4L80e question- VSS

[mrk5]

On the 4l80e controller I have, you can put the transmission into "manual" mode so it doesn't care if the gear ratios are off in 4Lo.

 

[Shawn]

We are talking GM TCM for controller, correct? What input is it looking for?

AFAIK those were still using DRAC, so it's either 2 or 4K per mile IIRC.

Note that whether or not something works, doesn't mean it's working correctly. (and I'm not saying it won't work correctly, but anytime I see people say "it works fine", I question that statement if there isn't concrete evidence to back it up). 4k for instance is just 2x 2k....which means whatever you are feeding the signal to, is assuming the vehicle speed (in this case) is double what it actually is. Made this mistake when I connected cruise control to the DRAC. It "worked fine", but I could set cruise control at something like 10MPH. Not a big deal. But I would assume when trying to control an electronic transmission, proper communication of vehicle speed is much more important.

I agree. This is actually a TCI aftermarket controller that needs to see the transmission speed. 2wd transmission have this ring but 4wd does not and I assume they put in the tcase since it needs the actual vehicle speed whether it be lo or hi gear.

Regarding the comment about putting the VSS on the transmission, it should work fine in 2wd or 4 high but it will be way off when using 4 low (exactly 2.72 times off, or the low range ratio of the t-case). For example, if you are in 4 low and actually running 10 mph (such as via a GPS) the speedometer will show 27 mph and the shift points will be all messed up. A guy in our club recently swapped in an LS into his truck and for some reason moved the VSS to the transmission and ran into this problem.

I was thinking of that too. Having VSS at the tcase would be better so maybe its not worth using the VSS inside the trans. Nobody has brought this up that has done these swaps and use the VSS inside the trans.

 

[dyeager535]

I was thinking of that too. Having VSS at the tcase would be better so maybe its not worth using the VSS inside the trans. Nobody has brought this up that has done these swaps and use the VSS inside the trans.

I want to think in years past someone here posted that they had used the transmission VSS and not had an issue. Perhaps depending on how hard you push the engine/trans in 4 low, you wouldn't notice? I generally am not running around in 4 low upshifting and downshifting, so depending on driving conditions, it seems plausible it may not always cause a problem.

I'd still prefer to do it "right" and feed it the signal it needs, at the proper speed, regardless of high or low range, unless someone can show an easier/cheaper way to accomplish the same thing.

I wonder if it's going to be worth it to save as many of the 241 passenger drop cases as we can now, particularly the 32 spline versions? Even at $100, it's hard to justify letting them sit around for years to sell someone the components for 32 spline and/or VSS.

 

[Shawn]

I want to think in years past someone here posted that they had used the transmission VSS and not had an issue. Perhaps depending on how hard you push the engine/trans in 4 low, you wouldn't notice? I generally am not running around in 4 low upshifting and downshifting, so depending on driving conditions, it seems plausible it may not always cause a problem.

I'd still prefer to do it "right" and feed it the signal it needs, at the proper speed, regardless of high or low range, unless someone can show an easier/cheaper way to accomplish the same thing.

I wonder if it's going to be worth it to save as many of the 241 passenger drop cases as we can now, particularly the 32 spline versions? Even at $100, it's hard to justify letting them sit around for years to sell someone the components for 32 spline and/or VSS.

I agree. Thanks for everyones input on this!

I did find a NP241 locally but its got 170k on it so I'm a little concerned with the chain on other wearable components.

The other thing I need to worry about is a RPM signal off the 6.2 diesel.

 

[mrk5]

I think most people that use the transmission for the OSS (output speed sensor) probably manually shift the trans. Or they don't use the truck in 4lo. I know I manually shift mine on the trail regardless.

 

[6.2Blazer]

I think most people that use the transmission for the OSS (output speed sensor) probably manually shift the trans. Or they don't use the truck in 4lo. I know I manually shift mine on the trail regardless.

Went back through the post on our local club board when a buddy swapped in an LS and 4L60E combo in his rig to refresh my memory. It goes about the same as this post where everything he read said you needed a speed signal on the trans. He bought and installed the Summit kit but as mentioned above the shifts were way off when in 4 low. He actually already had a 241 with VSS so fortunately all he had to do was plug the harness back into that.

Another thing he ran into, and may not be applicable to this application, is that the ECM does have a signal that tells it you are in 4 low coming from the t-case. He originally didn't have this connected. While the trans shifted OK and the speedo was correct in 4 low, it was still a little off. Once connecting that sensor it was a lot better. I should also specify that the vehicle he swapped the LS and 4L60E into is a strictly trail rig and not licensed for the street.

 

[dyeager535]

I did find a NP241 locally but its got 170k on it so I'm a little concerned with the chain on other wearable components.

The 241 is a robust transfer case, and replacing the chain is easy, just don't screw up the reinstall of the output shaft housing and crack it.

I think you can get chains for $60? You can find GM chains but they tend to be quite a bit more. I suspect GM still sells the chains.

No time to watch the video to determine if its any good, but there are a bunch of 241 teardown/rebuild videos:

I forgot the shift fork pads. Replace those too. But honestly, this case is one of the easiest components on the truck I've had to rebuild.

 

[6.2Blazer]

The 241 is a robust transfer case, and replacing the chain is easy, just don't screw up the reinstall of the output shaft housing and crack it.

I think you can get chains for $60? You can find GM chains but they tend to be quite a bit more. I suspect GM still sells the chains.

I rebuilt my 241 several years ago. Don't remember the complete kit (chain, bearings, shift forks, etc...) being very expensive and it wasn't that complicated. Funny the above post mentions cracking the output housing....exact thing I did the first time and why I had to find another case. I didn't have the oil pump installed correctly and tried to pull the case together with the bolts instead of making sure it was seated first.

 

[NorCalAnthony]

Another thing he ran into, and may not be applicable to this application, is that the ECM does have a signal that tells it you are in 4 low coming from the t-case. He originally didn't have this connected. While the trans shifted OK and the speedo was correct in 4 low, it was still a little off. Once connecting that sensor it was a lot better.

Not sure if this will be an issue with the aftermarket controller OP is using but @MAX89K5 ran in to this issue and wound up adding a momentary switch mounted by the t-case shifter to fix the problem. It was mounted on a little bracket he made so that when you went in to 4Lo the shifter pressed against the switch and sent the ECM the signal needed to correct the speedo and shift points.

Also I haven't seen anyone mention it specifically yet but once you switch to a VSS 241 you'll lose the mechanical cable for your speedo so plan on getting a gauge cluster from a 90-91 Blazer, Burb, or R/V truck or look for aftermarket one. Another thing I'll throw out there is to try and grab the t-case adapter that goes to the 4L80. I got a 32 spline 241 from a 90 3/4 ton Burb that had a TH400 and that adapter wouldn't work with my 4L80 (the mounting feet contacted the rear of the trans) but when I tried the newer 4L80 adapter it bolted right up to the 241.

Where abouts are you located? Have you tried looking on car-part.com? I've had good luck finding stuff on there when I'm not finding what I need on Craigslist.

 

[6.2Blazer]

Not sure if this will be an issue with the aftermarket controller OP is using but @MAX89K5 ran in to this issue and wound up adding a momentary switch mounted by the t-case shifter to fix the problem. It was mounted on a little bracket he made so that when you went in to 4Lo the shifter pressed against the switch and sent the ECM the signal needed to correct the speedo and shift points.

Just to clarify, the 4 low switch I mentioned in my buddy's LS 4L60E swap does nothing in regards to the speedo. With the VSS being on the output of the transfer case there is no correction needed. What it does is change the shift points of the transmission to better the accomodate the 2.72 low range. Think of the tow/haul button that many trucks have as it changes the shift points and shift firmness.

 

[Shawn]

I think most people that use the transmission for the OSS (output speed sensor) probably manually shift the trans. Or they don't use the truck in 4lo. I know I manually shift mine on the trail regardless.

Yeah I do too. And most of the time the truck is driven on the street in 2hi.

Went back through the post on our local club board when a buddy swapped in an LS and 4L60E combo in his rig to refresh my memory. It goes about the same as this post where everything he read said you needed a speed signal on the trans. He bought and installed the Summit kit but as mentioned above the shifts were way off when in 4 low. He actually already had a 241 with VSS so fortunately all he had to do was plug the harness back into that.

Another thing he ran into, and may not be applicable to this application, is that the ECM does have a signal that tells it you are in 4 low coming from the t-case. He originally didn't have this connected. While the trans shifted OK and the speedo was correct in 4 low, it was still a little off. Once connecting that sensor it was a lot better. I should also specify that the vehicle he swapped the LS and 4L60E into is a strictly trail rig and not licensed for the street.

Yeah I don't think that sensor from Summit is the correct 40 pulse so it will be way off. I'll have to check with TCI if there is a 4wd input. I don't think there is.

The 241 is a robust transfer case, and replacing the chain is easy, just don't screw up the reinstall of the output shaft housing and crack it.

I think you can get chains for $60? You can find GM chains but they tend to be quite a bit more. I suspect GM still sells the chains.

No time to watch the video to determine if its any good, but there are a bunch of 241 teardown/rebuild videos:

I forgot the shift fork pads. Replace those too. But honestly, this case is one of the easiest components on the truck I've had to rebuild.

Thanks for the video. I found one locally for 300 about 50 miles away if I go that route.

I rebuilt my 241 several years ago. Don't remember the complete kit (chain, bearings, shift forks, etc...) being very expensive and it wasn't that complicated. Funny the above post mentions cracking the output housing....exact thing I did the first time and why I had to find another case. I didn't have the oil pump installed correctly and tried to pull the case together with the bolts instead of making sure it was seated first.

I'll have to watch for that if I rebuild it. Appreciate it!

Not sure if this will be an issue with the aftermarket controller OP is using but @MAX89K5 ran in to this issue and wound up adding a momentary switch mounted by the t-case shifter to fix the problem. It was mounted on a little bracket he made so that when you went in to 4Lo the shifter pressed against the switch and sent the ECM the signal needed to correct the speedo and shift points.

Also I haven't seen anyone mention it specifically yet but once you switch to a VSS 241 you'll lose the mechanical cable for your speedo so plan on getting a gauge cluster from a 90-91 Blazer, Burb, or R/V truck or look for aftermarket one. Another thing I'll throw out there is to try and grab the t-case adapter that goes to the 4L80. I got a 32 spline 241 from a 90 3/4 ton Burb that had a TH400 and that adapter wouldn't work with my 4L80 (the mounting feet contacted the rear of the trans) but when I tried the newer 4L80 adapter it bolted right up to the 241.

Where abouts are you located? Have you tried looking on car-part.com? I've had good luck finding stuff on there when I'm not finding what I need on Craigslist.

I'll check to see if a switch is possible. I already have a GM electronic speedometer. I just need to try and make the mileage match. I do have the tcase adapter that came with the 4l80e. Its the thinner one. I live in Denver and theres one 50 miles away but thats the only one I could find on car-part.com. I always go there when I need a factory part.

Just to clarify, the 4 low switch I mentioned in my buddy's LS 4L60E swap does nothing in regards to the speedo. With the VSS being on the output of the transfer case there is no correction needed. What it does is change the shift points of the transmission to better the accomodate the 2.72 low range. Think of the tow/haul button that many trucks have as it changes the shift points and shift firmness.

Yeah I think the tcase method is probably the easiest. I can always sell the np208 to offset the cost on the 241. Otherwise I need to get this 4l80e all apart just to put the ring in.

REALLY appreciate all the input!

 

[Blue85]

I also have late 80's GM cluster with mech. speedo but with the wires coming out for thats used for cruise. I just don't know if that will work with the controller and probably not the proper count. The Dakota Digital SGI-5E is another $80 put provides another fault area if it stops working.

The standard for mechanical speedos was always 1000 rev/mile. The 80's cruise control uses an optical sensor on the back of the speedometer. The mechanism must pass the sensor 2x per rev which would make it 2000PPM. Anybody know it to be something other than that?

 

[NorCalAnthony]

I'll check to see if a switch is possible. I already have a GM electronic speedometer. I just need to try and make the mileage match.

If you figure out how to fix the mileage on the speedo let me know. I grabbed the cluster from the same Burb I got the t-case from and haven't figured out how to make the mileage match what's on my truck yet. Tried searching around online a few times but only came across people either saying you can't it's illegal or that they took it to a "speedo shop" which I hadn't heard of before and haven't been able to find yet...

 

[Maroon_Madness94]

I used a 241 on my 4l80e swap and I just had to buy a new input shaft for the tcase. It was getting rebuilt anyways so no better time to do it.