# tow capacity-350/700r4



## Detroitdan (Aug 15, 2005)

Can't find anything online that goes back far enough. Was wondering if anyone knows how much a fuel injected 350/700r4 can tow? Specifically an 89 Suburban 2500.
Thanks


----------



## B&B (Nov 4, 2006)

8000 lbs with the 3.73 or 4.10 ratio. :salute:


----------



## Detroitdan (Aug 15, 2005)

thanks. I couldn't find anything going back that far. The 99 Trailerlife chart shows a C2500 5.7 Sub as only 7500, of course it also shows a diesel 3500 as only 7500 too. I regularly tow over 10k with my 6.5, I'd really like to get a 2500 Sub that would pull my camper. Probably wouldn't take much to make the 350 perform torque-wise, but I don't think the 700r4 is supposed to pull that much. I read somewhere that even with adequate cooling the 700 wouldn't take the strain.


----------



## B&B (Nov 4, 2006)

Can't blame you there Dan. If I knew I was intending on towing an 8000 lbs (or more) trailer on a regular basis with the truck I wouldn't want the 700 in there either as your not going to tow 8000 lbs in overdrive anyway.


----------



## Detroitdan (Aug 15, 2005)

Well, I'd take it out of OD, it's supposed to be different than the 4l80e that has the different kind of electronic lockup. If that makes any sense.
I remember back in the early days of the 700 the owners manual said to tow in OD, but after a few thousand wasted trannies they started advising towing in 3rd. IIRC the 700 is very similar to the 4l60, which I've also been told won't tow that much.
If I were to buy a 3/4 Sub needing a tranny, would putting a th350 or 400 behind a 350 be much better? Personally I've always kind of like the 700, despite it's bad rep, because of the low 1st and OD.
Now that we're on the topic, what tranny was put behind the 454? They must have used the 400 and the 700 in the late 80s, before the 4l80 was around. Just curious how people towed 10k campers in the 80s. And I gotta admit I'm feeling more brave about pulling weight since all the major light truck manufacturers are now giving the go ahead to towing over 10k with their half ton trucks. I mean, if a 5 lug Toyota or Ford can tow 10k, I oughta be able to get an 8 lug to do it.


----------



## B&B (Nov 4, 2006)

Detroitdan;766866 said:


> I remember back in the early days of the 700 the owners manual said to tow in OD, but after a few thousand wasted trannies they started advising towing in 3rd. IIRC the 700 is very similar to the 4l60, which I've also been told won't tow that much.


 Correct, the 700 and 4L60E are similar both in their design and torque handling capacity as a general, although the 60E has gotten many improvements over the years that helped, which allowed GM to increase the tow rating/torque capacity on it since it's first inception.



Detroitdan;766866 said:


> If I were to buy a 3/4 Sub needing a tranny, would putting a th350 or 400 behind a 350 be much better?


 A 400 would be, if I was swapping amongst these transmissions in order to gain capacity I'd skip over the 350 and go right to a 400, or especially the 4L80E if the budget would allow and you demanded an OD equipped trans. The 350's are fine but the 400 will exceed it's durability in a towing application.



Detroitdan;766866 said:


> Now that we're on the topic, what tranny was put behind the 454? They must have used the 400 and the 700 in the late 80s, before the 4l80 was around.


The 454's used the 400 up until the 80E's came out since they of course had the highest rated torque capacity and were up to the job of a truck application.



Detroitdan;766866 said:


> Just curious how people towed 10k campers in the 80s.


 If they did it with a 700 equipped truck they did it until the trans died and then they swapped in a 350 (remember the store bought kits for that conversion that were so popular at one time?), sunk $$ into the 700 in an attempt to get it to live, or went right to a 400.



Detroitdan;766866 said:


> And I gotta admit I'm feeling more brave about pulling weight since all the major light truck manufacturers are now giving the go ahead to towing over 10k with their half ton trucks. I mean, if a 5 lug Toyota or Ford can tow 10k, I ought be able to get an 8 lug to do it.


No reason you can't. Just don't expect to do it with a 700 on a regular basis for that long....it's just out of it's element.

I ran an '86 K10 with a 454 for years, originally with a T-350, then a custom built 700 ($$$). Truck was equipped with 31's and 3.73's and towed 7-8000 lbs quite regularly. Of course it towed great with the 454 but never could keep the 700 alive in it for more than a year or two at a time. Trans had the best parts in it that money could buy (at the time), the biggest stacked plate cooler that would physically fit in the rad support, and I never ran it hot...just couldn't keep it alive. It'd either wipe the sun shell out of it, burn the 2-4 band up, or smoke the 3-4 clutches in it every time. The last time it broke a pump vane, left me on the side of the road that time. Finally replaced the 700 with a 400, swapped the 3.73's for 3.42's and ran it for 7 more years after that with the same trans in it. The 400/3.42 combo actually pulled better, had more usable power band, and only lost 1/2 MPG over the 700/3.73 combo. If I still had that truck today it'd have a 4L80E swapped in it. Since of course the 80E gives you the capacity of the 400 with the overdrive of the 700/4L60E. The best of both worlds.


----------



## Detroitdan (Aug 15, 2005)

so it sounds like I should be considering a 400. I guess I could live without OD. I know the tranny bolts up the same on the engine side, is the transfer case, or trans mount any different? I swapped a 700 to a 350 in an 83 C10, but it was so long ago I can't remember if I had to move the crossmember or anything. And the transfer case fitment was not an issue.
I suppose a th400 swapped in, exhaust and intake might help the 350 with power, but I know it's a TBI, what can you do with those? I've never even owned one.Obviously a cam and headwork or even a 383 stroker kit would make the torque I need, but if I have to sink that kind of money it would be easier to just drop a 454 in it.
Not that I really think I need a ton of power, I get by just fine with my 6.5 that has minimal power as diesels go.


----------



## B&B (Nov 4, 2006)

Swapping from a 700 to 400 isn't tough but finding a 400-to-208 (or 241 depending on the year) transfer case adapter can be a little tough as that stuff seems to be drying up these days. You'll also need to swap the input in the T-case from the 27 spline that the 350's/700's use to a 32 spline for the 400 but it's an easy case to tear down and the inputs aren't too hard to find if you look around. Only other modification is moving the cross member slightly but by the later years of these trucks the bolt hole were often times already there. No drive shaft or shifter mods are needed. Add a vacuum port in the intake for the 400's vacuum modulator and your done.

But of courses the easiest thing to do would be to find a truck that's already 400 equipped. They built plenty of the 3/4 and 1 ton trucks those years that were 400 equipped.

If your going to tow with it regularly (and heavy) the 454 will give you more bang for your buck than any 350 will with bolt ons. And if your thinking of doing some modifications to enhance power now, do it with the 454. There's no replacement for displacement when it comes to the TBI years.


----------



## Detroitdan (Aug 15, 2005)

Makes sense. I really don't need to tow the camper with it, but it would be nice if I could. I'd like to get a Suburban either way because of the growing family. Just had our third kid last month. I tell ya, as soon as I figure out what's causing it, I'm going to put a stop to it ;>


----------

