I have 95 6.5TD 2500 GMC 4x4 that according to my RPO codes has a 3.42 - I tow a 26' long and weighs around 14K fully loaded (most of the time we only haul with it half loaded so approx. 11-12K) and wanted your imput with pulling with this. How much would it benefit to get new axles with lower gear ratios?
I am just looking for imput of what you have and what you do with your truck.

I realize that this trailer is realitively large and we know that we are going to have to invest in a larger truck - but right now financially we are better to do the exhaust, cooling upgrade, air filter kit, and fan clutch. (a couple thousand is better then $40,000)

Thanks for your imput:cool:

4.10's are the standard gear on most F engine trucks. I can't imagine 3.42's

I have a 3.42 axle ratio in my suburban and as a result it is only rated to tow 6,000 lbs. I think with 4.11s it was rated at 10,000.

The truck pulls the trailer up the road fine just when we get to a big hill we put her in low range 2nd gear and slowly go up. It seems to work better that way - but you think I should look into finding a 4.10 - I would have to get a front and rear because my truck is 4x4. Or do you think if we haul it carefully that we can make this work for a couple years until we upgrade to a bigger truck (dually). I haven't done any checks on where its speed is at 1900 rpms yet but I also need a flat surface to do that on and that is hard to come by here.

Do the mods you mentioned and then try it and see what you're up against

11-12k most of the time and you should be OK with what you have.

Do the mods you said, and you'll be even better.

Make sure to add a chip...

Hey Diesel Chick;

I go along with doing your power upgrades, and cooling pulling that kind of wieght in the summer you will need the cooling upgrades no matter what gearing you have. If you do change gearing you will lose MPG when your empty too.
I would also change the factory transmission pan, get an deep pan that is aluminum it will help cool the tranny and with an added 3-4 quarts more transimission fluid it will stay cooler. Change the tranny fluid and filter once a year or twice if your doing plenty of pulling. Do your exhaust, intake, and gauges and chip it. If you have larger than standard tires (245-75-16's) go back to them as larger tires act like higher gearing. Aslo let us no speed and RPM as like I told you in the e-mail someone may have changed the gears before you. With that kind of wieght you might talk with Bill Heath too and check his water injecton, I don't know if you haul water with you in your trailer, but there is guy that uses his travel traler water tanks for water injection. The water injection isn't too bad like $249

What kind of mileage do you get with the current setup without a trailer? And what are your RPM at 70?

I have 3.42's and run about 2050rpm's at 75MPH. I wish I could find 2.73 gears, but I don't think GM or aftermarket make them that high for the front diff. I don't tow anything but with the mod's I have, I don't think I'd have a problem towing anything, even with the 3.42's. If you have 5min and a jack you can find out what gears you have by getting the rear axle in the air, turning the drive shaft and counting the turns to get one full revolution of the tire.

My 93 chevy c2500 has 3.73 gears. I pull a 29" and a 36" travel trailer with them. The only trouble i have is when i pull the hills, i have to gear down. otherwise, i can pull them both along around 70 without too much problem. seems like i am the oddball around here; everyone seems to have either 3.42's or 4.11's.

I switched the gears out in my truck. I started with 4.10 and went to 3.42. I usually only haul the kids around and was looking for economy. I have towed a large goose-neck with a '72 Wagoneer aboard and did fine. But that's nowhere near the weight you're talking about.

Well I finally took my truck down a "flat road" to see what my RPMS were - at 1900 RPMS I was around 60-65 mph. So is that still a 3.42?

sounds right

Automatic? I would definetely get a transmission temperature guage. As said, stick with the stock sized 245's- anything larger will make it worse. I would also be carefule using low range towing on asphalt. With a loaded truck, the rear tires are a bit compressed, therefore "shorter" then the fronts, and the differnece in tire height could do more damage then good to your drivetrain under that much strain. 1st gear high range should be just as good. I tow about 10,000# with my 3.73 truck, and rairly do I need 1st gear on the mountain passes around here.

My tires are 265/75R16 - they are huge they are just a heavier ply tire to withstand the weight of the trailer. We are going to be getting the guages, so that won't be a problem and I am going to look into the larger transmission pan - for all I know it may already be on there I'll have to ask Nathan. The transmission fellow up hear that we talked to stated that we should put her in 4 wheel drive low and second gear when climbing a steep hill - we don't usually use it all the time normally just when we are almost to our destination in the hills. For the most part we are planning our trips around the terrain to get there - as long as it is flat or has rolling hills we are ok (did Virginia this past Fall - long trip - too many big hills on route 68 - will never do that again with this truck - but she did and in one piece - GO GMC!)
Like I stated earlier I realize that this is not a truck that is going to uphold towing this trailer a lot I just want us to be able to go somewhere at the max a couple weekends a month during nice weather and get us there with no problems. Then once we get a new truck my truck will be used as the back up.

My Suburban has the 3.73's and I run the 265/75-16 tires as well. Most of the time just a big-capacity family highway hauler, 2000 rpms give me just over 65mph, indicated. On the northeast corridor I am hesitant to go faster as my efficiency really suffers. Times like this I wish I had the 3.42's. When I tow a trailer, which is relatively seldom, I am happy with 3.73's. I do not know how folks can take 4.10's, you reaaly need to rev the NON rev-happy 6.5 just to stay with traffic.

DieselChick;
Your turning the same RPM's at speed that I am so I would say you still have the 3.42's. If your tires are real good take them off save them for when you get the new truck. Get some good 245-75-16 E rating that will help some. Later you can use the larger tires when you don't tow, or sell them to some one or swap with some one in the area who wants bigger tires. I would NOT put the money in to the gearing, I would put it in other things and many of those will provide more power and not hurt your economy when your not towning. When I tow 10,000lbs+ with my 3.42 I do it in 3rd rather than over drive that will help, you turn about the same RPM in 3rd with 3.42 as 4.10's do in OD. I'd bet if your BF can do the work and you keep him smiling you can make it a decent tow rig for $2500-$3000 if your carefull werre your buy your stuff. negotiate with vendors for a package discount if you can buy several or all items together. Bill Heath is great about givng package Discounts and I'd bet JK would too.

I have a 96 with the 3.72 and 5 speed all box stock. Every 3rd day it hauls a 14000lb loaded trailer seven miles along and 800 ft. up. It'll hold 40-45 mph on an 7% grade in 3rd if I have a good running start. Does it nicely but I do worry about the u-joints.Cooling could be a problem if the haul were longer.

When you have higher gears 3.73 or 3.42, smaller tires make the final drive lower. Making the final drive higher with taller tires would make it worse when you're crawling uphills.

with 4.10's and a heavy trailer it's all I can do to keep steady 65-70 mph MPH at 12+psi boost going up a tall hill. used to raise the ECT's some too, but I have to see what the IC will do for that.

When we tow we never have it in overdrive - Always 3rd - Hauling 101. I don't think I will have to work very hard to get BF to put in the stuff seeing how he really likes the trailer plus I told him that when he goes to shows with me that we can fit his motorcycle in it so he can go riding when I am showing so it all is good. He drives Milk Truck so he doesn't have to time to research info on the truck that is why I am here.:)

We just put this tires on last fall so I will have to talk to him about that - I think I will wait though and see what happens after the mods are done.:grd:

Diesel Chick,
Look in your glove box for sticker with codes listed there, then look at RPO code list in FAQs it should show what equipment your truck came with originally.

TURBINE DOC

I did that - that is how I figured out that my axle was a 3.42.

DieselChick,

Keep a handle on your rear differential temperature. With the kinds of weight you're carrying, you're putting some stress on the rears. Just make sure you don't boil it over. After towing up a long grade, loaded, pull over someplace safe and put your hand on the diff. cover. If it's too hot to touch, then I'd be addressing this issue you're pondering. Maybe looking at a finned cover to start with and if that doesn't bring the temps down, then you may be looking at other solutions.

No one has mentioned this, so I thought I'd chime in.

Thank You Snowdrift - Everyone's Imput Is Helpful!

[QUOTE=DieselChick]My tires are 265/75R16 - they are huge they are just a heavier ply tire to withstand the weight of the trailer. We are going to be getting the guages, so that won't be a problem and I am going to look into the larger transmission pan - for all I know it may already be on there I'll have to ask Nathan. The transmission fellow up hear that we talked to stated that we should put her in 4 wheel drive low and second gear when climbing a steep hill - we don't usually use it all the time normally just when we are almost to our destination in the hills. For the most part we are planning our trips around the terrain to get there - as long as it is flat or has rolling hills we are ok (did Virginia this past Fall - long trip - too many big hills on route 68 - will never do that again with this truck - but she did and in one piece - GO GMC!)
QUOTE]

If your tranny guy is telling you to tow in 4 low and in second, he is trying to get you into his shop fast to take your money. You will grenade u-joints faster than you can replace them in the front too, even with an open carrier which I am ass-u-ming you still have. 4 low on pavement towing for any distance is, in my opinion, a VERY bad idea. I am sure someone will disagree. Oh yeah, never tow in overdrive, especially that weight!

Power mods look like a nice additive to your setup. . . but with that kinda gearing, I don't think that the crank would be too happy. You could make lotsa power, keep the engine cooler, but dats a bunch of torque.

Let me ask you this. How long do you want to keep this rig? Is it your everyday wheels, or more like the tow rig only? I *think* gearing may be better bet on engine longetivey (which is the side I like to err on) That may be a more expensive approach to this, but will help the engine in the long run. If you are only going to keep this for a few more months, to a year, that may be more money than you would want to spend on this one.

I guess it all boils down in the long run to how much moola would you like to fork out on this rig? By the time you have spent money on all the mods to bring this up to a great tow rig, you may have just bought yourself another vehicle. The 6.5 can be picked up at a really good price nowadays. You may want to just find another one a beef it up a little and you've got yourself a great rig.

Just a thought.

Diesel Chick,

I used to tow a 34' gooseneck with living quarters and a Jeep in the back, I was usually about 21,000 gross for the truck and trailer loaded. I was running a good running 6.5 with free flowing exhaust and a 5 speed. I had 4.10 gears and 35" tires which would bring me down to 3.73 with 31 inch tires. It pulled great, 2nd gear up any hard pull, held about 12 psi of boost and the only concern was water temp which on occassion hit 220f. Worst case scenario with 3.42 gears would be having to use first gear, instead of second, keep your rpm's at about 2800 rpms. Sythetic 80/140 in the rear end will keep it happy. I would invest in egt, boost and trans temp gauges before doing any thing else. Next would be open up the exhaust to a madrel bent 3" minimum with free flowing muffler or straight pipe. With the gauges you will be able to see what your turbo boost is doing. I have seen many "Weak" 6.5's that simply were'nt making turbo boost over 5 psi and according to GM that was acceptable from a service stand point. Are you having any cooling concerns pulling this trailer? When was last time fuel filter was changed? Sometimes we overlook the real simple things. Good luck:grd: Also, I tow on the heavy side still and now I tow a train during hunting season- Suburban-towinging 8000lb 26' Jayco with a 14' stock trailer behind it with 3 horses:muahaha:and like a dummy I was trying to resize the picture and I screwed it up, so you will just have to take my word for it.:rolleyes:

I used to pull a 35' gooseneck triaxle dually trailer with a D3 dozer on mine no problem. The manual tranny helped out the most for that though. I have no idea what the tatal setup weighed, but I know it was well over 20,000#. I was definitely breaking some DOT laws, but that's ok isn't it? As far as re-gearing, by the time you are done doing that, unless you can do it yourself, and all the mods to make this truck competant, you will have spent enough for a pretty substantial downpayment on a new, or newer truck. The gearing alone will probalby cost you about a grand just for the labor if it is done well. Just make sure you break them in before towing!!!

Dear mr. moderator . . .sir, uh, um, Dixie Chick is not equal to Diesel Chick. Just wanted to keep some flames from eruptin' over any differing policital views.:jawdrop:

TURBINE DOC

I did that - that is how I figured out that my axle was a 3.42.My apology I see that now when going back to top of starter thread but picking up at end, the topic heading, read to me more as a question; and I didn't see gear ratio in your sig added to confusion on my part.

I pull 18K GN trailer when my backhoe is on it using my 3:73s , no problems doing that with my mods, gages-gages-gages can't say enuff about them, you need to know when to back off, or you potentially will be walking.

My appology, I fixed it, but in my defense, I did have the first letter of each work correct.......:rolleyes:

If your tranny guy is telling you to tow in 4 low and in second, he is trying to get you into his shop fast to take your money. You will grenade u-joints faster than you can replace them in the front too, even with an open carrier which I am ass-u-ming you still have. 4 low on pavement towing for any distance is, in my opinion, a VERY bad idea. I am sure someone will disagree. Oh yeah, never tow in overdrive, especially that weight![/QUOTE]
The Tranny guy does just tranny's and he knew my boyfriend is a mechanic so he wasn't go to be doing any work for us. We has overheated the transmission once climb a back mountain road that was pretty steep with curves (fastest we could go would be 10MPH) When we got to the top we put her back in 3rd and realized that we weren't shifting out of 2nd so we thought we lost 3rd gear - we unhooked the trailer and he drove it around trying to get it out of 2nd and he could so we crawled home (about a 1 away from home but felt like a lifetime) and let her sit at the barn for a couple days - since we figured we would have to drop the tranny and get it rebuilt by this guy (he does a great job for around 3-400) when Nathan drove it the his buddy's shop to hook the computer on it, it shifted fine. He called the fellow and he told us that it has a anti-destruction device that keeps it in 2nd. All we had to do was shut her off and let her cool down then we would have been good to go. He did tell us to change the tranny fluid and filter which we did. When we climbed the hill we had her in 4 low and 3rd gear and when she tryed to shift into third she did it hard. That is why the fellow told us to simply put her in 4L and 2nd so she would try to shift into 3rd and since we were only doing it occasionally and on mountain roads we would be ok. And a u-joint is still cheaper then a tranmission.

That's called limp mode and I've turned the truck off at 55mph and restarted in N to keep moving. :D

The 4wd relay's stick sometimes and keep the front pumpkin turning even with the Tcase out of 4wd. The last time this happened I went 20 miles hauling 3 tons and smoke started coming out of the front pumpkin, gear oil was getting pushed passed the seals on the third member. The relay disengaged as soon as I turned the truck off for a few minutes while I was looking at the front end.

[QUOTE=knkreb]Power mods look like a nice additive to your setup. . . but with that kinda gearing, I don't think that the crank would be too happy. You could make lotsa power, keep the engine cooler, but dats a bunch of torque.

Let me ask you this. How long do you want to keep this rig? Is it your everyday wheels, or more like the tow rig only? I *think* gearing may be better bet on engine longetivey (which is the side I like to err on) That may be a more expensive approach to this, but will help the engine in the long run. If you are only going to keep this for a few more months, to a year, that may be more money than you would want to spend on this one.

I guess it all boils down in the long run to how much moola would you like to fork out on this rig? By the time you have spent money on all the mods to bring this up to a great tow rig, you may have just bought yourself another vehicle. The 6.5 can be picked up at a really good price nowadays. You may want to just find another one a beef it up a little and you've got yourself a great rig.


Just as a quick response to this - This is my truck (my first truck) that I drive every day Nathan and I understand that this truck is not going to be able to hold up to a lot of pulling - he is a mechanic so he is doing all the mods (he also drives milk truck so he understands trucks and towing) The truck tends to get to warm for our liking hence the reason for wanting to put mods in it to keep it cool - in another year we plan on buying a newer dually that will be our main towing rig and my will be just a back-up. Right now we have to fix the CDR and I think there is something wrong with the wastegate - he is going to put it on the computer again to get the codes so we can figure it out. As I stated in previous posts we are looking at only going once or twice a month and the farthest place I have scheduled this year is to the Stuart Trials in Victor, NY which is approximately 3 hours away.

Everyone's imput has been soo helpful not just for this truck but also for when we purchase a newer truck - I am beginning to understand these axle ratios. :p:

Everything you keep saying points towards the need for gauges. Boost gauge, will show you if your turbo and wastegate is working propperly. Pyrometer, will let you know if your exhaust is getting hot enough to damage something expensive in the engine. Tranny temp gauge, will let you know if low range is needed or not. The transmission is going to generate a lot of heat from running slow with a heavy load, because the torque converter is unlocked and the slipage is generating a lot of heat. Low range lowers your effective gear ratio so that less load is on the transmission. Add the biggest transmission cooler you can fit. Avoid use of 4wd low range on pavement, dirt road would be fine. 4wd on pavement is going to cause gear bind, especially when going around a turn. Gear bind doesn't care what part it breaks, it will always be the weak link. Sometimes gear bind can occur and the tire with the most load from the gear bind will slip. If the tire doesn't slip, breakage results. It could be a u-joint or a transfercase chain or a axle shaft or a ring and pinion set. It could be minor or major. If you really need to be able to use low range in the transfer case, you will need to put an interup switch to keep the front axle interlock from engaging. Then you would have 2wd low range and no gear bind. In order to do this the wires that go to the front differential interlock needs to be run through a separate switch. In you current configuration the interlock is energized when the 4wd shifter is placed in the 4wd mode. In this mode a switch is energized that supplies power to the front diff interlock. By putting in a separate switch you could interupt this power supply and thus the interlock will not engage. Flip the switch and the interlock would engage as normal. I hope I have made this easy to understand.
Next question, when you were towing up the steep grade that you limped tranny on, were you in 1st gear or 2nd? If you were in 2nd, shifting to 1st would have helped lower trans temp, if you were already in 1st then you have no other alternative than low range. 1st gear high range should be about 2.48:1 where as 2nd gear low range should be about 3.97:1., assuming 2nd gear to be about 1.46:1(I might be off a little on this) To further calulate your final drive ratio, transmission in 1st gear, 2wd, 2.48 x 3.42=8.48 final drive reduction, if you had 4.10's, it would be 2.48 x 4.10=10.16 final drive, compared to 3.97 x 3.42= 13.57. So it appears that 2nd gear low range is much lower than 1st gear high range even if you had 4.10 gears. It is even lower than if you had 4.56's which would only calculate out to 11.30:1. One other thing to consider is whether or not your transmission torque converter is locked or unlocked when trying to pull your load up such a steep grade. One trick is to gently tap the brake pedal while driving up the hill and see if your rpm's go up, this would indicate that the converter was locked and is now unlocked, giving your engine a little more breathing room. I hope this helps a little.:rolleyes:

Now that I realize this is a LD "S" engine with a 6 lug 9.25" sf with 3.42 gears in the rearend, I question how wise it is to tow the weight you have been towing up mountains? It makes since that you drop it in 4wd L but I think you should wire a toggle switch to disable the frontaxle thermal actuator so that you can tow in 2wd L for a much better final ratio and you should be able to use all gears (including OD!!!) in 2wd L.

We techincally have only had to do this three times - once when we went to the Flying W - and we only did it for maybe a 1/4 of mile if that and that was because we were trying to keep th engine cool - with the cooling mods we shouldn't have any problems with that - second time was when I made a navigational error and we went down a hillside that was pretty steep and curving below youngstown oh and that was when we initial learned about the limp mode in the tranny. The third time was in VA which we will not be doing again until we have a new truck because that was way to much for her. Everywhere else we went we never had to change anything. So the 4 wheel drive low was simply to keep the motor cooler - and with the mods we want to do we shouldn't have to put her in 4L anymore.

QM;
If Diesel Chick does have a S engine 6 lug wheel the she has much the same set up as I have except I have short box and 2 WD. If they where on a gravel road and in 2 low I would also have run it in 4x4 (if I had it) heavy loads on gravel at low speeds can casue your wheels to spin out and cease up hill progress. (been there done it got the soiled shorts for proof) If your on gravel towing a heavy load and you start spining tires you can eat up tires like real quick.