Ditto on that, Dan239!

 

Okay, I have one more question and then I promise to shut up, at least for a while.<br>From reading the posts, on my next trip, I would like to keep the truck to at least 2000 rpm while running in overdrive. Unfortunately, my first gen doesn't have a lot of extras, including engine tach. Could someone with a four speed auto transmission and with a tach, tell me what speed 2000 rpm occurs at in O/D and also in third? I'm going to post this also in 1st gen, so I hope no-one will be offended.<br><br>John

 

John H, depends on your rear axle ratio. ???

 

[quote author=Sierra Phil link=board=11;threadid=6898;start=45#69750 date=1037767974]<br>John H, depends on your rear axle ratio. ???<br>[/quote]<br>Duh! Sorry, I forgot all about that. 3.54:1 ratio.<br><br>Thanks John

 

John H., According to my calculation 70 mph should be about 2000 rpm in overdrive. 49 mph should be about 2000 rpm in third gear. <br><br>

 

At 2000 rpm mine is running 75 mph, but I have the 265 tires allso, so if you have 245's 70 would be close.

 

[quote author=Sierra Phil link=board=11;threadid=6898;start=45#69952 date=1037810555]<br>John H., According to my calculation 70 mph should be about 2000 rpm in overdrive. 49 mph should be about 2000 rpm in third gear. <br><br><br>[/quote]<br><br>I agree that 70 Mph is about right in O/D. However, I think the 3rd gear speed of 49 MPH is way too low.<br><br>Please double check your calculation.<br><br>Dan

 

John, D, Overdrive ratio for automatic is .69 compared to 3rd gear of 1.0, this would mean that in 3rd gear the engine rpm is approximately 1/3 greater in third gear than overdrive. To maintain the same 2000 rpm the speed would be reduced by approximately 1/3 which is 49 mph.<br><br>Here is the math:<br><br>70mph x .69 ratio of change = 49 mph<br><br>Ratio of change = .69 overdrive ratio/1.00 3rd gear ratio

 

Phil <br><br>You are correct. I even checked it with my truck and I am running just under 50 MPH at 2000 RPM in 3rd gear. I just did not think there was that much difference. It seemed too much to me. I hate being wrong, but it is better than holding on to a position of error. Thanks for the correction.<br><br>This has raised a question. It seems that many have mentioned that their automatic locks up the T/C in 3rd gear. Mine is not doing this. Is it supposed to?<br><br>Dan

 

Yes Dan you should have 3rd gear lockup. If your running around 50 at 2k you are most likely in 3rd lockup.

 

That's what I'm getting running 245's ,,,, 50mph @ 2k in 3rd and 70mph @ 2k in OD.

I know how you felt Dan, it took me a while to figure out if mine was locking up in 3rd. It's not as pronounced as hearing 4th unlock go into 4th lockup. This is why I had some problem when I towed in the mountains with the new 5er climbing Black Mountain on I-40. When I came out of OD, it went into 3rd unlocked, at which time I should have given it time to go into 3rd lockup by not being so aggressive on the throttle. However, I didn't do that and saw my trans temp rise to 220+ by the time I got to the top. After realizing what I was doing wrong and changing my driving habit a bit,, I don't have that problem any more. I don't know if all the trucks shift this way, but I think I know how to drive mine so that it performs the best when towing. I've found that my trans temp gauge is the best indicator of when the TC isn't locked,,,,,,, Man the temp climbs fast!!
Has anyone else felt like their trans has stayed unlocked for too long or had an experience as I have just described?

 

dan239, I don't want to sound like I know it all, just toop my experience from two trucks and did some calculations.<br><br>You should have a torque c lockup in 3rd gear. It is sometimes difficult to detect. On my 98 the only way you could detect 3rd lockup was when it was locked out of 4th. Then under light throttle, accelerate from a stop slowly and count the shifts, 1st to 2nd, 2nd to 3rd, and 3rd to locked converter. Under light throttle lockup occurs above 40 mph. Another way to detect 3rd lockup is to be towing and before you start up lock out of OD. If the grade is a steep enough one and long enough you will gradually lose speed down around 50 a slight increase in pedal will cause it to prepare for a downshift and unlock torque c. without a downshift. You will notice an rpm increase by the sound of your motor .

 

Thanks guys, I will check it out.<br><br>The reason I do not think the T/C was locked up is, in 3rd gear and running about 45 or 50, I can accelerate just slightly and the RPMs will go up before the speed increases. This indicates slip of the T/C.<br><br>In O/D and lockup, the RPMs will not change unless the speed increases because it is direct to the rear wheels and no place to slip.<br><br>If I am in 3rd and locked up I should get the same reaction, unless I am missing something here.<br><br>Dan

 

dan239, what you have described is normal behavior at that speed. You are so close to the minimum speed for lockup that a change in engine speed will cause it to go back and forth. <br><br>Try this. Lock out OD and take it up to 65 mph hr steady then let up on go pedal suddenly while watching rpm. It shouldn't have drop suddenly at that speed. My 98 helt steady under the conditions I just described because it wasn't near a downshift speed.<br><br>When vehicle is near a possible downshift speed and you let up on the throttle it will unlock and rpms will drop in anticipation of a shift.<br><br>Hope this helps. 8)

 

[quote author=Sierra Phil link=board=11;threadid=6898;start=45#69952 date=1037810555]<br>John H., According to my calculation 70 mph should be about 2000 rpm in overdrive. 49 mph should be about 2000 rpm in third gear. <br>[/quote]<br>Thanks Sierra Phil. On my way home tonight, I locked it out of O/D and floored it in third. It peaked out at 70 mph on the flat. Using your calculation method, I judge that to equal about 2850 rpm. Does that sound a bit high for the 1st gen, or am I just reading high on the speedometer?<br><br>John