1986 Chevy G20 3/4 ton, 6.2 Diesel

ktmrfs wrote:

well, actually the 3.73 rear end isn't a strke against you, many of these vans came with REALLY REALLY tall rear end ratios, a 2.73:1 IIRC was std, combined with a .7OD, was useless. The 3.73 is actually pretty decent rear end, probably a good one with the diesel.

However the 700R4 is a definite strike against you. Ours was going fine after 160K when I sold it and probably hit 200K or more, but that was with a gas engine AND an add on trasmission oil cooler AND NEVER towing in OD. One of the weakest links in the 700R4 was the overdrive and torque converter lockup clutch. Especially with diesels the 700R4 had a tendency to blow the torque converter clutch and/or OD clutches. My advice, only tow in drive, add an external transmission oil cooler, and ALWAYS make sure your above the torque converter stall speed when towing. With the gas engine this is about 2,000rpm, don't know about the diesel. If your below torque converter stall speed, you'll heat the transmission fluid real quick with all the torque converter slip.

I dug through my documentation, and couldn't find the tow rating for various combos, but I do recall for 87 the max for the 3/4 Ton was 6500lbs. The 350 with 4:11's was one combo with that rating, that's what we had, don't know what the diesel rating was.

I've never towed in anything other than drive. I forgot one time and all it did was shift back and forth, and that reminded me pretty quick. The PO told me the reason the transmission was rebuilt was because his son towed a ~6000lb trailer from Winnipeg to Saskatoon (~800km) and left it in OD. He was amazed he even made it home. Could smell him coming. At the same time is was rebuilt they added a cooler to it.

I've read elsewhere that 3rd gear in the 700R4 is pretty strong, but overall it's not the tranny you want for any hauling work.

Like I say, I don't need to get there fast. I'm pretty sure I can make the 35km trip without incident. Luckily it's on a stretch of road that is not generally all that busy and has no hills, so I won't be making too many people angry if I only travel at 80 km/h.

After two seasons hauling my Mallard 31T (~6500lbs) the transmission oil is still the same color as new, and it hasn't dropped any. I don't know if that indicates anything, but it seems to me that if I was doing damage with that combination, there would be evidence of it in the oil.