Howdy all,

My '66 130 (2 door) is currently wearing a m-41 transmission, and my speedometer hasn't read correctly since I did the tranny swap.

As it stands, the speedo reads too slow.

I don't remember how many teeth are on the gear inside the tranny at the moment, it's a D-type that came out of an 1800 (as I recall).

Does anyone know what gear I'd need to make the speedo read correctly?

Thanks as always.

If it came out of an 1800 it'll have the fine splined black gear. You can't fit a 120 speedo drive gear unless you swap the appropriate worm in out of an overdrive that started out life in a 140 or a 120. The fine P1800 worm just nibbles off the teeth from the coarser standard drive gears.

When you read that, the first thing you think is "why" does the 1800 have the fine tooth gears and not the Amazon with what would seem to be the same set up. Is it because the 1800 is likely to be fitted with the right angled drive adaptor and needs a more precise and efficient drive? The black gear and the RA drive would work together as a unit with close tolerances and then the cable drive, with rather less need for precision, drives from that.There must be a reason and that maybe it.
I'm more than interested as i have an 1800 M41/OD in the garage which is lined up for my Amazon. Perhaps I should be looking for an MGB RA drive as the Volvo ones are hard to find. Finding drive gears not so easy either.

The drive gears for the P1800 are available now. I think the reason will be the different speedo in the 1800, probably Volvo bought something with an off the shelf ratio.

The right angle drive and the actual drive gear are independent of each other; there is nothing to stop you from just unscrewing the RA drive and replacing it with with a stock speedo cable or indeed putting a RA drive on a box that started life in a 120.

You don't need a RA drive to put a P1800 box in a 120, just get the longer speedo cable.

Well, that's good to know. However I think there still may be a problem. The 1800 D type OD with the fine teeth is used with a 4.56 axle. I'll be using a 4.10in the Amazon. Are there any other gears available with fine teeth besides the black one? There are several with the coarse teeth.

Hello,

Heres the issue, you have to use the speedometer drive pinion gear that is correct for your rear end ratio and the brand of your speedometer, which happens to be a VDO.

AFAIK the parts were never made for a 4:10 ratio and a D overdrive nor is there parts for the same ratio and a J overdrive either.

But you can use parts from your M40 4 speed, but this will only work on a D overdrive.

You have to use the the speedometer drive pinion gear which should be yellow with part number 380164 which is the correct 1 for a 4:10 ring and pinion ratio and the metal speedometer gear from the rear shaft of the M40.

You will need to have the metal speedometer gear machined to match the height of the 1 in the M41.

You will have to pull off the back half of the overdrive to change the metal speedometer gear on the rear shaft.

Good luck,



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Eric
Hi Performance Automotive Service (formerly OVO or Old Volvos Only)
Torrance, CA 90502

Thanks Erik. Seems a simple subject but the facts are shrouded by an oily mist. I'll have to make a chart!

M40/4.10 in B18 120/130 16 teeth/yellow pt#380164
M40/4.56 in B18 220 17 teeth/Green? pt#380166
M41/D OD/4.56 in B18 Amazon 18 teeth/Blue? pt#380168
M41/D OD/4.56 in B18 1800 18 teeth(fine)/Black pt# ?

D type gears have thick shaft with spiral groove
J type gears have thin plain shaft.

If you or anyone can confirm the queried colours and part# that would be appreciated. I've seen a white gear mentioned but that may be either a faded yellow or a modern replacement.

If you know the speedo error when using the M41/D OD with a 4.10 axle, it should be possible to back calculate what size tyres you need to match it to true road speed and that size may be usable. Hopefully done before you've bought those expensive Michelins.

Realistically unless you get the speedo recalibrated it'll be out a bit, to further confuse matters there are from memory 3 different part numbers for the speedo to throw into the mix.

However the speedo is is so inaccurate; just where do you read it, at the point or in the middle? I've always just figured out how far it is out and done the mental arithmatic.

Of course you can get all the right bits together, but it is kind of pointless. After all most of us add an overdrive to end up with slightly longer legs for modern traffic, and the one thing Volvo never built as far as I'm aware is a 120 with overdrive and a 4.1:1 axle, cars that left the factory so equipped were all fitted with the 4.56:1 diff.

To be honest I don't find it is a significant issue, I certainly wouldn't alter the rear tyre size to compensate.

I agree it's not a huge deal in the grand scheme of things.

There are a couple of reasons why I'd like a more accurate speedo:

I'd like the odometer to work correctly, and the more important reason is for other drivers. (I'm planning a trip to San Francisco from Portland next week, and I won't be doing all the driving. My co-traveler will be behind the wheel some of that time.)
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http://dylans122.blogspot.com

How difficult is the swap?

It's a complete overdrive dismantle. The drive worm is on the axle of the annulus and it needs to be pulled out of the tail housing to get at the worm drive gear. It is invasive surgery.

Try one with one tooth less.
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George Downs, Bartlesville, Heart of the USA!