Light towing with a 700r4
 

Hey all, I did a search and really nothing stood out for an answer for me. I have a 98 Z71 that I have had for 19 years with a 4l60E , I believe? Anyway it is the equivilent of the more modern 700r4. The owners manual states to tow in 3rd and not 4th. Now my drivetrain in this truck (The 71in my avitar) was repourposed from an early 80s squarebody 2 wheel drive. I would like to put a hitch on it and pull my Scotty camper. Trouble is, I have heard horror stories on the OD trans not being up to it. Ive done it with previous trucks of this era with t350 transmissions. Anybody got a story or some tips and tricks? The trans shifts great now and I like the rpm reduction it gives. I would hate to rip it out by the roots. As a side note, the Scotty weighs 1000 lbs and a tounge weight of 175.

Re: Light towing with a 700r4
 

Tow away. I will tow just fine in stock form or properly rebuilt.
Yes you have a 4L60E in your Silverado.

GM renamed the 700R4 to 4L60's to keep the nomenclature consistency.
A THM is a 3L60. First number is the # gears, second is rear wheel drive and the last is the torque capacity.
The "E" on the end designates electronic controls.

I have a Silverado with 170K on it and have had to repair the transmission.
However, the center shell broke at the hub and this has noting to do with towing.
I do wish I knew the exact year of the transmission. 1982-1986 were not especially good transmissions. 1987 and up were excellent.
That said I would just tow and go. Doesn't sound like your load is a very heavy.
With lighter trailers, like an unloaded car trailer, I tow in OD.
GM has to make recommendations like everyone is an idiot.
Cheers

Re: Light towing with a 700r4
 

that is a light load for a trailer. I assume you have a lockup converter....might want to keep in in D (read not OD) going up hills.

A tranny temp gauge will show you when your trans is not happy

The 4L60E does not like much TQ (over 300) but otherwise should be OK. They always do better with an external trans cooler added. My 96, when it was a 4L60E),had a factory external air cooler and also through the radiator.....GM must have known it needed the help

Re: Light towing with a 700r4
 

All 4L60 and 4L46E are lockup transmissions.
Some electronic 4L60E can slip constantly with out damage.
GM uses this feature for a lot of things including keep speed in check going down hill while using cruise control.
On my Silverado the driver information system will tell me if the transmission overheats.
Their are plugins for your cell phone so you can read the temperature while traveling.
The Electronic transmission also automatically compensate for larger loads.
They measure every shift duration and adjust the line pressure to achieve a constant shift time.
I am a big fan of the Electronic transmissions.
Even the 87 to 92's are great transmission but with out the comfort and drive-ability features of the "E" transmissions.

Re: Light towing with a 700r4
 

It would fall in the 82-86 range. With the 3:73 gears, it is perfect on shift points and rpm drop. I also wired a manual 4th gear lockup switch interupted by a n/c 82 model brake switch to keep it from lugging at early braking. Ive heard that those old r4s were not happy in 4th without the lockup , but so far the way I drive around the house, 50% of the time, I dont have a straight enough stretch to lock it up. It seems like its a good trans. so far anyway. Appreciate the input guys.

Re: Light towing with a 700r4
 

I believe the reason they recommend towing in 3rd is because it is a 1:1 in that gear, so none of the planetary gearsets are spinning. The internals produce less heat that way.

Re: Light towing with a 700r4
 

I had a coworker who bought an 86 GMC 1/2 ton with a 6.2L Diesel with a 7004r trans. He towed a 28' travel trailer with no issues. He did not tow in OD.

Re: Light towing with a 700r4
 

I have the same drivetrain, a 6.2 Diesel, although it is in a 72 GMC. I don't wish to highjack, it is just that I have always wondered about this very question: is the 700R4 an appropriate or inappropriate transmission for towing. Because I have a little holiday trailer I want to pull.

I understand there is no point in pushing your luck when getting up to highway speed or up a hill, but could you slip it into OD on a straightway at 60mph and leave it there?

Re: Light towing with a 700r4
 

Actually I do seem to remember that on level ground he would shift into OD, but any hills it was D. I have the same trans in my 70 behind a mild 350 (built by Bowtie overdrives) and would not worry about towing 5 to 7 thousand pounds. I would add a trans temp gauge so I could monitor the trans temp. Heat is what kills trans.

Re: Light towing with a 700r4
 

Let's say we tow in 3rd with the r4. I run 235/75s on the back and calculated 55 mph at 1:1. Screenshots below. With the t350 in my 72, I went all over the place with it. I can see why now. I do have a 3:08 gear set and if I do tear this one up [700], i will swap to a 3 speed.

Re: Light towing with a 700r4
 

It works that way in a manual transmission.
https://www.youtube.com/watch?v=M90fPWg-7DQ
See the 30 min mark, of the video, for the power flow on the 4l60, 4L65 and 4l70.

Re: Light towing with a 700r4
 

My 85 with built up 350 with 3.23 ,700r4 is a dog going up hill empty in 3rd I never use OD unless I'm on level ground doing 70+ . Lockup is annoying at anything under that speed .
I wouldn't tow with any gearing higher than 3.50

Back in the 90s I had a 87 Suburban 350 with 700r4 with 3.73s I towed a 30 Gulfstreem trailer at right around 8500 loaded . Trans went at 139k put a Goodwrench 700r4 in it sold it with 250k

Re: Light towing with a 700r4
 

Yep...know a guy that was towing his large boat with a fairly new then truck with a 700R4 trans, it got so hot the fluid boiled up and out the dipstick tube onto the hot exhaust/cats ignited and the whole truck burned up on the side of the freeway. This happening fairly often is partially where the sealed/locking tranny dipstick came about.

Re: Light towing with a 700r4
 

So the jest of this is exactly what I was figuring. I'm going to pull it in 3rd and deal with the lack of cost effectiveness by turning more rpms. I won't be doing it all that often, so it is not a deal breaker. I like the 1669 rpms at 55 when I am out cruising. Most of my trips are 30-40 miles round trip as such. I will build a hidden hitch and update it in my build thread. Thanks all.

Re: Light towing with a 700r4
 

The early ones would also puke out the vent tube onto the exhaust . GMs fix was to make the tube longer so it just ran down the tranny. Fix the symptom not the problem . My truck did it once and man I pulled over quick . Never had it come out the fill tube .

Re: Light towing with a 700r4
 

As far as 4L60E I tow just leaving it on OD and do turn on the tow/haul. I have towed boats, tractors and cars/trucks on a trailer. Had a '95 Suburban that was just over 200K when we sold it and never had the transmission out. The first Tahoe I had ('01) went 299,956 miles on the original transmission and the second ('07)is still going at about 230K on the original trans with my son. Same thing in my '14 Suburban but it has the 6 speed.

I have an '83 K20 that came factory with a 700R4. The original went about 80k and ate the front pump ('83 is known to be weak). Got a GM reman and it was pulled un-necessarily at about 150K for a noise that turned out to be a bad pinion gear. It was rebuilt again and is still going. That truck towed a lot of trailers in its day. I usually towed in direct (at least up hills) when it was carbureted. With the TPI fuel injection I generally just leave it in OD.

Re: Light towing with a 700r4
 

"fairly new then truck with a 700R4 trans, it got so hot the fluid boiled up and out the dipstick tube"

May be more to the story. If it happened in a 1999 or newer Silverado it would have lit up the drivers information system. It tells the driver when it's getting hot and if it gets even warmer it says to pull over and idle the vehicle to cool it down. It would have had this warning before ever getting so hot as to boil the oil.

When the oil boils you are not going any further! The boiling temp of modern transmission fluids is roughly 570 deg F.

Yes it happens, but typically when someone is stuck or power-braking. Both can heat up a transmission to dangerous levels in minutes.
Otherwise it was typical when the transmission was slipping and they kept driving the vehicle.
Cheers.

Re: Light towing with a 700r4
 

That's a really neat calculator, I punched my own numbers into it and was surprised just how great an influence tire diameter is upon rpm.

My 2500 has a 35 inch tire and so even with my (probably) 4.10 rear gears I pull 2160 rpm in third.

Re: Light towing with a 700r4
 

Handy to have if you dont have a tach for sure. I pull the Scotty every year to Bowling Green Ky (156 miles), one way, every August in my 55 chevy. It has a t350, and a 3.55 rear gear. Puts it in the neighborhood of 2355 rpms at 55. Of course I take the road less traveled to keep from getting ran over by a texter. That isn't too far from 3rd in my c10. I was hoping to give it a go and see. I'm sure I will. I just like to learn from others how they did this over the years. Nothing like experience. Im on my 3rd transmission in the 98 and its only towed a couple of hundred miles in it's life. I can't blame those two failures on towing.

Re: Light towing with a 700r4
 

Yes, the calculator is good to see what RPM you will get with x size tire & rear gear....in lieu of having a tach

I just got my 72 C10 a few months ago. The tires on it, BFG WWL, were full tread....but 21 years old so I put new, larger, tires on it. About 2" more in diameter (29.8"). Even with my 3:73 & 3 OTT the RPM's are tolerable now at 65 mph so yes tire diameter certainly makes a difference in RPM's

Re: Light towing with a 700r4
 

Just a few weeks ago I ended up towing my Jimmy. Ended up around 6,100 lbs loaded behind a 96 K1500 Suburban (350 with 4L60E). Unfortunately, it happened to be about 103 F that day, 260 miles round trip with a 5000' mountain pass in the middle.

This was not a fun trip. My Suburban did it, but it's really pushing it. At one point, I pulled onto the highway at an uphill section. Even at wide open throttle it took about 30 seconds to get to 30 mph. Every time I accelerated to 60 from a stop the engine would heat up 20-30 F even doing it very slowly. When I climbed the pass, I shifted into 2nd and ended up doing 30 mph for most of it. Kept the engine temp under 220 F and even ran with the windows down and heat on. I passed several vehicles broke down on the side of the road, hood open. When loaded I never used OD. I didn't want to take the chance, and I would rather do a few more RPMs than lugging the engine constantly.

It's not always about your truck but how you use it. Treat your transmission nice. Keep it cool, don't have a lead foot and it should be fine.

If I had a choice, I would tow with the 4L80E. The gear spacing is better. The 1-2 shift in the 4L60 is 3.06 to 1.62, the 1-2 in the 4L80 is 2.48 to 1.48. The 4L60 drops you too far outside the power band. All the gears are closer and the overdrive isn't so deep in the 4L80E.

Re: Light towing with a 700r4
 

"It's not always about your truck but how you use it."
Perfect as nothing will last long with a driver without common sense.

The 4L80E and the Tubro 400 share the same ratios in first, second and third.
You correctly identified the bigger jumps between first and second in the 4l60E.
As the first gear ratio, across the board, has continued to move down over time as the final drive ratios moved up.
Will get you load moving easier with the 4L60E but the 4l80E has better ratios after that.
The different over-drive ratios, between the two transmissions, will result in a 129 rpm difference at 60 mph using 3:73 gears.
.70 on the 4l60E and .75 on the 4L80E.

The 400 and it's derivative are less sensitive to oil change intervals. Mostly because the bushings diameters are so much larger in the 400 & 4L80E than the 4L60Es. Keep the oil clean in the 700 & 4L60E and they will last much longer.
Glad you made it home with the load. Heater on at 103 deg had to be an experience I will pass on. But much better than at the side of the road waiting for a wrecker.
Cheers

Re: Light towing with a 700r4
 

Speed at different ratio.

Re: Light towing with a 700r4
 

Just a note. A big external trans cooler will keep everything cooler. I like the B&M stacked plate coolers. You can add a temp controlled electric fan to the front of the trans cooler.

Re: Light towing with a 700r4
 

Definitely run a trans cooler and don't tow in OD unless you're on level ground.

454, 700R4, 3.73 gears and 265/75/16 tires.