4L80 damaged

[adzints7]

I have a LS swapped k10 suburban that is running the FiTech ECU with transmission controller. This system requires a VSS installed into the rear position on a 4L80. A few months ago I noticed that my VSS sensor on my 4l80 was on the forward position, not the rear. I did not do the install and this is on a new crate tranny from GM behind a 5.3 LM7 and in front of an NP205 T-case in my 1972 K10 Suburban. I identified the incorrect location and switched the sensor location...did not shift or work. I spoke to FiTech a few times and ultimately they determined that if it was running and shifting before then leave it in the forward position. fast forward a few months and 2 weeks ago I had a somewhat separate failure at my transfer case, which has now been rebuilt. During this rebuild, it was identified that the 4L80 output shaft was incorrect and slightly contributed to the transfer case failure. So the 4L80 went into the shop for a output shaft swa and I am being told that I did not have the rear reluctor in order for the rear sensor to work...thats fine. The shop that did the initial install had ordered a 4wd transmission but should not have. Either way, they are now saying that the VSS being installed in the forward position caused damage to internal components in the 4l80 as well as the converter, requiring a rebuild. They are stating the bill is $1600. I am not paying that, but I am sure they will try to get something for it. Transmissions are not within my comfort zone at all but I am skeptical that there is so much wrong with the transmission just from the wrong sensor.

So, does anyone have any ideas if these claims are realistic? Can the use of the forward VSS create such damage? FYI the truck shifted and ran through the gears fine, although there were occasional hard shifts. I adjusted the speedo correction per FiTechs instruction and ensured my initial setup was correct...several times. I am frustrated with this shop, but they are trying to remedy the mistakes and acknowledging the part they played in the failures we are dealing with. I just want to make sure this doesn't happen again and whether this is that last time I am going to deal with this shop.

[kwmech]

I do not understand how it could have shifted correctly with the sensor being used in the forward position. My understanding is the computer has to sense output speed for proper shifting unless there is a sensor in the speedo cable that is tied in some how. 1600 for a rebuilt, ready to roll with upgrades is not a bad deal

[adzints7]

Thanks for the response. I do not understand either, but it did. I wish I understood better, it confused the heck out of me before and I decided to let it ride. I’m going to find out exactly what they did for that 1600, cause I was never asked about it or if I wanted to do the work. I know he said the converter, not sure what else cause I was at work when he told me. I don’t believe anything was upgraded.

[clinebarger]

4wd 4L80E's don't have a OSS (Output Speed Sensor) Reluctor Wheel on the Output carrier.

I can see using the ISS (Input Speed Sensor) which is actually the Forward Drum Speed with a aftermarket controller & have the false sense of the trans shifting correctly....But it's NOT.

As your NOT using a factory controller (PCM/TCM), They can't definitely say that using the ISS by itself caused a failure.

If the Output shaft was too long & was pushing on the trans geartrain....That can cause several problems in the trans & T-case.

[adzints7]

Cline, thanks for your thoughts. So if the shop adds a rear output reluctor will that correct that particular issue? Also, I’m aware now that the forward vss should never have been used, unfortunately I was given that direction by FItech and had no real reason to question it further. What would be noticeable or felt that would indicate the shifting was not correct?

It’s possible the output shaft issue was the problem, but it was too short not too long. The other issue I had was the T-case was a complete mess. The snap ring on the input was backwards and there were a few other issues that led to the Tranny output moving within the T-case about 1/8 - 1/2 inch constantly. T-case has been repaired by Tod at T’s cases and I feel THAT issue has been remedied. Fingers crossed.

I have so many more questions but at this point o just want to make sure the repair from this point is correct and fair given the expenses I’ve already paid!

[b454rat]

The only reason for the rear VSS is so it shifts properly. If you put it in 4 low, then the computer doesn't know when to shift, and think it shifts at a really hi RPM. If the rear VSS is in the tranny still, say like a 2wd, even tho it's 4wd, then when in 4 hi it will shift normally. Again, in 4 lo it will shift weird. But I can't see how that could screw a tranny up. If the output bottomed out in the t-case, that would be the problem. The VSS is just electrical...

[adzints7]

Thanks for the explanation. At this point, the tranny now has a rear reluctor and I assume will shift correctly regardless of the t-case positioning, correct? I have converted to a dual stick with the modified rails so I really want this to work correct. I don’t see how the incorrect vss would mess up the tranny either, unless the computer was telling it to shift hard or incorrectly. It would shift into 2nd at about 10-20 mph, hold 3rd until 60 or so, then eventually shift into OD. That was one area I had attributed to settings that maybe was actually a result of this whole issue? At fwy speed it would hold 3rd for a long time unless I let off the pedal, then it would shift into OD and stay there. But that only happened upon merging onto the fwy, after that it would engage the TC or downshift appropriately. Or at least I THOUGH appropriately.

[Richard]

As mentioned in the prior post ideally you would want the VSS after the t-case. That position will take into account when you are in low range. Places can modify the output on the NP-205 to install the reluctor/tone wheel. https://www.offroaddesign.com/transf...machining.html. Still trying to work out rear speed sensor details for my 6L90 swap. Seems as most do not do anything about it.

[adzints7]

So I just spoke to Tod at T’s cases who is extremely knowledgeable in these NP205 cases. He is not a 4l80 expert per se, however he has helped with many conversions involving them in front of the NP205’s and he said that as long as the ecu can read correct output speed at the rear transmission sensor, then it doesn’t need to know what the case is doing, 2hi, 4hi, 4lo, front only etc...I had asked if I should make provisions to utilize the VSS on the NP205 and he said no.

So maybe that is all I need? I appreciate the help and the more advice, thoughts and opinions the better. To me it makes sense that the controller doesn’t need to know what the case is doing, as long as I don’t try to drive 75 in 4lo, right? Appropriate speed will leave the tranny in the appropriate gear thereby driving the case within its rpm range.

Am I on the right track or am I missing something? Thanks again!

[Richard]

What I would expect him to say. That is what I come across when speaking to a lot of folks. Most people do not use low range much, if at all. So it is not dealt with. The question I would ask is why do most of the 4x4 "e" transmissions have the rear reluctor eliminated? The 205 is only a 1.96. So in low your wheel speed is almost double what the computer sees. The much newer version electronics like mine are handled by a separate TCCM (transfer case control module) works with the TCM and ECM. I believe a separate shift table is used for low range operation in this combo. Sorry for the ramble. Short answer has already been said, it works. But I am not convinced it is right.

Originally Posted by adzints7

So I just spoke to Tod at T’s cases who is extremely knowledgeable in these NP205 cases. He is not a 4l80 expert per se, however he has helped with many conversions involving them in front of the NP205’s and he said that as long as the ecu can read correct output speed at the rear transmission sensor, then it doesn’t need to know what the case is doing, 2hi, 4hi, 4lo, front only etc...I had asked if I should make provisions to utilize the VSS on the NP205 and he said no.

So maybe that is all I need? I appreciate the help and the more advice, thoughts and opinions the better. To me it makes sense that the controller doesn’t need to know what the case is doing, as long as I don’t try to drive 75 in 4lo, right? Appropriate speed will leave the tranny in the appropriate gear thereby driving the case within its rpm range.

Am I on the right track or am I missing something? Thanks again!

[HAULIN' IT]

adzints, After reading through all of this, I'm having trouble with several things you have mentioned. Now I must say...I'm not a transmission expert by ANY means or really have all that much knowledge about them, but I do have some knowledge about some of what you are dealing with. Unfortunately I think you are either being given incorrect information or misunderstanding what you are being told.
Some things just don't add up...the transmission output shaft endplay should never be controlled/limited by the input shaft of the T-case.
Are you using some sort of aftermarket T-case input shaft (female instead of factory male) with an adapter/mount like Advance Adapters & others sell to swap a 4L80 in front of a 205? Use a 2wd trans, take off the tailshaft housing/extension & cut a couple inches off of the output shaft?

Also, I feel Richard is "Right on" with his thinking. The manufacturers as far back as I can recall (mid -60's) moved the speedometer input from the transmission (2wd) to the transfer case (4wd) on the trucks because they must have felt there was value in the speedometer working correctly in Lo range...why wouldn't one want the computer that will be trying to shift the transmission knowing the true speed, after all it is an input to the computer?
Just like he is thinking: "Hey, it works. Who uses Lo range much anyway?" must be the mind-set of the aftermarket suppliers.
Please respond as to how this pair is hooked together & maybe we can get you some help. Lorne

[clinebarger]

Originally Posted by adzints7

Cline, thanks for your thoughts. So if the shop adds a rear output reluctor will that correct that particular issue? Also, I’m aware now that the forward vss should never have been used, unfortunately I was given that direction by FItech and had no real reason to question it further. What would be noticeable or felt that would indicate the shifting was not correct?

It’s possible the output shaft issue was the problem, but it was too short not too long. The other issue I had was the T-case was a complete mess. The snap ring on the input was backwards and there were a few other issues that led to the Tranny output moving within the T-case about 1/8 - 1/2 inch constantly. T-case has been repaired by Tod at T’s cases and I feel THAT issue has been remedied. Fingers crossed.

I have so many more questions but at this point o just want to make sure the repair from this point is correct and fair given the expenses I’ve already paid!

Most trans shops WILL NOT tear a trans completely apart & change one component. It's just not part of the business model......They're in business to completely rebuild transmissions OR at the very least charge for it.

But without inspecting the unit myself.....I can't say for sure!!!

You certainly need the OSS operational, Using the ISS will cause early 1-2 & 2-3 shifts assuming the tire rollout & final gear ratio was correct in the controller calibration.
The 3-4 shift would be on time because the Overdrive Carrier is in front of the Forward Drum.

The ISS & OSS read the same speed in 3rd/Direct & 4th/Overdrive, First gear ratio would be the furthest off.

[clinebarger]

Originally Posted by HAULIN' IT

Also, I feel Richard is "Right on" with his thinking. The manufacturers as far back as I can recall (mid -60's) moved the speedometer input from the transmission (2wd) to the transfer case (4wd) on the trucks because they must have felt there was value in the speedometer working correctly in Lo range...why wouldn't one want the computer that will be trying to shift the transmission knowing the true speed, after all it is an input to the computer?
Just like he is thinking: "Hey, it works. Who uses Lo range much anyway?" must be the mind-set of the aftermarket suppliers.

Correct......BUT, The old 3 speeds & Hydraulic 4 speeds still had the Governor on the Trans Output & have no way to alter shift points based on T-Case Reduction.

[adzints7]

Ok, great stuff guys! So I am using the advance adapters kit to mount between the 4L80 and NP205. I purchased the 2wd kit (50-0410)because my original trans was 2wd from a junk yard. That had a epic failure because my “friend” dropped it, welded it and ran it...lasted 50 miles. Long story...

I freely admit I could be completely off regarding the VSS location and how it works with the T-case. I am reduced to trusting the experts and that has proven to be difficult...interesting thought given the current times. But it sound like I am best served to use the OSS on the transmission and drive accordingly? I guess I will have a good comparison because my ecu will show OSS and my dash will show T-case speed.


Clienbarger, what you are describing for shift behavior when using the ISS is exactly what it was doing. I just did not have a good reference to compare it too. I knew something was off but considered it to be setting in the controller and it dropped down on the list of priorities...my mistake.

[b454rat]

Offroaddesign.com can modify the tail housing of the 205 for VSS. Or if your steady with grinder or just happen to have a milling machine, then can do it yourself. The parts come from an NP241, the tone wheel is slightly different, being the 205 version is thicker, but will work. ORD even says there the same lol. But if using a 2wd trans and the VSS on the rear of the tranny, and have no t-case, 1, 2, or 12 t-cases behind it, and if all in 2wd, then the trans should shift like stock. Putting it in low will change the shift points.

[adzints7]

B454rat- I have a vss sensor and tone wheel on my np205. Second gen so it’s the plastic one but it is new and will send a signal to my electric Dakota digital dash sensor.

Clinebarger - could the early 1-2 and 2-3 shifting damage a torque converter? Theoretically at least? I’d just like to understand when dealing with this. Thanks for any help.

[clinebarger]

It's not likely AT ALL that the early shifting caused damage!!!

[adzints7]

Originally Posted by clinebarger

It's not likely AT ALL that the early shifting caused damage!!!

Thank you for responding.