F-150 gear ratios

If my 86 4.9L had the 3.55 gears, I would have never owned my 90 with the 5.9L. With the change in speed limits, the

4.9 was simply working full time at 70 mph and had a top end in 5th gear of 82 mph if I had a couple of miles to wind it up. It was considerable better in 4th gear. It was in serious need of more gear. I believe the 3.55 would have bee pretty close to what was needed for it with 235 tires. If you have 31 inchers as many folks installed on them, a 3.73 would be more like it. You will need to change the speedometer drive gear in the transmission which will take every bit of 15 minutes once you get hands on the correct one. A knowledgeable parts man or even a few web sites can help you determine the correct part number or tooth count for an accurate speedometer. IIRC, the drives usually cost around $15US. Is this a worthwhile swap? If you are looking for better performance, it it one of the best upgrades for the cost if you like your truck. Expect to spend around $500 parts and labor to change the gears. A far better route to me is to look around for a complete salvage yard axle from another truck. Many of the V8's had the 3.55 gears from the factory and you can simply bolt in the complete axle in a couple of hours.

Lugnut

The speedo cable goes into the trans on the drivers side. Remove the retaining bolt and pull the cable out. On the end of the cable is a plastic gear held by a C-Clip. Remove the Clip, swap the gear.

The factory gear might have 19 teeth, you can buy a new gear with 20,

21, 22 teeth. Each additional tooth is something like a 4 to 6 mph decrease on the speedo reading. More teeth slows down the speedo, less teeth increase the speedo reading.

I had to swap my speedo gear to adjust for a different tire size.

I don't know anything about swap the gears in the differential.

You could put >I have an 89 F-150, 4.9L six, 5-sp manual and 3.05 diff gears. I have

Also remember tha you have a OD tranny and even a 3.55 is pretty tall in OD so do not let the numbers scare you. I hand a freaind that had a 86 F150 4x4 with a 300 and a 4speed NP435 granny gear tranny. Were it not for the deep first and second gears it would have not been able to get moving with any load with it 3.08 rear axle. Not knocking the

4.9 but it can only do so much and with a 3.55 or 3.73 it would run like a completely different truck vs current 3.08. Below is a link for a online axle ratio calculator that will let you see before and after effects of ratio changes with current or plan tires sizes too. Feel free to use it whenever you want too.

TheSnoMan.com

I'm planning on pulling an entire axle out of a yard. I researched what swapping gears takes a couple of years ago when I had a 78 Dodge Magnum, and while do-able, seemed like the long way around. On the Magnum I swapped a 2:40 rear for a 2:90 rear and it made a noticeable difference, but about that time I screwed up the 360 in it and had to get rid of it.

Thanks!

Mark

So you're saying I just have to change the gear on the speed sensor, not the one inside the tranny? That shouldn't be too hard.

Thanks!

Mark

Thanks for the link. I have to have this truck moving at least 50 mph to use OD, and that only on the flat and level. This being Pennsylvania, nothing is flat and level. I have the standard wheels and tires, 235-15's. I'm trying to find the factory steel sport wheels in the yards, but they seem to be pretty hard to come by.

Mark

Given where you live I would strongly suggest a 3.73 over a 3.55 as the little bit extra will help where you are at. I have been through PA and like you said there is not too much that is flat over there.

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Yes, that should do it.

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He's saying that, except you ain't got no speed sensor in 1989. "Cable" is the word you're looking for.

The factory service manual lists only two ratios for this truck, 3.08 and 3.55. Is the 3.73 ratio from a different year? This is a 5-lug bolt pattern rear.

Mark

Well, actually it's got both. I had to replace the speed sensor when I first got the truck to get the cruise control to work. This gizmo has both a cable fitting and an electrical plug.

Mark

Doesn't some 89's thru 91's have Rear ABS with some sort of a sensor in the rear axle.

Does changing the gear ratios in the rear diff. effect the Rear ABS?

What gears you can use/install is determined by the type/style rear axle that you have not the year is was built or the amout of lugs it has at wheels. You should have a Ford 8.8 inch rear axle which can at least be geared as deep as 6.14 to 1 (not what you need) and they make a 3.08, 3.27, 3.31, 3.55, 3.73, 3.90 ratios just in the 3.x range for that axle. It is just a matter of choosing a ratio and matching up the speedo drive gear on that model. Worst case senerio, if you cannot get the correct speedo drive gear combo (which is not too likely) you can have speedo recalibrated as a speedo shop. You want to buy these gears in aftermarket (not dealer) with Yukon and Precision being tops choices for brands to use. A 3.73 would be a good compromise between power and cruising in the hills there and increase to towing capacity a noticeable amount if you ever pull anything (both in starting the load moving and going down the road) If you never play to tow anything then a 3.55 might suit you a bit better. (if you plan some srious towing, going to a 3.90 or 4.10 would be in order hence the reason of the 3.73 as somewhere in the middle and a good compromise) That truck should have never shipped with a 3.08 to begin with and should have had at least a 3.31 anyway as you have found that it lacks a lot at times with 3.08.

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It can if speedo is not properly recalibrated on some vehicals. It depends on how wheel and vehical speed as monitored because most have wheel speed sensors and watch speed too to calculate proper wheel speed for ABS.

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On Tue, 24 Oct 2006 14:37:34 +0000, SnoMan rearranged some electrons to form:

Not in 1989. The ABS uses a tone ring on the ring gear, not wheel sensors.

Some vehicals used a toner ring for vehical speed but even with that you still need wheel sensors at each wheel with ABS to compare wheel speed against refference from "toner" and with each other wheel to determine which wheel is skiding and which is not.

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There is no speed sensor at each wheel on an 89 F-150. ^^^^

On Wed, 25 Oct 2006 04:36:37 +0000, SnoMan rearranged some electrons to form:

Snowblower, you are wrong again. In 1989, as the OP stated the year of his truck, the ABS did not measure wheel speeds, only the ring gear speed with a tone ring (not a "toner" ring). Even my 1998 F150 does not have wheel sensors, only a tone ring on the ring gear.

I said some vehicals as I did not say exactly what a 89 F150 has.. Some get by with a speedo and one or two front sensors on one or both front wheels depending on ABS design (4 wheel or 2)

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