Speedo photos to Munie speedo post
Positions of driven gear shown all the way in and a few millimeter out because of ware on housing rest stop.
Jack
Jack
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Re: Speedo photos to Munie speedo post
Jack -- I doubt that is "wear". My pic shows minor wear but it's only about 2 thou deep. What shows in your pic is really the factory-machined depression to provide the flat thrust surface. I have two '584' tails here, and checked them both; they show same minimal wear. This shot shows a bit of 'tip wander' which might have been caused by a worn plastic shaft.
Your plastic gear is being 'eaten' on the center of the teeth. Means it's in the correct position relative to the steel gear. Wear on edges would point to improper bullet insertion or something wrong on plastic shaft length. -
Re: Speedo photos to Munie speedo post
Thanks for your input. I can move the gear in and out more than 1/8 of an inch. The distance you can see between the in position of gear in photo and the out position shown. In an other post (different forum ) a member posted the driven gear and fitting in a photo ( with housing off main body) shows it flush with driven gear fitting when in locked position.
Mine would show the space you can see in photo
JackComment
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Re: Speedo photos to Munie speedo post
Jack------
What you have shown here is the 22 tooth "silver" (or, gray) DRIVEN gear. This gear is of the "small" series of driven gears (0.80" OD).
Assuming that you have the original DRIVE gear installed in your transmission (i.e. for an M-20 transmission originally used with a 3.36:1 rear gear ratio), that gear should be the GM #3708144. This gear is 1.85" OD.
The above two gears should mesh perfectly.
However, if someone changed the DRIVE gear at some point to the GM #3708145 (1.77" OD and designed for use with the "large" series DRIVEN gears), then you would have incomplete engagement of the gears and, possibly, the problem you have.
If the above is the case, then you should be able to install the 22 tooth GREEN DRIVEN gear of GM #3860345 and solve the problem.
By the way, some "looseness" in the fitment of the speedometer gear fitting (the bullet-shaped piece the driven gear installs into) in the extension housing is quite normal.
Also, assuming that you have stock size tires and a 3.70:1 rear gear ratio, a 22 tooth DRIVEN gear ought to be about the right one. WHICH 22 tooth driven gear is the question, and that depends upon which DRIVE gear is installed in the transmission. Since the 22 tooth "silver" gear doesn't seem to work properly, it seems likely that, barring other problems, the 22 tooth GREEN gear will work.In Appreciation of John HinckleyComment
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Re: Speedo photos to Munie speedo post
Jack------
1) I doubt it. If that were to occur, I think the cable or the speedometer head would break first.
2) If, apparently, NEITHER the green or silver 22 tooth gears work, then you've got some other problem than an incorrect DRIVEN gear. Absent other problems, one of these should have worked.
Are you absolutely certain that the installed speedometer DRIVE gear (the gear installed on the transmission mainshaft) is the gear ORIGINALLY installed in the transmission (or, one IDENTICAL to it)? If it is, then the "silver" 22 tooth gear should have worked. If the other common DRIVE gear was, somehow, installed, then the 22 tooth GREEN DRIVEN gear should have worked.
However, there were a few other "odd-ball" DRIVE gears that were once available that would not work with ANY of the nylon DRIVEN gears. These were designed for use with the steel DRIVEN gears used with numerically high rear gear ratios (like 4.56 and 4.88). If one of these gears had gotten installed "along the way", it would not mesh with ANY of the gears you've tried. These special gears are quite rare and have not been available from GM in MANY years. However, it's still possible that years ago one might have found its way into your transmission. Since you've had what sounds like speedometer gear problems ever since you've had the car, this possibility takes on some credibility.In Appreciation of John HinckleyComment
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Re: Speedo photos to Munie speedo post
Jack -- if you think there's a possibility that you have one of these "oddball" drive gears that Joe mentions, here's a few details. The diameter is even larger, at 1.922" (so this might partly explain the interference on both the grey and green 22-tooth gears). It has only 6 teeth, instead of the 8 teeth of #145 and 144, so the teeth are are at a shallower angle, both on drive and driven. So plastic driven on this drive will have mismatched angles, as well.
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Re: Speedo photos to Munie speedo post
I went out to garage and took the following photos:
I believe I have an odd gear. I count only 4 large teeth and two small lead in for a total of 6. It looks like your gear in photo
Can you tell from my pictures.
JackComment
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Re: Speedo photos to Munie speedo post
Jack-----
I'm not sure that you have one of the "odd-ball" DRIVE gears; it's very hard to tell by just looking at a section of the gear. However, one thing I am sure of is that you have distorted teeth on whatever DRIVE gear you have in there. It's very evident from at least 2 of your photos. That sort of situation will "chew up" nylon DRIVEN gears in short order. So, I think that's your problem. The only solution to it is to remove the transmission from the car, partially disassemble it, and replace the gear. The gear is GM discontinued but available in the aftermarket.
Now, the question is just how did this gear get distorted? It sure didn't occur from interfacing with nylon DRIVEN gears. Most likely, it was damaged when the transmission was previously apart and some "klutz" went ahead and re-used it.In Appreciation of John HinckleyComment
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Re: Speedo photos to Munie speedo post
Thanks Joe,
I spent all day yesterday on my back taking out transmission. I just hated to go on my trip with no speedometer. I will have it changed out. It looked a little distorted to me. Thanks for the confirmation.
JackComment
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Re: Speedo photos to Munie speedo post
Jack, looking at your pics, I don't think so. When I turn my 4.56+ drive gear, when there's a tooth "merging" into the edge of both sides, I count 3 whole teeth in the middle.
The 6-tooth gear is the thinnest of the three, (which is the best way to differentiate, using a dial or digital caliper, if you have one in your hand
).
Another way to tell, since your trans is still in the car, is to mark the driveshaft and have someone rotate a rear wheel (if on a lift) while you count the number of times the drive gear tooth "merges" with the edge of the gear for one complete turn of the driveshaft. If 6 times, that confirms it; if 8 "merges", it's one of the other two, and you're back to square one
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Re: Speedo photos to Munie speedo post
Jack-----
As long as you have the trans out of the car, it's really not that much work to replace the DRIVE gear. If you have the skill, you could do it yourself. You don't even need to completely disassemble the transmission. Just remove the extension housing and the reverse gears.
The speedo DRIVE gear is an interference fit on the shaft. It's easiest to remove with a press or a special puller. Make absolutely certain that the new gear is installed at the exact correct position on the mainshaft.
It would be nice to see a photo of the gear that comes out.In Appreciation of John HinckleyComment
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Re: Speedo photos to Munie speedo post
Jack-----
One other thing I should have asked about and commented on is this: when you are talking about moving the gear in-and-out, are you talking about moving just the gear or are you talking about moving the fitting with the installed gear in-and-out?
You will note that there is a groove in the fitting into which the retainer (the "trapezoidal" shaped piece that attaches to the extension housing with a single 1/4" screw) fits. Usually, this groove is wider than the thickness of the retainer. So, the fitting will have end play equal to the difference between the width of the groove and the thickness of the retainer. Under some circumstances, the end play might be slightly less than this, but it can never be more than this. The end play of the fitting is usually very small (like, maybe, 0.010"), but there can be some.
If you are talking about the end play observed relative to the DRIVEN gear shaft with the fitting secured by the retainer to the extension housing, that end play can very well be in the range of 1/16" to 1/8" without any problems being created..In Appreciation of John HinckleyComment
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Re: Speedo photos to Munie speedo post
The end play I spoke of was with the fitting locked into position with the tab. The tap , when screwed down flush with housing would allow no movement of fitting.
The movement was of the driven gear in and out of fitting. With about the 1/8 or so of end play in fitting bushing.
I do believe that my driven gear appears to have some damage to it , from what we can see in photo.
I will have it replaced. Do I order the standard drive gear as shown on Zip an other vendors. Do I ask for a specific one that will match my 3.70 rear.
JackComment
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Re: Speedo photos to Munie speedo post
Jack------
As far as which gear to order, I guess it depends upon whether you intend for the car to be "permanently" a 3.70:1 or whether you might change it back someday. Actually, I think you're better off with the equivalent of the GM #3708144 gear (which may be what's in there now if it's actually the original gear). This way, you can use the 22 tooth silver DRIVEN gear with the 3.70:1 and you can also change to a 20 tooth blue gear if you ever go back to 3.36:1.
If you were to change the DRIVE gear to the one that would normally be used with a 3.70:1, you'll use the 22 tooth green DRIVEN gear and you won't have the option of changing to a lower tooth count DRIVEN gear if you ever go back to 3.36:1.In Appreciation of John HinckleyComment
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