I recently bought a 70,000 mile 1990 F-150 to tow my race/street car. It has the 4.9 litre engine and E40D transmission. Being a gearhead, I've already added a Dynomax catback (with twin tailpipes), and bumped the timing up a little to give it a little more power. According to the door sticker, it has axle code 18, which I can't find anyone that can tell me what ratio that is. (I don't have the owner's manual. Not that it would tell me anyway). It had beat tires on it when I bought it, sized 235/75/R15. I swapped the tires off of my old truck onto the new one. They are size 31x10.50x15, which are about 3" taller than the stock sized ones. My trailer/car combo weighs roughly 4500#'s. It has decent power, but can definitely benefit from some more!! Can anyone tell me what gear ratio I have?? The metal tag on the rear cover doesn't tell me anything. I know a gear change would be beneficial, but don't know what I have, so I don't know where to go with it. I don't want a "HOT ROD TRUCK", just something to tow a little easier than it does now. Thanks in advance!
BOB

 

If your truck has a tach, you can use this to find the axle ratio:

https://www.ford-trucks.com/articles/gearcalc.html

 

No, it doesn't have a tachometer.

Also gas mileage with stock sized tires was 18mpg combined city/highway. It is now considerably less. I'm trying to figure out if it would be smarter to change the axle ratio, or just buy the correct sized tires.

 

Count the axle by jacking up one rear wheel, putting a mark on the drive shaft and counting the revolutions of the drive shaft as you turn the tire 20 revolutions. If you have a locking rear end, you will only have to turn 10 tire revolutions to get the axle ratio. Do this with the vehicle in neutral, engine not running, and chocks for the three ground tires.

 

You have the lightest axle they put in the F150 (3,800 Lb.) with a 3:08 gear. According to my 1989 owners guide you can safely tow up to 2,000 lbs. at this time. Swapping in the heavier rear axle from a donor truck, and if you already have the towing package and the same gear ratio you could step up to a max tow rate of 5,000 lbs.


Deen Hylton
Ford F250 460 C-6, K&N, Headers, Dual Exh.,Comp. Cams,Shift Kit
Pioneer CD w/Bose Speakers.
Other Passion: Blown 77 Corvette (Sorry Guys/Gals)
How I can afford to Drive the above: 93 GEO Metro

 

Turning the driveshaft isn't an accurate way to try to find the rear axle ratio on an open rear, which I have...

I borrowed a co-worker's owner's manual today, and found out it is a 3.08. I also stopped on the way home from work, and bought a set of 4- 235/75R15XL tires, which are the stock size. I hope with the 2-1/2" to 3" shorter tires back on, power will come back up, and it will tow a little easier. If not a swap to 373's or 410's should take care of it.




1990 F-150, 4.9 Tow Vehicle
1986 Mustang LX 10.54@129
You MUST be FAST,
cause you were FLYING,
When I PASSED YOU!

 

Even with lower gearing, your truck is still not rated to tow that much weight. Getting a load moving is one thing, but stopping it is another. You will exceed the GVWR of the truck with that trailer, and definately will exceed the GCWR. You need a bigger truck to haul that trailer.

Rich

 

I'm pretty sure that the 2000# tow rating is for the manual tranny not the E4OD. Your rating is limited by the 3.08 axle ratio though. Swapping to a 3.55 or 3.73 will bring it up (sorry, I don't have the specific numbers handy). 4.10 is too much gear for a 300.

 

No problems whatsoever stopping...truck has excellent brakes, and so does my tandem axle trailer. Just had a little trouble on the hills.....
Geez guys, I towed it for two years with a light duty 1/2 ton CHEVY. But, it had 4.10's and a 350 4 barrel carbed engine.
Don't tell me these Fords can't handle it.

1990 F-150, 4.9 Tow Vehicle
1986 Mustang LX 10.51@129
You MUST be FAST,
cause you were FLYING,
When I PASSED YOU!

 

I'm not telling you the truck can't "handle" it, I'm telling you it's not legal! These trucks are rated for max weights for one reason, safety. That safety includes both your's and that of the other dirvers you share the road with. If you are overweight and cause an accident and they prove you were overweight, tuck your head between your legs and kiss your... you know the rest. Your insurance company can drop you and not pay a single dime towards the court settlement.

There is no way to increase either the GVWR or the GCWR of your truck. Yes, you can add helper springs, but this does not make you legal to haul the weight.

If you ever get into a panic stop situation, I feel real bad for the poor soul in front of you, you'll more than liekly end up in his back seat.

Rich

 

Thanks for your concern, and the "heads up" on the legality issue Rich. I appreciate it. AND, I don't want to get into a pissing match with you....
But as you know, I'm sure, you could be towing a single rail motorcycle trailer with an F-450 Super Duty with a 12,000# GCWR, and still run into someone in a panic stop situation....A heavy trailer equipped with an inadequate, or even non-existent, braking system would be the only morally "negligent" reason for rear-ending someone IMHO, not a truck with not enough gear ratio, or not enough leaf springs...But I do agree, it may not be as safe as a heavier equipped truck.
BTW, if you see an underpowered little red F-150 motoring down the highway with a purple race car on the trailer....YIELD.

1990 F-150, 4.9 Tow Vehicle
1986 Mustang LX 10.54@129
You MUST be FAST,
cause you were FLYING,
When I PASSED YOU!

 

At 4500# you're probably fine. Your door sticker should list your GVWR at about 6100#. I don't have GCWR ratings handy, but with the E4OD it should cover you easily. My 95 Ranger 4.0 V-6 w/AT and 3.55 LSD had a trailer towing rating of over 5000#, which was pure BS but the F150's higher for sure. Ford derates the trailer towing of their manual tranny F150s because 1) the M5OD is a POS and 2) the light duty clutch can't take it. They also derate for the 3.08 axle because it abuses the E4OD too much. If you put a good cooler on it and change the gears you'll be fine. If you're towing on hills you'll want to switch off the OD, so the 3.55 may be a better bet.

 

That's what I was thinking also. The door sticker says 6250#'s. I also had a new set of the correct sized tires put on yesterday, which seems to have helped greatly, as far as driveability goes.

1990 F-150, 4.9 Tow Vehicle
1986 Mustang LX 10.54@129
You MUST be FAST,
cause you were FLYING,
When I PASSED YOU!

 

I'm just stating what Ford has in their owners manuals for 1989...the MAX GCWR with a manual trans is 6,450 lbs., maximum towed trailer is 2,600 lbs. (4.9 engine, 3:08 gear).
The MAX GCWR with the auto trans is 8,000 lbs. light axle...9,000 lbs. heavy axle. Their MAX trailer weight is 2,000 lb. light axle, 5,000 lb. heavy axle and "towing package" (4.9 engine, 3:08 gear). Another common misconception is if you have a light axle ...just add more leaf springs, that does not replace the light duty axle bearings or axles that can break. Years ago I had a friend with a light duty pickup that just HAD to haul fire wood with it (F100)...after the first two axle bearing replacements we just considered it part of the cost of his "free" firewood gathering.
You may be able to tow for miles with no mishap, but when it does break just consider it part of the cost of not stepping up to a truck that is adequate for the job...it's kinda like your Mustang,
it will get you to the end of the track, in a timely fashion I might add, but it wiil never win any races running a Super Comp car or Funny car because you didn't build it for that. Same thing with your F150...it was never intended to do what the F250/350 was designed to do. Now if your only towing a FEW miles and its pretty level you'll PROBABLY be O.K., but if your towing any distance (let's say 30+ miles) or a lot of hills/steep hills bite the bullet and step-up.

Deen Hylton
Ford F250 460 C-6, K&N, Headers, Dual Exh.,Comp. Cams,Shift Kit
Pioneer CD w/Bose Speakers.
Other Passion: Blown 77 Corvette (Sorry Guys/Gals)
How I can afford to Drive the above: 93 GEO Metro

 

[font size="1" color="#FF0000"]LAST EDITED ON 09-Aug-01 AT 11:45 AM (EST)[/font][p]What most people don't understand is that Ford's towing guide is not accurate, read the fine print. The guide was definately written by a lawyer. Your front and rear axle weights can NOT exceed the GAWR for their respective axle. Add the two GAW's together and this can not exceed the GVWR of the truck.

Here's where most guys screw up, the hitch/pin weight of your trailer applies to the GVWR of your truck. Say your truck, loaded and ready for the road with people, tools, fuel, generator, firewood, etc., weighs in at 6200 and your GVWR for the truck 8800, this leaves you with only 2600 for hitch/pin weight.

Also, the GAW of the trailer can not exceed their respective GAWR and the GVW of the trailer can not exceed the trailer GVWR.

Here's the last factor, the GVW of the truck and trailer can not exceed the the GCWR of the truck.

It's definately a pain in the you know what to figure out your weights, but in the end wouldn't you sleep better at night knowing that you and your passengers are safe and so are the others you share the road with?