Wheel size, towing, transmission issues

[Crazyro]

Hey guys. I'm having issues with my 66RFE (same as others have; P0871 code; limp mode every so often; losing overdrive; etc.) and will get a remaned dropped it as soon as one becomes available. Anyway, just trying to see if anything I did could have been a contributing factor. I know some of these have been quirky anyway. Two things - first, truck has been towing for the past five years (and done a great job!) so there's extra stress - then again, they're made to haul and tow; second, I run 20s (35/12.5/20) while truck originally came with 18s (275/70/18). I know there's obviously a difference and I'm assuming that the truck would have to work just a wee bit harder to spin those - would it make sense/would it help to go back to stock sizes? Love my truck, plan on keeping it, but I don't want to go through this again, although I know this is not a guarantee even if everything was bone stock. (Truck has 90k just FYI). Any advice would be appreciated.

 

[2003F350]

Transmissions will tend to last longer when everything is stock and they stay within designed parameters, but nothing is 100%. Running 35" tires on a truck that came stock with roughly 33's on it is going to give your driveline some added stress, nothing the truck shouldn't be able to handle on its own. Towing is going to add a lot of stress, and depending on the weight and coupled with the larger tires arguably contributed to your transmission giving it up early.

There's a lot of unknowns that you haven't given us though - what axle ratios do you have? How much weight are you pulling routinely, and what is the max you've pulled? 4.10s will help your transmission more than 3.73's will, but there aren't a lot of 4.10 trucks out there that aren't Power Wagons. Guessing since it came factory with 18" wheels you don't have a Wagon. If you're pulling a LOT of weight all the time, you're definitely going to shorten that transmission's lifespan, but by how much is a shot in the dark.

HOW you drive also contributes. If you're easing into it you're adding a lot less stress than if you are constantly putting it to the floor when you take off. If you're running 65mph towing that's easier on your transmission than if you're running 75+.

There are guys on here who have had nothing but trouble from 66RFE transmissions. There are guys who have had zero issues with 66RFE transmissions (I put 110k on one and had zero trans issues). They aren't the best on the road but I wouldn't say they're the worst either, if everything is staying within designed specifications they seem to hold up pretty well. If you're exceeding those specifications or doing modifications to the driveline (bigger tires, for instance), you certainly aren't doing yourself any favors.

NOTE: if you're getting it replaced, make SURE they replace the stand-alone transmission cooler and do a good flush on all other non-replaced components (the cooler in the radiator, for instance) to make sure any and all contaminants are removed from the system. It would be terrible to put a new transmission in and have it fail in short order due to contamination that could have been removed.

 

[Crazyro]

Transmissions will tend to last longer when everything is stock and they stay within designed parameters, but nothing is 100%. Running 35" tires on a truck that came stock with roughly 33's on it is going to give your driveline some added stress, nothing the truck shouldn't be able to handle on its own. Towing is going to add a lot of stress, and depending on the weight and coupled with the larger tires arguably contributed to your transmission giving it up early.

There's a lot of unknowns that you haven't given us though - what axle ratios do you have? How much weight are you pulling routinely, and what is the max you've pulled? 4.10s will help your transmission more than 3.73's will, but there aren't a lot of 4.10 trucks out there that aren't Power Wagons. Guessing since it came factory with 18" wheels you don't have a Wagon. If you're pulling a LOT of weight all the time, you're definitely going to shorten that transmission's lifespan, but by how much is a shot in the dark.

HOW you drive also contributes. If you're easing into it you're adding a lot less stress than if you are constantly putting it to the floor when you take off. If you're running 65mph towing that's easier on your transmission than if you're running 75+.

There are guys on here who have had nothing but trouble from 66RFE transmissions. There are guys who have had zero issues with 66RFE transmissions (I put 110k on one and had zero trans issues). They aren't the best on the road but I wouldn't say they're the worst either, if everything is staying within designed specifications they seem to hold up pretty well. If you're exceeding those specifications or doing modifications to the driveline (bigger tires, for instance), you certainly aren't doing yourself any favors.

NOTE: if you're getting it replaced, make SURE they replace the stand-alone transmission cooler and do a good flush on all other non-replaced components (the cooler in the radiator, for instance) to make sure any and all contaminants are removed from the system. It would be terrible to put a new transmission in and have it fail in short order due to contamination that could have been removed.

Great points! Yes, 3.73 rear end and I'm a grandpa when it comes to towing. I take off very gently and hardly ever give it a lot of gas even going up hill. I'm ok with slowing down a bit and then pick up speed again. Usually keep it at 65 or so (with the occasional 70 down hill to get going up. I've towed several campers ranging from 5,500# to 9,500#. The biggest stress was one camping trip when I had the golf cart in the back while towing an 8k camper and went up a 6% grade (have had this setup on a few trips also but nothing major). Both payload and towing were well within the limits (below actually). I tow 8-14 times a year. Other than that, truck is a daily and my commute is short. Even then, I don't like to lay into it. I'm guessing both towing and bigger tires could have contributed but it's hard to say. I have a friend who dailies the truck and his 66RFE gave out at 75k. I'll make sure I talk to the shop about the trans cooler and flushing other systems. Much appreciated!

 

[62Blazer]

It's not really the 18" vs 20" rims, it's more of the 33" tall stock tires versus the 35" tires you currently have. The larger diameter of the tires (not the rims) and probably heavier weight of the package will cause more stress. Now I said "more" and not necessarily "too much" stress. There is a decent chance that even if you had kept the stock tire size you would still be in the exact same situation.

 

[olyelr]

Like 62blazer said, in stock form you could very well be dealing with the same issue.

Larger/heavier tires do absolutely no good things for the drivetrain, however, in your case the change is somewhat minimal overall. Ive had 35’s on my power wagon for the last 80k+ miles of the 108k it has and never had a single trans issue yet…still operates just as ****** as it did when brand new haaa (gonna go knock on wood now lol).

 

[mtofell]

Fwiw, my 66RFE failed twice and I hadn't been towing anything for quite some time. The first failure literally happened sitting still. Was in stop/go traffic, traffic moved, my tach pegged and I didn't move. Of course, I'm just one person but from reading around here on a fair amount of 66RFE issues I don't recall many (any?) of them being while towing or on trucks that were reported to tow a lot.

Same goes for larger tires, etc. I don't recall seeing a pattern of more failures with more stress on the drivetrains. It seems the main issue is the valve body fails/clogs, whatever, and leads to other issues. That was reported to be the case with both of my failure.

 

[2003F350]

Fwiw, my 66RFE failed twice and I hadn't been towing anything for quite some time. The first failure literally happened sitting still. Was in stop/go traffic, traffic moved, my tach pegged and I didn't move. Of course, I'm just one person but from reading around here on a fair amount of 66RFE issues I don't recall many (any?) of them being while towing or on trucks that were reported to tow a lot.

Same goes for larger tires, etc. I don't recall seeing a pattern of more failures with more stress on the drivetrains. It seems the main issue is the valve body fails/clogs, whatever, and leads to other issues. That was reported to be the case with both of my failure.

I think that's what I was trying to say, I just tend to get wordy. It sounds like OP didn't necessarily do anything WRONG, and while their changes added stress, it wasn't likely a massively contributing factor.

You, on the other hand, I think just have bad luck. REALLY bad luck when it comes to that transmission...LOL.

 

[Crazyro]

Thank you guys for your replies. I am learning that these 66s (heck, even the 68s) are just hit or miss unfortunately and there's really no set pattern on them failing. I went ahead and placed my order for a remaned one today and hope it'll treat me better. I guess we'll have to wait and see...

 

[Gary-QEC]

What was/is your maintenance protocol? How often do you change fluid and filter?
Have you added a deep pan?

 

[Tominator223]

A bad maf or tbs can cause some OD issues. The screw on filter falling off will cause the high rev no move issue.(like mto had.) So if that happens & you did filters not long ago . Probably a dropped filter. They’ve had some bad screw on filters out there. Also bigger tires without a gear upgrade wear out transmissions quicker.