411/412 4 speed conversion

[GOFFJASON]

Has anyone had the experience of retro-fitting a 4 speed transmission to their V8 Bristol? I am interested to know the extent of any modifications required to the rear crossmember and transmission tunnel to accommodate this.

I have seen the article relating to the conversion done to the 603 by ACCS in London, but it mainly deals with the effect on the drivability of the car. The Torqueflite A518 is the transmission of choice, as it is thenext development of the 727.

I have also done a fair bit of homework on the Gearvendors Overdrive unit (which is an excellent product), unfortunately I cannot see it fitting without major modification to the crossmember, self leveling suspension and transmission tunnel.

[Barrie]

Although not of course directly comparable you may find the Jensen Owner's Club useful where a number of these conversions have been carried out.
518gearbox
Steve Payne is very adroit at the conversion and generous with his advice on this searchable open Forum The Jensen Owners' Club • Index page
My CV8 has had this work done which involved cutting out a cross member and remaking it to fit the 518 gearbox.
The conversion has improved the car considerably. Be sure also to get a torque lock-up device included in the gearbox.

[Kevin H]

I looked into it once for my 411. The biggest issue for me was that it appeared I would need to modify of the floor pan, including the tunnel in front of the rear seats, and the prop shaft would need to be shortened. I've a feeling the cross member also needed to be modified as well.

I've made some minor modifications to my car but I felt this was too much.

Incidentally, I have already removed the self leveling suspension. It didn't work and I enquired about parts for it but was recommended by someone at Bristol not to bother. He said that it only really ever came into effect when the car was fully laden and basically the system was more trouble than it was worth.

[GOFFJASON]

I was aware of some required modification to the gearbox mount and possibly the crossmember. Also the need to relieve some areas of the tunnel cover, I was just hoping the area around the handbrake mounting was not affected.

Having now read the Jensen forum experience, I have not heard a single negative comment (although the Jensen seems more work).The significant improvement to the drivability of the car seems to weigh in its favor. I think I will bite the bullet and order the parts.

In regard the self leveling suspension, I too have decommissioned mine. I have just about completed reassembling my rear suspension, and will then write up some articles on mods to the self leveling unit, adjustment of the torsion bars and rear brakes, etc.

[peter dowdle]

I recently had the auto box on my 411 mk 2 serviced because of a poor kick down operation ( wouldnt kick down at all). The specialist advised me they only kick down under almost full throttle. Can any member please advise me how and when their gear box changes down. The service man advised there is a kit available that will enable a part throttle change down to occur but needs to change the throttle body and some other valving.I find that when for example,when pulling away from a round about the gearbox will still hold top gear, a part throttle change down would be nice . I can of course do this by hand which gives a brisk burst of acceleration. Any advice would be appreciated

[peter dowdle]

This article is worth a read Chrysler A-518 Overdrive Transmission | Hemmings Motor News

[devadmin]

Originally Posted by peter dowdle

This article is worth a read Chrysler A-518 Overdrive Transmission | Hemmings Motor News

It's not worth the work and fairly serious modifications unless the car is your daily driver.

[Kevin H]

Peter,
you do almost have to be at full throttle to achieve kickdown, same on every car I've driven with a 727 Torquelfite.

However it definitely shouldn't still be in third/top gear when you're coming out of a roundabout. Sounds like your tranny isn't set up properly, or perhaps your fluid level isn't right, that can cause odd behaviour (needs to be checked with tranny warm, with engine running, in Neutral).

There are lots of different modification kits for the 727, but I would get it working properly before you contemplate fitting one.

Having it kick down earlier may not be that desirable, especially going round a bend in the wet

[Philip]

About time someone stuck a (more) modern gearbox like a 6L80 or W5A580 in one now there are aftermarket controllers ...

[GOFFJASON]

I have liaised closely with the firm in the US mentioned in the article link, and ordered a complete conversion package from them. New A518, lock up converter, conversion kit with vacuum switches for kick down and overdrive, and adaptor plates for mounting to the RB/BB engine block.

As with my suspension refurbishment, I will keep a good photographic record and post the experience on this forum. Good, bad or otherwise I will be as objective as I can. Just give me a few months, as the nights are cold at the moment.

Having spent may hours under my car I have thoroughly measured the areas around the tunnel and crossmember. Whilst I expect to make changes to the transmission mounting and some relief of the tunnel cover, I do no think changes will be too extreme. keep you posted....

[peter dowdle]

The mistery of the lack of kickdown has been solved.In about 1971 the 727 had a new control body fitted that provided what crysler called part throttle kickdown. My mk 2 was built in 1971 but has an eatlier box ( probably old stock).mk 3s and latter would have the new control valve. It is possible to have the earlier boxes modified. This is currently being done to my car.