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fun nonetheless.

Amazing how stiff this suspension is, as it has the 10,000 pound GVWR and NO weight on the back. )[/QUOTE]

And remember, no shocks on the F4 makes for a more interesting ride. I will install fronts on mine. Believe me, even with a bed on the truck it will ride rough and you think it is jumping off the ground at times.

 

Wrong direction... you're going faster than your speedometer says... your tires are larger than stock. For any given RPM, a larger diameter tire will go faster.

You were turning the RPM calibrated for 30 mph based on a smaller tire size. I have the same issue. At 65 mph, my speedo says 54.

 

Well then, something else is wrong, because my current 32" tall 2.25/70 R19.5" rear tires are shorter than the stock 7.00 x 18" bias ply tires. Those were about 34" tall.

 

The first step is to get your odometer reading correctly. The Ford factory literature has a nice table on what speedometer cable drive gear you need with each axle ratio and rear tire size. Once the odometer is reading correctly you can adjust the spring tension so the m.p.h. reads correctly.

 

OK. I'm confused. As far as I know, this truck... speedo and drive gear... are stock. The thing that was changed is the rear tires/wheels. I never drove the truck with the widow makers on it, and even if I had, the speedo cable was broken. The rear gears are stock 5.14:1. The "new" tires are now about 2" shorter than the original 7.00 x 18"s.

Can you post the table you mentioned? Or do you have a link to it?

And I have no idea what spring tension you're talking about... Where is this spring? Any help is appreciated.

 

Since we don't know when 38 coupe will return, I'll just throw this out.
As you know the speedometer drive gears at the output of the transmission are replaceable to compensate for various axle ratios and tire sizes. The spring he mentioned is within the speedometer. When the cable turns the speedometer head it rotates a magnet that is in close proximity to a metal shoe part of the speedometer needle. The faster the magnet is spun equates to the needle indicating more speed. The spring he mentioned is the spring tension that keeps the needle at zero MPH. The faster the magnet is spun the more force is felt against the needle.
After the mechanics of the odometer is calibrated correctly with the right gears, the spring can be adjusted to get the right needle movement.
I am sure 38 coupe will have a better explanation and perhaps a link to gears. Been 50 years since I played with a speedometer.

 

Thanks Ray.

I found a chart online to calculate gear teeth. I'd have to change to a 20 tooth driven gear to make it right. Ford Speedometer Calculator

I just looked in my parts book. The stock gears for my truck are a 6 tooth drive gear and a 19 tooth driven gear. But I think this spring may be most of my problem, since I have to be moving about 15 mph before the needle moves off zero. I'm sure I'd have to change the gear to 20 teeth, but I don't believe that's making me 15mph slower at 45 mph. And, as my son said earlier, the smaller wheels should make the speedo read faster, not slower.

 

Does anyone have any diagrams of the insides of the 51 - 52 speedometer? Or a reference link somewhere? Or a book?

Mine works, but poorly. And now I think I'm going to need to take it apart. But before I do, I'd like to know what it's supposed to look like when I'm done.

 

I too had issues with the speedometer cable when I first hooked it up. It would not register until I went about ten feet and then was very slow to return to zero after I stopped. Out on the street it would make a skweeking noise. I took the speedometer out and sprayed a little Blaster in it and maybe I am one of the lucky ones in that regard but it works as it should now and no more skweek.

 

Thanks Kevin. I guess I'll take a look at it this weekend.

 

My apologies for an unclear post! raytasch is correct about what I should have posted.

Unfortunately I do not have a 48 and later Ford Truck Chassis Parts Manual. The 28-47 parts manual shows 18, 19, and 20 tooth driven gears used with 5.14 rear axles. The smaller the rear tires the more teeth on the gear.

Basic speedometer maintenance is actually pretty easy. One of the hardest parts is crawling under the dash and removing the gauge. I think on your speedometer you get to carefully pry the chrome bezel off the front of the gauge as the first step in disassembly. You will find a cover on the back of the speedo held on with 2 little bolts. Remove the cover and carefully clean all the moving parts. I use motor oil on the end of a tooth pick to lubricate all the shaft ends and a small amount of grease on the gears. Remember to oil around the input shaft. Do not get any oil, grease, cleaner, etc in the magnet or aluminum cup. Worst case scenario you can try to flush the aluminum cup out with alcohol. While you are at it you can clean up the face of the speedometer and clean the inside of the glass. The numbers on the odometer are usually really fragile so be careful when cleaning them.

If you look closely you will see the tension spring that works to set speed of your needle. Don't mess with it until you are ready to calibrate your speedometer to itself.

To calibrate your speedometer do the following (this process is based on the fact that at 60 miles an hour you travel exactly 1 mile in 1 minute):
1 - Get a broken off speedometer cable or some way to drive your speedometer
2 - Use a variable speed reversible drill. Drive the speedometer with the drill in reverse.
3 - Run the speedometer up until it is indicating 60 m.p.h. Hold it at exactly that speed.
4 - Watch the odometer. It should move 1 mile in 1 minute.
5 - If the odometer moved less than 1 mile your speedometer is reading fast. Adjust for less spring tension. If the odometer moved more than 1 mile your speedometer is reading slow, adjust for more spring tension.
6 - Repeat speed test and adjustment as necessary.

I find that once cleaned and lubricated usually the speedometer needs only minor adjustment.

Hopefully this post makes up for my prior confusing post.

 

Thanks 38 Coupe. That makes a lot of sense, and was exactly what I needed to know.

My speedometer is easily removed to the rear by removing two nuts. I've had it out a couple of times. Hopefully I'll get a chance to check it this weekend.

 

That's worth remembering. Also, I now know why I saved that speedo cable that got too close to the exhaust.

 

I followed these instructions to the letter. I cleaned it and lubricated it as advised.The speedo still doesn't work.

Now I have a new question. There is nothing in this unit that I can detect being magnetized. I touched a flattened staple to both sides of what I assume has to be the "magnet" ( it spins by the action of the cable) and also to the cup you mentioned, but the staple was not attracted to anything in there. Could this be the problem? Since it doesn't start to move the needle until I'm moving about 25 mph, maybe the magnet is really weak? It is, after all, 63 years old.

And if that's the case, is there any way to re-magnetize it?

 

Betsy went to breakfast this morning... at least she took us to breakfast. We drove to our friend's restaurant 9 miles away.

I discovered that I still have a lock-up problem whenever I take the tranny out of 4th gear before I come to a complete stop.

If I leave it in 4th until stopped, it works normally. If I put it in neutral, it sometimes locks up. If I leave it in 2nd or 3rd, it sometimes locks up. Sometimes it locks severely, and I have to put it in 1st to move.

So, what's wrong with my transmission?