700r4 temperature

[brian wafer]

i installed a temperature senser in the back off oil pan on a 700r4.the gauge i installed only starts reading at 160degrees .over weekend took out my travel trailer in the woods where i could not pass 35 miles per hour because off dirt roads to reach a lake.on one long hill i was climbing in second gear the temperature was about 190 to 200 degrees down shift too first so it would turn faster wanting too try and cool it off but the temperature kept climbing so i stop for a 15 minute break and finish off the hill ok,if it wasn,t the gauge i wouldn,t off stop, i would off pulled it in second gear. what kind off temperatures are safe to hold,with senser in pan would a loc up manual switch help .i have a 6.2 with a banks turbo.thanks for any response.by the way the hill is 2.5 miles long there is no grade sign but its fairly steep.

[DmaxMaverick]

160° is minimal operating temp. Normal range is 160° to 180°. It should be fine up to 200° for extended periods, and up to 240° for short periods. Higher than that, even for very short periods, should prompt a service ASAP. You can give yourself a more liberal comfort zone by using synthetic fluid (Amsoil, Mobil 1, RedLine), which will protect the tranny and fluid up to about 300°. It has an added bonus of less generated heat, due to the nature of the fluid. A good aux. cooler is never a bad idea, either. The main tranny killer is fluid failure, due to overheat. The tranny hardware will hang in there, as long as the fluid is healthy, to a point, of course.

Your tranny will generate greater heat under higher loads with the TC unlocked, regardless of the RPM's. To get it to cool down quickly, you need to either remove the load, or get the TC locked. Slowing down lessens the load. Speeding up to get the TC locked (if safely possible) will generate less heat. Lowering the gear and increasing the RPM's will do little, if anything, to shed heat, as long as you try to maintain the same ground speed with the same load. The fluid friction will be essentially the same, with the same load.

[brian wafer]

thanks alot! i was scared 200degrees was way too high! i want too install a loc up switch,i read alot about it ,but i not sure off how to install it,some say just too splice in a wire, some say you have too get inside transmission to do correctly,do you know how its done correctly! or where i could get information.i will try too get synthetic oil in after figureing out for locup. THANKS!!

[DmaxMaverick]

The lockup bypass is simple for the 700R4. There is a "TC diagnostic lead" at the ALDL port. The brake switch is also in the circuit, which I toggle bypassed, as well. There is an electrical diagram at the "truck stuff pics" link in my sig. Just so happens the TCC circuit is one of the circuits highlighted (green, IIRC). My Blazer has had a lockup switch for over 15 years. I don't have a temp gage on mine, but the pan has never been too hot to touch (redneck temp gage). The tranny is original with over 1/2 million miles on it. Other than the lockup, I installed a shift kit and some upgraded hard parts into it very early on (the best that was offered in ~1988), as well as a performance converter, as a preventive measure. Still goes strong an bangs through the gears now just like the first time. I attribute the longevity to heat control and synthetic fluid. At the same time, it's eaten more 10 bolt rear diff's than I care to count (reason I upgraded to a 1978 12 bolt, which has been flawless).

It is more critical the TV cable is properly adjusted. Lower speed lockup allows for locked shifts, and this removes some of the buffer (TC fluid buffer). Off speed/pressure shifts can be detrimental to the tranny, especially with the buffer removed.

[Edahall]

At the same time, it's eaten more 10 bolt rear diff's than I care to count (reason I upgraded to a 1978 12 bolt, which has been flawless).

It is more critical the TV cable is properly adjusted. Lower speed lockup allows for locked shifts, and this removes some of the buffer (TC fluid buffer). Off speed/pressure shifts can be detrimental to the tranny, especially with the buffer removed.

You mention about locked shifts. Is locked shifts bad for the tranny? I also added a manual lock up to my 700r4 and I usually just leave the torque converter locked up all the time. When the tranny shifts into 2nd gear, the torque converter also locks up. I also make sure the tranny never shifts when there is any significant load on it. I let up on the accelerator each time I'm ready for the transmission to shift. My transmission is set up so that it won't even shift unless you let up (slightly) on the accelerator. I was also thinking that if having the transmission is locked up all the time, could be this be hard on the sprag gear? When I'm coasting (with the TC locked) , I notice the rpm's drop (to idle) so it must be the sprag that is doing the ratcheting.

It's interesting that you mention about eating 10 bolt rear differentials. I have never had one go out on mine with 1/2 million miles on it. I've done a lot of towing as well. I wonder if it could be due to gear ratios? I have 3.08 gears in mine.

[DmaxMaverick]

Mine's locked all the time, and as you, I let off during shifts. As long as the shift points are correct, it shouldn't be a problem if you aren't shifting under full power. Mine has a beefy Rhino (IIRC) sprag installed, which may attribute to some of the longevity. Your RPM drop is the TC unlocking at zero throttle input, which can be worked around (depends on the year and how your brake switch and/or TPS is in the circuit). The sprag allows for ratio advance as the bands engage, not coasting. One of the greatest benefits I've seen with a full time locked TC is the compression braking, which you are apparently missing.

I don't know about the 10 bolt failures. Could have been a bad housing from the start, causing a misalignment of the set, but I doubt it. Also, a higher gear ratio allows for more "meat" in the ring gear, and/or thicker teeth on the pinion. Both failed catastrophically each time (as well as the carrier), so I couldn't tell which failed first (no reusable parts). Failures all happened at low speeds under heavy load. Still, the 12 bolt 4.10 ring gear is heavier than the 3.73 10 bolt. My "heavy" towing was likely not the same as your heavy towing (would have been impossible with 3.08 gears, and barely possible with 3.73). On reflection, I was real lucky bad things didn't happen. Not a part of my history I'm particularly proud of, except surviving it.

[Edahall]

Mine's locked all the time, and as you, I let off during shifts. As long as the shift points are correct, it shouldn't be a problem if you aren't shifting under full power. Mine has a beefy Rhino (IIRC) sprag installed, which may attribute to some of the longevity. Your RPM drop is the TC unlocking at zero throttle input, which can be worked around (depends on the year and how your brake switch and/or TPS is in the circuit). The sprag allows for ratio advance as the bands engage, not coasting. One of the greatest benefits I've seen with a full time locked TC is the compression braking, which you are apparently missing.


Thanks for the reply. If I manually select 3rd gear (with TC locked) on my gear selector, then I don't get any RPM drop and I can take advantage of compression braking like you said (in 2nd and 3rd gear). However, if I select D on my gear selector (with TC locked), the rpm's can drop in every gear except 4th gear. I had always assumed that it was something else that was unlocking other than the torque converter. The RPM drops however makes the shifts a lot smoother. There must be something internal to the transmission that is unlocking the transmission.

[DmaxMaverick]

You must have a later year. What Y/M is it?

When I modified mine, I also went into the tranny and bypassed all the gear switches. Power applied to the TCC goes directly to the TCC solenoid, with no interruption, regardless of the gear. The hydraulic circuit will interrupt the fluid pressure below about 30 MPH (or 8 MPH in low range), though. It will not automatically unlock for any reason other than ground speed or about 99% throttle input. I was going to modify that, too, but never really saw a need for it.

[Edahall]

You must have a later year. What Y/M is it?

When I modified mine, I also went into the tranny and bypassed all the gear switches. Power applied to the TCC goes directly to the TCC solenoid, with no interruption, regardless of the gear. The hydraulic circuit will interrupt the fluid pressure below about 30 MPH (or 8 MPH in low range), though. It will not automatically unlock for any reason other than ground speed or about 99% throttle input. I was going to modify that, too, but never really saw a need for it.


From what I remember, it's a 700R4 out of a post 89 truck. The original 82 700R4 had been rebuilt numerous times and it finally died with a huge bang after I made some power upgrades. I had a top notch transmission rebuilder build me this transmission and so far, it has held up even when stressed with a 10k lb loaded trailer.

[DmaxMaverick]

I haven't messed with one newer than '87, so it may be different. You should still be able to bypass the gear range switches, though. I installed jumpers on the wires from the connector (inside) to the solenoid. The TCC has no input from the gear range pressure switches. Not sure if it will lock in first, or if it will unlock at low speed, but I've heard of the later trannies staying locked until the engine stalls at a stop. Robyn would probably know better than I. You should be able to bypass all but the first gear switch, I'd think. It depends on what you want in the end.

10K is a pretty fair load. Still a few K less than my stupid days. If the truck could haul it, it did. I wouldn't do it now with the same rig.

[Edahall]

I haven't messed with one newer than '87, so it may be different. You should still be able to bypass the gear range switches, though. I installed jumpers on the wires from the connector (inside) to the solenoid. The TCC has no input from the gear range pressure switches. Not sure if it will lock in first, or if it will unlock at low speed, but I've heard of the later trannies staying locked until the engine stalls at a stop. Robyn would probably know better than I. You should be able to bypass all but the first gear switch, I'd think. It depends on what you want in the end.

10K is a pretty fair load. Still a few K less than my stupid days. If the truck could haul it, it did. I wouldn't do it now with the same rig.

Yes, this tranny releases from locked just about when the engine is about ready to stall. If I stopped fast enough, the engine would in fact stall. I really like the programming on this transmission so I'll leave it alone.

Towing 10k was way overloaded for this rig however, I went to a rock quarry with my dump trailer and they overfilled it. I remember having to use two feet on the brake pedal to stop.

[aloharovers]

The tranny is original with over 1/2 million miles on it. Other than the lockup, I installed a shift kit and some upgraded hard parts into it very early on (the best that was offered in ~1988), as well as a performance converter, as a preventive measure. Still goes strong an bangs through the gears now just like the first time. I attribute the longevity to heat control and synthetic fluid. At the same time, it's eaten more 10 bolt rear diff's than I care to count (reason I upgraded to a 1978 12 bolt, which has been flawless).


How often do you change the tranny fluid and filter?
Standard duty cooler or hd?

Pete

[DmaxMaverick]

Changes have been about 30-50K, depending on how hard I worked it during the time.

Just a standard cooler, but it doesn't get hot when it stays locked up. I back off quite a bit if I have to load it up with the converter unlocked, and get it locked ASAP. A larger cooler probably wouldn't improve anything, the way I drive it. Temp control has been the key.