90 diesel transmission, which one?

WMB · July 25, 2004

Hi all, new to this forum, looks good. I just bought a 90 diesel suburban with four speed auto. Anyone know what tranny model this is? It feels like it has a lockup convertor, does it? Doe it lock up in third and fourth? Is it hydraulic or electronic control? I'll be changing fluid and filter soon. Can anyone recommend a good shift kit. I may also add a trans temp gauge and tranny cooler. What trans temps should I expect and what is ideal? Vehicle may pull a 16' boat, no heavy hauling. My objective is to make it reliable and increase longevity. Any answers, comments, and suggestions are appreciated. Trying to get educated on the tch side of this truck. Thanks, Mike

Cool Zr2 · July 25, 2004

I would expect you wouldn't need a shift kit or temp gauges for pulling a 16 foot boat......

4L80

Just go to the parts store and they will know what you have.

Colorado Kid · July 28, 2004

1990, make that a TH700R4

Yes, it has a lockup converter.

Yes, it will lock in third and fourth.

It, the tranny, is all hydro-mechanical. The T-C clutch is electronically controlled.

Cooler is better. Over 250F is probably shortening tranny life. I wouldn't tow anything with a 6.2L without a tranny temp guage and auxilliary cooling . . .also avoid O/D while towing like the plauge with that tranny.

Shouldn't need a "shift kit". The "TV" (THrottle Valve) cable adjustment effects shift timing and harshness, and clutch apply pressures. If it's short-shifitng and slurring the shifts the adjustment is too slack and the clutches are toast. If it won't shift up, or hits like a rear-end collision the cable is too tight. Err on the side of higer RPM, harsher shifts to keep things cool and reliable . . . but you can go too far and break hard parts with all the banging.

WMB · July 29, 2004

Thanks for the replies, I just changed the trans filter. Only took 5 quarts to get it topped off, not to impressed. Oil didn't look or smell bad. I've rebuilt some

chrysler transmissions with a lot lees miles than this has on it. 185000 miles. I'm a firm believer in maintanance, especially tranny. It seems the big three build for super soft shifts, when its shifting - it's slipping and heating the oil.

What is the difference between the 700 and 4L80. I thought the 4L80 was an electronic overdrive version of the TH400. The 4L60 an electronic version of the 700. And the 700 a hydraulic overdrive trans allnew to itself when introduced.

If the trans ever takes a dump, I will probably put in a 5 speed. If you can't find em, grind em!

Thanks