speedometers for 1929 long 4
-
Dhbangham
- Posts: 75
- Joined: Sat Sep 21, 2013 7:47 am
- Your interest in the forum: Jowett long four owner. Jowett club member. (Former Armstrong Siddeley 20hp 1932 owner and ASOC member and former Lancia Belna 1935 saloon) Lanica owners club member. Interested in driving my cars especially in europe and making and repairing parts for the cars. I consider myself an oily rag owner.
- Given Name: Daniel
- Contact:
speedometers for 1929 long 4
I would like to know more about speedometers for my car. I think it has the wrong one in it at the moment, but it could also be that the wrong gearing is installed under the car. Can anyone tell me what model of speedometer I should look for or how to determine the gearing? Thanks in advance.
-
Keith Clements
- websitedesign
- Posts: 3968
- Joined: Wed Feb 08, 2006 11:22 am
- Your interest in the forum: Jup NKD 258, the most widely travelled , raced and rallied Jowett.
- Given Name: Keith
- Contact:
Re: speedometers for 1929 long 4
Getting the gearing correct on a speedometer is a common challenge for rallying. The way I did it was to find a relatively straight stretch of road with distance posts. If you are lucky there may be posts in a lay-by , if not then you will need an assistant to note the trip meter as you pass them. If the speedo does not have a trip meter then travel at a constant speed and note the time taken to do the distance on the distance posts on a stopwatch . Either way you should get an error in distance or speed as a percentage. Then you need to count the teeth on the gears and work out the desired ratio to correct the error.
With the Halda Tripmeter that we used I had many gears to correct any error which would occur if we changed tyres or wheel sizes on my Jupiter or Javelin. Note that load and inflation pressure will affect the readings but probably not enough to worry you. The Halda was accurate to better than 10m in 10km.
I guess a man with your ability will cut the new desired gears but a watchmaker should have the required tooling to make it easier.
The Jup in rally trim also had Halda Speedpilot fitted. This used a variable adjuster to alter the gear ratio and was calibrated using the same method. The Speedpilot was used on regularity sections where you had to keep to a set average speed (or sequence of set average speeds). It was not as accurate as using tables of distance versus time which were contained in a large volume. However, it was a good check for the driver whilst the navigator tried to keep them on the correct road. A needle on the dial showed the error from the desired average speed and could be adjusted if the driver span the wheels in the snow or cut the corners.
With the Halda Tripmeter that we used I had many gears to correct any error which would occur if we changed tyres or wheel sizes on my Jupiter or Javelin. Note that load and inflation pressure will affect the readings but probably not enough to worry you. The Halda was accurate to better than 10m in 10km.
I guess a man with your ability will cut the new desired gears but a watchmaker should have the required tooling to make it easier.
The Jup in rally trim also had Halda Speedpilot fitted. This used a variable adjuster to alter the gear ratio and was calibrated using the same method. The Speedpilot was used on regularity sections where you had to keep to a set average speed (or sequence of set average speeds). It was not as accurate as using tables of distance versus time which were contained in a large volume. However, it was a good check for the driver whilst the navigator tried to keep them on the correct road. A needle on the dial showed the error from the desired average speed and could be adjusted if the driver span the wheels in the snow or cut the corners.
skype = keithaclements ;
-
Dhbangham
- Posts: 75
- Joined: Sat Sep 21, 2013 7:47 am
- Your interest in the forum: Jowett long four owner. Jowett club member. (Former Armstrong Siddeley 20hp 1932 owner and ASOC member and former Lancia Belna 1935 saloon) Lanica owners club member. Interested in driving my cars especially in europe and making and repairing parts for the cars. I consider myself an oily rag owner.
- Given Name: Daniel
- Contact:
Re: speedometers for 1929 long 4
accuracy of +/- 10% is good enough for me! So you are probably saying that I can work with the speedo I have and just work out the gearing with some trial and testing. Thanks.
-
Keith Clements
- websitedesign
- Posts: 3968
- Joined: Wed Feb 08, 2006 11:22 am
- Your interest in the forum: Jup NKD 258, the most widely travelled , raced and rallied Jowett.
- Given Name: Keith
- Contact:
Re: speedometers for 1929 long 4
Many rally cars had stickers on the Speedo face indicating the calibrated speed not that which the Speedo was showing.
skype = keithaclements ;
-
ian Howell
- Posts: 963
- Joined: Thu Feb 09, 2006 10:46 am
- Your interest in the forum: From 1962 to '63, CA Bradord LLG 125 (Repaired and used).
From 1966 to '67 Black deLuxe Javelin LDF 738 (Scrapped with broken chassis)
From 1967 to '87 Black de Luxe Javelin MKC 1 (later 6469TU). (Sold as non-runner with tons of spares, 1987)
From about 1980 to '87 ex WD Jowett stationary engine. (Sold on)
From 1966 to present, 1930 Long Four Fabric Saloon, Dark Blue / Black.
Taken in a part-repaired state to the 2010 Centenary Rally, returned to a roadworthy state by 2013. - Given Name: Ian
- Location: Eastbourne, East Sussex, England
- Contact:
Re: speedometers for 1929 long 4
If it is any help: -
The BRAND NEW Smiths speedo (it was full of very sticky grease - possibly Ex-MoD?) that I found at Beaulieu Autojumble a few years back, seemed to show about double the road speed.
I made a small reduction gearbox using a couple of small gears from my son's kit for model car racing.
It consists of three brass plates soldered into a square 'U' with the end fittings from an old Javelin cable that I had from years ago soldered on the outsides. I made a couple of shafts using my battery drill as a lathe and filing the square for the speedo drive.
This gives me a 2:1 reduction and seems to be about right - say within 10% which is OK for road use.
If the ratio had not been near enough, there are a wide range of these pinions available from model suppliers with various numbers of teeth from which it would not be difficult to find a pair to give a closer accuracy.
I have been told that there is a company? that will change the internal gears to suit - given the vehicle details.
I investigated this but I found that there was no internal gearing in my speedo so that option may not have been open to me.
Others may know of the company in question. Has anyone made use of their services?
The BRAND NEW Smiths speedo (it was full of very sticky grease - possibly Ex-MoD?) that I found at Beaulieu Autojumble a few years back, seemed to show about double the road speed.
I made a small reduction gearbox using a couple of small gears from my son's kit for model car racing.
It consists of three brass plates soldered into a square 'U' with the end fittings from an old Javelin cable that I had from years ago soldered on the outsides. I made a couple of shafts using my battery drill as a lathe and filing the square for the speedo drive.
This gives me a 2:1 reduction and seems to be about right - say within 10% which is OK for road use.
If the ratio had not been near enough, there are a wide range of these pinions available from model suppliers with various numbers of teeth from which it would not be difficult to find a pair to give a closer accuracy.
I have been told that there is a company? that will change the internal gears to suit - given the vehicle details.
I investigated this but I found that there was no internal gearing in my speedo so that option may not have been open to me.
Others may know of the company in question. Has anyone made use of their services?
The devil is in the detail!