Discussion in '1973-1991 K5 Blazer | Truck | Suburban' started by FatBoyBlazer, Oct 6, 2001.
is it bad to drive around in overdrive, like undr 65 mph?
It wouldn't really hurt anything unless your lugging your engine... (cruisin at really low RPM's)
6in 87' K5 w/ 35" BFG muds.
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I'm assuming that you have a 700r4...........YES, OD AT CITY SPEEDS WILL SLOWLY KILL YOUR TRANSMISSION. Driving around town in overdrive causes your tranny to "gear hunt". As you accelerate your tranny will cycle through the gears. Once you've reached your cruising speed, it will drop into overdrive If that's what you've selected. The problem is that it takes very little pressure on the gas pedal to kick the tranny back down to drive, and after the pressure is released from the pedal again back into OD she goes. On a two-mile stretch of road with regualar traffic this could happen a dozen times easily. Heat is the enemy of a 700r4, and all that shifting really causes heat buildup. Take it from a guy who learned the hard way obout city speeds and OD......
On the same note, if you haven't installed an auxilliary tranny cooler yet, do it ASAP!!!! PM me if you have any questions, brother.
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I usually dont drive in overdrive unless I am out on the open road. I just keep the Tranny in D around town.
If your running gears and tires pretty close to stock. it doesn't hurt to drive it in overdrive under 65. But if you have tall tires and low(numericaly) gears it may be a good idea to use drive under 65. 700r4s like to be running around 1900 RPM down the freeway at 65 in OD. That way they are getting plenty of lubrication and cooling. If you are running less RPMs than that you may be doing harm to the tranny.
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I can't say I agree 100% on the gearhunt theory. It obviously works the tranny more, but usually won't cause an overheating condition as long as you run an aux. cooler. Can was right that it will cause the tranny to run a bit hotter though. The main thing that kills the 700 is lugging the engine in a range that won't allow your torque converter to lock up. Now this is gonna be different depending on the power/torque of your engine, converter choice, gears, tire size, etc. The main thing is make sure that the converter is locking up when you are cruising at a steady speed. Most times under 50mph that is 3rd or D. Another interesting item to point out is the downshift... the downshift from 2 to 1 is valved totally differently from when you are in D. Generally an unmodified 700 tends to wear the 1st gear out faster if you drive around in D. Supposably I guess it along the lines that towing is suppost to be done in D and regular driving w/ no load is suppost to be done in OD.
The best way to solve the whole debate IMO is buy yourself a tranny temp gauge and see what temp the tranny is running where... if no overheating occurs in OD then I would use OD... if heat seems to be a problem use D.
1987 Chevy K5 Blazer- 350 TBI
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FWIW, I would have my K5 going 50 in OD. 305, 3.08's, 31" tires. IF on flat ground. I would keep it in 3rd at all times, and manually shift to OD when I was going fast enough/conditions warranted it. Thats the way the tranny shop recommended to drive it, and thats what I did for about 3 years, with no problems.
Of course, I had an auxiallary tranny cooler as well, that was one of their other "must do" mods. Now I know its a good idea, at the time, I just did what they said.
If I were running gears that would allow OD at lower speeds (3.73's and numerically higher) without too much tire, I'd probably leave it in OD.
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