Sprint - 1850 O/D

[Mad Mart]

I'm in the middle of rebuilding an 1850 single rail gearbox and a Sprint O/d to fit it. I am reliably informed these are compatible. My question though is, do the speedo drives need changing? The internal drive gear is a 6 start, which needs replacing as it has a large groove around the middle of it. The speedo pinion has 18 teeth on the Sprint but, I believe, the 1850 has 19? Are both speedos 3:1?

[xvivalve]

Both speedos will be 1000 turns per mile, but as the axle ratios are different the speedo pinion will need altering

[Richard the old one]

I believe that the late 1500 and 1850 dolomites have the same final drive ratio which is 3.63:1 and the to get the correct speedo reading the O/D units have to be fitted with an internal speedo drive gear which has 6 starts which is normally blue or made from steel and this mates with a drive pinion which has 20 teeth.

I have been unable to confirm that a sprints final drive ratio is the same as an 1850 / late 1500 dolomites as I have read a document seem to indicate it is 3.45:1 with and auto having a final drive ration of 3.27:1

For info the early and majority of 1500 O/D's have a serial number 25/115867/***** , the serial number for a late 1500 is 25/115868/ ******, the serial number of an 1850 is 25/115869, I am not certain about the sprint serial number but I have been told it is 25/115842/*****

Can fellow club members please advise what the final drive ratio of sprint is.

[Mad Mart]

You are correct with the Sprint final ratios and the serial number, Richard.

[DOLOMITE 135]

I'm in the middle of rebuilding an 1850 single rail gearbox and a Sprint O/d to fit it. I am reliably informed these are compatible.

I think you may need to check on the compatibility of a 1850 single rail gearbox and a Sprint O/D. The three rail 1850 O/D is compatible with a Sprint (Rimmers list two overdrives for Dolomites, one part number for Sprint/1850 three rail and one part number for 1500 /1850 single rail).

There is a marked difference in lenght between a three rail and Single rail O/D mainshaft. I cannot without getting a measuring tape onto the gearbox to O/D adaptor plates of both types of gearbox compare them to confirm if any difference in their lengths adjusts for the difference in lenght of mainshafts, but confirming compatibility might be prudent to ensure the gearbox and O/D mate together.

Below is a picture of a Single rail O/D mainshaft (Top) and a three rail O/D mainshaft:

[Carledo]

My info is that ALL Dolomite speedos run at 1000 Turns Per Mile (TPM) and that the speedo drive AND driven gears vary accordingly with whatever final drive is fitted, to make it all come out even.

Steve

[xvivalve]

You are correct with the Sprint final ratios and the serial number, Richard.

Except the Sprint auto' is also 3.45. It is only the 1850 auto' which is 3.27

Was it the earlier manual 1850 which was 3.89...or the earlier 1500? I always have to look it up!

Only the drive or driven would need to change...I do have a few different speedo pinions in the lock up...

[Richard the old one]

The official Triumph 1500HL Dolomite handbook Edition 6 states that the later 1500HL models have a 3.63:1 final drive ratio and that the earlier 1500HL cars have 3.89:1. This is not something widely known and obviously was not known when Rimmers produced their catalogue.

To get to speedo to read correctly both the drive gear and the drive pinion are different. As previously stated the 3.98:1 requires a speedo drive gear with 5 starts and a drive pinion with 18 teeth. The 3.63:1 requires a speedo drive gear with 6 starts and a drive pinion 20 teeth. This is based on what Martin found when he worked on 3 O/D s for me.

I do not know what is needed for the sprint 3.45:1 ratio! If anyone has access to a sprint O/D it is possible to remove the pinion drive and to count the teeth. Then if you look down into the O/D it is possible to count the number of starts on the drive gear. I used snowpack (white correcting fluid) to mark one of the teeth and so count the number of teeth.

[Mad Mart]

The bottom line, for me is, do I need to change the driving gear NKC0045 (6 start)? Obviously that is an internal part and I would have to strip the O/D completely to get at it if I put the incorrect part (number of starts) in there.

[xvivalve]

The spreadsheet Tony sent to us both by PM shows that all 1850 and Sprints used the same: NKC0045

[DOLOMITE 135]

Further to my post above I took the opportunity to measure both a three rail and single rail O/D gearboxes today to try and determine why there are different part numbers for the Sprint/1850 three rail and 1500 /1850 single rail gearboxes and came up with the following (all dimensions are approx):

Three rail gearbox adaptor face to face 42mm
Single rail gearbox adaptor face to face 64mm
Difference 22mm

Difference between three rail and single rail mainshafts 21mm


Reviewing Rimmers website they sell O/D RKC684R for the Spitfire IV and 1500 and state it is suitable for both three rail and single rail gearboxes,
however they sell O/D RKC684R only for Dolomite 1500 /1850 single rail gearboxes and 312377R for Sprint/1850 three rail.

So looking at the above it should physically fit, but the question remains why the different part numbers?

[Mad Mart]

Thanks Dolomite 135 for your research. I have just measured the adaptor and it is 63mm.

This is the offending drive btw...

[DOLOMITE 135]

I have just measured the adaptor and it is 63mm.

Both gearboxes I measured are in cars so 1mm parallax error is not bad!

[Mad Mart]

I have just measured the adaptor and it is 63mm.

Both gearboxes I measured are in cars so 1mm parallax error is not bad!

No, not bad at all. I had the part on the bench & measured with very nears.

[Mad Mart]

I've just spoken with ORS and they confirmed it to be the 6 start for both Sprint & 1850.