8hp70 heater bypass

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JHoward

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Same here. I know @caulk04 said its a couple ounces but tranny fluid laying in a puddle on the garage floor looked like a couple gallons. I thrashed on it good today and saw my temp reach 154 and then within half a mile or so right back down to 145.

I lost maybe about way less than an 1/4 cup of transmission fluid ... I guess a couple of ounces, for arguments sake ... I reacted quickly plugging the "hole" with a clean microfiber type hand towel.

I'll drive a few days and will post the results then ...

My main concern at time of reinstalling the new bypass valve was making sure that that damn snap ring was snug. So far, nothing has blown apart, lol.
 
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caulk04

caulk04

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Same here. I know @caulk04 said its a couple ounces but tranny fluid laying in a puddle on the garage floor looked like a couple gallons. I thrashed on it good today and saw my temp reach 154 and then within half a mile or so right back down to 145.
Years ago I was doing a trans service and part way through removing the pan I decided to drop the opposite end from my original plan. Forgot to put bolts back in that side, cracked the RTV loose and the whole thing hit the floor. Looked like I butchered a cow. Idiot
 

ThunderMug95

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Well I went to install mine today…dropped the driveshaft and then went to unbolt the shift bracket. Anybody know what torx those bolts are? I tried a T30 and it didnt feel good, so I aborted.
 

Heathen-19

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Well I went to install mine today…dropped the driveshaft and then went to unbolt the shift bracket. Anybody know what torx those bolts are? I tried a T30 and it didnt feel good, so I aborted.
If my memory serves me correctly it is a T40.
EDIT: Just crawled under my 19 Classic to double check and it is a T40
 

JHoward

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Ok, all is good after the install of @caulk04's THB(transmission heater bypass/thermostat delete)valve. Trans temp(s) are ~ 45° cooler with the average outside temperature 80°.

The before the install the transmission temps was ~ 179°-185°. After the install the temp(s) are ~ 129°-150°ish while driving highway and idling at stop lights, etc. That's much better.

However, the coolent and oil temps were up about 10° from where they normally were, coolent hovered around ~ 199°-203° and oil was ~ the same.

I resolved that by doing an partial AGS delete(removing all the shutters except for the top and bottom rows)and now these temps are back down to where they normally were.

All is good.
 

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joesstripclub

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Well I went to install mine today…dropped the driveshaft and then went to unbolt the shift bracket. Anybody know what torx those bolts are? I tried a T30 and it didnt feel good, so I aborted.
It's been a while since I installed mine, but pretty sure you dont need to remove any of that stuff. I definitely didn't drop the driveshaft, and I'm 90% sure I didnt unbolt the shift bracket. Tried to go back through the thread but that's too many pages lol.
 

ThunderMug95

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It's been a while since I installed mine, but pretty sure you dont need to remove any of that stuff. I definitely didn't drop the driveshaft, and I'm 90% sure I didnt unbolt the shift bracket. Tried to go back through the thread but that's too many pages lol.
I can get to it, but shift bracket partially obscures it. I should've done it when I did the longtubes. It was right there staring at me!
 

CoZo6

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It's been a while since I installed mine, but pretty sure you dont need to remove any of that stuff. I definitely didn't drop the driveshaft, and I'm 90% sure I didnt unbolt the shift bracket. Tried to go back through the thread but that's too many pages lol.
I can get to it, but shift bracket partially obscures it. I should've done it when I did the longtubes. It was right there staring at
I’ll be paying attention to this thread. I am in on not removing the driveshaft, but looking at it I also see the shift bracket on my ‘21 is certainly in the way. Good luck.
 

MRFREEZE57

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I’ll be paying attention to this thread. I am in on not removing the driveshaft, but looking at it I also see the shift bracket on my ‘21 is certainly in the way. Good luck.

I guess one could do it without removing front driveshaft but for what little time involved on dropping the driveshaft it was so much easier to get to and install the T Stat bypass with it dropped.
 

CoZo6

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I’ve read your post Daniel. Very good (pictures too) and it would be easier as you suggest.
 

hawsk99gt

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Well I guess I am revisiting my one and only issue with my truck and that is the heat issue with the transmission. For the most part the truck drives great, but occasionally after driving around for a few hours when slowing down there might be some slipping and then the occasional coming to a stop I'll get the transmission bump. But yesterday I was driving around and it was hot outside 88*. Truck drove fine, I stopped at a Costco which is about an hour away. Started my drive back home and then the gauge for the trans took off. Just a reminder I do have the heater by-pass installed going on a couple of years now. For the most part I believe it has done the job, but I think there is something deeper going on that I can't seem to figure out. Again the dealer will not touch this until it flags a code. I have left it with them in the past and as usual for the short drives it operates as expected, making me look like a lunatic. I really want to keep the truck. It's paid for, it looks good. Does anyone know if there's mechanics that work on these transmissions. Heck the dealer doesn't even want to do a filter/pan fluid change on this. I asked a good local mechanic in my area who does custom rebuilds as well as servicing and as soon as I told him what I had, he was "nope, don't touch those transmissions". I think I would pay 3 grand just to replace the trans in it. My only alternative to me is to trade it in. Which, I would hate to do. I love not having a payment. Anyway there it is, my venting for the day. Here is an image from my drive on the way home yesterday. It gets a cooler the slower I drive, but still above 200*. For example between 50 - 55mph. As usual I'll drive it today and it will be fine locally, not getting over 55mph.
Hot Trans Temp.jpg
 

crazykid1994

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It’s not hard to do the fluid and filter if you have the tools. I would definitely put in the thermostat bypass or buy someone else’s used thermostat to see if the thermostat is sticking because 233° is no bueno
 

star_deceiver

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. It gets a cooler the slower I drive, but still above 200*. For example between 50 - 55mph. As usual I'll drive it today and it will be fine locally, not getting over 55mph.
Your truck probably has a bunch of cooling rads sandwiched around the radiator, additionally, a dual radiator itself. I would not be surprised if you have a bunch of crap clogging all the fins in the various coolers and rads. Might be an idea to pull apart the front end and separate the radiators and back blow each one.
 

Shawn Burns

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what is happening to your truck is not normal, especially with the thermo bypass. I rarely get about 140 while towing (7x12 enclosed race trailer full of motorcycles and gear, likely overloaded). The fluid change is not very difficult. If you love the truck as much as you say, I'd suggest a PPE pan to ease with future fluid changes. I would do several fluid drain and fills after the initial pan change to get nice clean fluid in there. Many of us are using valvoline maxlife ATF, which rates pretty well against the ZF fluid and is a much less expensive alternative.

That will eliminate the fluid level/quality variable. Star-deceiver may be on to something too.
 

EdGs

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Would the 3-way valve possibly have anything to do with the high temp issue?
 

Wild one

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3-way valve?
I don't think your truck has the 3 way valve,as it was only used on the earlier 8 speeds,and i think they quit using it on the 16's. Do you still have the shutters in place? As Star said it might be worth pulling the grill and hosing out the A/C condensor and rad with a spray on rad cleaner and a trip through your local coin-op carwash .
 
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