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8 & 10 cyl Bristol cars From Type 407 onwards

Overdrive Unit

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Old 07-07-19, 08:23 AM
Join Date: Jul 2008
Location: woodhouse australia
Posts: 99
Default Overdrive Unit

Does any one have any knowledge or experience with the American made overdrive unit "Gear Vendors". Its designed to bolt on to the back of the Chrysler auto boxes as fitted to V8 bristols. You remove the extension housing and replace it with the Gear Vendor overdrive unit. This gives you 6 forward gears. The fitting requires a shortening of the tail shaft. Im wondering if there would be room under the Bristol for such an installation.

Regards Peter Dowdle
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Old 07-07-19, 09:48 AM
Join Date: Mar 2011
Location: Further up the creek
Posts: 6

You could do worse than join the Jensen Owners' Club forum, which has a wealth of technical info on the Chryslers V8s, and there have been quite a few discussions on the Gear Vendors unit.

You have to join the forum to get access to the technical areas.
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Old 07-07-19, 12:55 PM
Join Date: May 2008
Location: Melbourne, Australia
Posts: 973

The guy who rebuilt my engine looked into this and if I remember correctly he concluded that some fairly significant modifications would be required to use that overdrive unit. This included cutting a chassis crossmember and expanding the width of the tunnel that the prop shaft runs through. Neither of these were something I was prepared to do. Given the narrowness of the Bristol and the proximity of the front seats to the tunnel I doubt it was even feasible.

However, this was circa fifteen years ago and the dimensions of the overdrive unit may have changed since then.

Another option would be to change the whole powertrain as Bristol did with the 411 S6. With hindsight I wish I had done that and just stored the original engine and transmission in case a future owner wanted to restore it to original.

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Old 07-07-19, 10:56 PM
Join Date: Nov 2010
Location: Vineyard Lodge Sydenham Hill
Posts: 42

The Jensen Forum route suggested below is a good idea.
I investigated Gear Vendors and discarded the idea because the shortened prop shaft would have restricted movement of the rear axle causing handling problems. This MAY not be so severe with a Bristol because of the longer wheelbase compared to my Jensen.
I replaced my CV8's Torqueflite 727 with a later 4 speed with torque converter lock-up 518.
Gears 1 to 3 are roughly as the 727 so you still have the previous performance but at more than 40mph the car drops into 4th then torque converter lock-up giving 38mph per 1000 rpm (3rd gives 27mph). It's very relaxing, quiet and economical. Less wear too. It transformed the car.
I bought the 'box from USA as second hand rebuilt from a reputable source and the cost 7 years ago was 2200 plus shipping. Fitting cost c.2k and was quite difficult but a 411 will be easier as there's more room. You need to wander around the internet looking at USA where there's a wealth of up to date info on the subject.
Good luck!
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