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Username Post: C20 Suburban 454+700r4. Light towing?        (Topic#348688)
Makeshift 
Forum Newbie
Posts: 1

Loc: South Australia
Reg: 12-13-17
12-13-17 07:08 PM - Post#2717855    

G'day from sunny Down Under,

I'm looking at picking up a RHD converted '82 square body C20 4x2 Suburban with a stock 454 and the 'trailering package'. However, the original TH400 has been replaced with a 700R4 in the early 1990's and after several rebuilds every 6-7yrs, was finally upgraded to a 'Street Machine' spec performance rebuild 2yrs ago and has held up OK (same mature owner last 25yrs)

Everyone online seems to say a 455+700R4 is a timebomb, but from what I can find, the 350's came with the 700R4, and the 454's with the stronger TH400, so I assume that it's the extra torque that kills them.

It will be my daily driver to make the 8mile commute in 40mph Suburbia; but I also tow a small racecar (3500lb including trailer) 4-5 times a year 30miles to the local track (which I figure would be within a 350+700R4 capability anyway). Otherwise it will just be a nice burbly town cruiser and I won't be hauling much more than groceries and bicycles.

Since I have other fun cars to get my fix; IF I babyfoot the 'burb and keep it out of O/D all the time, what are the chances of the 700R4 holding up? The logic in my head says that if I don't exceed using the torque the 350 would have put out anyway, the trans should last, right?

Anyone with experiences?

Thanks.



 
someotherguy 
Moderator
Posts: 28614
someotherguy
Age: 47
Loc: Texas
Reg: 08-01-03
12-14-17 01:16 PM - Post#2717913    
    In response to Makeshift

Rule of thumb is it's rated for 6,000 lb. GVWR. You can creep up on that just by loading your C20 Suburban down without actually hooking a trailer to it.

You might get by for a while with a built 700 transmission, as long as you only tow with it in "D" not "OD" and put a heavy duty cooler on it.

The notorious weak points in the transmission family (TH700R4, 4L60, 4L60E) are the sun shell and the 3/4 clutches. There are other failure areas but those are the common ones even in stock applications.

Richard

06 Silverado ISS / 06 Silverado SS / 06 300C SRT8


 
BigChevys 
Forum Newbie
Posts: 12

Loc: Maryland
Reg: 11-25-09
12-14-17 02:36 PM - Post#2717920    
    In response to someotherguy

I don't think you're giving the 700R4 enough credit (or maybe too much to the stock 454, lol). The 700R4 was rated at least up to 10,000 lbs. gross combined weight (truck + trailer), and at least in later years the maximum GVWR was somewhere around 7000 lbs. I've had good luck with two of them and love the gear ratio spread - first is 3.07:1 as I recall and overdrive is .7:1. One of mine was pulled out of an '86 C10 with about 150,000 miles, given a Trans Go shift kit with increased pressure and a couple other basic improvements (but not an internal rebuild). It was then installed behind a new Vortec 350 long block with Edelbrock port injection TBI conversion and headers in an '87 C10 Suburban. That was the strongest 350 I've driven in terms of low to mid range torque, but with 31" tires and 3.08 rear gears it was no tow monster. However, I had the truck loaded as high as 17,500 lbs. GCW (weight slip from a scrap yard) and routinely towed anywhere from 2000 to 9000 lbs. I put many miles on that truck both towing and solo before the torque converter clutch began showing signs of slippage. I parked the truck several years ago due to corrosion and other issues but the transmission still worked. If they built the transmission right and you don't drive abusively, I think you'll be fine.

Ed

[list]
  • 2007 Trailblazer SS
  • 2003 Avalanche 2500
  • 1972 Nova 307 TH350
  • 1970 Chevelle 4D 350-300 TH350
  • 1968 Caprice Wagon 396-325 TH400
  • 1968 Impala SS 327-300 TH400


  •  
    BigChevys 
    Forum Newbie
    Posts: 12

    Loc: Maryland
    Reg: 11-25-09
    12-14-17 02:43 PM - Post#2717921    
        In response to BigChevys

    I should add that I agree completely on the advice to install a good transmission cooler and use overdrive sparingly. I sort of take both of those for granted when it comes to towing. I used overdrive when towing, but my method was, if because of load, hills, acceleration, etc. it couldn't hold the converter locked up in overdrive, then it shouldn't be in overdrive and I'd drop it to drive.

    Ed

    [list]
  • 2007 Trailblazer SS
  • 2003 Avalanche 2500
  • 1972 Nova 307 TH350
  • 1970 Chevelle 4D 350-300 TH350
  • 1968 Caprice Wagon 396-325 TH400
  • 1968 Impala SS 327-300 TH400


  •  
    someotherguy 
    Moderator
    Posts: 28614
    someotherguy
    Age: 47
    Loc: Texas
    Reg: 08-01-03
    12-14-17 02:44 PM - Post#2717922    
        In response to BigChevys

    I've had about a dozen of them grenade even in stock applications, so I don't think I'm denying them any due credit. Your mileage may vary.

    Richard

    06 Silverado ISS / 06 Silverado SS / 06 300C SRT8


     
    1983G20Van 
    Super Senior Member
    Posts: 3687

    Loc: Bedford, Texas, USA
    Reg: 11-13-02
    12-14-17 03:09 PM - Post#2717924    
        In response to someotherguy

    I grenaded the junk 700R4 behind the GUTLESS 2.8 in my S15 Jimmy. That being said they are a ticking time bomb behind a good running 305 much less a 454. Even the 4L60E in my Express van with lots of torque management to kill power during shifts died in less than 40K. The slightly built up 4L65E replacement only went 40K. The TPI engine in my 1983 G20 was eating one every 10-20K. I did not even add a trailer hitch to the Express van until after I swapped a 4L85E in place of the 4L60E!

    1983 G20 Van, 350 TPI, Ported 906 Vortecs, Edelbrock 3817 Base, ASM oversize runners. Reed Custom Roller cam, 700r4, 12 bolt with 3.08 gears, Doug Thorley Tri-Y headers, true duals


    Edited by 1983G20Van on 12-14-17 03:11 PM. Reason for edit: No reason given.

     
    Stinky 
    Senior Member
    Posts: 1590

    Loc: Whitewater, CO
    Reg: 05-25-01
    12-16-17 11:05 AM - Post#2718139    
        In response to 1983G20Van

    I had an '86 Sub (the year matters greatly, to a stock one). Twas 1/2 ton, stock 350 & 3.73. I had a huge cooler on it, and an external filter put on the lines....twas a 2 qt. PH373 behind the bumper (same HD filter that the motor takes). I put it behind the bumper....back to this later.

    The PO would tow to Lake Powell...250 miles & 100 degrees (or more)...we did not talk about this. But, I assume that he went to LP on 3 day weekends w/at least 5 adults and that the Suburban was FULL. I also assume that they went 2-3X a year. He had a small boat, by today's standards...a large boat for when I was growing up...about 3000# when loaded w/gas, ice chests, skis and what not. I am sure that it did this for at least 5 years, if not 10.

    I got it at 186K...I think that it was the original trans. Here we go, wait for it, here it is...when I bought it, it did all of the above w/o a trans cooler.

    At about 200k...while in Las Vegas, coming back from CA, I noticed that the trans was slipping (BTW, the 1st thing I did was put a cooler on it, above). IT took 2 gallons of ATF (that is correct). The front seal was gone. It operated fine...but every 100 miles it would need a gallon. From the motel office to our room, you could follow it by the ATF on the ground. So, the night before we had to back track from the Sierra Nevadas back to our original starting point due to the pass being closed by snow (we were a day behind schedule)...do we wait here or press on? (Twas a Sunday, couldn't get it fixed then). We pressed on...the closer it blows to home, the easier it is. On that trip, I learned that a trans would operate on motor oil...why would I do such a thing you say...because I left LV w/a full trans and ONLY about 2-3 gallons of ATF....Every 100 miles, or every bladder break, put in a gallon. I bought all of the ATF that they had at Checker/Oreilly's in Salina UT (about half way, 250 miles to go). I also got a few quarts of oil that eventually went in. So, the long story is this...I drove it to the trans shop, here, 550 miles from LV.

    My wife drove it as her mini-van....5 kids. I suspect that every time she drove it, that it was in OD. When we drove it out of town, we had 5-7 full sized people in it, and all of their gear. I don't know how fast a Sub will go, as the speedo only goes to 85...but it when you take the foot off the gas, after about 10 secs...the needle will start to drop off of 85mph (the middle of UT and NV is wide open and flat)....BTW, this is cruising, at about 1/2-3/4 throttle, not pushing it.

    I have a trash trailer...I haul ATVs, hay, move people and who knows what else w/that thing. I don't even take it out of OD for that thing(Except for hills and etc....like I normally drive it). It weighs about a ton....loaded. I have towed that trailer a bazillion times, w/several dif vehicles. I have only towed it about 100 times w/that Sub...I also towed hay w/a borrowed trailer (only about 10 miles) and other borrowed trailers.

    I blew the trans on the Sub at about 75K...the TV cable retaining clip was setting on the intake and the cable was flopping. So, it self-destructed...and not from all of the above.

    Soooo, that is my experience w/a 700r4 in a Sub.

    '92 Astro....it came before the Sub. I think has the same trans. 208K on it and running like a top when it was sold (or so the ad read, LOL). But, it towed the same trailer on at least 3 vacations...tent, bikes, all kinds of crap, all over the SW US, w/every seat full, 6-8 people...but it was in D, except when going down hill.

    So, IMHO, the trans design is sound....change the fluid every 20K, at the start of the warm season.



    Edited by Stinky on 12-16-17 11:09 AM. Reason for edit: No reason given.

     
    gchemist 
    Senior Chevytalk Moderator
    Posts: 24272
    gchemist
    Loc: Austin, TX 78748
    Reg: 05-09-00
    12-17-17 06:09 AM - Post#2718230    
        In response to Stinky

    Strong solid parts are needed for towing. Add an inline trans cooler, low speeds, and D driving.



    '95 Jimmy SLT (Bought @131,814)
    '83 Silverardo XST - ZZ4 powered
    '96 GMC Jimmy LS Ret. @236651 miles


     
    junkman104 
    Frequent Contributor
    Posts: 1166
    junkman104
    Age: 59
    Loc: Murphy N.C.
    Reg: 01-25-14
    12-17-17 06:23 AM - Post#2718236    
        In response to gchemist

    I too think the 700r-4l60 gets a bad wrap. My last pickup was a 90 C1500 5.7 I bought new and drove for 397,000 miles. It was a daily driver and used it for towing as well. never had a problem with it and was serviced regularly.

    My current 04 Z71 with a 4l60 now has 230,000 miles on it and I tow a car trailer and camper with it as well with no problems.

    No doubt they are not as strong as a 4l80 but I believe it has more to do with the driver than the transmission. I always tow in "D"



     
    gchemist 
    Senior Chevytalk Moderator
    Posts: 24272
    gchemist
    Loc: Austin, TX 78748
    Reg: 05-09-00
    12-17-17 06:55 AM - Post#2718239    
        In response to junkman104

    I agree. I had a 96 GMC Jimmy. A rebuild in it failed at 50k. It was installed by the previous owner. I took it out and had it rebuilt by my trans guy. The Jimmy did light towing. The heaviest was a 4200 lb or so lift. The longest towing weight was a 1200+ lb loaded popup camper. It would tow it at 70 MPH in OD. An external in line oil cooler helped. Driver habits are important.

    '95 Jimmy SLT (Bought @131,814)
    '83 Silverardo XST - ZZ4 powered
    '96 GMC Jimmy LS Ret. @236651 miles


     
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