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Discussion Starter · #1 ·
Another info overload after reading so many threads and almost all mention doing an SYE at the same time I do the Tcase mod. I will be scavenging parts from an S10 231C and the 4L60E from a '99 model Blazer along with the Vortec V6 (more issues and info overload). One SYE kit I really like is the one from JBC. http://www.jbconversions.com/products/sye/np231j_std_sye.php It has a CV style double Ujoint which would seemingly help correct a excessive angle in the drive shaft. This kit is pretty affordable and since I am throwing the bank at this YJ build up, why not do this when everything is on the bench. The 231C has some beefier components and I need the GM front half and input shaft for the GM trans. The 231J back half with the JBC kit should work well. I need to call JBC at some point to discuss speedo/trans/computer issues, another can of worms.

So, is a SYE absolutely necessary or a highly recommended option along with me doing a 2.5" lift at the same time I do my 8.8 swap. I dont mind spending the money but with so much modding in the future, I would like to not over buy and find out it isnt necessary.I can do this SYE before I do the hybrid and change out the driveline or now. Either way its what the cool kids are doing.

Many many questions to follow on all my upcoming mods. The 8.8 is first along with the lift and then the V6/auto/transfer mod hopefully by next hunting season.
 

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It's probably not necessary for 2.5" of lift but if it is in the budget then i would do it now. Especially if you are setting up the pinion angle on a fresh axle. It would be pretty silly to either move the perches or fix it with shims later on, and have to tear the transfer case back apart to install the SYE.

You may be fine without the SYE as far as vibrations but a fixed yoke is preferable for several reasons.

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I'd definitely do an SYE if you can afford it but I do think the super short SYE is overkill for you and probably overcomplicates things. Even a basic one will likely be plenty. I'm running a normal SYE with a flat skid and 10" of axle droop (limited to 9" with a center strap though). I did push my axle back approximately 1.5-2" before it touched the stock tank at full bump but I'm running the 5.3/4L60E combo and was able to keep the transfer case in basically the same place fore/aft as stock.

The other thing to consider... The advance adapter conversion for the NP231J and 4L60E is around $550 and will convert your input gear to 23 spline for that price unlike Novak who charges extra for that. That kit includes a tone ring that the ECU can use to determine transmission shift points and a speedometer. You'd still have to buy the SYE kit but you could sell the NP231C as-is to help cover the costs rather than cannibalizing both transfer cases to make one. I'm not really abusive to my stuff on the trail but my NP231J has held up fine to my 5.3L engine and that included me being dumb and accidentally running the transfer case about 75 miles with zero fluid in it immediately after the conversion. I also liked the concept of using the thicker chain from the Chevy t-case but so far the Jeep one is doing fine.
 

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The other thing to consider... The advance adapter conversion for the NP231J and 4L60E is around $550 and will convert your input gear to 23 spline for that price unlike Novak who charges extra for that. That kit includes a tone ring that the ECU can use to determine transmission shift points and a speedometer.
This right here is key if you are running the 4L60E. Trying to duplicate that VSS signal with a Jeep VSS and a Dakota Digital box is problematic at best. I have a NV3500 manual, so the VSS signal isn't as critical. I too did the SYE before moving any further. Transfer case sits back about 2 inches, so I figured it was a good idea.
 

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An NP241c may be a better option for you. It's stronger with a 6 pinion planetary. They are readily available - I see them regularly for $100-150. They come in 27 spline to mate directly to the 4L60e. (they also come in 32 spline behind a 4L80e - so be sure you count the splines.)

1991 or 1992 and later NP241c will have the VSS that you need. 1990 or 1991 and earlier used the mechanical speedometer. They also came in passenger drop in 1990-1991, so be sure you get a driver drop NP241c. Be sure that you get the NP241c and not the electric shift NP243c. They had a couple of front output yokes through the years - I think the later ones are better, which is the one that I have. Also it looks to my eye like the NP241c has a larger drop than a NP241c, so it may be worse for ground clearance.

JB has SYE kits for the 241c. The process is the same as the 231. Tom Woods has them too - I used Tom Woods when I did mine - see 2 pictures below:

In process:
Automotive tire Motor vehicle Rim Table Gas


Finished:
Gas Auto part Machine Nut Motor vehicle


Drivetrain before I did the SYE:
Motor vehicle Automotive tire Table Gas Engineering
 

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The SYE probably isn't critical, but I'd certainly do one. There are basically three types of SYE kits available (in both the super short and standard length) JB Conversions, AA and then all the other AA clones. IMHO JB builds the best ones. You're going to need a new driveshaft, or at least a modified driveshaft when you put that 8.8 in, so it makes sense to do it all at once.
 

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Discussion Starter · #7 ·
The SYE probably isn't critical, but I'd certainly do one. There are basically three types of SYE kits available (in both the super short and standard length) JB Conversions, AA and then all the other AA clones. IMHO JB builds the best ones. You're going to need a new driveshaft, or at least a modified driveshaft when you put that 8.8 in, so it makes sense to do it all at once.
JB is definitely the way I will go when I crack open the cases. BTW, I appreciate the deal on the flange adapter and thanks for the ujoint which I was not expecting. What other mod is necessary on the drive shaft? Is it SYE specific? I was thinking initially after just installing the 8.8, the OEM shaft would work with the adapter. Maybe I got that wrong? Doesnt matter in the long run but I dont want to mod the drive shaft twice. Plan is to swap in the 8.8, run it until I get the Chevy drive train ready, T/C, tranny and engine.

I did not anticipate the 4L60E shift issues in low range. I am reading about the Dakota Digital adapter but someone else figured out how to use a simple toggle switch to let the tranny know the T/C is in low range. I have much more research to do on the drive train swap.
 

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JB is definitely the way I will go when I crack open the cases. BTW, I appreciate the deal on the flange adapter and thanks for the ujoint which I was not expecting. What other mod is necessary on the drive shaft? Is it SYE specific? I was thinking initially after just installing the 8.8, the OEM shaft would work with the adapter. Maybe I got that wrong? Doesnt matter in the long run but I dont want to mod the drive shaft twice. Plan is to swap in the 8.8, run it until I get the Chevy drive train ready, T/C, tranny and engine.

I did not anticipate the 4L60E shift issues in low range. I am reading about the Dakota Digital adapter but someone else figured out how to use a simple toggle switch to let the tranny know the T/C is in low range. I have much more research to do on the drive train swap.
Just for the record... If your lift is low enough, you can use the OEM shaft with the 8.8 but it's a band-aid so might as well do it right.

As for shifting issues with the 4L60E, I run my speedo/ECU off of the transmission tailshaft using the Advance Adapter kit. When I'm in low range, the speedo and subsequently the ECU will think I'm doing the 2.72x faster than I'm actually going but I don't have any shifting issues. Worst I've experienced is sometimes I get bucked a little harder on the 1-2 shift in low range but it's kind of rare and really only an issue when I'm in low range in an open field. I generally wheel in "D" and let the transmission figure it out. I pulled my Jeep out of the garage in low range last week and didn't really notice any issues until I got up around 25-30mph and my engine revs sounded way higher than normal. I thought something was wrong with the transmission but when I counted the shifts to determine which gear it was stuck in, I realized I was in 4th but in low range like an idiot.
 

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JB is definitely the way I will go when I crack open the cases. BTW, I appreciate the deal on the flange adapter and thanks for the ujoint which I was not expecting. What other mod is necessary on the drive shaft? Is it SYE specific? I was thinking initially after just installing the 8.8, the OEM shaft would work with the adapter. Maybe I got that wrong? Doesnt matter in the long run but I dont want to mod the drive shaft twice. Plan is to swap in the 8.8, run it until I get the Chevy drive train ready, T/C, tranny and engine.

I did not anticipate the 4L60E shift issues in low range. I am reading about the Dakota Digital adapter but someone else figured out how to use a simple toggle switch to let the tranny know the T/C is in low range. I have much more research to do on the drive train swap.

That was all in the box I had in the tool box as spares forever, didn't even remember the u-joint was in it until I went to ship it. Pretty sure that's a 1330 u-joint vs the stock 1310 so you probably want to double check that for sure when building a new shaft. I suppose you could use the stock shaft and get a 1330x1310 joint, but the driveshaft would likely need other modifications (length etc.).
 

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Discussion Starter · #10 ·
That was all in the box I had in the tool box as spares forever, didn't even remember the u-joint was in it until I went to ship it. Pretty sure that's a 1330 u-joint vs the stock 1310 so you probably want to double check that for sure when building a new shaft. I suppose you could use the stock shaft and get a 1330x1310 joint, but the driveshaft would likely need other modifications (length etc.).
Yeah I thought the Ujoint looked bigger than a 1310. I will check and make sure. I checked NAPA and they do stock the 1310X1330 joint locally. Sometimes living in the city has advantages. My YJ isnt a DD so using the stock shaft for a while until the rest of the drive train mods are done hopefully wont be an issue. I bought a 2.5" lift so we shall see once the axle and lift are installed. Fingers crossed.

Waternut, I appreciate the lead to the AA low range adapter. I will definitely check it out. Spending a bit of money to prevent a lot of hair pulling is well worth it to me. When I decided to frame off a CJ years ago it was a challenge figuring out many aspects of mods. Today, with the wealth of knowledge and the dogged determination of community members, unstoppable tinkers and dedicated engineers posting their developments makes building an awesome Jeep much easier. Sometimes its information overload but well worth the time invested.

My eternal thanks to this community and all respondents to my sometimes inane (insane?) wanderings!!
 

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The SYE is definitely worth doing.

Why are you swapping in a 231J back half onto the GM front? Is it the C or the CHD?
 

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Discussion Starter · #12 ·
The SYE is definitely worth doing.

Why are you swapping in a 231J back half onto the GM front? Is it the C or the CHD?
The idea is swapping in the Vortec 4.3 and the 4L60E from an S10 Blazer. Along with the stronger chain and gear, I understand the 231C drops on the wrong side for the front axle. I may have terminology wrong or may be wrong in my supposition but the ultimate objective is a closer to bolt in configuration for my driveline mods, matching the D30.

My intent isnt to build a rock crushing, mud slinging wonder, just a dependable commuter and get me to my hunting spot that occasionally turns muddy. I put a 2.5" lift to clear the 31X10.50X15 mud cleats at deflection. I put a 9.5lb winch on front just in case. A bit more power with 4:10 gearing and I think the result should work for what I need. My YJ sits most of the time as I drive my cushy Yukon most of the time. Truthfully, my company truck does most of the driving and when I get home from the 150mi commute and 8 hours of working. I dont get out much til the weekend. A run to the grocery or a Dr's appointment during the week are the exceptions.

I love my YJ. Its about the fifth Jeep product I have owned. Its still mostly simple enough for me to wrench on and dropping the top and windshield is pure bliss, even with bugs in my teeth. With the help of this forum and the Jeep community (and Just Empty Every Pocket), I should have something I can make the run to my camphouse and the woods with the turn of a key.
 

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The 231 series (J, AMC, C, CHD, D) all drops onto the driver side stock. I think usually folks do the TC back half swap in your situation who have already done the SYE on their 231J...I think.

If that's the reasoning, you could potentially save yourself a small bit of labor and just use the complete GM version 231.

P.S.

I have a 231CHD in mine. I used the JB regular SYE made to receive the regular speedo drive gear. I had also used a GM 5 bolt to 6 bolt TC adapter on mine off ebay for $20. Took an AA tone ring like they have in their bigger adapter kit, and epoxied a vss sensor bung after drilling the adapter. I got the bung off a 2wd 4l60e tailhousing ($30 ebay, you already have it on a 2wd trans though). Will save you some decent cash and works great, just a suggestion.
 
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