O/D Conversion from '72 sunbeam rapier

Phil.NZ

Phil.NZ

New Member
Hi guys, first time on the forum so please let me know if i'm not doing it right!
I have just been offered a '72 sunbeam rapier fastback with what I have been told has the 4 speed + O/D box. I seriously need to sort the gearing in my comer but would like to keep it in the rootes family if possible. Is this conversion worth it? I can get the complete car for $1200nz which I think is a good price. Also what is involved in the conversion i'm assuming cutting the driveshaft down and possible slight modification to gearbox mount? ill try upload some pics to confirm it is the O/D box. Thanks for any info!
 
Hi Phil and welcome to the madhouse:D
Such a shame to break a fastback, one of my favourite cars:(, but if that's all it's fit for then at least it's going to good use.
The overdrive conversion is so well worth the effort but with an Arrows series box it's not straight forward as the engine, and so gearbox, is canted over to one side - so when you bolt it to an upright engine the gearbox sits at an odd angle, and the bell housing and input shaft is longer than the comer one as well. You need to use the Commer bell housing and fit the comer input shaft to the Rapier gearbox - but the Rapier 1st gear wheel must be fitted to the Commer shaft as the gearing is a different ratio but this means a complete gearbox strip down. I found this out to my cost as I did the conversion but used the Commer gear wheel, it didn't last long before it spat it's teeth out:( Apart from that everything else is straight forward, fabricating a new support cross member and shortening the prop and wiring it up is all that's left to do.
 
Panky said:
Hi Phil and welcome to the madhouse:D
Such a shame to break a fastback, one of my favourite cars:(, but if that's all it's fit for then at least it's going to good use.
The overdrive conversion is so well worth the effort but with an Arrows series box it's not straight forward as the engine, and so gearbox, is canted over to one side - so when you bolt it to an upright engine the gearbox sits at an odd angle, and the bell housing and input shaft is longer than the comer one as well. You need to use the Commer bell housing and fit the comer input shaft to the Rapier gearbox - but the Rapier 1st gear wheel must be fitted to the Commer shaft as the gearing is a different ratio but this means a complete gearbox strip down. I found this out to my cost as I did the conversion but used the Commer gear wheel, it didn't last long before it spat it's teeth out:( Apart from that everything else is straight forward, fabricating a new support cross member and shortening the prop and wiring it up is all that's left to do.
Click to expand...

Thanks! yes it is a bit worse for wear the only good stuff is the gearbox and chrome, and it also has twin carb which im thinking would be great as i have the alloy head.
I have been offered another gearbox from a guy over here who said it is the correct O/D box for me as it is not canted to one side i have not asked him what it was out of but he said i will need to adjust my x member and drive shaft? he did say the boxes that are from canted cars do take more work to install.
 
He's correct the other box will bolt straight on but you need to make sure your prop shaft(drive shaft) has the same splines as the gearbox output shaft, early cars had coarse splines later cars had fine splines, and it will need to be shortened as the OD box is longer than the standard four speeder. The same goes for the input shaft but that is just a clutch plate swap to match the shaft. And yes you'll need to sort out a cross member.
 
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