Duramax Diesels Forum Truck of the Week
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Old 07-04-2011, 02:41 PM
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Default Allison Speed sensor???

I have an LLY/Allison that was originally from a 4wd model, but I have replaced the factory 261XHD with a 241/241 doubler. I have very limited knowledge about the electronics on these trucks/transmissions, will I need to do anything sensor wise for this to shift properly in 2wd, 4wd or double low with the factory case missing? Maybe add a VSS to the tailshaft in the Allison so that it will continue to shift regardless what range it's in???
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Old 07-04-2011, 03:21 PM
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the allison MUST have an output speed sensor present, otherwise you'll never make it out of 1st gear.

Im not sure how it would work with the doubler...since the TCM is only designed/programmed to work with a 2-range transfer case. If the TCM sees a gear ratio its not programmed to expect it will immediately limp.
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Old 07-04-2011, 05:12 PM
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Will placing the sensor in front of the cases keep it happy? I don't really care if the speedo is correct when in either low range.
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Old 07-04-2011, 05:24 PM
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Originally Posted by DieselS10 View Post
Will placing the sensor in front of the cases keep it happy? I don't really care if the speedo is correct when in either low range.
Yes
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Old 07-04-2011, 07:44 PM
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Originally Posted by DieselS10 View Post
Will placing the sensor in front of the cases keep it happy? I don't really care if the speedo is correct when in either low range.
This will be how you must do it. Search at pirate 4X4 for the post of how I believe pussow did it with his 205. Also the guy that built the DURAMAX search and recovery buggy also installed his TOSS in the transfer case housing before the transfer cases(he used a SUNCOAST housing though to avoid the cracking problem).
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Old 07-04-2011, 09:08 PM
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Ok guys, thanks for the input.

So lets see if I understand this correctly. BTW, these are Okie terms, lol. Since the Allison is "keeping track" of the RPM's coming into the tranny, in the middle and as it exits it's able to tell that something isn't right when the final sensor isn't rotating at the speed that it's pre-programmed to be at? Except when you have it believing it's in low range on a 4wd model, but for only one low range because the doulber would throw it off again??

If that makes any sense to you guys and I can use it with it in low range in the 1st transfer (same reduction as factory 261) and everything shift as it would have stock while in low range, could I mount the sensor between the 1st and second case as it would have been in the stock transfer and have perfectly normal shifts and an accurate speedometer when in high and single low range and then just throw the speedometer off when it's locked in double low? Make any sense? If I can fit it there I won't have to fool with the Allison tail housing or output shaft.
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Old 07-04-2011, 09:25 PM
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Ok, I'm just thinking here, so bare with me. I read that the low range gear ratio can be changed with EFI Live, so would it be possible to place a speed sensor just after the 1st case (as mentioned in the last post) and make it think that it is a factory setup from a 4wd model, then add another speed sensor to the rear of the second case (which it already has) and wire it so that it can be switched manually from one to the other from inside the cab. Then when I am doing my EFI Live tuning I will do a "Crawl" tune where I will tell it that the low range gear reduction is 7.40:1 and just manually switch between the two speed sensors when in and out of that "crawl" tune. Could that work?

My electrical skills are somewhat limited, so I really don't know if any of that is even possible, but if it is wouldn't that get me a fully functioning Allison in 3 different ranges with an accurate speedometer in every range??
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Old 07-05-2011, 03:30 AM
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Or you could just run one speed sensor. The ECM / TCM is only looking for a signal to tell it what the slipping inside the transmission is while in overdrive and TC locked.

If you are running the ABS, then there will be a complete different issue to deal with. IIRC the ABS light will stay on since it also reads signals from the Trans sensor and the wheel sensors. If they are different, then it does strange things. Since I see it is in an S10, it may not have the ABS.
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Old 07-05-2011, 05:19 AM
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Quote:
Originally Posted by DieselS10 View Post
Ok, I'm just thinking here, so bare with me. I read that the low range gear ratio can be changed with EFI Live, so would it be possible to place a speed sensor just after the 1st case (as mentioned in the last post) and make it think that it is a factory setup from a 4wd model, then add another speed sensor to the rear of the second case (which it already has) and wire it so that it can be switched manually from one to the other from inside the cab. Then when I am doing my EFI Live tuning I will do a "Crawl" tune where I will tell it that the low range gear reduction is 7.40:1 and just manually switch between the two speed sensors when in and out of that "crawl" tune. Could that work?

My electrical skills are somewhat limited, so I really don't know if any of that is even possible, but if it is wouldn't that get me a fully functioning Allison in 3 different ranges with an accurate speedometer in every range??
No, that wont work. Well I guess it would, but to do it the way you are thinking, you'll have to reflash the TCM each time you want to go in and out of your "crawl tune".
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Old 07-05-2011, 05:24 AM
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Quote:
Originally Posted by jlawles2 View Post
The ECM / TCM is only looking for a signal to tell it what the slipping inside the transmission is while in overdrive and TC locked.
no, its using it ALL THE TIME. Unlocked, locked, reverse, and all forward ranges.

The TCM is constantly calculating the ratio between the turbine speed sensor and output speed sensor. If the calculated ratio doesnt match the intended/programmed ratio, the TCM will limp. Meaning, if, in 1st gear, the ratio/difference between the turbine speed and output speed is anything other than ~3.10:1 (the first gear ratio in an allison), the TCM will detect this as trans slip, and go into limp mode.

Remember this ratio calculation has nothing to do with converter slip. Its measuring turbine speed and output speed when it does this "ratio calculation". Turbine speed is POST CONVERTER. Turbine speed is NOT THE SAME as "input speed".


Quote:
Originally Posted by jlawles2 View Post
If you are running the ABS, then there will be a complete different issue to deal with. IIRC the ABS light will stay on since it also reads signals from the Trans sensor and the wheel sensors. If they are different, then it does strange things. Since I see it is in an S10, it may not have the ABS.
This is a serious offroad rig...I doubt he has ABS still on it??
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Old 07-05-2011, 07:31 AM
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Duratothemax is right about the ABS, it hasn't ever and won't ever have it.
It is driven nearly everyday when it isn't under construction though.
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Old 07-09-2011, 06:30 PM
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One more question guys, I have seen references to cruise control modules here and there, is this something that I will need to make the cruise work or does it have everything with the ECM, TCM, BCM and the factory full size harness and steering column intact?
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Old 07-09-2011, 07:06 PM
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Originally Posted by DieselS10 View Post
One more question guys, I have seen references to cruise control modules here and there, is this something that I will need to make the cruise work or does it have everything with the ECM, TCM, BCM and the factory full size harness and steering column intact?
You don't need anything else, just simply wire in a cruise control switch to the ECM.
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Old 07-09-2011, 07:50 PM
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It has the factory cruise switch in the '05 full-size column that I'm using, will that do it?

On a side note, what kind of mileage have you been getting since the Duramax swap?

I think I finally figured out how to simplify the wiring to the point that I can actually make it work, lol. I ended up using the PDC, the cluster, the dash harness and the steering column from an '05 Duramax. That way it seems like it is basically a plug and play. I actually went ahead and plugged it all in today and powered up the cluster, did the relearn for the Passlock and cranked the engine. Now I just need to permanently mount/route everything. Finish the fuel and tranny lines/cooler and mount the VSS sensor and reluctor ring. Oh, one more thing, what controls the Odometer? My engine/tranny has 90,000, but my ECM, BCM, TCM, and cluster are from a truck that had 396,000 on it, is there a way to get it to what is one the engine?

BTW, thanks for all of your assistance through out this little undertaking.
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Old 07-10-2011, 05:02 AM
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mileage is stored in the cluster ONLY.

The only way to reset the mileage is to buy a new cluster (or used one with lower miles in it) or send the cluster to a speedometer shop.
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