[fenderbender]

Looking for some input on a 700r4.. I have a long list of upgrades to my 1991 GMC K1500. Any body up to a good head scratching. Here it is and I will try to keep it short. Truck seemed to be running great. I bought a 23' 4000lb camper, pulled a few times was heading south on I81 level ground @ 70mph seen smoke from behind felt a hit on the frame rail, slipped to neutral cut it off key back on for steering. It lost it fluid & the Governor 100 yrds back.
Towed in had it rebuilt with good stuff - Z pack clutches, corvette servo, a gov. to hold a little deeper, a cooler, and some other things for better towing. All back together drives great hits hard & solid. Made the first trip with the camper, Something did not feel right when I backed into the site somewhat level ground after that is when the double hit started when going into reverse, was told felt like just drive line slack uh not. Well the next up grade was going to be gear ratio, In luck I stumbled across a 3.75 rato 6 lug 14 bolt from a light duty K2500, swapped out the front and rear, All is great pulls better than the 3.42 10 bolt for sure. @ about 8000 miles later @ the trans shop he said leave me the truck we will look into the reverse double hit keep in mind things seem to be running and shifting great.. he found that the reverse clutch pack had exploded disk & spacers also all of the ears except 1 were gone from the outside of the pack. Cleaned all replaced what need to be replaced including the converter, flushed the cooler the flow is great. I made a pull with the camper on my way back home it developed a leak front seal at the shop he said trans has gotten really hot. Need to leave it the first of the week. I installed a temp gauge on the way to the trans shop on level I81 about 20 miles it pegged out to 280deg still holding and shifting great. He pulled it out and down and found that the converter changed colors the band had cut into the drum about .30 thous. he check my theory a cracked or warped case from the first incident, all looked good back together with new parts including a pump and another converter flow through the cooler is still great. Running and shifting tight, temp from shop to home about 160 deg. next up grade a 180 deg thermostat with a flush of the cooling system and refilled with new coolant ( I have had a chip in the comp. for awhile , 8mm wires, a hot coil & a module, p/up, a cap & rotor with brass contacts) Left the house truck running great, shifts great eng temp 180-185. Trans temp 160 deg. Heading to the interstate 3 miles hit the on ramp up to 80mph oooh no the trans temp climbed to 200-210 by the time I leveled out. eng. temp @ 180deg. It dropped the trans temp back to 180 for a few miles but it was back up to 200 by the time I got home. Oh and the reason for the 180 deg thermostat to get more umph and to stay off of the edge where the clutch fan locks in it really sounds like it is going to go air born at that time. Anybody ever had this going on, or any thoughts or ideas
Thanks

[briscoe]

First thing, if you get a trans 280 degrees, thats bad, real bad.

Do you know for a fact that this transmission is going into lockup?

When the converter clutch is applied the trans will run the coolest.

[oldbogie]

Originally Posted by fenderbender

Looking for some input on a 700r4.. I have a long list of upgrades to my 1991 GMC K1500. Any body up to a good head scratching. Here it is and I will try to keep it short. Truck seemed to be running great. I bought a 23' 4000lb camper, pulled a few times was heading south on I81 level ground @ 70mph seen smoke from behind felt a hit on the frame rail, slipped to neutral cut it off key back on for steering. It lost it fluid & the Governor 100 yrds back.
Towed in had it rebuilt with good stuff - Z pack clutches, corvette servo, a gov. to hold a little deeper, a cooler, and some other things for better towing. All back together drives great hits hard & solid. Made the first trip with the camper, Something did not feel right when I backed into the site somewhat level ground after that is when the double hit started when going into reverse, was told felt like just drive line slack uh not. Well the next up grade was going to be gear ratio, In luck I stumbled across a 3.75 rato 6 lug 14 bolt from a light duty K2500, swapped out the front and rear, All is great pulls better than the 3.42 10 bolt for sure. @ about 8000 miles later @ the trans shop he said leave me the truck we will look into the reverse double hit keep in mind things seem to be running and shifting great.. he found that the reverse clutch pack had exploded disk & spacers also all of the ears except 1 were gone from the outside of the pack. Cleaned all replaced what need to be replaced including the converter, flushed the cooler the flow is great. I made a pull with the camper on my way back home it developed a leak front seal at the shop he said trans has gotten really hot. Need to leave it the first of the week. I installed a temp gauge on the way to the trans shop on level I81 about 20 miles it pegged out to 280deg still holding and shifting great. He pulled it out and down and found that the converter changed colors the band had cut into the drum about .30 thous. he check my theory a cracked or warped case from the first incident, all looked good back together with new parts including a pump and another converter flow through the cooler is still great. Running and shifting tight, temp from shop to home about 160 deg. next up grade a 180 deg thermostat with a flush of the cooling system and refilled with new coolant ( I have had a chip in the comp. for awhile , 8mm wires, a hot coil & a module, p/up, a cap & rotor with brass contacts) Left the house truck running great, shifts great eng temp 180-185. Trans temp 160 deg. Heading to the interstate 3 miles hit the on ramp up to 80mph oooh no the trans temp climbed to 200-210 by the time I leveled out. eng. temp @ 180deg. It dropped the trans temp back to 180 for a few miles but it was back up to 200 by the time I got home. Oh and the reason for the 180 deg thermostat to get more umph and to stay off of the edge where the clutch fan locks in it really sounds like it is going to go air born at that time. Anybody ever had this going on, or any thoughts or ideas
Thanks

Unfortunately this is an all too common experience, I've had several friends driving Chrysler, Ford, and GM products in recent years all loose their auto-trans to heat when loading the machines up for camping and towing a trailer. None were originally equipped with OEM or dealer tow packages and none would listen to me when I told them they weren't going far without putting more than a trailer hitch on the back.

These days, the OEMs cut it real close, welcome to the world of computer design and finite element stress analysis. there ain't no extra meat anymore to cover what the engineers don't know about structural loads and the finance guys want all the cost possible cut from the product. So when they say you need a tow package, they mean it!

In your case the 700R4 is a derivative of the TH350. With a 350 cubic inch V8 on one end a 4500 pound (empty weight) truck with an 4000 pound camper on the other, this gear box is in way over its head. With the best of hot rod parts, it's still in way over its design limit, so lets hear it for the conquest of the finance people in American industry, but GM has a long history of cutting cost at the transmission. You need a upgrade forward or backward to a 4L80E or back to a TH400 to get the strength you need.

Either of those being unlikely- then you need a TCI rebuild with tons of good stuff in the 700R4 and you need to add an external oil cooler capable of keeping fluid temps between 180-200 degrees tops, that means 200 degrees F going up a 25% grade on a 100 degree day, all day long. The cooler needs to be remote mounted with its own fan so as not to add heat to the radiator which is already on the edge of what it can do just to cool the engine and it's oil. It (the cooler) needs a thermal bypass valve that shunts the oil around it on cold days.

The radiator has become a pretty busy place these days, it not only is cooling engine coolant, but it has the additional duties of heating or cooling the engine oil to help hold the engine in an emissions friendly temperature zone; plus it's trying to cool the transmission. Now the cost guys have sliced these down to size so that when the truck is new it has just enough capability to pull these tricks out of the hat; but put a few tens of thousands of miles on it and a few years and the edge is gone, you have no margins anymore with anybody's machinery.

The attraction of the OEM cost guys to trucks is based upon looking at sales, i.e. where do they go. Used to be a pickup worked for a living, now most pickup sales are just for macho city slickers who are poseur cowboys; kind of like the modern Harley pilot, they ain't the real thing, just doctors and lawyers playing at being 1 percenters. The same with trucks, so the cost guys reduced their expenses by slicing truck abilities from them at every turn while adding off road graphics so it looks like you've got something special. The average showroom Z-71 Silverado or TRD Tundra wouldn't last long enough in the dirt to get to 20 miles south of Ensenada. So today (1980's to present) if you expect your truck to earn its keep, you've got to belly up to the option bar and spend some real money.

Bogie

[fenderbender]

Yes it got very hot. Per the gauge. @ that time I had a 195deg stat the eng. never runs hotter than 210. It now has a 180 stat in it and has not gone above 195 deg. the temp outside this morning was about 70 deg. @ 4:30 am trans temp was showing 210 after a 20 mile run south on the interstate. As for the t. converter it was replaced again. And at about 65-70 the rpm is @ about 2400 if I get into it, shifts down rpm to 2900 @ about 75 mph. temp up
It does take a good while for the temp to start back down when back into overdrive. I have a question I called the parts store about a flexplate they said it was two styles, need a #. I had the trans shop replace the plate they supplied it. What is the chance that the offset is not correct and the t conv. is not completely into the trans/pump? A friend that drag races asked me about the measurement between the plate and the conv.
Also I just got the truck back on 8-10-07 and I have not pulled with it. I have pulled bigger with less and never had a problem. It has to be something simple. like pressure what should the pressures be and does it stay the same through all gears?