressed to screw this up & it will only take a few minutes to do.

As an aside, I have a friend with a 2.8 that swapped his 1.4 for a 1.2 and is very happy. I'm sure you won't regret it.
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Old May 19th, 2013, 04:59 PM
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Quote:
Originally Posted by Roadsiderob View Post
The 1994-1995 D1 boxes will have the coarse cut 1.2:1 gears but may or may not need an updated input gear. Putting in a new input gear is no big deal. The 1996-1999 D1 boxes will be the newer fine cut gears. Either should work. I'd just try and find a nice clean lowish mileage one. As far as the park brake bracket goes, you'll probably have to drill & tap holes in the rear output housing. It's no big deal & not difficult. Attach the park brake bracket to the forward holes on the side of the case. Mark the centers of the holes you need in the rear bosses, drill & tap to 8x1.25mm. The exact position isn't super critical, just get the holes generally in the center of the bosses.

As an aside, I have a friend with a 2.8 that swapped his 1.4 for a 1.2 and is very happy. I'm sure you won't regret it.
Fantastic. I'll look for the 96-99 D1 box, since I'm in no rush. If it doesn't have a cross drilled input, and it's easy enough to do, i can just pull the cross drilled one I have in my 1.4 and transfer it then or buy one correct? I have a metric tap and die, so the boss work is not an issue for me.

great advice here.
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Old May 19th, 2013, 05:09 PM
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Rob, regarding your friend, did he have a 90 or 110? any idea what mpg he was getting before and after?
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Old May 19th, 2013, 05:14 PM
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The input gear in your 1.4 box will be a 26 tooth, so it won't work. All 1996-1999 D1s should have had the cross drilled gear. If you find you need one, I have bunches...just let me know tooth count.

My friend has a D90 with a 2.8. I'm pretty sure the swap netted him a couple of mpg but I don't know the exact mileage numbers.
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Old May 19th, 2013, 05:17 PM
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Based on Rob's advice, maybe a D90 1.222 case may be the easiest way to go.
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  #12  
Old May 19th, 2013, 05:33 PM
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Rob is truly the master.
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Old May 19th, 2013, 06:09 PM
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Quote:
Originally Posted by JSBriggs View Post
No, the input gear is what gives the different ratios.

-Jeff
No, it is more of an age thing. A 1.4 and 1.2 from the same era will have the same input tooth count.
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Old May 19th, 2013, 08:27 PM
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Quote:
Originally Posted by Overlander View Post
Based on Rob's advice, maybe a D90 1.222 case may be the easiest way to go.
I think I have a rebuilt 1.2, swap for the 1.4?
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Old May 19th, 2013, 08:41 PM
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Quote:
Originally Posted by JSBriggs View Post
No, the input gear is what gives the different ratios.

-Jeff
Thought it was the intermediate gears and you just need to make sure the intermediates you are swapping in match the tooth count on the input gear? Perhaps I misunderstood but think thats what Dave Ashcroft told me. I have three toasty 1.4 box's here and had asked about swapping the intermediates into some tight quiet lt230q 1.2 box's I have and he said "should work shoot me the serial numbers off the box's to confirm they are interchangable" and thats where I dropped the ball.
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Old May 19th, 2013, 09:42 PM
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Originally Posted by crown14 View Post
I think I have a rebuilt 1.2, swap for the 1.4?
if it's cross drilled and matches up, I'm interested! What's the suffix for the box you have?
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  #17  
Old May 19th, 2013, 11:28 PM
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Keep the 1.4 and add a roverdrive. Enjoy the best of both worlds.
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  #18  
Old May 20th, 2013, 04:45 AM
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1. Please keep me in mind when you go to sell your 1.4.

2. How soon will you be doing this?

3. Might I interest you in swapping for my 1.2 from a 98 D1? It has about 125k miles now.

My exMoD 90 came with a 1.6 which was too low. I found this 1.2 and it is too high for my 2.5D N/A. I believe a 1.4 will be just right for my engine.

Mike
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Old May 20th, 2013, 07:32 AM
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After I put a 1.2 in, I want to drive it for a few days to make sure the replacement is sound and that the ratios are in fact an improved driving experience for my powertrain, which I suspect from all accounts should be. I need to have a replacement on hand to do it, since i'ts my DD. I"m interested in doing this perhaps in next month. The alternative is to get the Ashcroft kit to convert mine, but that involves a shop with a press, which means a longer downtime.

I think a D90 1.222 would probably be my ideal swap candidate. A 29D or 32D suffix, but I'm not sure of the difference between those 2. Can anyone advise on that?
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Old May 20th, 2013, 08:18 AM
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May work out well if I'm headed towards charlotte in the next month. Once I check on that case I'll give you all the details.
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