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Old 07-08-2005, 05:08 PM   #1
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Cooked THIRD 700R-4 GM Suburban Transmission.

I pull a 22" Flying Cloud with an '89 1500 Suburban 5.7 TH-700R4 373 rear axle. This is my third summer towing and my third trans just cooked after a 400 mile round trip from Chicago to the Dells. Truck has all RPO towing equipment - is spec'd out to 12,000 GCVW so this thing shouldn't even be breathing hard, much less cooking transmissions. Trans guys find no specific failures - just cooked guts. Does anyone have experience with this trans??? Have received conflicting advice about where to put selector - some say D4 (overdrive), some say D3 (1:1) - consensus from 5 "experts" is that selector should be in D4 on the highway and D3 in city and suburbs - mostly so trans doesn't "hunt". Been doing that and am getting bummed out here. Also, has anyone heard that the OEM fluid/fluid cooler in radiator should be disconnected when using an Air/Fluid trans cooler behind the Grille?? The factory/dealer setup has the air/fluid unit in series with the radiator cooler. I appreciate any help anyone can provide. Thanks. Sincerely, Andy
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Old 07-08-2005, 05:12 PM   #2
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I'll let the experts answer the technical questions, but did the dealer check for a plugged cooler? Doesn't matter if it's series or not if it's plugged.
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Old 07-08-2005, 05:37 PM   #3
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Based on the same axle/engine combo that was on two different Chevy vans that I owned (1989 and 1999), you should be towing in 3rd. OD was a no no based on my owners manuals on both vehicles.

Normally the output from the internal radiator cooler goes to the input of the external. That will get you temps down below the water temperature. If you are reversed you probably are heating the fluid.

Good advice on checking for a plugged cooler (check both external and internal).

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Old 07-08-2005, 06:33 PM   #4
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Quote:
Originally Posted by markdoane
...but did the dealer check for a plugged cooler? ...
Once again, Don scores the best possible problem area to check.

As long as you don't have a lead foot you failed to mention...

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Old 07-08-2005, 07:08 PM   #5
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I have shelled out half a dozen 700R-4 Transmissions.
They ARE a piece of CRAP.
I FINALLY found a tranny mechanic that fixed it though.
You need to have the valve drilled out inside the valve body that is a 90 degree electric ball valve that shuts off fluid to the converter when it goes into lockup. You build up all that heat accelerating, climbing hills, and if you go into lockup the HOT fliud just sits there trapped in the torque converter unable to dissipate the heat. GM engineers think that once you are in lockup, there is no further need to circulate that fliud. Must be geniuses...<eyeroll>.
Drilling out the valve allows the fluid to circulate through the converter even when it is in lockup.
Also, install the largest tranny cooler you can find, a deeper optional pan to increase fluid capacity, and a TRANNY TEMP GUAGE so that you will know when your temp is coming up too high so you can slow down and get your foot out of it.
Only then will you stop cooking 700R-4 transmissions when towing.
One more thing....NEVER tow in OD with that tranny....only in 3rd.
---just my 2 cents---
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Old 07-08-2005, 08:16 PM   #6
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Quote:
Originally Posted by Andrew M. Franklin
Truck has all RPO towing equipment - is spec'd out to 12,000 GCVW so this thing shouldn't even be breathing hard, much less cooking transmissions. Trans guys find no specific failures - just cooked guts. Does anyone have experience with this trans??? Thanks. Sincerely, Andy

I don't see how your 89 350 1/2 ton can be rated 12k when my 88 3/4 ton with 3.73, TH400 and a 454 is rate 9500lb max trailer and 16k GCVW. A 3/4 ton burb with a 454 is around 6,300lb by itself. Actually that rating might be with a 4.10 rear. Its not clear in the brochures. If it is with the 4.10 that put my 454 down around 8300. Your R10 down around 6000 of trailer and gear or maybe even less.



You need taller gears. 4.10 will take a LOT of strain off the transmission. Get a BIG cooler and a temp gage. Pep boys has both. the Stack plate made by Hayden they sell I have had on three trucks .Works great and very rare that I see 200 degrees on my transmission.

http://brochures.slosh.com/
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Old 07-08-2005, 08:57 PM   #7
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Ok I found the page with the towing/load info.

Your trucks Combination weight of truck truck trailer and all gear and people is 12k. Knowing that your truck weights close to 6k that puts your trailer all cargo and passenger max weigh at about 6k according to GM's published weights.

Now most people feel that you never want to exceed 80% of the rated capacity. Blowing out transmissions is one reason why. So 4800lb is what many will consider the safe load including trailer people and cargo.

Not know what year your FC is I am guessing the weight is around the same as my coach and about 3500lb with hitch gear and water. Then we add in about 500lb for food, clothes, and personal items for two people if your packing light. And we will average 150lb per person on the conservative side. So I now have 4300lb for two people packing light (no tools and stuff like that).


Need a 4.10 gear or a TH400 tranny to fix this. If this truck is driven a lot without the trailer I would go wit the 4.10 gear. With the OD tranny it will be quite drivable.

Also I find that if I run my 454 over 2700 on the hwy for extended time it starts making a LOT of heat. I have temp gages on tranny, oil and the regular water temp. Truck has a aftermarket 19k tranny cooler and the factory stand lone oil cooler.

If I keep it under 2700rpm on the why (I have no OD with my TH400) tranny runs 180 degrees Engine coolant right at 195 (rated thermostat) and about 240 oil. If I start running 3k My coolant runs about 210, Oil gets to 300 and tranny is around 210 as well. Thats EMPTY. I never run over 65mph loaded to keep the heat down. My truck is in perfect condition and has 85,000 original miles. New radiator, fan clutch and water pump.

My truck runs a VERY tall tire as well. Its nearly 32 inches at the factory 235x85xR16 The R10 is more around a 28 on a 2wd. So you are spinning more RPMs without being in OD then me already.

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Old 07-08-2005, 10:23 PM   #8
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One other thing. It is my understanding that there are 5 different torque converters that will fit the 700R-4 tranny.
Most shops rebuild them with the lightest and cheapest to compete on price.
You should not give a HOOT about that. You want the heavest level 5 priciest converter and should be willing to pay the extra to get the extra heavy duty rebuild....which they will not warrant because they will figure out REAL FAST that you are wanting it that way for a REASON....to pull a trailer. So forget about a parts warranty except for quality of labor there will be none..
59Toaster is right about your weight limits....about 3500 lbs plus light packing is all you are equipped to pull. And he is right about the rpm's. When I towed with my Yukon, prior to the Duramax 2500HD that I have now, I had to keep rpm's less than 2700 or the heat went right up.
The Yukon was rated to pull 6300 lbs at 100% capacity, and I was pushing that considerably. Even the slightest uphill grade would necessitate downshifting to 2nd, and grinding out even small hills at 2700 rpm's and 42 mph.
Because I did all the upgrades to the tranny in the Yukon BEFORE pulling my Airstream, I have not burned up a 700R-4 tranny pulling the trailer. I burned up all those transmissions prior to that by just driving fast and hard 80-90 mph on West Texas flat straight roads. Since the heavy duty rebuild, HUGE tranny cooler, tranny temp guage, and having the tranny valve body modified, I have not shelled one lately.
I also went Amsoil synthetic in the new rebuild.
Lastly....GAWD I love my Duramax/Allison!!!! I will NEVER go back to a weak tow vehicle. It is a pleasure to drive/tow without any strain or worry about equipment.
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Old 07-09-2005, 09:09 AM   #9
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After cooking my trans pulling a lite-weight SOB my dealer came back with the strong recommendation that I only tow a trailer in D3, no overdrive. I did this and no trans problems. Gas mileage sucked, but gas is a lot cheaper than trans rebuilds. That was the only thing we've done differently. I had already added the largest trans cooler I could install. My current tow vehicle does not have O/D but I intend to install a 700 this winter and other than a HD rebuild and the best torque converter and trans cooler I can buy as suggested by others on this thread, I will tow in 3rd and leave the O/D for when I'm not towing. Several of my travelling companions have 700's and only tow in D3 and not one has had a problem, and we live right at the mountains so much of our travelling is up and down mountain passes and no problems. It's always been our understanding that the 700R4 was not made to tow in O/D mode, or at least the early versions. Barry
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Old 12-19-2005, 01:25 AM   #10
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This is a very interesting thread. On a recent trip from Coos Bay to Crater Lake Oregon we burned up the 700R4 tranny (using OD) in our 89 Suburban 1/2ton 2wd. We found that the PO of the Burban bypassed the stock cooler with a very small external cooler.

Once the 700R4 was replaced we had a supercooler installed but again the stock cooler was bypassed. The installer said that since it was bypassed in the past for some reason so he didn't want to risk using it. I have not pulled our 74 Arogsy 28 since but am now planning a trip to Las Vegas and want to make sure that our burban with 170,000 miles is ready for the task. Not long before our first trip towing with our burban we had the exhaust replaced from the cat back. The new exhaust seems huge and it sounds great...much quieter than the stock exhaust.

One thing this thread had me thinking about is how to determine what the ration of the rear end is and if the seemingly standard 3:73 are enough to drag that twinkie on a 2500 mile trip.

What about balancing the wheels on the trailer? I've read threads from Andy about hubs exploding.

Also what kind of milage do you think I'll get keeping on the interstate in D3 at highway speeds (55 - 65 mph)? It would be great if I could closely project fuel costs and plan refueling points along the way. On our trip to Crater Lake we averaged 8 MPG with a burned up tranny.
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Old 12-19-2005, 01:52 AM   #11
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You should tow in "3rd" unless the torque converter locks sooner than later. The heat is generated by the torque converter not being locked under load. If you had a trans temp gague, you prob would have seen temps in excess of 200 degrees. A plugged or restricted cooler would also lead to trans failure too.

I have a 4l60e 5.7L combo and towed in overdrive regularly (prob close to 8,000 miles). I programmed the PCM (powertrain control module) to lock the torque converter at 41 mph. This for me solved the towning in OD issue since the torque converter was locked reducing heat. I did several other things to make the trans happy too...like adding a deep pan trans cover, better oil/air coolers, RAM air type torque converter cover, etc. Towing our 6300lb Safari on a bit longer than a mile steep grade, the trans never got real hot.

The proper trans cooling route is transmission, to the oil/water in the radiator to a good oil/air cooler and back to the transmission. It is not advised that anyone bypass the factory oil/water setup, but rather add a better oil/air cooler.

Transmissions should be about 175-195 degrees max when towing. Above that temp, life expectancy of a trans goes south fast. Adding a gauge is a great tool to monitoring trans temps real time.
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Old 12-19-2005, 07:10 AM   #12
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Quote:
Originally Posted by Silvertwinkie
The proper trans cooling route is transmission, to the oil/water in the radiator to a good oil/air cooler and back to the transmission.
Twink:

I disagree (partially) with this statement.

On all of my recent vehicles equipped with both water/tranny fluid AND air/tranny fluid heat exchangers the factory elected to install the air cooler UPSTREAM of the water (radiator) cooler. That is to say, FACTORY ROUTING is tranny to air/tranny fluid exchanger to coolant water/tranny fluid exchanger and then back to the tranny.

I have the factory service manuals on most of these vehicles, and from what I can discern the reason for this setup is to make the tranny fluid temp as stable as possible - even though (in the case of the motor home) the engine temp is regulated to about 210 degrees - not the ideal temp for tranny fluid longevity. The 210 degrees is the set point of the thermostat (regulation the "internals" of the engine, and of course the "cool side" of the radiator will be less than this setting. I do not know what water temp the "intake" of the water pump sees.

I think the primary reason for this setup is to add temp to the tranny to "get the fluid up to temperature" (by HEATING it in the radiator - a true temperature exchanger) on the short distance commutes the vehicles in the northernmost parts of the country are subject to. What I am saying is that, depending on the conditions, the radiator either adds heat to the tranny fluid or takes it out - and maintains the tranny fluid at the same temp as the radiator fluid. On the MoHo (if memory serves my correctly - I will not bet the farm on this) the oil heat exchanger is on the "hot" radiator head (drivers side on a cross flow radiator), and the the tranny exchanger is in the head on the "cool" side of the radiator (curb side).

In the case of the Motor Home (my opinion only) the air cooler should be DOWNSTREAM of the radiator cooler - the MoHo RARELY sees temps even approaching freezing, and once started, is usually run for at least 200 miles.

Anyone have a FACTORY INSTALLED air/tranny fluid cooler DOWNSTREAM of the radiator heat exchanger?
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Old 12-19-2005, 08:03 AM   #13
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Quote:
Originally Posted by 87MH
Twink:

I disagree (partially) with this statement.

On all of my recent vehicles equipped with both water/tranny fluid AND air/tranny fluid heat exchangers the factory elected to install the air cooler UPSTREAM of the water (radiator) cooler. That is to say, FACTORY ROUTING is tranny to air/tranny fluid exchanger to coolant water/tranny fluid exchanger and then back to the tranny.

I have the factory service manuals on most of these vehicles, and from what I can discern the reason for this setup is to make the tranny fluid temp as stable as possible - even though (in the case of the motor home) the engine temp is regulated to about 210 degrees - not the ideal temp for tranny fluid longevity. The 210 degrees is the set point of the thermostat (regulation the "internals" of the engine, and of course the "cool side" of the radiator will be less than this setting. I do not know what water temp the "intake" of the water pump sees.

I think the primary reason for this setup is to add temp to the tranny to "get the fluid up to temperature" (by HEATING it in the radiator - a true temperature exchanger) on the short distance commutes the vehicles in the northernmost parts of the country are subject to. What I am saying is that, depending on the conditions, the radiator either adds heat to the tranny fluid or takes it out - and maintains the tranny fluid at the same temp as the radiator fluid. On the MoHo (if memory serves my correctly - I will not bet the farm on this) the oil heat exchanger is on the "hot" radiator head (drivers side on a cross flow radiator), and the the tranny exchanger is in the head on the "cool" side of the radiator (curb side).

In the case of the Motor Home (my opinion only) the air cooler should be DOWNSTREAM of the radiator cooler - the MoHo RARELY sees temps even approaching freezing, and once started, is usually run for at least 200 miles.

Anyone have a FACTORY INSTALLED air/tranny fluid cooler DOWNSTREAM of the radiator heat exchanger?
Tranny does need some heat and I agree the current thought may be to get the tranny up to operating temp a little faster routing it that way.

I might play around with this some. The way my truck is plumbed with the extra cooler I installed I can pretty easily swap directions. With the temp gage I have I can see what’s happening. I will say this that in the winter it takes a LONG time to get the transmission hot with the AUX cooler after the factory one. Once it’s warm its stable it just takes its time getting warm.

My Truck can easily get into thermal runaway. Once I get near that point while running on the hwy at about 2900RPM with A/C on (EMPTY) when I get off the temp spikes and it takes several miles to get the temp down. It never exceeds220 on coolant (where the factory electric fan kicks in) but its hotter then I like and I notice the oil temp saying elevated for a long period of time.

The oil temp is what really bothers me. Once that oil temp is up it just runs hot all around. Its nothing for me to be near 300degrees on the oil in the mid summer.

What I want to see is if I go AUX first if it will help drop engine temp a little. Thought is it will be passing less heat into the engine coolant. That would hopefully allow the radiator to get rid of more heat and in return also lower oil temp since there would be less heat in the engine.

I also plan to move my AUX off the front of the radiator. Probably duct the air to it and mount it under the battery. lower the air temp to the radiator and remove some of the items slowing airflow.

I will also put a lower temp switch in for the AUX cooler. I may relocate the oil cooler with its own electric fan as well. Again get that heat out from in front of the A/C and Radiator.

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Old 12-19-2005, 09:42 AM   #14
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I bout an '82 GMC 6.2 diesel with the 700R OD trans thinking it would be great for the 20' Argosy I had at the time. It would not tow in OD even on flat freeway, so I always ran in 3rd. The converter would lock up at 17mph just after it shifted to 3rd and power would drop to nothing. Truck was equipped with trans cooler through radiator and I added an aux. cooler after the radiator so there was never a problem cooling. I found the wires to the electric lock up clutch and put a toggle switch beside my brake controller so I could prevent the trans from locking up until I was moving at cruising speed. I used this all the time, with or without trailer. Made for much smoother shifting and increased torque while accelerating. When two-foot-itis hit and the 20' Argosy became a 25' Caravaner, I replaced the engine and trans with a rebuilt '73 454 gas and a turbo 400 trans which was a perfect fit and an excellent solution. Darol
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