Author Topic: Bristol gearbox modified 1st gear  (Read 1323 times)

Exowner

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Bristol gearbox modified 1st gear
« on: November 01, 2021, 18:51:04 »
Does anyone have a information/knowledge of aftermarket/modified 1st gears used in Bristol gearboxes? That is - gearboxes made by Bristol. The modification evidently removed the free-wheel used in many Bristol car g/boxes and also brought the 1st up closer to 2nd.
I'm told that this modification was possibly around in the 80s.
Any helpful info of any kind would be gratefully accepted.

James Eastwood

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Re: Bristol gearbox modified 1st gear
« Reply #1 on: November 01, 2021, 21:35:31 »
I'd guess it's more of a gear set change as you'd need a new lay shaft and 1st gear (for the main-shaft).

It might be an idea to post on the Bristol forum, if you haven't already. http://www.bristolcars.info/forums/

Exowner

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Re: Bristol gearbox modified 1st gear
« Reply #2 on: November 02, 2021, 07:32:29 »
James, yes, it did need as you say, obviously, and that is what was apparently available.
This post is to try and add to the many replies and comments on the BCOE forum. The topic being - non-working 1st gear freewheels with the 1st gear still operating. If the f/wheel goes 'pop' the drive is not connected, so I'm reliably informed.
 I have no f/wheel, but the gear seems to be the original 15:1 (ish) ratio, the period (80s?)  mod used on Aces had a 1st gear closer to second as the ACs were considerably lighter that Bristols (405)

James Eastwood

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Re: Bristol gearbox modified 1st gear
« Reply #3 on: November 03, 2021, 14:17:02 »
15:1 would be very low for an Ace.

I've attached a pic of the gearing page from the Ace FIA document, which agrees with the Rinsey Mills book. With the standard 3.9 dif ratio, the Ace first gear overall is 11.4:1 (used with a 16" wheel with a 550 tyre).

If you're looking for alternative ratio it might be worth sharing your current dif and box speeds.

If you begin to think about keeping your existing box together and fitting an alternative, perhaps a five speed, then it's worth noting that the Bristol box when used in Aces (not sure about Bristols) did not have a remote control housing as the powertrain sits very aft in the chassis.

AC used quite few Ford parts including the RS2600 and Cobra engines, some heaters etc, so fitting something like a Ford Type-9 wouldn't be too out of keeping (imho). I believe you still need to solve the remote change problem though.

Exowner

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Re: Bristol gearbox modified 1st gear
« Reply #4 on: November 04, 2021, 08:09:54 »
James, Thanks for the info, especially the gear options chart. For clarity the gearbox in question is in a Werner Oswald Frazer Nash Le Mans Replica replica. The donor car being, as far as I can tell, a Bristol 405. Which has a 4.22:1 diff and (1st to 4th) 15.24, 7.71, 5.46 & 4.22 ratios and with the overdrive 3.28. interestinly the 404 has a 3.91:1 diff and the same ratio as shown in the chart with the exception of a 14.08:1 1st gear ratio.
The whole point of the original post being the question of the freewheel not working but the gear still working and the fact that my 1st is seeming to be something of a 'stump-puller' when I would have thought it would be close rto second if the non-freewhell parts change option had been taken up.  Until I have the drive-train out, I'll not know what is inside and as it has no starting handle, establishing the exact rartos will have to wait till the salt is down which last year wasn't till the new year