speedo jumping

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blavatsky
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Joined: 20.06.2011
Location: okehampton devon uk

My speedo is jumping on my 1992 300GD manual diesel and i have been advised to remove the clocks and send them off for repair, do you have to take the complete dash out to remove cluster, is there any particular way of getting the clocks out without trashing my interior  :  }=

fixwin38
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Joined: 09.07.2006
Location: northern ireland
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Re: speedo jumping

Hi Your 1992 G' has a a speedo cable attached to a geared interface on the transfer box ..the lubricant inside the speedo cable dries up and creats drag on the nylon gear at the transfer box interface...I have withdrawn the inner drive cable by removing the steering wheel ( pop the the plastic star out of the centre and with a 27mm socket   braaker bar or ratchet undo the nut that holds the wheel to the column) use two thiin blades (at least 2cm wide) and insert  at each side between the binnacle and the instrument cluster. after the cluster has come towards you 10mm gently slide it out of the binnacle and unscrew the speedo cable from the back of the speedometer....*** keep an eye on any wires that may come off and remember where they go.....crawl underneath and unscrew the speedo cable from the transfer box ..you will see the inner drive cable protruding from both ends ...with a pair of pliers or small adjustable spanner rotate the drive cable..if stiff remove it by pulling it out of the outer sheath...flood the outer sheath with WD  40 and work the drive cable in and out until all the old lubricant has been removed...wipe the drive cable clean and smear with light oil...next remove the  interface head from the transfer box and check for damage to the nylon gears ...if none clean and re lubricate... if damged get a new one from MB ....put the inner drive back into the outer sheath and  rotate with vari speed drill at low speed ..refit  cable to speedo head and check that speedo is reading and not jumpy using variable speed drill at VERY LOW SPEED  while another person is monitoring the needle movement of the speedo ..if all is well re instal ..if speedo still jumpy then the the drag cup mechanism inside the speedo instrument is faulty......expensive to get replaced ..same instrument in W124 saloon so of the the breakers....

blavatsky
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Joined: 20.06.2011
Location: okehampton devon uk
Re: speedo jumping

Ok, Fixwin38. thank you very much for giving me such a detailed explanation to my problem and spending the time to do that.

first if all i removed the cluster and with a drill tested to see if that was where the problem lie but it was working fine. then got it up on the ramp, checked the nylon drive in the transfer box, that looked fine, also put drill on transfer box end of cable to check, and it was jumping at the speedo cluster, so drive ok. then checked the speedo cable at the cluster end, this looked slightly worn and rounded off, so with some help of the mull grip tried to square the cable end back off. this cured the jumping but the speedo still clicking, (as loud as if were like it was the indercator on). i tried to remove the cable from its outer sleeve so that i could give it a good clean like you said, but i couldnt get it out. think this is the only option left apart from buying a new cable which has to come from Germany and is not far off £100. any suggestions would be well receieved.

fixwin38
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Joined: 09.07.2006
Location: northern ireland
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Re: speedo jumping

Hi
check if the drive cable has a circlip/ferrule holding it it to the outer sheath...alternatively spray WD40 into the cluster end of the cable until it runs out at the lower end then spin the drive cable with the drill forward and reverse until the notchiness disappears..drizzle light oil in the sheath from the speedo end and spin the drive with the drill ....only a temporary cure but could last 3/4 years before repeating.......

blavatsky
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Joined: 20.06.2011
Location: okehampton devon uk
Re: speedo jumping

thanks once again for your quock responce. i did exactly what you said, took some time, but when i put the speedo back on it was still clicking. After a few minutes thought it would be a good idea to check the speedo clock again, the first time we tested it we rigged it up to an air compressed drill, which was pretty loud, this time i hooked it up tpo my battery drill and listened to the back of the clock, yeah the clicking was coming from the clock. on closer inspection notice that one of the cogs had worn. so ive ordered a second hand one from a w124 off of ebay  for £38 inc postage.

fingers crossed. thanks again for you time.