Gears

[Andylad13]

Got some questions, new to the site. thinking about gearing. i have 4.10s in my diesel now and was thinking of a higher ratio like 3.73 or 3.55. i was surfing a thread and someone insisted on 3.05? how does the diesel like that high of a gear? i do some towing around 5,000 average and have pulled 9,000lbs before. i know that the gearing is going to affect the towing substantially and i would probably never pull anything close to 9,000 ever again with a high gear but i would like to go faster than 55 on the highway since the limit is 65 here. when im traveling even 55, she's at 2k rpms and thats alittle high for my diesel especially in the summer time when she overheats at even that speed on the highway.

 

[Exekiel69]

2k at 55mph with an e4od? I don't have one on mine but seems like something is wrong there.

 

[tonkadoctor]

3.05 isn't available. 3.08 is for the 10.25 sterling.

I swapped from 4.10 to 3.08 as a fuel economy experiment. 3.08 is OK for running around empty all the time, hwy fuel economy at 62 mph went from 17/18 to 21/22. Towing much more than 5k took a while to get to 60 mph and was having to drop to 4th on the zf5 tranny to pull small grades.

You also can't get a speedometer gear to calilbrate it properly with 3.08 gears and stock 235/80/16 tires and will always be about 5 mph off.

Enjoy.

 

[MUDKICKR]

i think i would just put a small lift on it or add a leafs and bigger tires. reason is when you want to tow with it go back to the stock size and it will be the same as factory, and put like 35"s on it to drive and knock the final gear ratio down and get better milage. Just a thought i mean a 235/85r16 is 31 inches tall, 4.10-1 with 35's you would have a final gear ratio of 3.63-1, or with 36's it would be 3.53-1 it would be like the best of both worlds

 

[tonkadoctor]

i would like to go faster than 55 on the highway since the limit is 65 here. when im traveling even 55, she's at 2k rpms and thats alittle high for my diesel especially in the summer time when she overheats at even that speed on the highway.

This just caught my eye reading it again. Going to a higher gear ratio will make an overheating problem worse not better.

If you are having an overheating problem going over 55 & 2000 rpm it ain't your gearing, it's your cooling system. Only time I ever overheated one of my duallies was on my 2000 and it was because the waterpump failed.

Even ran the 2000 through the Ozarks in Missouri this summer grossing 20,000 lbs dragging an overloaded 24' haulmark enclosed trailer at a constant 80 mph in 100F temps for a 160 mile stretch and the temps never got hot.... and that truck had 4.10 gears too. Sure was a thirsty truck running that hard though... 6 mpg ..... backed back down to 70 and below for most of the rest of the trip to Texas because of the poor fuel milage.

These trucks should run all day under governed RPM and not overheat. Might be time to recore or replace that 18 year old radiator or find out what is really wrong.

BTW...... How are you determining that it's overheating, if it's overheating just by the factory gauge, they are notorious for being wrong... get a real mechanical guage on it.

 

[Andylad13]

Cool, i got some feedback that is actually usefull. tonkadoctor, the guage might be faulty thats for sure, heres whats happening. when its cold out, i can drive 65 all day long and be in the "O" of normal on the guage. when its hot and i do 65, mainly towing than unloaded, ive had the guage passed the damn "L" in normal and the engine light came on. so even if the guage is faulty and inaccurate, the sensor thats reading the temp knows shes hot enough to cue the engine light to turn on.

when i drive normal speeds like on country roads it will never get hot, even on a hot day she might get up to the "M" in normal and if i drop the speed down like 5mph, you can literally watch the temp decrease. for that reason i am almost sure that the cooling system is operating correctly.

I swapped from 4.10 to 3.08 as a fuel economy experiment. 3.08 is OK for running around empty all the time, hwy fuel economy at 62 mph went from 17/18 to 21/22. Towing much more than 5k took a while to get to 60 mph and was having to drop to 4th on the zf5 tranny to pull small grades.

was this swap with your 6 liter or with a psd or idi?

i think i would just put a small lift on it or add a leafs and bigger tires. reason is when you want to tow with it go back to the stock size and it will be the same as factory, and put like 35"s on it to drive and knock the final gear ratio down and get better milage. Just a thought i mean a 235/85r16 is 31 inches tall, 4.10-1 with 35's you would have a final gear ratio of 3.63-1, or with 36's it would be 3.53-1 it would be like the best of both worlds

it might be counter productive for my diesel to spin 4*36"tires for better fuel economy.
thanks to everyone for replying and giving me advice.

 

[aaklingler]

It sounds like you have a cooling problem, i'd start with replacing the radiator. If you do a lot of towing I'd probably stay with the 4.10. 80 mph might be plenty fast but I've run diesels with 4.10 at 70 mph. If you really want to change gears I wouldn't go any higher then 3.73 if your towing much.

 

[tonkadoctor]

I did the gear swap in my IDI. If I was towing all the time I wouldn't go below 3.73 gears, nice compromise between 3.55 and 4.10. If it's mostly just a go to work and the store ride and tow only once in a blue moon then 3.55 would be fine and just expect to drop a gear or 2 when needed.

Also, I've had 2 gasser 4x4s that I put big tall wide tires on and both times the fuel milage went down by as much as 4 mpg on just a 3" to 4" taller tire. I'd never recommend that as a way to increase fuel economy.

Test or replace the sensor for the idiot light and gauge and check it againt a mechanical gauge to see what is really happening before throwing money at the cooling system. That stuff can get spendy really fast just throwing parts at it and not actually fixing the real problem.

 

[Agnem]

Might be time to test that fan clutch too. Get a real gauge before you do too many experiments.

 

[Cowboy_Customs]

If ya want some better gears for all around towing/driving, and this is based on my towing lately in the Northeast. And I know the terrain yer on up there in Conn. I have 3.55's in my '92, and its an absolute dog with 3K+ in tow on a little grade untill I drop it into Direct. I acctually found its sweetspot bringing the horse home from Cornell university up in Ithaca today. 1900RPM's. I held any hill I wanted as long as I was at 1900+RPM's in anything but overdrive. Without any smoke on 3/4's of a turn on the fuel screw (where 1 full turn bottoms out the screw )

SO, based on my current engine condition, fuel, trans, ect ect ect. I think 3.73's would be a nice compromise for my daily driven tower.

 

[Exekiel69]

Before replacing any parts You can wash Your radiator, just grab a garden hose (when the engine is cold) and spray gently against the fins (meaning don't make holes with the pressure), You can also spray the rad with some engine cleaner and spray more water after You let it sit a few minutes. This rads can get build up with a lot of crud some times and give the idea it is clogged inside, give it a try it will cost You nearly nothing.

Now You could test Your t-stat or just replace it ($24) and see if this cheap option makes the difference You need.

 

[argve]

You have a cooling issue because I used to run the Enterprise (91 7.3 E4OD 4.11 Dually) at 75-80 mph all the time and not have cooling issues - the only time I had cooling issues was when she was pulling 10k lbs.

As stated clean the rad and check the condition inside the rad. I bet you will find that is where your problem lies because over the years you probably have bugs built up on the outside and lime/calcium build up on the inside.

 

[kcw12]

I'd go 3.73s and as soon as a find a truck in the pull a part yard with 3.73s in it, (new ford i believe has the 3.73s)

 

[2manydsls]

I just recently put new rear tires on my wife's truck. 90 F-250 in sig. I changed from the 235-85-16's to 245-75-16's. I figured this changed the overall gearing to around 3.73. Was 3.54. I feel that this made the truck a lot more fun to drive. It seems to have more power and doesn't downshift as much in hilly terrain. Also, improved speedo error. I gained a little tread width in the deal and still have E load rating. And although, it hasn't been on any long trips yet, I don't think the fuel economy was affected.
Ross

 

[Andylad13]

thanks a lot for the replies guys!! time to check the cooling system, and throw some gears in.