Where to buy speedo gears

[Henry Hopper]

I picked up my new 40 Standard coupe last night.....the minute I hit the motorway the speedo started to whine...I reached under the dash and moved the drive cable slightly and it went quiet....it did this three or four times on the way home but eventually it would not quieten down and was making a heck of a racket.Ireached under and disconnected the cable from the head.

I will look into the noise issue at the weekend, but ,when it was working ok it read too fast....about indicated 40 ish at 30 mph....where can I get new gears to alter the ratio.It has radial tyres, so the diameter will probably be out of whack over the stock size.....I don't know the rear end gear ratio either, or how to find out.....any advise welcomed.

[Walt Dupont--Me.]

Are you sure the 40 didn't have a 60HP in originaly and 4:44 rear gears? Walt

[alan]

go to the rear axle and look for two numbers stamped into the banjo where the torque tube attaches, these are ring and pinion gear teeth count dividing the two will tell you ratio. Under the floorboard bolted to the torgue tube and having the speeddometer cable attache to it, is a housing commonly called a "turtle" read the number on it. this is what you change to alter speed. measure the diameter of you radial tyres--post all these numbers and some one will help you

[desotoguy]

The noise could be the result of a dry cable. I remember some time ago you could buy a small bottle of oil that screwed onto the spedo end of the cable, and as you drove the oil would lubricate the cable. I would try to lubricate the cable to get rid of the noise before think of a gear change.

[JM 35 Sedan]

Once you determine the rear gear ratio, as alan mentions in his post, you can go to Bratton's Antique Auto Parts website and buy most any turtle gear you may need. These are repro gears made of Nylon (or some other very durable plastic) that they claim will outlast the original type gears. You can also buy the different turtle housings and other parts for the turtle assembly from them. They may tell you these parts are for Model A's but they will also work on the early V8 era cars.

[Henry Hopper]

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Walt, not sure what the original gear set was/is.

Alan, thanks, Ill get underneath on Saturday and look for the numbers.

Desotoguy, Ill lube everything ....the change of gear is not about the noise issue, it's about the recalibration to get the reading more in line with reality...


Thank you for the responses, much appreciated.

Anyone know where you can buy the gears??

JM ...you posted as I was typing....thankyou very much, I give them a call when Ive got the numbers off the banjo.....

[Bluebell]

It might be that the gearing is fine. The fault might be in the speedo head it's self.

[Henry Hopper]

Could be Bluebell......but it was reading steady before we got on the Motorway and the previous owner told me it worked fine apart from being inaccurate....Im working on the basis that I can sort the noise out and then tune the ratio to get it closer to the truth...this is the closest Ive come to getting a Forty speedo working in one of my cars over the years lol.the others were shot and too expensive to post to the US for refurb.

[jdl]

also oil the speedometer head, on top of head where the cable screws on you will see a real small cup, pry this cup out with a pocket knife or such, add a drop or two of 3 in 1 oil then replace the tiny cup.

[Henry Hopper]

Will do, thanks.

[40cpe]

Originally Posted by jdl

also oil the speedometer head, on top of head where the cable screws on you will see a real small cup, pry this cup out with a pocket knife or such, add a drop or two of 3 in 1 oil then replace the tiny cup.

I agree. I had one with the same symptoms. No noise until had driven for a while. Then could wiggle the cable housing and help it some until nothing helped.

My theory is the longer it runs it thins out what lubricant is in there until there is no film left to protect the bushing. The wiggling relieves some pressure on the bushing.

I replaced my speedo and made sure the cable entered the speedo at an angle so as not to put a side load on the bushing in the speedo.

[Henry Hopper]

Just a follow up on the speedo problem......I tried the 3 in 1 oil in the little hole but no change...I then went to try and find some graphite grease at the local motor factors but they would have to order it in..being a bit impatient I tried CopperSlip grease that I had on the shelf in the garage.I pulled the inner cable out a few inches and greased it up a tad,and then I put a little bit on my finger tip and pushed it in the housing where the cable enters the guage.

So far so good....no noise, no bounce,smooth action...about 100 miles on it since the lube job.Last night it was sitting at 100 mph on the Motorway with no trouble.....bear in mind that the speedo is reading fast by around 30% lol.....just need to get the drive gear swapped for something a bit closer to reality now.

[woodypecker]

Stewart warner makes some gear dvices that you but in line between the turtle and the cable which can speed up or slow down speedo.

[JM 35 Sedan]

I recently had a similar problem with the speedometer cable in my 35. It was reading about 10 mph under actual speed indicated on GPS and by road markers. During a long trip in June it started making a noise like something was dragging under the car. Then many miles later it started squealing so loud that I had to pull over and disconnect the cable at the speedometer and remove the center drive cable. I later coated the cable with powdered graphite and 3 in 1 oil. After that the speedometer needle was dead nuts steady and the error was reduced to about 5 mph under actual speed. So maybe the friction drag and bouncing of the needle was causing an increased error reading.
I am running 3.78 rear gears, #19 turtle gear, and oversize tires, so I knew there would be some error in the speedometer reading anyway.
I think before I would order a new turtle gear I would know exactly what that rear gear ratio actually is. There has been some recent threads posted here on how to determine this.

[32phil]

Just a bit of info on this "turtle business". The MOST common gears are 18 tooth (3:54 rear gear)...19 tooth (3:78 rear gear) and 21 tooth (4:11 rear gear). I think there is a table in one of the parts books/service bulletins that details rear gear vs. turtle gear vs. tire size... You cannot just change the gear as the size of the "turtle shell" is different for each gear......ask me how I know......BTW....This "Turtle" analogy is killing me.....

[Henry Hopper]

Originally Posted by 32phil

Just a bit of info on this "turtle business". The MOST common gears are 18 tooth (3:54 rear gear)...19 tooth (3:78 rear gear) and 21 tooth (4:11 rear gear). I think there is a table in one of the parts books/service bulletins that details rear gear vs. turtle gear vs. tire size... You cannot just change the gear as the size of the "turtle shell" is different for each gear......ask me how I know......BTW....This "Turtle" analogy is killing me.....

I never knew that the gear housing(turtle) was specific to each gear.....very un-Ford, they usually go out of their way to make parts that fit multi range.

[JM 35 Sedan]

Originally Posted by Henry Hopper

I never knew that the gear housing(turtle) was specific to each gear.....very un-Ford, they usually go out of their way to make parts that fit multi range.

That's not 100% correct. There are some turtle housings that will work with different gears. I don't recall the specifics. The problem is you could have too little or too much gear tooth engagement possibly reducing the life of the gear. Plus the housings are cast with either the number of teeth on the speedo gear or the number of teeth on the ring and pinion gears that the speedo gear is to be used with. Example: the turtle gear housing for 4.11 gears could have #21 or 9/37 cast on the housing. What Ford standardized was the speedo gear that's located inside the torque tube on the drive shaft. This same gear will work with almost any of the turtle gear assemblies. This way if you need to make a correction to speedometer reading because of tire size change, you do not have to disassemble the rear to change the inner speedo gear. I believe that was the thought process that was probably used by Ford.

[flat-v8]

If you need a good turtle that was paired with a 4.44 rear end, I have one for FREE! I think the number stamped on it is 23

[Henry Hopper]

Originally Posted by flat-v8

If you need a good turtle that was paired with a 4.44 rear end, I have one for FREE! I think the number stamped on it is 23

Thanks for the offer, extremely kind of you.......I just bought one last night off ebay over here ,doh!......the number on it is 25!!...I also have a 39 torque tube kicking around the garage somewhere with the gear housing on it if I remember correctly.
Again, I appreciate your kind offer......

[Bluebell]

Now I see why they are called a turtle!
So is this a 4.7 diff ratio (43 divided by 9) She must be slow on the road?

[Terry,OH]

This is the incorrect turtle for any 40 car. It is off of a truck. You may want to take flat-v8 up on his offer. Your speedometer will read higher with a turtle with less teeth. Take a look at several of the posting up now about determining the gear ratio. If you can find the numbers they are stamped into the lower rib on the center differential housing.

[Henry Hopper]

Thanks for the identification Terry,I thought it was an oddball at 25 ...but my rear tyres are 235/70/16" and my speedo seems to be reading fast by about 30% or so.I will get it up in the air and try to read the diff ratio numbers off the banjo.