speedometer drive assembly fault

[Pierre_Smits]

Hi,
My 1983 Marlin, 1.8 Marina Based, has a problem considering the speedometer: It’s not working. The cable is NOT broken and the Smith Gauge is fine (tested while connected to drilling machine)
I found out that when I push the inner part of speedometer drive assembly (Pinion?) a bit up while driving the cable (and pinion) started turning around again. (I rather not perform this test anymore because it can hurt/kill me easily when something goes wrong. I had the wheels of the ground and the car running while I was underneath the car….you better not try this at home…)
Ok, luckily still alive, problem detected but no solution yet!
Can anybody give me some advice what to do to solve the problem? I rather not take off the gearbox or that kind of major operations. Attached are some photos maybe somebody notices anything strange? I noticed that I could not turn the square center (to pinion) but I could turn the outer silver part (housing?) by hand
Maybe the whole assembly should be pressed further in? or out? Hand how do I do this? Using a hammer :-)?
All help is welcome! Thanks!

Kind regards
Pierre

[dogoncrazy]

Re: speedometer drive assembly fault

Pierre
It shouldn't be possible to turn the inner part but you can turn the outer - so this is correct. I would suggest that you remove the items in the picture to ascertain the state of the speedo drive gear - the 'outer' will pull out of the gearbox extension assy , its only a push fit with a o ring seal .You can then remove the drive gear which may be worn.There is a further 'worm' or scroll type gear on the gearbox output shaft which drives the aforementioned which could also be worn /damaged in which case I'm afraid its a gearbox out job as its pressed on to the shaft.you will lose some oil when you take out the drive pinion so be ready to plug the orifice.I presume you have the forked retaining plate and bolt as this holds everything in situ?

[stevejgreen]

Re: speedometer drive assembly fault

Probably the speedo drive gear that is plastic and is easily removable. The steel gear on the gearbox output shaft is unlikely to be worn.


Replacement from Rimmer Brothers

Part Number 219003
Description SPEEDO DRIVE PINION 22 TEETH (red)
Retail Price £23.74 inc. VAT (£20.64 exc. VAT)

Probably worth changing the speedo cable as a precaution. If it was stiff in its housing it would put excessive load on the plastic gear. Available from Speedy Cables. It will be a custom one as the original instruments had a clip connector, perhaps a Triumph Spitfire cable will fit as they used Smiths gauges. They will be able to make one no problem.

[Pierre_Smits]

Re: speedometer drive assembly fault

Alan: I do have the forked retaining plate and bolt. I can use this to put pressure on the temporary cover of the hole, good idea! Tomorrow I'll try to get it out. I'll try to 'just' lift it out.
Steve: thanks for the info!!
the speedocable innerpart is very flexible and looks still fine. I replaced the plastic end of the inner cable by a steel one so that this will not break. When I bought the car it used to have a cut-off cable squeezed not to be round again anymore. Now I made a small square 'tube' to go in the square center to the pinion.

Now, I have to go underneath the car and get it out to see what's the current condition of the drive gear.

[Pierre_Smits]

Re: speedometer drive assembly fault

hi,
Today I disassembled the speedometer drive gear and photos are attached. By the way: No oil came out wile the hole was open but the gear wheel was wet of oil. Should I refil the system?
Steve: I counted the number of teeth twice and the current one only has 20 teeth!! As can be seen in the pictures the teeth are worn and one part is quite flattend as if the number of teeth is incorrect. How can I make sure a marina gearbox is used or maybe a MGB (e.g.21teeth)triumph(e.g.17teeth)?? just to prevent installing the wrong type. Probably you are right but I found somewhere that MGB has 21teeth, however I might be wrong...
which car+type is the 22teeth coming from? then I can have a look in the netherlands first before ordering in the UK.
Thanks for all the help so far!

[dogoncrazy]

Re: speedometer drive assembly fault

Pierre
Do you have a overdrive gearbox fitted? If so it's probably from an 1850 dolomite which I believe had a20 tooth drive pinion - part no NKC48 from Rimmers

[Pierre_Smits]

Re: speedometer drive assembly fault

I do NOT have an overdrive: only 4 gears and reverse.
So, probably the wrong one was installed by the former owner. it never worked since I have the car (Oct last year). This is also why you see that the teeth are damaged and some are even 'splashed'(completely flat)

How can I be sure that the 22teeth is correct? how about the 21teeth used in MGB? can I some how check which brand gearbox is fitted? any number or so? remarkable differences?
thanks

[stevejgreen]

Re: speedometer drive assembly fault

Sorry my mistake

If the gearbox is a 1.8 Marina (It looks like it) and you have a Marina Back axle from a 1.8 with a 3.63 ratio then the gear I quoted was the wrong one it should have been 219001 with 20 teeth.
The Spitfire used a very similar gearbox and has the same axle ratio but different tyre size to the Marina.

I have just checked my spare 1.8 gearbox and it has a 20 tooth gear like yours.

The MGB gearbox is quite different to the Marina as it has an integral bell house.

I would still suggest a new speedo cable. The inner may look fine but the wear could be in the outer and invisible though possibly a good clean will make it OK.
I have a spare cable though it is second hand with about 10000 miles.

[Pierre_Smits]

Re: speedometer drive assembly fault

Thanks for the help!!
I replaced the pinion for a new one and also the speedometer cable is new (production year 1984 on the original box :-)...). It all seems to work now, although the gauge is a bit whobbly. Any final suggestions on this?
thanks!