Sprint auto speedo

[Daz50]

Hi all,
I think i've pestered Alun enough so here we go ........
All is good now and improving at a rate.
Apart from the speedo.
It's the gear inside the box that's the problem. It rotates fine, but the slightest of pressure ( my finger ) and it stops. I have a perfectly working 1850 back bit but not suitable for the sprint. So, has anyone replaced the inside gear drive on a auto ?
All suggestions welcome !
Thanks,
Daz

[xvivalve]

Ah, you didn't say your Sprint was an auto as well!

But still, the 1850 parts might make your speedo work, but it will be at the wrong ratio because the rear axles are different. Your speedo therefore won't be accurate.

[Daz50]

Sorry,
Thought I mentioned auto.

Daz

[gmsclassics]

I am going from memory, BUT when I converted my mimosa Sprint to Auto I did use an 1850 auto speedo as the speedo drive in the auto box is the same for Sprint and 1850, but different from the Sprint manual. What I found from both distance measure calculation and matching with a GPS speedo app on my phone is that the speedo is actually now spot on, whereas the standard manual Sprint speedo actually reads about 5% fast, as do most mass market moderns, especially Japanese models.

In the auto box, are the plastic gears worm and therefore not meshing enough, or perhaps the worm gear is rotating on the shaft. The pinion drive should simply pull out but the worm drive is I think another matter. Best get hold of a workshop manual to work that one out.

The BW65 boxes for the Sprint and 1850 are essentially the same (although these has been debate over the number of plates) so you could substitute. Mine auto box comes from an 1850 and has worked just fine in a Sprint (and I don't drive slowly). I just added an oil cooler and the correct automatic fluid.

Geoff

[Magenta Auto Sprint]

I have a similar issue on my 1850 auto in that the speedo reads under by quite a large amount such it reads 35 MPH when my GPS says 50.

I know the auto box was rebuilt or replaced by the previous owner, so i don't know what was done etc. I was suspecting the wrong speedo drive, the sprints and 1850 have a green drive gear while the 1500 Auto has a red one. so it may be a 1500 box.

The only differences between the BW 65 range for the Dolomites is the torque converters; 3 part part numbers listed and the 1500 has the dipstick on the other side.

Access to the speedo drive when the box is in the car is tricky due to the cross member being in the way and removing this can be difficult as the brake pipes and fuel pipe are close to the cross member. It can be done as I have removed the rear extension on my auto box with it still in the car.

Malcolm

[Daz50]

Many thanks guys.
The drive I pulled out of the sprint is red. The one from the 1850 green. They both have the same number of teeth and are the same diameter ?? I cannot find any mention of the main drive in the book.
Daz

[Magenta Auto Sprint]

the green Gear has 21 teeth (1850 & Sprint) and the red one has 22 teeth (1500), looks as if you have the wrong one.

I have looked at many auto boxes and found that there is a green splash of paint on the extension housing if a green gear is fitted.


I may have a spare one if you need it.

regards
Malcolm

[Carledo]

The Sprint and 1850 autoboxes should, to my way of thinking, have different drive ratios to match the different final drive ratios and tyre sizes on the different models, 3.27 and 155/80/13 on the 1850 and 3.45 and 175/70/13 on the Sprint. From what I have heard, all Triumph speedos are calibrated the same at 1000TPM.

But what do I know!

Steve

Have you tried tightening up the rear flange nut yet Daz?

For those who don't know, there is no keyway on the output shaft of the trans for the drive gear, it's kept from spinning on the shaft purely by the tightness of the prop drive flange nut!
If you think THIS is a ludicrous idea, I had a Peugeot 605 with no oil pressure, this turned out to have the same cause, in this case the crank dog bolt wasn't tight and the oil pump drive gear was spinning on the crank! A swift belt with the airgun on the crank dog bolt was enough to see normal running resumed. Unfortunately not before I'd dropped the sump and fitted a completely un-necessary new oil pump!

[MIG Wielder]

Here is a comparison I did earlier ...
( 2 files JPEG from .xls so left and right halves of the file )
HTH,
Tony.

[Daz50]

Thanks guys, this is really appreciated.
Looking at that, then, the green gear is correct for sprint auto? Where the red came from ???????????

Steve, I'm going to do a practice run on the spare gearbox first. When it works, I'm popping over to give you a man kiss ! Just been hectic here so not had the time.

Daz