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My Tranny got HOT!

xc2
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xc2

xc2

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So the entry road to the Laguna SECA race track has a 16% grade and my trailer weighs just south of 10k pounds. No way to get enough speed to lock up the torque converter. So I'm stuck crawling in 1st. I had to run for a few hundred yards with the transmission temp gauge north of 280 degrees. Ouch. A high idle at the top of the hill brought the temp down quickly.

 

The fluid doesn't look or smell burnt. I think I'm going to have it flushed out anyway. What are the chances that I damaged my freshly rebuilt 48RE? Is it typical to see the trans temp get up around 220 before TC lockup? You know - on a hot day leaving stop lights and such. As soon as the TC locks up, I can literally see the needle move back to 180.

 

What do you guys do in these situations? Would a transmission cooler fan help?

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notlimah

notlimah

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Laguna's grade is no joke that's for sure. Driven up that 100s of times!

 

As far as your trans temp, where are you reading the temp from? That'll sorta sway the answer one way or another for if that was too hot or not. That is definitely on the high end for what you'd want to ever see though. I doubt you did any damage to the trans (a 47re btw unless you swapped in a 48re) especially over that short of a time, but a flush would probably be the same thing I'd do as well.

 

A trans cooler or a slightly deeper trans pan would help for sure but I honestly think for your situation a lock up switch would've worked the best. If you have your valve body built and setup properly you could drop all the way down to 1st and hit your lock up switch and crawl up the hill with the TC locked. Your trans is getting that hot because the TC isn't locked which is why you're seeing the temps drop so quickly once it does lock.

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Russ Roth

Russ Roth

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59 minutes ago, notlimah said:

A trans cooler or a slightly deeper trans pan would help for sure but I honestly think for your situation a lock up switch would've worked the best. If you have your valve body built and setup properly you could drop all the way down to 1st and hit your lock up switch and crawl up the hill with the TC locked. Your trans is getting that hot because the TC isn't locked which is why you're seeing the temps drop so quickly once it does lock. 

 

 

Lockup switch is needed for sure in that scenario but you need a modified valve body to be able to lock in first I believe.  Mine can do that and I use it on a stretch of backroad with my toyhauler.  The last 50 yards is so slow I can't lock it even with 4.10 gears though.  Be bad trouble at black rock if it was a long pull like you are talking about but 50 yards or so no real problem.  The answer to that would be low range but my '02 has solid front axle so not possible without locking hubs which I am thinking I will do eventually.

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Mopar1973Man

Mopar1973Man

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Sad part is lock up can't be done in 1st or 2nd gear. If you have a modified valve body you can lock up in 2nd gear. So a lock up switch won't do much good. I've not seen any that can lock up in 1st though. :think:

 

A better transmission cooler is needed possibly an electric fan as well being that mechanical fan most likely wasn't locked. Deeper pan just mean longer time till its hot and longer time till it cools. I would vote for bigger transmission cooler though. 

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notlimah

notlimah

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28 minutes ago, Mopar1973Man said:

Sad part is lock up can't be done in 1st or 2nd gear. If you have a modified valve body you can lock up in 2nd gear. So a lock up switch won't do much good. I've not seen any that can lock up in 1st though. :think:

 

It's because you don't have an auto and haven't had Jon work his magic! He said I can lock up in any gear I wanted both in D or manually dragging the handle down to 2 or 1. :cool:

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Mopar1973Man

Mopar1973Man

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4 minutes ago, notlimah said:

because you don't have an auto and haven't had Jon work his magic!

 

Excuse me...1996 Dodge 1500 is a 46RE. :nono:

 

I'm the one that took my 46RE to Jon and posted all the install and rebuild. I've got a modified valve body but without the 2nd and 1st lock up.

 

DSCF6860.JPG

Edited by Mopar1973Man
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notlimah

notlimah

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I knooooooow Mike! :thumbup2:

 

I meant no auto in a diesel! Would you ever need 1st or 2nd lock up with the 46re? Just was pointing out that the 47re can lock up in 1st & 2nd if the valve body is built properly.

Edited by notlimah
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notlimah

notlimah

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Yea, I thought the same thing! I asked when that would ever need to be used and he mentioned that going down a steep grade instead of riding the brakes, just drop into 1st and lock it up and you can use it as an engine brake.

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Mopar1973Man

Mopar1973Man

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I'll admit the work @Dynamic did do to my valve body made a huge improvement even towing with the 1996 Dodge. Hold back much better and pulls excellent without getting hot. I just ran it down to Boise on one of my trips and transmission shift good and crisp and holds back on grades nicely. As for temperatures I've not been over 190*F yet. 

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Mopar1973Man

Mopar1973Man

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The whole tranny temp problem is really common out here. There are roads out her with grades around the 12-18% bracket. Most don't have signs. People will attempt to drag large RV's or stock trailers into the back country and blindly end up overheating the transmission. Deeper pan with stock cooler just means you get to go farther before it overheats. Now if you have a stock pan and oversized cooler you might not ever over heat. It's about shedding the heat in the cooler with limited air flow. So an oversized  transmission cooler and electric fan do more for keeping the temperatures down.

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notlimah

notlimah

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I agree.

 

I think for the OP's original issue a lock up switch would've worked wonders. In your example where you could pull long steep grades where you could have the TC locked and it still overheats, then bigger coolers with fans are a must!

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Mopar1973Man

Mopar1973Man

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29 minutes ago, notlimah said:

I think for the OP's original issue a lock up switch would've worked wonders.

 

As long as the transmission is modified to lock up in 1st or 2nd gears. Other than that stock transmission only locks in 3rd and 4th. So if your road speed is way down there is no way to lock up still. So this now fall back on being able to dump the heat rapidly which is mostly the torque converter shearing the fluid. 

 

So back at the OP, we need to know if you modified to lock up in 1st or 2nd gears? If it's still stock transmission, there is nothing a lock up switch would have done. You would be still unlocked and creating heat. So either you can have the transmission modified to lock up in lower gears and/or add a larger cooler and electric fan. 

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xc2

xc2

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Thats a really good question about the lockup switch. I bought the truck with a BD transmission and an exhaust brake. Ended up snapping the input shaft a few months ago and had it rebuilt by a local shop. He kept the BD valve body. I do have a TC lockup switch that works in conjunction with the exhaust brake, but it doesn't seem lock sooner than normal or in lower gears. Let me look at the manuals again when I get some time, because what the PO told be it supposed to. IDK, maybe the exhaust brake needs to be on......The last time I used the exhaust brake going down a hill at highway speeds, the tranny got hot (220+) and I didn't recover quickly, so don't use it anymore. Then add a Gear Vendor which can also lock/unlock...... Lots going on here and I'm not certain it's all working together.

 

I do have a deep pan with cooling fins. I think I'm gonna look into a better cooler (I believe have the stock one) with a fan. I dread coming to a stop sign/light before a grade on a hot day.

 

Yeah - 47RE (not 48RE). I really don't know where the temp sensor is. I'll have to take a look and get back to you. Thinking it's in the pan but not 100% sure.

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Royal Squire

Royal Squire

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On 7/2/2017 at 6:38 PM, Russ Roth said:

 

 

Lockup switch is needed for sure in that scenario but you need a modified valve body to be able to lock in first I believe.  Mine can do that and I use it on a stretch of backroad with my toyhauler.  The last 50 yards is so slow I can't lock it even with 4.10 gears though.  Be bad trouble at black rock if it was a long pull like you are talking about but 50 yards or so no real problem.  The answer to that would be low range but my '02 has solid front axle so not possible without locking hubs which I am thinking I will do eventually.

 

Couldn't you just put it in 4lo?

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notlimah

notlimah

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@Mopar1973Man A stock valve body will lock in 2nd, just not a good idea to do it unless the trans is built to handle it.

 

@xc2 Something seems off. If you have the switch, how are you activating it? If it's setup to work in conjunction with an exhaust brake I'm wondering if it can even be used while accelerating. I'd check the wiring to make sure you can use them separately but also at the same time if you wanted. The lockup switch should lock the TC as soon as the switch is activated.

 

As far as the input shaft, if you already snapped one, I hope a billet one went in this time to avoid it happening again. Are you running a BD triple disc converter as well? 

 

Given your usage and what you've already experienced I'd say a lockup switch and bigger/better trans cooler are what you need to avoid any overheating issues.

Edited by notlimah
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Russ Roth

Russ Roth

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2 hours ago, Royal Squire said:

 

Couldn't you just put it in 4lo?

 

 

I could but if you are on hard surface and 4x not needed is not a real good idea.  Worst place for me is my driveway which is paved but that same hill would be nice in 2x low.  It is actually an old logging road that is gravel and I do use 4x high range at the toughest part.  Last bit is slow enough I have to unlock the convertor but short enough distance not a problem.

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Mopar1973Man

Mopar1973Man

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7 hours ago, xc2 said:

I do have a deep pan with cooling fins.

 

As I thought deep pans with cooling fins won't cool unless you moving at highway speeds. 

 

7 hours ago, xc2 said:

I think I'm gonna look into a better cooler (I believe have the stock one) with a fan.

 

Stock cooler is rather small and without a fan. It relies on the engine fan for slow speed cooling.

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