Speedometer lag possible cause
Is it possible to have excessive side or end play on a PG output shaft that would cause the drive gear and the driven gear to separate enough to cause speedometer needle lag on acceleration and when kicking into passing gear? Speedometer has been rebuilt and plastic gear, bullet holder, replaced along with the drive cable and housing. Looking for possible sources prior to removal of the cluster for another attempt at speedometer head rebuild. BTW, the position of the steel gear was checked and found to be centered on the shaft and showed no signs of wear or damage.
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Re: Speedometer lag possible cause
Al,
Shot in the dark, but the lube on the cable may not be good. Cold will do that to a speedo cable as the lube gets thick and causes to much resistance to turn.
Dom -
Re: Speedometer lag possible cause
I agree that if the cable is too resistive due to over lubrication, it could cause that, but you said you changed it. You didn't use grease to lube it, right?
I'd try to isolate the fault......Remove the cable from the transmission and connect it to a high speed drill, running in reverse. Simulate the tranny shifting etc with your finger on and off the trigger and see what happens. You will always get a slight fluctuation, but it shouldn't be excessive.
If it still does, then attempt to isolate if the speedo head or the cable. If it doesn't then the tranny gears, etc could be the culprit.
I think you still have a little more testing to do before you get in there with back pain pending.
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Re: Speedometer lag possible cause
Al,
Wrote my post to fast. What lube did you use on the cable? Incorrect lubes will get thick when cold and will cause a lag then a large jump in speed.
Dom
UOTE=Domenic Tallarita (51287);732191]Al,
Shot in the dark, but the lube on the cable may not be good. Cold will do that to a speedo cable as the lube gets thick and causes to much resistance to turn.
Dom[/QUOTE]Comment
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Re: Speedometer lag possible cause
Suspect you have a bad odo or both are bad causing cable "wind up".Comment
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Re: Speedometer lag possible cause
Dom & Richard, this is on-going from this past summer when I put the car back on the road following a 20+ year restoration. I 1st used the repo cable and housing as supplied. Then at the speedometer rebuilder's suggestion, I checked the plastic gear which appeared to have no signs of wear and checked to see if the steel gear was centered in the hole, which it was. ( had a transmission man put it on the lift, pull the tailshaft back and verify that it was centered). The rebuilder told me to send back the unit and he would recheck it. Called and said he would send me a new unit out. Same results. Installed the old original cable (1st with wheel bearing grease and then washed it out and greased the cable with speedometer grease), new plastic gear and new bullet retainer, with same results again. Also need to note that both ends of the cable were loosely hand tightened and the cables were checked for short excessive bends. My wife wanted to drive the car during the summer and fall some (approx. 350 miles), so it was put on the back burner while I recovered from a broken thumb and then work picked up. Now during the winter months, I want to get the 2-3 problems fixed the were discovered during the shakedown drives. BTW Dom, the AC compressor works great. Thanks again for outstanding service!!Comment
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Re: Speedometer lag possible cause
Richard, I will try the drill test as soon as I return home from Tn, that is assuming my wife will watch the speedometer needle for me. Any tips ypu can supply? I have a Dewalt 18v cordless drill. Will this be sufficient?Comment
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Re: Speedometer lag possible cause
Yes, that will be fine. Run it in reverse after you clamp the cable up in the chuck. Try to keep it straight so it doesn't hurt the cable.
May want to double check this too. One other thing I thought of. Some repro cable assemblies have the inner cable tip at the speedo head a tad too long. I had one that eventually hung up when the cable clamp was tightened over the speedo housing. I loosened it a bit and it was fine. So........
I then removed it from the head and filed some of the tip off to shorten it. Then it was fine all snugged up.
RichComment
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Re: Speedometer lag possible cause
Thanks Richard, I'll post back when I get this checked. AlComment
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Re: Speedometer lag possible cause
The idea of cable resistance or wind up is not really possible. Take an old cable and attempt to hold one end while twisting the other. If enough torque is applied to actually turn the input end, one or the other end fittings will shear right off. The cable, when in it's outer sheath has almost as much resistant to winding up as a solid rod.
Even if it did somehow wind up, this extra twisting would have to then release itself, which would be expressed as speedo over shoot for as much and as long as the gauge originally lagged in the first place.
I think you've just got a sticky gauge. Best speak to whoever rebuilt it for you.Comment
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Re: Speedometer lag possible cause
I can tell you with a good degree of certainty that windup is not only possible, it is common, in the colder areas of the country. Your second part scenario was the complaint brought in. Speedo noisy and would bounce off the stop pin until warmed up. Sometimes it was the head, but often the cable was gummed up. Pull the core, wash down the core and pour some solvent down the casing. Wet the core with a bit of atf and the problem would go away. Those that ignored the problem long enough broke the cable (the cable unravels before the end breaks off).
SteveComment
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Re: Speedometer lag possible cause
Steve-
I live in one of the coldest areas of North America. Sluggish mechanical gauges during winter were/are common. They magically fix themselves as soon as the passenger compartment warms up. Not the cable.
A dry or gummed cable can cause awful noises and an oscillating needle as the cable binds/releases but the idea that the output end of the cable would lag behind the input side by the dozens of revolutions required to induce noticeable gauge lag is very far fetched. The plastic gear in the transmission would shear almost instantly.Comment
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Re: Speedometer lag possible cause
Do you live in Winnipeg too? That's where I was, working in the trade in the 70's and 80's. While -30 to -40 F might not be the coldest in Canada, it was cold enough to bring out complaints you wouldn't see in most other places. And I fixed many a bouncing needle doing just as I described and only that.
I should have elaborated, no I'm sure as well that this is not the op's problem. Binding cable reacts just like you said in the second part of your post, not what his is doing.
I am also iffy on it being sticking in the speedo head. When the needle's spindle begins to stick in the frame the first thing you ever notice is you will slow down and/or come to a stop and the needle will be stuck momentarily then drop to the bottom. The force to return it to 0 is the weight of the needle only, whereas the force driving it is obviously greater than the weight of the needle. Where will you see it stick first?
I believe he is on the right track looking for something slipping. The most common thing is the square drive ends of the cable slipping in either the head or the driven gear. The next most common would be the driven gear slipping on the drive gear. But even with this, what you usually see is moments of the needle dropping when it slips, not holding it's own but lagging behind.
All that said, I dealt with a reasonable number of speedo complaints over the years, and this one is quite uncommon.
SteveComment
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Re: Speedometer lag possible cause
Steve-
I'm about an hour south of Ottawa. We agree on the bouncing needle cause- but that's not what the OP has.
If the cable was binding and causing under-indication- why would it been seen only under acceleration and resolve itself once the vehicle is at a constant speed?Comment
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