Speedo problems

G

Gloster

New Member
Long time lurker looking for some help. Dougal, 72 Highwayman has just received a spanking new overdrive and gearbox. The problem is the speedo is now showing 48mph where I'm actually travelling 30!!

Any ideas short of a speedo app for the phone??
 
Hi Gloster and welcome to the Madhouse:)
I've heard of people getting their speedos re-calibrated but not specifically a Commer one, they are all similar in their operation but I cant think of a company who would do it. A Googling session should see you right.
A simpler method would be to place markers on your speedo to correspond with readings taken off a satnav, not perfect but it will give you an idea. If you are any good with photoshop they you could possibly print your own scale. or just sit back and wonder why all the motorway traffic is flying past and your sitting at 70;)
 
Thinking about it the speedo on my Auto-Sleeper reads fairly accurately but the one on the Jennings is rather optimistic. They both have overdrive but I remember messing about with the one on the Auto-Sleeper and I may have swapped over the speedo drive gear for the original four speed gearbox one. But like I said I'm not sure. The other difference is the A-S has a 'J' type and the Jennings has a 'D' type OD so there could also be a difference there.
 
Where does the speedo read the speed from (more of a question than help). 48kph is 30mph could it be that its measuring kph?
 
The speedo drive is taken from a drive gear in the gearbox tailhousing, so in effect it is measuring prop shaft rotation speed. That means whether it reads correctly is related to the number of teeth on the drive gear, the final drive ratio and the tyre size. If the overdrive has come from a much faster vehicle, (on which the prop shaft will likely be rotating slower at any given speed), in your van it will register too high a speed on your speedo. The only thing you can realistically change is the drive gears. They are available, as these overdrives were fitted to a whole host of vehicles. I found some for a D type on a classic Volvo website.
On my Karrier Bantam, (on which I'd changed the final drive ratio) I couldn't find any way of adusting the actual speedo, and my mind melted at this point, so I printed out a scale and stuck it to the speedo glass.:)
 
I have same issue on mine, reads well over...says I’m doing over 80 mph sometimes, would be nice like. I’m buying a load of old spares and hoping there’s a different drive gear in that lot
 
I changed to a six speed and had this problem. Told that a calibration would be about £300 but can't remember where... Since my speedo wobbles so much I decided not to bother. Tippex on the original?
 
colinthefox said:
The speedo drive is taken from a drive gear in the gearbox tailhousing, so in effect it is measuring prop shaft rotation speed. That means whether it reads correctly is related to the number of teeth on the drive gear, the final drive ratio and the tyre size. If the overdrive has come from a much faster vehicle, (on which the prop shaft will likely be rotating slower at any given speed), in your van it will register too high a speed on your speedo. The only thing you can realistically change is the drive gears. They are available, as these overdrives were fitted to a whole host of vehicles. I found some for a D type on a classic Volvo website.
On my Karrier Bantam, (on which I'd changed the final drive ratio) I couldn't find any way of adusting the actual speedo, and my mind melted at this point, so I printed out a scale and stuck it to the speedo glass.:)
Click to expand...
Ahh. Thanks. Bit more complicated than my motorcycle then lol
 
Thanks for message, I has hoping for a mod but the mobile on the dash will suffice.

As a side note does anyone have a diff lying around??
 
Gloster said:
Long time lurker looking for some help. Dougal, 72 Highwayman has just received a spanking new overdrive and gearbox. The problem is the speedo is now showing 48mph where I'm actually travelling 30!!

Any ideas short of a speedo app for the phone??
Click to expand...
Hi. Think there's still 2 Commer speedo's on eBay... Ones £12? Other is £38 of the top of my head... Don't know if this'll help.
 
On the other hand does s Commer actually go fast enough to break the speed limit..? Everything overtakes me when I'm out & about
 
I had a head on crash with a bumble bee going up hill. It looked rather upset as it bounced off. One thing that can be said about Commers, they preserve the wild life. (no squashed flies on my windscreeen)
 
Hi. All FYI
There's a couple of Commer Speedo's NOS on eBay at the moment... 1 is for a late PB & the other a early one.
 
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