Joined: Jun 09, 2011 Posts: 776 Location: Bellmore, NY
Posted: Thu Jan 24, 2013 10:47 pm Post subject: So, on my speedometer problem
I have 7.00 x 16" round shoulder military tires. I have 5:38 gears in the axles. I have a t 90 transmission and Dana 18 transfer case, both rebuilt by Novak. I have the waterproof cable with a 15 tooth, keyed military driven gear. I have a rebuilt, military speedometer. And the mileage readings are still high. Like 60 when I'm doing 35 according to my GPS. I've talked to several military parts distributors, and no one seems to know what it could be. Any help would be greatly appreciated. The only thing I can think of, is that Novak gave me a T90C, with has different (lower) gears than the T90A1 that the M38A1 normally had. But would that really matter? It reads high in 3rd gear, and I think all the T90s had the same third gear ratio. I know the Dana 18 came in gear variations as well. Mine is 26 tooth, with a 2.24:1 low. _________________ 1952 M38A1
Marine core reinforced rear bumper, military transistorized turn signal upgrade, arctic heater, 11" drum brakes, 200L PTO winch, Huffy overdrive, deep water fording kit, RT 68 vehicle mounted radio, Trac Locs front and rear.
www.danhenk.com
You have left a lot of info behind on the other four posts you made on this topic. It would have been better to have kept this all in one thread.
As I recall you still have not had the two speedos tested by a speedo shop shop. That was my suggestion back in those posts and until you do that I can offer no other suggestions.
This topic needs a connection to the beginning of this problem which was addressed in four previous posts:
Joined: Jun 09, 2011 Posts: 776 Location: Bellmore, NY
Posted: Fri Jan 25, 2013 12:36 am Post subject:
I only have one left right now. The reconditioned military one I bought from "circleburner" on this site. I sold the other one, and the guy who has it says it works perfectly. The one circlerburner sold me, and the old one, read the same. Both had high readings. I'm pretty new to Philadelphia, but all the shops but one that I called said they didn't know how to deal with a speedometer as old as mine. The one that said they could, just said they would try, but no guarantees. I'll try that one next week, but with two speedometers in a row reading high, I'm thinking it's not the speedometer. _________________ 1952 M38A1
Marine core reinforced rear bumper, military transistorized turn signal upgrade, arctic heater, 11" drum brakes, 200L PTO winch, Huffy overdrive, deep water fording kit, RT 68 vehicle mounted radio, Trac Locs front and rear.
www.danhenk.com
Joined: Jul 18, 2008 Posts: 639 Location: Melrose, MA and Santa Fe, NM
Posted: Fri Jan 25, 2013 8:38 am Post subject:
Beachwood Canvas is in your area, as is Army Jeep Parts. I would link up with them for parts information and help as you could go directly to their shop and see the parts.
The speedo gears in the transfer are two each: one drive gear (4 teeth) and one driven gear (15 teeth). The only big differences from application to application for the jeep D18 is the tooth count of each gear. As long as that tooth count is correct for your M38A1 application the problem of a very high reading speedo falls to the speedo, the drive cable assy, and the tranny/transfer gear drive ratios. The high reading Dan describes is double what he believes the jeep is actually doing as determined by a GPS. The assortment of drive gears for the tranny/transfer should only generate a mild increase or decrease in error. Not twice the actual speed. This is why I believe the problem really lies in the speedo or the drive cable assy. Worn outer drive cable housings allow the core drive cable to vibrate and stick and quickly release which pops the speedo way over on speed. A damaged or kinked drive cable housing will do the same thing. _________________ Wes K
45 MB, 51 M38, 54 M37, 66 M101A1, 60 CJ5, 76 DJ5D, 47Bantam T3-C & 5? M100
Joined: Jun 09, 2011 Posts: 776 Location: Bellmore, NY
Posted: Fri Jan 25, 2013 10:57 am Post subject:
I have a NOS, military waterproof speedometer cable I got from Pete Debella. It's thicker than say, the one that Kaiser Willey's sells, and is a bit crammed in there. It isn't worn, and the end is keyed and fits in the speedometer driven gear correctly. Is there anything I can check on the cable? _________________ 1952 M38A1
Marine core reinforced rear bumper, military transistorized turn signal upgrade, arctic heater, 11" drum brakes, 200L PTO winch, Huffy overdrive, deep water fording kit, RT 68 vehicle mounted radio, Trac Locs front and rear.
www.danhenk.com
NOS is synonymous with ancient. Lubricants inside that cable housing could be rock hard and completely dried out.
Take an electric screw driver type drill. Connect it to your speedo using a 2 or 3" piece of old speedo drive cable and run the drill motor at full RPM (I believe the direction should be backwards) and record the steady MPH reading of the speedo. Now connect the top end of your NOS speedo drive cable assy to the speedo. Disconnect the bottom end from the transfer case and connect it to the drill motor and run the drill at full rpm again. What does the speedo read now? _________________ Wes K
45 MB, 51 M38, 54 M37, 66 M101A1, 60 CJ5, 76 DJ5D, 47Bantam T3-C & 5? M100
Joined: Jun 09, 2011 Posts: 776 Location: Bellmore, NY
Posted: Fri Jan 25, 2013 2:07 pm Post subject:
that's a great test! I'm away for the weekend, but I'll do that on Monday and post the results. _________________ 1952 M38A1
Marine core reinforced rear bumper, military transistorized turn signal upgrade, arctic heater, 11" drum brakes, 200L PTO winch, Huffy overdrive, deep water fording kit, RT 68 vehicle mounted radio, Trac Locs front and rear.
www.danhenk.com
Joined: Nov 01, 2011 Posts: 199 Location: Escondido, CA
Posted: Fri Jan 25, 2013 7:17 pm Post subject:
Does your odometer also read about twice the actual distance you have traveled? The speedometer and the odometer use the same input consisting of all the wheels and gears already discussed, but use totally different mechanisms within the speedo housing. The odometer is a series of reduction gears and counter wheels - all direct mechanical, while the speedometer is a magnetic device. The vibration and stick/slip within the cable that Wes describes can make the speedometer act up, but shouldn't affect the odometer much because it is just counting total revolutions of the cable.
You can gain some added understanding with Wes's drill test as well: , record the odometer reading before the test (best to turn it to a neat and tidy 1/10 mile reading first), run the drill for one minute, divide the MPH reading by 60, and see if the odometer advanced that much. _________________ Jim McKim
1952 M38 son-father project
Slowly turning rusty parts into OD parts
Joined: Jun 09, 2011 Posts: 776 Location: Bellmore, NY
Posted: Thu Jan 31, 2013 3:25 am Post subject: The mystery deepens!
So, I pulled the speedometer cable from the transfer case housing. I did Wes's test, using both a scrap speedometer cable with my DeWalt drill, and then the real cable. Both had the same results. I will say, I was checking over something else, and had straighted up the line of the speedometer cable a bit. Now, I was thinking, since I had all this apart, I'd pull the speedometer driven gear. To my surprise, the new one had the anchoring tip broken off just like the last one! I used a magnetic rod, got real lucky, and managed to pull out the broken tip. So, I have an extra driven gear, and tried I using that one. It clicks into the correct spot, but it's at a little of an upward angle, and I can't get the waterproof metal sleeve to go over it. This wasn't a problem last time, so that anchoring hole that holds the tip of the driven gear must have moved. I have a photo here of the spot where the driven gear goes, and the furthest the waterproof sleeve will go in. Any suggestions would be appreciated.
_________________ 1952 M38A1
Marine core reinforced rear bumper, military transistorized turn signal upgrade, arctic heater, 11" drum brakes, 200L PTO winch, Huffy overdrive, deep water fording kit, RT 68 vehicle mounted radio, Trac Locs front and rear.
www.danhenk.com
Joined: Jun 09, 2011 Posts: 776 Location: Bellmore, NY
Posted: Thu Jan 31, 2013 12:55 pm Post subject:
I don't know what the "worm" is, and I don't know how it could be the wrong one? The transfer case is a Dana 18, the speedometer driven gear I got from John at Midwest Military, and it's the correct 15 tooth waterproof gear. _________________ 1952 M38A1
Marine core reinforced rear bumper, military transistorized turn signal upgrade, arctic heater, 11" drum brakes, 200L PTO winch, Huffy overdrive, deep water fording kit, RT 68 vehicle mounted radio, Trac Locs front and rear.
www.danhenk.com
Joined: Nov 01, 2011 Posts: 199 Location: Escondido, CA
Posted: Thu Jan 31, 2013 3:17 pm Post subject:
Technically, what Xamon was referring to is called just a "worm", even though it is a gear. A "worm gear" is the gear that is driven by the worm. Quite confusing, but that is the way it is. Since it is practical to transmit power in only one direction with a worm/worm gear pair (they don't back drive), the worm is the driving gear and the worm gear is the driven gear. _________________ Jim McKim
1952 M38 son-father project
Slowly turning rusty parts into OD parts
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