1098 van with 3.7 diff correct speedo readings ?

[vanboy]

hi,ive fitted my 1968 standard 1098cc van with a 3.7 diff,im very happy with this as the vans lovely to use on the motorway as it sits lovely around the speed limit and is still nice in town with the standard gearbox its also oh so econmical but does anyone know a speedo i can use that will show the correct speed as its now reading a lot slower than your going,or are there any very clever people who can work out what the correct speeds will be,then i can take apart a spare speedo and make my own speedo face? i know i could try and get my girlfriend to drive at constant speeds and record what they are but id rather keep my minor away from her when shes on the road,thankyou.

[Multiphonikks]

Hi There!

To quote from the Smiths Care of Instruments Book:

Disconnect flexible drive from Speedometer. With gears in Neutral, count number of turns of inner shaft for six turns of the rear wheels when vehicle is moved forward in a straight line. Measure rolling radius of the rear wheels with tyres at correct pressure- centre of hub to ground. Apply figures in formula below.

FORMULA

1680N
______ = T.P.M. No.
R

Where N = Number of turns made by the inner shaft for 6 turns of rear wheel and R- Radius of rear wheel in inches meausred from centre of hub to ground.


EXAMPLE:

Cardboard pointer on inner shaft rotates 9 1/8 times as vechicle is pushed forward 6 turns of rear wheel. Rear wheel radius = 12 1/4" Flex turns per mile.


= 1680 x (9 1/8)
_____________
(12 1/4)


= 15330
_______ = (approx.) 1251 = T.P.M
(12 1/4)



Number shown on speedometer should correspond within 32 either way with the T.P.M Number obtained from the above.

The T.P.M number you have on your speedo is the one on the right of the serial number, or sometimes below the odometer.

Hope this helps!

Nikki

(It'll certainly mean all you have to do is to find a speedo which has the right T.P.M number

And since all you need is the right gearing, you may (I'm not sure on this one) be able to change just the lower shaft and magnet part of the speedo, keeping the original Moggie speedo face and dragcup.

Nikki

[Kevin]

Or you can send the speedo to someone like Speedy Cables or Richmonds with the diff Ratio and wheel tyre combination being used and they will recalibate the speedo for you.

[wanderinstar]

I have been thinking about putting a3.7 diff out of a Wolsley 1500 into my 1098 2 door. But I was led to believe that it would be to higher gearing for the 1098. Do you not have any such problems?

[vanboy]

i think its fine,you can do 65-70 in comfort on the motorway and in town first gear is so low anyway you still can pull away and keep with mordern traffic.theres no way i could have a van with standard diff,even if its a 4.22. and also when your going down the motorway criusing along at 70 its nice to see peoples faces as your "slow" old minor criuses past.ive had a lot of cars in my time including silver shadow,daimler db18,porshe 911,my mordern car at the moment is anew 2.5 x-type and it hasnt seen the light of day in three weeks,im happy driving my van so it cant be bad!

[Kevin]

Vanboy I assume your local driving area is fairly flat, as even a 3.9 with the standard engine will have problems with hills, on a steep local hill I can go up it in top gear with my 1275cc engine but with the previous 1098cc it struggled to make it in 3rd without a bit of a run at it and this is with a 4.22 diff, with a 3.7 I would imagine 2nd gear would stuggle on the same hill with a 1098cc.

[rayofleamington]

yes - you may need to change down gears for hills, however the diff doesn't change the engine power so changing down one additional gear doesn't mean you will necessarily go any slower.
I was looking for a 3.9 for my 1098 as the standard ratio is dreadfully undergeared for motorways but didn't find one in my price range (cheap).

[Kevin]

so changing down one additional gear doesn't mean you will necessarily go any slower.

Agreed Ray but having to use 2nd for hills that can be taken in 3rd is I feel going a bit far which I am sure would happen with a 3.7 diff.

[vanboy]

well i drove the van from hertfordshire to the cotswolds,then around north wales (they have a few hills there)and at the weekend going to new forest,yes on really steep hills in wales you have to change down sometimes but thats what the gearbox is for,works for me!

[rayofleamington]

Hmm... And I just sold my 3.7 diff thinking it would be too much for a 1098

[wanderinstar]

When I got my 3.7 diff from the Wolsley I worked out that if you used 13" rims (A35) with 155X13 tyres it just about equates to 3.9 with 14" rims. I,ve just forked out for set of A35 wheels and tyres which I now may not need.