Normal 4L80E temp?

[stutaeng]

I've never been inside a 91-93 4L80e, but apparently the harness from the 94+ also work on the 91-93. I had a harness laying around from my 94 4L80e that I rebuilt. I was going to mess around checking resistance on the sensor to see if it behaved when heated similar to the typical GM temperature senders, but I forgot and threw it away.

4L80E Internal Wiring Harness (1991-2003) 24222798

Highest quality aftermarket replacement wiring harness for GM's 4L80E automatic transmissions manufactured from 1993 to 2003.

globaltransmissionparts.com

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So yes, they had a temperature sensor, used by the ECU to change shift strategies based on load, RPM, input/output sensor reading, and temperature. I don't know if that was also true for the OBD1/TBI generation or if that generation originally had the sensor.

 

[Dropped88]

I dont believe it makes those adjustments in TBI era.

Mine had a bad harness and the temp was a constant 306 F. And only reason i figured out it was bad is i seen it in the PID list on my scan tool and had no codes.

And still drives, shifts the same after harness replacement but reads right temp now

 

[Supercharged111]

I installed the sending unit in the hard line just before the cooler. I understand and accept that this may give me higher readings than the pan, but I'm okay with that. As Stutaeng said, I'll be mindful that it may be reading higher than if in the pan. The whole point of installing the gauge is too pull over and let things cool if, while towing, the temp starts climbing too high. The problem I've having is the cheap-ass gauge I bought is reading too high and it doesn't have a zero set for the needle (when off it does not return to zero but rests on the 60 degree mark). I ordered a new, better gauge. Supercharged111, are you saying there is a temp sending unit in the transmission pan? I can't find it if there is supposed to be one. Being a 92 and OBDI, I'm doubtful of that.

Eric, the Awful, being a K2500HD, I have the larger front disks and larger rear drums. I just rebuilt the drums and installed new rotors and pads on the front. I deleted the rear ABS sensor and installed a larger model master cylinder (from a 2003). Brakes work so much better than before.

Supercharged111, regarding your question about the torque converter staying locked up, I always have troubled determining that, especially where I live since I'm rarely on a flat road - there's always a grade. However, it seems to be fine. I can see by the tach it holds pretty steady unless I'm accelerating. I think some of your comments are leading me to believe you have an OBDII, especially if you're reading it from a laptop. I can't do that with an OBDI truck.

Appreciate all the comments and help.

Rich
Maple Valley, WA

The only possible problem with that worst case temp reading is you're seeing an artificially high value (Chinesium junk notwithstanding), which is better than the opposite. I wouldn't be surprised if there was a temp sensor in there and yes, if you buy the right stuff you can hook a laptop up. I am OBDII, I can speak more confidently to that stuff. I've always found that the trans in my 1500 stays under 200 no matter what with the converter locked. I have yet to put a gauge in my 3500, but when I do I'll put the sending unit in the pan. Apparently the pressure port is a bad place to put the sensor even though that's what I did with my 1500. It's about due for a flush though, so can zap a bung in then.

 

[EmeraldCityGuy]

JB/JD7 brakes?

I don't know what you deleted, but it wasn't the sensor.

More likely, the valving/accumulator unit.

The unit underneath/next to the Master Cylinder. As you probably know, ABS on a 1992 was only the rear drum brakes. Yes, this truck has the JB7 brake package.

 

[EmeraldCityGuy]

The only possible problem with that worst case temp reading is you're seeing an artificially high value (Chinesium junk notwithstanding), which is better than the opposite. I wouldn't be surprised if there was a temp sensor in there and yes, if you buy the right stuff you can hook a laptop up. I am OBDII, I can speak more confidently to that stuff. I've always found that the trans in my 1500 stays under 200 no matter what with the converter locked. I have yet to put a gauge in my 3500, but when I do I'll put the sending unit in the pan. Apparently the pressure port is a bad place to put the sensor even though that's what I did with my 1500. It's about due for a flush though, so can zap a bung in then.

Yes! The renovation of this truck has been an evolution. I delve into the topic dejeure in this forum and sometimes I hit pay dirt, other times it doesn't come until I post what I did and kind folks like you, offer more sage advise. I did a good job plumbing in the tee fitting (no leaks, looks good), so I'll live with the temps I get there. I think I'd rather know the highest temp the fluid gets rather than something that is lower - at that spot, the fluid is coming directly out of the transmission gearing. I hope to not be over 8500lbs, but at that weight and going over several mountain passes, I don't know what to expect. At least, with the Trans Temp and Oil Temp Gauges I've installed, I'll have more info than without them.

 

[someotherguy]

I'll say this and keep it simple - the temp sensor installed in the pressure test port provides a solid means for reading temperature without introducing the potential for several new leaks and possible blown lines under pressure.

When you tee into the cooling lines you better do your homework and be 200% sure your connections are solid, and I mean OEM-quality solid, same as when you add an aftermarket cooler. Anything less than that and you are risking popping a line loose under load and all the preparations you thought were preventing transmission failure end up CAUSING transmission failure. The couple degree difference you thought you were gaining in accuracy end up costing you everything.

My opinion.. FWIW

Richard

 

[Erik the Awful]

I deleted the rear ABS sensor and installed a larger model master cylinder (from a 2003). Brakes work so much better than before.

There's a debate that's ongoing about swapping the GMT800 master cylinder onto a GMT400. A few of the guys who've done it says it works great right up until you have to perform emergency braking, and then it nearly put them in accidents. Many people have done it and never reported an issue.

I'm in the "don't do it" camp, but I understand I won't be able to talk some people out of doing it.

Here's a good article on the math required when selecting a master cylinder. www.joesracing.com/master-cylinder-math/

 

[Schurkey]

There's a debate that's ongoing about swapping the GMT800 master cylinder onto a GMT400.

Realistically, there's only two parts to the debate: Suitability with low-drag calipers; and the overall master-to-slave bore ratio. An "NBS" master cylinder with JN/JB/JD3, 5, or 6 brakes is just crazy from both perspectives.

Since the OP has removed the low-drag calipers, the only part that's left is the master-to-slave bore ratio; and I'm not going to touch that.

Here's a good article on the math required when selecting a master cylinder. www.joesracing.com/master-cylinder-math/

Thanks for that link. Downside is that he never mentions the effect of low-drag calipers on the fluid requirement from the master cylinder.

And it's low-drag calipers that cause the main part of the problems with the "NBS" master cylinder.

 

[Supercharged111]

Hydroboost is the only correct answer. Everything else is a waste. Well, hydroboost and good pads/shoes.

 

[tayto]

trans temp should be measured in the pan or in the return line, do not use pressure port it will read higher IIRC. FWIW, 4L80Es have a temp sensor in the pan, it is in the data stream.... can get a OBD1 cable and datalog with free software. i would put as big of a cooler you can fit if you will be towing heavy. run it after the cooler in the rad.