converting 948 gearbox to fit 803

[martin418]

my 803 gearbox [1955 s2 ]is not well and it's got a 1098 attached to it so i am going to need an upgrade , i would like to retain the original gear lever position and not have to modify the floor so am i right in thinking the 803 end casing will fit the 948 box no problem but the 1098 box needs modifications , the 948 unit will be fine for the local use my car will get ,

[bmcecosse]

Yes - the 948 fits with the 803 tailshaft fitted - no mods required. I think the speedo drive is different ratio -someone will be along to confirm that I'm sure.

[liammonty]

Hi,
It's true that it will fit with no mods - however: you'd be wise to change the reverse selector, as they are different between the boxes. On the 948 box, you don't have to lift the lever to engage reverse, you just push against a spring to get into the reverse gate. therefore, when you change the tail piece, if you don't change the selectors, you'll find that there's nothing preventing you 'hitting' reverse instead of 4th gear, which can be irritating (and damaging!).

BMC is quite right about the speedo drive. Unfortunately, the SII is 1000 TPM, compared to 1500 or thereabouts on the 948 box. If you don't change the drive, your speedo will read around 50% fast. Unfortunately, it's not simply a job of changing the drive itself - you'll actually need to change the helical gear that drives that, which is inside the gearbox (3rd motion shaft I think?) - it's not that hard, but for goodness sake do it before you fit the box, as otherwise you'll have to take it all out again to do it. You can guess how I know that!

You'll be happy with the results - the ratios are far better than the hopeless 803 gearbox ones - makes the car much more driveable. I loved my early SII after I'd done this engine and gearbox swap!

[bmcecosse]

I knew someone who KNOWS would be along! Great tips there !! The facts of doing the conversion should be made a 'sticky' !

[IslipMinor]

You could also use the later 948 M1000 1504 tpm speedo to replace the SII 1000 tpm speedo? Assuming yours is the later central SII speedo?

[martin418]

hi yes i have the central speedo i am also running a 4.22 1098 diff and need to change the speedo anyway so no problem ,

[bmcecosse]

1408 speedo for a 4.22 final drive.