Really, really want to get rid of my 700R4 in 88 suburban and upgrade

[Rockhounder]

Hey all,

I have an 88 suburban, with the stock 700R4, 3.42 axles, and 33" tires. I like how the rpm's at highway speeds are really low, if you keep it at 55-60 mph it feels like 1200 to 1500 rpm's and gets noticeably better gas mileage.

But.... I am doing a LOT of high torque driving by going up and down the hill from Big Bear all the time, and am concerned that the tranny is just not up for the job. It overheats like crazy, even with the 3 extra tranny oil cooler radiators, and the radiated large capacity oil pan. Going up the hill, in 3rd, or even down to 2nd, on hot days, I literally have to pull over several times to cool off (tranny temp sensor gets to 210 degrees, and I pull over, if I don't, then at 230 degrees or so, I start smoking, and blowing radiator fluid out the vent tube on top) Some people told me that it is a bad tranny, but this is the 3rd tranny, and all before have done the exact same thing. Was embarrassing going up the grapevine from the north, in the emergency lane pulling a trailer, having to be in 4 low at 5mph, just to get up the hill.

I wish to upgrade to a better tranny, have heard that the 3/4 ton version is better, but do you know if anyone makes a swap kit with all the needed changes (mounts, fittings etc)?

Or does anyone have any other advice? It seems like there is much more power available in the engine, so if there was a stronger, and less heating up tranny out there that is an easy(relatively) swap, then I want to do this. I am tired of driving up the hill, in 2nd, going 20 mph, constantly pulling over to cool down tranny, yet only using perhaps 25% throttle, and engine is nice and cool. Towing our boat up the hill, we did 10mph, and with literally had to pull over in every single pullout, to cool down. Normal 1 hr trip to big bear took 5 hours that day... bleech...

 

[warrpath4x4]

there is no difference that I know of between a 1/2 ton 700R4 and a 3/4ton. unless your talking about a 1991 3/4 ton suburban then it had the 4L80E transmission but 91 3/4 ton 4x4 is the only old body style with that trans.

with the right money you can put anything in there you want, do you want to stay auto or go manual? do you want 4 speeds or 6 speeds?

 

[Rockhounder]

there is no difference that I know of between a 1/2 ton 700R4 and a 3/4ton. unless your talking about a 1991 3/4 ton suburban then it had the 4L80E transmission but 91 3/4 ton 4x4 is the only old body style with that trans.

with the right money you can put anything in there you want, do you want to stay auto or go manual? do you want 4 speeds or 6 speeds?

Well, I want to have something that I can get put in that lets me not have to worry about the tranny being stressed to its sustainable limits, thus causing accelerated decrepitude. I know that if you keep loads on a machinery system below a certain stress level, then that system goes forever. I worked one summer in Colorado on a cattle ranch servicing and using heavy machinery and road grading vehicles, left over from WW2... they were so overbuilt that I know they will be going strong long after I am dead and gone.

I know if a tranny is used lightly, and never stressed, you should be able to use it for the life of the vehicle. With my weight and driving conditions, it seems like I am able to get about 8k to 15k miles out of my 700R4's before they wear out. I would like to just get something bulletproof, for a budget. (I know there are $$ versus performance tradeoffs, but was hoping that by going to the next level up tranny that hopefully is not too hard to kitbash in, then I can get perhaps 50k out of the tranny. That would be an acceptable level for me.

As to the manual shift, that would actually be pretty cool, with a large clutch so I am not constantly changing out discs. But how is manual, when towing heavy boats or trailers, when first getting going from a stop, especially when going uphill? That seems like a potential for burning/wearing out your clutch pretty easily. (If there is a way to eliminate/minimize this, then I would definitely love to have a manual. I just remember driving the old 1948 Coleman gravel spreader road truck, and if I was going uphill, it was a ***** on the clutch. (with 12 speed truck tranny). Even my wife does great with manual, her vehicles she owned before we met, she deliberately chose manual (VW bug, Ford Mustang, Lotus Esprit).

 

[warrpath4x4]

theres a reason most people who tow regularly, use a manual transmission. if you want to go manual look for a nv4500. if you want to stay auto go for a 4L80E, you can even have a 4L80E built into a 6 speed auto.

 

[Rockhounder]

theres a reason most people who tow regularly, use a manual transmission. if you want to go manual look for a nv4500. if you want to stay auto go for a 4L80E, you can even have a 4L80E built into a 6 speed auto.

I like the idea of the nv4500, looks like you can get a rebuilt one for less than $2k. but what would be needed for the swap? I can see needing adapter bell/plate, and as for the shifting, since I already have the 4wd shifter in the floor, how would that fit? Also obviously I would need to fab in a clutch pedal and all linkages as well. Would I need to go with a different t-case as well or can the existing one work?


Perhaps the 4L80E 6 speed might be a lot easier, but since I am running TBI, do I need a computer to control the gearbox as well?

 

[ZMagic97]

I'm going to pop in a vote on the 4L80E. My lifted 1/2 ton GMC will have one if the 4L60E ever goes. I use my truck for light payload and cruising, but the steps needed for a beefy auto seem worthwhile to me.

As for auto vs manual: While i like the selective gears of a manual, I like the care free and attention free use of an auto for most everything.

 

[rayra]

I would suggest that something's wrong with your cooler plumbing, if the drive up and down from Rim of the World is overheating that trans. It really shouldn't be getting hot like that.
Do you have a lot of 90deg elbows in your cooler circuit? The more sharp angles, the more the flow rate is reduced. Add all the coolers you want, but have a lot of sharp turns in the feed lines and it's all for nought.
Did you disconnect the trans cooling line from the in-radiator loop?
I think you've likely actually constricted the flow, if you are getting higher temps with 'three' trans coolers. Just doesn't make sense.
What about your lockup converter, is it functioning properly. You really shouldn't be having heating problems if it's locked up in 4th gear.
But you are also not really running much out of the normal range, particularly if you are towing ('high torque'?) up that hill often. Normal is ~180-200F.


eta went back and re-read your post, particularly about 2nd gear and 4 lo on the steep side of the Grapevine. You're doing something very wrong if that's what you are reduced to. Just how much weight are you trying to tow? There's no way you should be having such troubles at all with a 700r4, unless you are trying to haul / tow several thousand pounds with it. I've been hauling crap over those very grades and in and out of Lake Isabella for decades with THM350, 700r4 and 4L60Es and have never been reduced to such a state. But I've never pulled / hauled much over 4000#, either.

The 700r4 is a good transmission. Your experiences are well outside the norm for it. Something is very wrong and it's not the design of the transmission.

 

[warrpath4x4]

yes the 4L80E will need a trans computer, you can either do a stock one or a stand alone.

 

[Rockhounder]

I would suggest that something's wrong with your cooler plumbing, if the drive up and down from Rim of the World is overheating that trans. It really shouldn't be getting hot like that.
Do you have a lot of 90deg elbows in your cooler circuit? The more sharp angles, the more the flow rate is reduced. Add all the coolers you want, but have a lot of sharp turns in the feed lines and it's all for nought.
Did you disconnect the trans cooling line from the in-radiator loop?
I think you've likely actually constricted the flow, if you are getting higher temps with 'three' trans coolers. Just doesn't make sense.
What about your lockup converter, is it functioning properly. You really shouldn't be having heating problems if it's locked up in 4th gear.
But you are also not really running much out of the normal range, particularly if you are towing ('high torque'?) up that hill often. Normal is ~180-200F.


eta went back and re-read your post, particularly about 2nd gear and 4 lo on the steep side of the Grapevine. You're doing something very wrong if that's what you are reduced to. Just how much weight are you trying to tow? There's no way you should be having such troubles at all with a 700r4, unless you are trying to haul / tow several thousand pounds with it. I've been hauling crap over those very grades and in and out of Lake Isabella for decades with THM350, 700r4 and 4L60Es and have never been reduced to such a state. But I've never pulled / hauled much over 4000#, either.

The 700r4 is a good transmission. Your experiences are well outside the norm for it. Something is very wrong and it's not the design of the transmission.

Yes, we thought about the constrictions, and looked, it is stock from the tranny into the radiator oil cooler, then from the output we ran heavy duty hosing, to the three coolers (each of which is the 8x14 inch oil cooler radiator.) Checked flow levels by disconnecting the oil lines right before it goes back into the tranny, and at 2000 rpm, in first(with the foot on the brakes to keep from moving), fluid comes out at a peeing rate. Should it be coming out faster than this? We have an infra red thermometer, and checked while engine was hottest, during a run up the hill, and before it gets to the radiator cooler, it was 260, at first radiator it was 210, at second radiator it was 190, and at third radiator it was 180. We never tow in 4th, but the lockup in 3rd does work, except sometimes in 3rd first going up a gradient, trying to get as much speed as possible, we start smelling the kevlar band burning smell. We were told by the 2 different shops that replaced our tranny (both under warranty thankfully, that they thought the tranny was just not up to the weight pulled.

Our Suburban weighs significantly more than stock, with all the solar on the roof, 6 volt dual battery systems, all the extra bumper work, bigger tires, freezer fridge, etc. With our camping gear in it, and my family (wife, daughter, 2 dogs inside) we scaled at 5,840 pounds. When we were towing our 28 foot 1968 Boles Aero travel trailer back from an extended job in Montana building an antique homemade mountain cabin resort, we went to the truck stop weigh station, and combined weight was 16,400 pounds(no joke, that was sooo overweight to what we should have been able to tow). That was the time we were doing 5mph in 4 low up the grapevine first upgrade from the north side. When we have nothing to tow, going up to big bear, we are the poor guy doing 35-40 mph, and in the winter, we can get up with no stops, but in summer/hot says, we need at least 2 pull overs to cool down. Keeping the tranny in first while stopped cools the temps down twice as fast as just keeping it in park or neutral.

Our Chris Craft and trailer combined is about 4,000 pounds.

So you can see, we are always lugging around a LOT of weight. Interesting, however, that our gas mileage is still pretty good for this year rig, we get around 10 mph city, and can squeak 12.5 mph on highways if we keep speeds to 60 or lower.

Here are pictures of our Suburban, and the things we tow:

 

[Deleted member 9101]

1. You at the limit of what the 700R4 can take, hence you destroying them. I'm guessing that 16,400 pounds is probably waaaaay more than it (and your truck) was designed to tow, especially up a mountain.

2. A 4L80E swap is pretty straightforward swap, it's a kit and can be done in a weekend in a garage with pretty common hand tools. They can be made damn near indestructible, for a price.

3. You can get your 700R4 rebuilt to take the abuse that you are throwing at it. You might want to discuss with the shop that does the work about changing the lock up RPM's of the torque converter and shift points. This is most likely going to be your cheapest and least complicated option. Buy a used one, have it rebuilt to fit your needs, then swap it out in a day.

4. Change your gears. With all your weight 3.42 gears and a stock SBC you are asking for performance problems and tranny problems.

5. I would get one good quality- massive- tranny cooler with it's own fan and ditch the rest of them. You are creating a massive pressure drop and that's going to nuke a tranny with a quickness regardless of what option you choose. It should come out under more presser that you could ever pee...lol (should be upwards of 100PSI IIRC).

6. Slow down and realize that you are over your GVW, going up hill; you are not going to keep up with traffic with out sacrificing something to the auto-part gods. ;-)

*Just found a pic of your truck... your bumper is probably blocking some of the air flow to your tranny cooler and radiator. You might consider knocking some holes in the front of it to bring in more fresh air.

 

[Deleted member 9101]

to the three coolers (each of which is the 8x14 inch oil cooler radiator.)

Dude... how the heck do you fit all of them behind your grill...lol. I gotta see a picture of this.

We were told by the 2 different shops that replaced our tranny (both under warranty thankfully, that they thought the tranny was just not up to the weight pulled.

They are 100% correct.

 

[Rockhounder]

Dude... how the heck do you fit all of them behind your grill...lol. I gotta see a picture of this.




They are 100% correct.

I will take pics of the coolers tomorrow when it is light and post. THey are situated (2 of them) right in front of the upper third of the AC radiator, and the third (last in line) catches the air from under the bumper.

 

[justcuz]

I agree with Rayra, something is way wrong.
People drive up that hill literally every day with the same trans and gears with no troubles.
With the weight you are towing you definitely need more gear.
Who is rebuilding your transmissions?
I am going to go out on a limb here and suggest Performance Allison Transmissions in Upland.
Dave and his crew do great work and if you have a problem he will stand by his work.
He will be the first to tell you though that you are towing more than a 1500 Suburban with 3.42 gears was ever designed to tow.

Oh and if you go to a 4L80E or even a turbo 400, your going to need a 32 spline input to your transfer case.
Turbo 350's, 700R4's and 4L60E's use a 27 spline input T-case.
I would suggest 3/4 ton axles with at least 4.10 gears too. You need a full floater to tow that house trailer.

 

[rayra]

Yep, that's WAY too much weight for that drivetrain / trans. And the cooler line pressure can be that low ('peeing') at idle, but ought to be much higher under load. A pressure gauge tied in AFTER your array of coolers would give the best indication, 75-100+psi. But it's sorta moot. Way too much weight. I don't think GM ever rated any Sub with towing setup at over 12,000 combined. You're going to have to step up to a heavier-duty trans.

I too am curious about the cooler arrangement, how and where they are fit. I have to say I'm less than impressed with the factory location on my '02 sub, much of it is located directly behind the bow tie logo on the grill, only its bottom 1/4 or 1/3 is in a direct fresh air path.
You can just see it in this pic, the bow wave from the chevy logo on teh grill probably wipes out ANY direct airflow to the stock cooler location.

I'm seriously considering relocating it or even ducting some fresh air to it. My Z71 'driving lights' are weak and soon to be replaced with an LED bar. I could turn those light locations into ducts and channel fresh air right onto my trans cooler. Planning a chin skidplate and other cahnges to the front. Relocating the trans cooler and ductign fresh air to it will most likely be part of those changes.

 

[Rockhounder]

1. You at the limit of what the 700R4 can take, hence you destroying them. I'm guessing that 16,400 pounds is probably waaaaay more than it (and your truck) was designed to tow, especially up a mountain.
Yes, that was way over, but it was a one time occurrence, as we had packed the trailer solid with all our woodworking tools and equipment from our 4 month cabin job.
2. A 4L80E swap is pretty straightforward swap, it's a kit and can be done in a weekend in a garage with pretty common hand tools. They can be made damn near indestructible, for a price.
I think this would be our first choice, any leads to the kit manufacturers would be appreciated.

3. You can get your 700R4 rebuilt to take the abuse that you are throwing at it. You might want to discuss with the shop that does the work about changing the lock up RPM's of the torque converter and shift points. This is most likely going to be your cheapest and least complicated option. Buy a used one, have it rebuilt to fit your needs, then swap it out in a day.
we had this done the last two trannies.... so need to go heavier duty

4. Change your gears. With all your weight 3.42 gears and a stock SBC you are asking for performance problems and tranny problems.
what ratios do you suggest, where when we are not towing, but going on long trips we can get halfway decent mileage as well?

5. I would get one good quality- massive- tranny cooler with it's own fan and ditch the rest of them. You are creating a massive pressure drop and that's going to nuke a tranny with a quickness regardless of what option you choose. It should come out under more presser that you could ever pee...lol (should be upwards of 100PSI IIRC).
Yes this sounds like a good idea

6. Slow down and realize that you are over your GVW, going up hill; you are not going to keep up with traffic with out sacrificing something to the auto-part gods. ;-)
Yes, we already do this, thus when towing our Chris Craft up the hill to big bear, it took 5 hours... I keep a hawk eye on the tranny temp gauge, and go as slow as I can... usually in 2nd, going 25 mph. Towing the boat, our combined weight is in excess of 9,000 lbs

*Just found a pic of your truck... your bumper is probably blocking some of the air flow to your tranny cooler and radiator. You might consider knocking some holes in the front of it to bring in more fresh air.
I will take pics of the underside and top rear of the bumper to show the airflow is actually unimpeded flow. The bumper actually was built and designed to slide onto the existing front bumper, then bolted onto bumper and frame. It is open on the underside