What gear to tow in? 6spd

[forcefed88]

I am sure that it has been covered before, but what gear do you tow in?

I know that you want to keep the engine in the right RPM, but I have been told that the ZF trans can not be run under heavy load in 6th gear. In 5th everything is 1:1 and the gearsets stay at a good temp. In OD the headset temps get too hot and basically start melting the metal.

My trailer weighs 10-12K depending on where I am going.

Does anyone run a cooler on their 6spd?

Thanks

[Believer45]

Your 6 speed has a transmission cooler on it from the factory. I would keep an eye on the temperature (install a gauge if you don't have one) and run the highest gear that will get the job done without lugging the engine. You should be able to tell when the engine is working too hard.

A pyrometer is a better indication of engine load. If you have one and the sensor is mounted in the exhaust manifold (pre-turbo) it will give you constant and almost immediate indication of the load on the engine. If temps go too high (1200 degrees or so) drop a gear and/or back out of the throttle until things cool back down. I have read that ideal operating temperature is in the 600-750 degree range for fuel economy so that can be taken into account as well.

Dave / Believer45

[Frankenstien]

I tow a weight slight higher than yours... set the Cruise in 6th..... and tow all day....

[jimmy]

I tow 16000 pound and 19000 pound trailers with my 6 speed in 6th all the time. I put synthetic oil in the gearbox when it was new as I have done with the other 5 and 6 speeds and have never had a problem with any of them.
I admit that 5th is stronger as it does not stress bearings very much at all since you are directly ataaching input from clutch to mainshaft w/o use of counter shaft. If you don't lug it and you put something better in it than regular Dexrom ATF, the trans will give long life with no problems.

[forcefed88]

Thanks for the replies. I am going to put a synthetic in it this week.

I was honestly was disappointed with this message board at first. I sold my cummins and bought the PSD. The Cummins forums are overwhelming with help when you have a question more difficult than where to mount your XM antenna. I posted early about a smoke issue, and have gotten almost no response.

I appreciate everyone's advice on this trans issue.

Thanks

[Pat Dolan]

I think the overheating in 6th thing can only be found in the advertisements from one certain OD manufacturer. It is complete BS.

I pull 26k with what was until now a nearly stock (maybe 250 HP) 7.3, and I have lost some gearboxes, but nothing to do with their strength, just the failure of pilot brgs that will cause the cluster gear to lose the tips of the teeth.

A while back, I got USGear to build an experimental 0.8555 OD to split 5th and 6th evenly, and instrumented the gearbox, OD and rear axle to collect data. The main trans will only get up to 220F or so with a half hour climb up a 6% grade, using lots of indirect gears. The ideal high end temp for trans lube oil is in the 250 - 300F range. I can run flat out in 6th and direct in the splitter for hours on end at 80+ (only do that once in a very rare while on emeregency callouts) and in that case, can't get the main trans over 240F.

BTW, I had always been told that the rear axle gets so hot, "it blisters the paint on the cover". I found out that I had lost some rear ends, not due to overheating, but due to water accumulation. So, obviously, the rear axle doesn't get anywhere near 212F. In my current setup (increased capacity plus a lot of cooling area added), I need a pretty good hill in the summertime to get the gauge off the bottom peg, and have never seen the topside of 160, and believe me, I am trying.

And, of course you are right, in 5th there are no countershaft gears loaded, so the gearbox runs really cool. If you have the right gearing, it wouldn't hurt one bit to run in 5th all day long.

Pat

[forcefed88]

Pat, thank you very much for your reply. You obviously know your stuff.

What brand fluid do you recommend/use in your trans and rear diff?

Thanks

[Pat Dolan]

I use Mobil 1 synth ATF in the gearbox and xfr case and their 75W-90 full synth in both diffs. Any one of the real synths will do just fine, but I like to keep one brand in the shop and, since I use Delvac 1 in all of the engines around here, it is easy to be able to pick up any other product while I am at the bulk plant. Also, I have a thing about paying dues to the originators of mass market full synthetic lubes.

(No I have never worked for them oir been their customer - they were always my competitor).

Pat

[lee_redneck]

I just made a trip across the country, WA to VA Via I-10, pulling a 18' car hauler weighing in at @8000lbs loaded with @3000lbs of tools and household goods under the camper shell. I couldn't tell I had any weight behind me or in the truck. I made the whole trip in 6th gear with the cruise control on, with the exception of @250 miles through the mountains of OR and CA on I-5. I filled the gear box of the tranny and transfer case with Mobile 1 synthetic ATF and didn't have any problems. I did the speed limit the whole way, 70 in same places, 55 in others. I averaged 13 MPG overall on the trip. Not as much as other's state they experience, but I was happy with it. The only time my pyrometer ever got close to 1100 degrees was through the mountains, but on the flats and hills, I averaged 600-800 degrees. I Love my truck.

Lee

[BIG JOE]

I have a Trans Temp gauge on mine, pull a 12K+ FW. My Trans temps have never been over 130*. I've pulled my FW all over the country, over most of the "Big Hills". Never a heat issue. 6th (OD) gear on CC most all the time. 5th & 4th when needed. I put RedLine synthetic in the ZF at about 30K, 86K on it now, no problems.

I keep my RPMs at, or above, 2K, on CC, EGTs never higher than 850*, or so. When I come to a grade, I shift to what ever gear I need to be in to maintain 2600 RPM and 25 lbs of boost. For the most part... 5th gear is my Pull'n gear. 4th if traffic gets me.

As Posted, the 6 speeds Have a trans cooler. By what my gauge tells me, I don;t think I need any additional cooling.

[img]/ubbthreads/images/graemlins/shrug.gif[/img]

JOE

[forcefed88]

Man thanks for all the replies. I really appreciate everyone's input. I am going to change out all the fluids today. I had to tow about 250 miles last night. Kept it in 6th with the CC at 75. I was only hauling about 6,000#'s.