Speedometer is Wrong

[The_Handier_Man1]

From: Boise_Chief1 (Original Message)
Sent: 4/11/2005 11:19 AM

When the family and I took our mini-maien voyage the other day I realized somethign was not right.  At 55 in a 55 I was crawling up on everyone on the road.  at 55 in a 65 I was with the flow of most traffic but did not seem to be going 55.  So I timed off of mile markers. 
at 55 I travel i mile in 53 seconds
at 60 I travel 1 mile in 50 sec
at 50 I travel 1 mile in 60 sec.

So my speedo seems to be 10 mph slow.  That explains why it didn't want to get up to 70 on the freeway.  I always felt like I was pushing it.  Anyone know why my speedo might be off this much.  I run 7.5x17 bias ply tires which I think is the correct tire for a 71' winnie chief.  The trans is a 727 b.  I think the trans is original.  Is there a way to adjust the speedometer?
Sean



From: 73RVDUDE
Sent: 4/11/2005 9:22 PM

Did you change your tire size?



From: HeavyHaulTrucker
Sent: 4/11/2005 9:29 PM

Boise_Chief,  have the bands on your tranny ever been adjusted?  They are supposed to be checked and/ or adjusted every 25000 to 30000 miles.  If they haven't, then I suspect that your tranny is slipping.  I would take it to a professional transmission shop; they can drop the pan, adjust the bands and the pressure spring, install a new tranny filter,  re-fill it with new fluid and button it up with a new gasket.  That should run you less than $100.00



From: cooneytunes
Sent: 4/11/2005 10:34 PM

John HHT is probably right and a transmission adjustment would cure....but another possiblity is PO changed the rear end gear, that would put it off 10 to 15 mph......

Timmy



From: Boise_Chief1
Sent: 4/12/2005 12:03 AM

No I didn't change tire size.  I am the new owner the PO seemed to fix everything wrong. So its possible he replaced the gear for the speedo cable to the wrong one. 
You really think it could be the trans slipping?  I would think I'd notice if it was slipping and overreving.  Is it possible for it to slip slightly and not notice?  Any description would be appreciated.
Also I was going to service the trans myself and the guy at the auto parts store said I shouldn't.

He said that older transmissions can be damaged when changing filter and fluids, because the newer trans fluids have more detergents and will strip out the old crud and varnish and cause more trouble than if left alone.
he contends that if the fluid is full, clear and unburnt I'd be better off not changing the filter.
I don't know I think I'd prefer to change it but I'd welcome your thoughts.
Thanks Sean



From: denison
Sent: 4/12/2005 7:37 PM

I would not think the previous owner had changed the rear axle drive ratio. That is a big job, rare and expensive. It would have had to be a lower numeric ratio. You can find your axle ratio 2 ays. One is to read the tag on the differential (if it hasn’t gotten knocked off) and divide. The 2 numbers are the # of teeth on the bevel and ring gears.
The other way is to jack up the axle (chock front wheels very well first) so you can turn the axle two complete turns, while counting the number of times the driveshaft rotates. If you only rotate the rear wheels once, then you double the number of turns you see the driveshaft make; to get the rear-end ratio. The usual ratios were 4.10, 4.56, and 4.88.
It is possible the plastic drive gear in the tranny was replaced with one having too many teeth on it. That could make the speedo read low. It would also read low if the spinning magnet in the speedometer had lost some of its “strength”. This is more common in cars from the 20s and early 30s, most all of which used Stewart Warner speedometers like our dodge based vehicle.
I would think you would know if the tranny was slipping, as the engine noise would change Radically depending on how much you put your foot down, when it had not yet changed gears.
Still, a tranny fluid and filter change is a good idea. Its not hard to do, and if you want to do the adjustment that is possible with the pan off, that is also a good idea. You should have a torque wrench that can read in inch/pounds however. There is a good explanation in a thread called “Transmission Band Adjustments for 440”. If the search doesn’t work well, use the search feature of your browser. It was in the Eng/trans/fuel board, in early March. The transmissoin adjustments are the same for the 727, whether its behind a 413 or a 440. Try to get the "kit" having the rubber composition pan gasket, it seems to seal better than the cork gaskets.
I have no idea why the parts guy would tell you not to put Dextron III in an old transmssion; and I think the info about different detergents is of no consequence. I have no qualms in advising you to change your fluid. It will take about 6 or 7 quarts. The dipstick tells you how to measure it. While you are down there, make sure your ground strap, from tranny to frame, isnt corroded away, and check that your tranny fluid lines going to the oil cooler arent too rusty, and the two hoses taking the lines into the radiator arent senile and leaking. You can also remove the speedometer drive gear and count the number of teeth. Too bad I don’t know what the correct number would be.
I think the only way you would not notice your tranny slipping, would be if you drove very gently, and very slow, or had the radio turned up as loud as my kids like to have it!



From: HeavyHaulTrucker
Sent: 4/12/2005 11:04 PM

Chief, after doing some calculations, I have come to the conclusion that your tranny is indeed -- without a doubt -- NOT slipping.

According to your recorded times, I come up with actual speeds of:
Speedometer Reading          Time In Seconds           Actual Speed
              50                                     60                  =              60
              55                                     53                  =              67.9
              60                                     50                  =              72

There is a 7.9 mph gap from 50 to 55, and a 12 mph gap from 55 to 60; this progression shows that the tranny cannot be slipping -- when it is slipping, you go slower than your speedometer shows.  This leaves two possibilities... either that the rear end ratio has been changed, or that the speedometer drive gear was replaced with the wrong one.  Since it is unlikely that the rear end ratio has been changed, it is most probable that the PO replaced the speedo drive gear with the wrong one.

You're right about not wanting to get it up to 70 on the speedometer... according to the progression above, you'd be doing almost 89 mph actual speed!  That has its good points, though.... no cop would stop you; there would be no way that he could convince his Sargent that he clocked an old motor home that close to 100 mph!

John



From: Boise_Chief1
Sent: 4/13/2005 4:17 AM

Thanks for your input guys.  I've been worrying about our little trip this weekend.  We are going to load up on sat am and take a short overnighter.  We will go about 75 miles and then come back the next evening.  I'll be traveling with a friend and I'll have him keep track of speed and make sure where my speedo is reading.  I'm pretty sure that my times are accurate, I only timed three mile points.  but the times hit pretty consistently.  I'll check for a replacement gear while I look for gaskets, hopefully i can get it fixed so I can keep accurate track of milage and MPG.
Thanks again
Sean



From: Sea Hag
Sent: 4/13/2005 11:01 AM

A GPS would be a good thing to have or borow . A poratble hand held like the Garmin E trex works nicely . that is the model I have . It works fine just sitting on the dash , they do make a mount for it , I have my navigator operate it . The prices have come way down . The etrex has real speed in MPH , maximum trip MPH ,Trip Odometer , time , ect. Not quite as fancy as the dash mounted LCD screen model but it works for me .  Replacement  tires may have the same size on them but do vary in actual size or profiles from different manufacturers , II think yours are a little taller makeing your spedo read low . so you may have to experiment with different spedometer out put gears . The GPS is very helpfull  checking the mph . Sea Hag 



From: chip
Sent: 4/13/2005 12:22 PM

drive a 10 mi. course that you have already run with a vehicle that you know has an accurate speedo. see how much your odometer is off. then call a speedo repair shop that can supply you with the correct gear reduction adapter. it just screws onto the output at the tranny tailshaft. the "big three" used these adapters for years on the transfer cases of their four wheel drive vehicles.



From: denison
Sent: 4/13/2005 2:44 PM

Or take out the existing plastic drive -pinion- from the transmission, I think its easy to remove....and find out how many teeth it has. The Dodge Motor Home Parts Catalog lists them with 24 teeth to 46 teeth, in one tooth increments. From the 26 tooth to 46 tooth pinions, the mopar part number is 25389xx, where the xx is the number of teeth. 



From: SpudFamily
Sent: 4/15/2005 7:49 PM

Hello, Boise Chief:

Wwhen I bought my 1972 D 22 Indian. I drove it up from Phoenix to Boise just before Christmas. Scary, very scary. Since then, I have made a few improvements, but she's still pretty stock.

My speedo squealed very loudly one day and then dropped the needle!  I dont even have a working ODO!  I just drive with the flow.  Like HeavyHaulTrucker said, no one would believe you were speeding anyway.  I usually try and pass at least one $100,000 diesel pusher on each trip, then slow down to a speed where I don't over-run any one and am not a bottle-neck like the guy in "Meet The Fockers"! 

I have to get some brake work done before I can take her out again, and she really needs a tune. My biggest problem is the fuel lines and tanks are full of crud and I am too cheap and lazy to drop them and do the right thing.

Let's keep in touch and see if we can't hook up for a mini-jam: my brother-in-law has a 22 foot 1979 Minnie Winnie and a Jeep he can tow.

Hope to hear from you,

Spudboy and Family



From: Boise_Chief1
Sent: 4/16/2005 1:53 AM

Spudboy,
It's good to finally "meet".  I'm a new owner, I got mine this january and am in the process of fixing all the previous problems  I have the interior (what the Mrs. cares about) almost done.  I am planning on a partial re-paint before summer.  We should swap numbers or E-mails.  BTW Boise Auto down at 30th and Main is outstanding for finding parts others can't.
Ttyl
Sean