diff change - speedo issue?

Post by **wibble_puppy** » Mon May 19, 2008 4:54 pm

hi guys,

new diff - probably a saloon one rather than a van - will I need to do anything to the speedo to compensate for the different ratio?

/yet another ignorant question

wibble xx

Post by **Peetee** » Mon May 19, 2008 5:03 pm

Yes or no.
The van diffs were generally the same ratio as 948 minors ie 4.55. If you have a gold faced speedo you should be fine.
If you have a black speedo it would be calibrated for a 4.22 diff so would be slightly out for a van diff. % difference this way would be in the region of 6% over.

The diff should have a marking on the crownwheel that will tell you the ratio (expressed as the number of teeth on each gear eg 9/38). Divide the big No by the small No and that gives you the ratio.

Post by **wibble_puppy** » Mon May 19, 2008 5:31 pm

thank you so much peetee!

the van has a black speedo but I don't know what year saloon the diff was out of. I'll go and look at the casing and post again!

wibble xxxxxx

Post by **aupickup** » Mon May 19, 2008 6:10 pm

saloon diff was 4.22 with black speedo, so the year of the diff is not a problem.

either find a saloon speedo black face or have your one re calibrated

i may have an excellent condition speedo from a saloon later for grabs

Post by **MarkyB** » Mon May 19, 2008 6:24 pm

If you have or can borrow a GPS you can check how far out it is.
If you are lucky it might be more accurate than before as car speedometers seem to invariably read faster than you are actually going.

Post by **wibble_puppy** » Mon May 19, 2008 6:34 pm

thanks for the info, guys!

Am hauling the diff out of the axle tomorrow so will check the crownwheel markings then

au thank you very much for the offer of the speedo!

more ignorance here, but if you put in a new speedo how do you get it to read the correct mileage?

and where would one get a speedo recalibrated?

wibble xx

Post by **alex_holden** » Mon May 19, 2008 7:15 pm

wibble_puppy wrote:more ignorance here, but if you put in a new speedo how do you get it to read the correct mileage?

I answered this yesterday! It's a bit of a fiddly job - you have to take the mechanism out of the case, alter the odometer rollers as I described yesterday, then put it back together. If you have to remove the face to get better access to the mechanism then you should carefully mark where the 'drum' is when the needle is at zero so you can put the needle back in the right position later.

and where would one get a speedo recalibrated?

There are companies that do this but I don't think it's cheap. I would like to know how they do it. They must have a test bench that can spin the rotor at a programmed RPM to check how much it is out by, and to alter it they presumably either magnetise or demagnetise the rotor slightly as appropriate.

Post by **aupickup** » Mon May 19, 2008 7:20 pm

if the spedo is the correct one for a 4.2 diff then all is ok

Post by **wibble_puppy** » Mon May 19, 2008 7:46 pm

ah, yes, i saw that thread - thanks, Alex. I think I'll just send it to you to do, if it needs doing, as it does sound extremely fiddly!

Post by **alex_holden** » Mon May 19, 2008 9:10 pm

No problem.

Post by **IslipMinor** » Mon May 19, 2008 11:34 pm

For cars, the gold faced speedo with 80 mph max is for 4.55 diff's and the later one with 90 mph max is for the 4.22, as are all the black faced ones - sorry, don't know about the LCV.

If you look on the face there is a number around 1500 for the 4.55 and 1370-1380 for the 4.22 - this is the revs per mile the speedo is calibrated for.

Post by **wibble_puppy** » Tue May 20, 2008 9:41 am

alex_holden wrote:No problem.

awww bless ya alex - I was joking - but it's very very kind of you to allow me to twist your arm like that!

you are lovely

and you never know, you may get a heavy, round package in the post one day

IM I'm not sure how to apply that info to my van-speedo-plus-saloon-diff set-up. what am i missing? sorry to be thick

Post by **alex_holden** » Tue May 20, 2008 10:27 am

What numbers are written on the face of your speedometer and is the new diff a 4.55 or a 4.22?

Post by **mike.perry** » Tue May 20, 2008 9:14 pm

Speedy Cables in Swansea do a speedo repair and calibration service.
Their tel no. is 01639 732238. I have used them myself and their service is prompt and not too expensive. I intend using them again to calibrate my speedo for my 3.9 diff. You will need to supply then with details like the crown wheel and pinion teeth ratio (look in the workshop manual) and the circumference of the tyre

Post by **alex_holden** » Tue May 20, 2008 9:22 pm

mike.perry wrote:You will need to supply then with details like the crown wheel and pinion teeth ratio

In other words, the diff ratio (3.9 in your case).

Post by **wibble_puppy** » Tue May 20, 2008 9:50 pm

thanks everyone!!

alex_holden wrote:What numbers are written on the face of your speedometer and is the new diff a 4.55 or a 4.22?

Face of speedo: this is the very small print underneath the mileage recorder, right? It says "SN - 4423/14" and then "1504". So does that second number mean this speedo is calibrated for a 4.55 diff, then?

Diff couldn't come out today, will be out tomorrow hopefully, will report back then

Thank you all very much for all this advice!

wibble xx

Post by **alex_holden** » Tue May 20, 2008 9:58 pm

wibble_puppy wrote:Face of speedo: this is the very small print underneath the mileage recorder, right? It says "SN - 4423/14" and then "1504". So does that second number mean this speedo is calibrated for a 4.55 diff, then?

Sounds like it. If I were you I would get the vehicle back on the road and check the accuracy with a GPS before worrying about changing it or getting it recalibrated. It won't fail the MOT on a slightly inaccurate speedo.

BTW a 4.22 diff is better suited to a 1098 engine than a 4.55 if you're not lugging very heavy loads around. Ray actually has a 3.7 diff in his 1098 pickup but that is probably taking it a bit far!

Post by **bmcecosse** » Tue May 20, 2008 11:06 pm

It doesn't need to have a speedo at all for the MOT! But it does for 'Construction and Use Regs'.

Post by **wibble_puppy** » Tue May 20, 2008 11:38 pm

alex_holden wrote:If I were you I would get the vehicle back on the road and check the accuracy with a GPS before worrying about changing it or getting it recalibrated. It won't fail the MOT on a slightly inaccurate speedo.

that's great

yeah recalibrating the speedo is way way down the To Do list...

BTW a 4.22 diff is better suited to a 1098 engine than a 4.55 if you're not lugging very heavy loads around. Ray actually has a 3.7 diff in his 1098 pickup but that is probably taking it a bit far!

yeah i am looking forward to it! the only heavy load it will have to carry 99% of the time will be me

cheers again alex

Post by **Roni** » Wed May 21, 2008 10:21 am

I found a page that has some interesting links including "Repairing Jaeger & Smiths Speedometers". There are some other interesting reads there too.