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6 cyl Bristol cars Type 400 to 406 - restoration, repair, maintenance etc

Fitting a non overdrive gearbox to a 405

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Old 09-01-16, 03:26 PM
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Default Fitting a non overdrive gearbox to a 405

Is it a practical proposition to fit a standard non overdrive gearbox into a 405, what snags would we encounter and what extra parts would we need.
I am looking at a car which has been robbed of its engine and box, I have considered the alternative engine and box option but I also have a spare 85C engine and box which at least would keep it all Bristol.
Geoff.
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Old 09-01-16, 10:42 PM
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Geoff,
Although I have never fitted an early gearbox to a 405 , there would be sufficient space around the box to make the necessary mounting brackets to adapt it .
Other things to consider is the lower diff ratio of the 405 would not suit the non overdrive gearbox .
The prop shaft would need to be a 401 - 403 type
A special speedo cable would have to be made to suit and speedo recalibrated .

But it will be a much easier fitment than a non original engine & box
Good luck if you go ahead with this project , I commend you for trying to reverse what your fellow country men have done in the past just to make a Pound .

Geoff D
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Old 10-01-16, 05:49 PM
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Geoff,
I have the prop from a 401 but for some reason my pal thought there might be a problem with this hitting the crossmember, I could not work out why but did not have the benefit of an earlier car to compare it with or sufficient access to see what the differences were, I think the 405 prop is still with it so I suppose the answer would be to try and locate a reasonably priced overdrive box but as I am going through a mean phase at the moment having recently retired I would like to try and do this with what I have got.
Would I be right that the lower geared diff ratio would give better acceleration but lower top speed and if so what do you think this would knock off top speed, perhaps where I live in Wales the effect it would have on climbing hills would be more important than maximum speed.
I am pleased to say my current project is in some ways a reversal job as well, we are going to put a factory reconditioned engine into a 401 that lost its engine many years ago, not as a result of someone wanting to make a few extra pounds but due to one of our cold winters where frost wrecked the block and head.
Regards,
Geoff K

Last edited by Geoff Kingston; 11-01-16 at 12:00 AM. Reason: Change of word.
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Old 13-01-16, 02:49 AM
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Geoff ,
I'm glad to see you are interested in saving cars ,
they are too good to let them rot .

The 405 diff is a 4.2 to I ratio where as 400 - 404 ratio is 3.9 to 1
So fitting a standard early box without overdrive will reduce the speed in each gear by about 10% but improve performance up hills .
Once on the road ,a 3.9 diff could be changed for the 4.2, if you felt the gearing was too low.

The other item to consider is whether the long gear lever of the early gearbox will clear lower section of the parcel tray under the dash , as all 405 were fitted with a remote shift box

Geoff D
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