Volvo RWD 120-130 Forum

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Bouncy Speedometer after Transmission Switch. 120-130

As some of you might remember that I finally tracked down a 122S of my own, but it required an 800 mile trip to Texas to get it. Low price, original owner, upgraded ignition, sway bars, brake light switch, and a ton of spare parts included - absolutely worth the trip.

I picked it up in early may and drove it 650 miles towards home. It started out with a crippled transmission. 1st gear was gone, but the B18D engine was more than powerful enough to get me going from a dead stop. The problem is that I was losing 2nd and 3rd gear 150 miles out from home. Instead of chancing the last leg, I rented a car carrier and pulled it the rest home with my 940.

I had two extra gearboxes, so as soon as I got it home, I put it up on jacks, and dropped the old gearbox (the shape of the firewall makes it NOT easy) I installed the bellhousing and new gearbox separately, using 3/8 allen socket to secure the gearbox to the housing.

The strange part came when I went to hook up the speedometer. There was no speedometer gear in my new gearbox. I figured that I would just switch the gearing from the dead gearbox - after all it gave me nice and smooth speedometer readings for the whole trip back. I went to pull the gearing and found the melted remains of a green gear - a clue about the death of the old gearbox, but not a huge issue. I had two spare gearings, both yellow. Th color difference bothered me but I ended up pulling the gearing from the other good gearbox. It too was yellow. "Weird" I thought, and put the transplanted yellow gear into my "new" gearbox.

Now, ever since the switch, I get a really bouncy speedometer reading. It seems to be giving me a proper speed, but it jumps all over the place with every little jostle or acceleration. The other owner (seller) tells me that the green and yellow gears are different, but I was unable to see any difference in teeth between the remains of the green gear and any of the yellow gears. plus, why would the other box have a yellow gear in it. They are all M40 gearboxes.

In checking some of the parts suppliers I could not find any green gears for sale, only yellow. Is there really a difference? Would this make my speedo jumpy? Do I just need to relube some components? Any other thoughts?
--
You mean Volvo makes cars that are *NOT* Wagons?!?








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    The cable could be hanging up in the housing, causing the bouncing. 120-130

    The cable could be hanging up in the housing, causing the bouncing. If it is too tight end to end or not lubed, it winds up like a spring and lets loose and bounces the speedo.
    --
    MPergiel, Elmhurst, IL '74 145e T-5 'Orange Alert'








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    Bouncy Speedometer after Transmission Switch. 120-130

    The different colors are indeed to indicate a corresponding rear-end ratio. Each gear has the appropriate number of teeth to read the proper speed from it's rear-end match.








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    Bouncy Speedometer after Transmission Switch. 120-130

    There are even pink, brown and blue gears besides your yellow ones and the green! All differ on the amount of teeth on them and are used for matching different gearboxes to different speedo-units (different models too). I think I have a pink one installed on my 67 wagon.
    The bouncy thing I would think could be a result of broken teeth of the gear or a bad speedo-cable. Is the connection cable-gear all right? The end of the cable should be very NOT round. I would try and replace the cable before taking any other steps or before looking for another (colour)gear. If your originial gear was stuck in the housing it could very well be that your cable died.
    If the speedo-reading is not correct you can adjust by using another colour gear afterwards.

    Good luck!

    Leon







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