Transmission Question

Very good thread guys - thanks for the replies and interesting reading...

It's a 97 GMC K1500 Suburban - don't know tranny codes or axle ratios off hand... I live in eastern Washington and talked to a tranny shop owner who says he frequently rebuilds trannys of people who drive over Snoqualmie Pass and abuse their overdrive. Having had my last Suburban tranny rebuilt, I tried to learn what I could from that experience. In my own observations, the ones who are asking for trouble are those who leave their cruise control set at 70mph up a grade and just sit there on the way up conversing with passengers, as the tranny kicksand out of passing gear (3rd), as the vehicle tries to maintain that cruise control speed setting of 70mph up the grade. From what I now believe to be true, that's definitely a tranny killer so I'm now generally kicking the cruise control OFF during those uphill occasions and settling back to a comfortable climbing speed of

55-60mph when climbing a fairly steep grade. I think experienced drivers know when they're putting their vehicle at risk and increased stress by kicking it in the butt with passing gear and forcing it to maintain that 70 (or better) up a steep hill. All that said, I don't want to end up in a tranny shop again if I can ever avoid it in this lifetime... lol

I don't know a lot about how torque converters work (lock vs unlock) and how that impacts the hill climb but a big question I *have* had is, if I'm going up a grade starting in overdrive at the bottom of the steep grade and as my speed slows, depress the accelerator gently to get it into 'passing gear', is there any reason at that point that I can't just pull the transmission handle into 3rd gear (while in 'passing gear')? I would normally DO this while holding my constant speed and without letting off the gas. So in essence - for a given speed, just pull the tranny handle into 3rd to get it out of OD and save the transmission. OR... does it matter? In other words, if I'm climbing the grade at a comfortable 60mph, no cruise on, engine temp is good, at approx 2300 RPM in overdrive though 'passing gear' that we've hashed about, is there indeed any difference?

thanks again guys for the replies... It's very informative. :-)

You drive that stretch a bunch, so smoothing a pattern out should be easy. Hit the grade at normal speed with cruise on and in OD. You should know by now when the tranny will want to kick down. Just go ahead and shift the tranny into 3rd at about that point. Use the set/ coast button to lower rpm's if desired and just let the truck keep on going. As you level out over the pass, shift back into overdrive and bump up your speed to desired level with the resume/accel slide.

If you know for a fact that the tranny will only downshift once, on a grade, don't even bother with anything. Depending on the grade you can even use the set/coast button to lower your speed a bit at a time and the tranny won't downshift, but this is dependent on the vehicle and how good you are at hearing what your truck is telling you. It generally has a certain hum to it when it is ready to downshift and you just tell it to slowdown a bit and this will delay the shift.

Now, this isn't recommended for long or steep grades, or grades you are not familiar with. I generally don't like my truck downshifting and blowing the extra fuel out the pipe for a measly 5 mph, so I'll just drop the speed down a bit, and if the cruise control is being extra sensitive I just flick it off and let my foot keep the tranny from downshifting. If I drop below 55, or traffic speed, It's blow the fuel time, though.

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I'm not sure I see the difference. Locked means it's locked. Engaged means it's locked.

That defeats the advantages of a torque converter and would reduce performance. That's why they UNlock when you give it a lot of gas.

I'd prefer one that will stay engaged if I let

I think your reasoning here is sound but it's not going to happen because that would cause the vehicle to get reduced gas mileage on the EPA test. No one wants to do anything that will lower that number.

You could massage this yourself if you wanted by repositioning your brake light switch so that it takes more then just a bare tap to turn the lights on (and unlock the TC).

The reason you slowed down in those was because they did not have a

4th gear overdrive. Their TCs didn't have any lockup capability. Drive your car in third gear and you while have the same thing today as you had back then.

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