Too many revs? !!!

[johny]

Hey even I make mistakes sometimes!

[GT6M]

If yer speedo,or rev counter twitch,n all owa the spot,

then a good chance the inner drive sheaths gon awol in parts

 

Mine did this since I got it, my Spitty did it,

last yer the speedo packed up, found it wer drive cable snapped

the coiled wire inside has all curled up,

 

2 new cables, and speedo an rev counter are  noo as smooth as a moderns/

 

It could also be that some one es put in a 4.55 diff

Best thing for ye t,doo is to jack car up, get under it,

an mark prop flange an diff crossbeam

 

then mark both axle flanges an the diff case

then turn the input shaft , and count hoo many times the prop end goes aroond,

till the marks on the axle shafts doo 1 full turn

 

a 4.55 will be just owa 4 1/3 turns

a 4.11 just over 4

a 3.89 just short of 4

 

If one wheel wont turn, or sticks, yee,l get a false reading,

if so, then move both wheels at same time  1 full turn,

an count the turns of the prop end.

above figs will be same, just reversed.

 

its really the only way t,fin oot wots int rear end.

 

 

[euan douglas]

Thanks for all the replies  -  I'll try and figure out what diff I have and take it from there.

Euan

[Alex59]

Hello,

i've the same issue on my vitesse. The read on the speedometer seems fine, when i'm driving at 60mph on the speedo, i obtain 56/57 mph with gps.
But when i'm driving at 60/62mph, my tacho indicates 4000rpm with the OD on.

I bought a laser counter rev which confirm the difference between the engine rpm and tacho indication. 

But to confirm that my tacho is out of order i'd like to check if the rpm of the cable is correct (maybe the gear under the ignition system is not correct)

So Can you give me the rpm of the cable in order to indicate 1000rpm on the tacho. My tacho is a jaeger 3.55-1. So i think the cable have to do 1000/3.55 =282 rpm but i'm not sur.

 

To check the cable rpm i'll cut a disc in cardboard, put a reflective sticker on it and use the laser counter rev.

 

Thanks for your answer

Alex

 

 

[dougbgt6]

On 13/07/2020 at 15:09, JohnD said:

I KNEW,  I just KNEW, that someone would call me out for not getting the list of models and their diffs not absolutely, perfectly and completely correct!

You try to help people and then some smart ass pops up to tell you where you went wrong!😡

Doug

[Clive]

27 minutes ago, dougbgt6 said:

You try to help people and then some smart ass pops up to tell you where you went wrong!😡

Doug

In this case, not wrong, but added a little extra detail. All helps expand the knowledge base. Sadly I keep forgetting things (like where my phone/keys/glasses etc are, but can remember stupid stuff like diff ratios)

[thescrapman]

Alex

if the distributor is the correct one, then the gearing in it should be correct, never heard of anyone changing it.

I have checked speedo and rev counters with an electric drill in reverse in the past.

you could use your laser counter to check reverse speed on drill and then run rev counte r off it.

 

[Alex59]

Thanks thescrapman for your answer.

Can you confirme the 282 rpm of the cable to indicates 1000rpm on the tacho. (tacho 3.55/1)

[Pete Lewis]

yes 282 rpm  cable revolutions will give a reading of 1000 on the tacho dial 

Pete

[Alex59]

Thank you, so this weekend i'll check it  

[Steve P]

3 hours ago, thescrapman said:

I have checked speedo and rev counters with an electric drill in reverse in the past.

Was that just before selling the car with "low mileage" Colin?.

Steve 

[Alex59]

So I have checked my tacho with an electric drill and a laser counter rev.

When my electric drill is close to 612 rpm, the tacho indicate 3000 Rpm instead of 2150 / 2200 rpm.

So i have to send my tacho to refurbish it.

[Pete Lewis]

i would remove the rim   remove the glass  undo the two screws and remove the mechanism  and give it a good look 

it may be the magnetic ring is in contact with the light ally disc , it may have oil inside , it may just need the needle moving on its spindle

easy to try hold disc   with needle at 3000  and just move the need to read 2200   then re test do not take the needle off as then all is lost as the hair spring unwinds  

if the needle spindle  bearings are worn its  send for a rebuild 

a dash of lube on the main shaft is also advisable as these dry out and then seize

but simple ideas to try 

Pete

[Roger K]

Couple of things might help:

To remove the glass retaining ring, sometimes a very gentle twist between the lugs that clamp it on and the body of the instrument with a small flat-bladed screwdriver will help to break the seal from old rubber, rust etc. and make it easier to remove.  In severely corroded examples it is sometimes necessary to bend the lugs right up to 90˚, but do that very carefully and be prepared for some of the lugs to break and watch you don't deform the retaining rim.

NEVER, EVER LUBRICATE AN INSTRUMENT DRIVE CABLE - they don't need it as they usually have either a nylon or PTFE lining, which gums up with oil;  any lubricant you apply WILL find its way up into the instrument head as the spiral wound inner will take it up there like an Archimedes Screw.  The instrument will soon start to fail.

NEVER, EVER LUBRICATE AN INSTRUMENT MECHANISM - lubricating these things is a specialist job, requiring tiny drops of clock or watch lubricant administered with a fine needle.  A single drip is too much.  As Pete says above, if the instrument is old and very dry a tiny drop of clock oil on the mainshaft shouldn't hurt but needs to be applied very carefully, not dripped on the end to allow it to run down and soak in!

Good job no Triumphs of this period had Chronometric instruments.  I've had a few of those over the years and whilst the action of the flicking needle is gorgeous, maintenance and repairs are a nightmare - in both frequency required and cost.

[Alex59]

4 hours ago, Pete Lewis said:

easy to try hold disc   with needle at 3000  and just move the need to read 2200   then re test do not take the needle off as then all is lost as the hair spring unwinds  

 

Thanks Pete and Roger for your answer.

I tried this Pete's tips and it worked. But how is it possible the needle rotate on the axis ?

Does it means, i have to send it for a rebuild?

 

Alex

[Pete Lewis]

the needle is only a light press/push fit on its spindle , so it can reposition itself its not bullet proof  

being mostly plastic needles a small dab of supa glue will stop it moving again ...

pete

[NonMember]

3 hours ago, Alex59 said:

I tried this Pete's tips and it worked. But how is it possible the needle rotate on the axis ?

Does it means, i have to send it for a rebuild?

It works for the specific speed you tried, or to correct a fixed offset in the reading. You now need to re-test at several other drill speeds to see whether it's correct at each (any!) of them.

If the needle was originally reading always 800RPM high - so 1600RPM at idle, 4800RPM at a real 4000, 800RPM when stopped etc. - then the trick of moving the needle works. If it was consistently reading 30% above the real revs then it's just made things more confused and you probably need to send it for a rebuild.

[Pete Lewis]

yes agree thats all down to the tension on the small hair spring and the changing load as it winds up as the needle rotates

it has the same base  mechanism as the speedo 

having had a Smiths head drive unit to play with in the past its a right pain getting the magnetic flux to drive the needle disc and keep a linier load so  the hair spring  readings are aligned to the input revs 

which  i had kept it but like many factory closures it got binned , it ran off a 13a socket but when you energised the electro magnets to alter the mag drive you could attract all the canteen cutlery and half the assy line hardware   very potent ..    happy days 

Pete

 

[Alex59]

I tried differents speed and it’s pretty good between 1500 & 2500 rpm, above 2500 rpm the indication is not correct. For exemple 4000rpm indicate indicates on the tacho instead on 3500.

So i’ll send it for a rebuilt.