412 Diff Ratios/Gearing Upgrade

[peasantslife]

Hello all. I'll just introduce myself - a medium term owner of a 412 S2, since 2001. Bought as a running but rotten smoker...I ran it solidly through the first winter, then we gutted it from lockers to rear wheelarches and up into the roll hoop to put back metal. Of course with so much damp for many years all the trim was shot, so took a Rover 800 Coupe and 'installed' trim (not quite finished but useable). I now alternate use with other classics and neo classics Aston/Rovers/Triumphs. So the Bristol is asleep in France at the moment and I'm in the UK. My next projected enhancement is to improve driveability by diff ratio swapping...3000rpm not required for 70mph....So, looking in my Owners Handbook I see possibly 2.88 or 3.07 may be fitted. I'll take a stab it is the 3.07, but short of the ratio tag or actually checking by rotation is there any wisdom out there as to what was actually fitted? (I could happilly fit the 3.07 into the V8 Aston replacing the stock 3.54 - a recognised improvement on manual AMV8's), then sourcing a 2.88 from a V12 Jag (some XJS models only?). Or what about 4 or 6 speed box swaps. Any good knowledge of options? I' m not afraid of buying stateside and shipping and 'engineering' to make fit is no issue. Though probably would go Injected engine with associated box...circa 300-350bhp I dont need sprinting but want legs for better cruise refinement.

[GREG]

Martin Barnes at ACCS , London has done more of these types of mods to a V8 Bristol than anyone else and is probably best to advise - Jeff Marsh at Brabazon as well

[Kevin H]

A 3.07 ratio diff won't make enough difference

Assuming of course that it doesn't already have that.

I looked at retrofitting either an overdrive or a 4 speed box to my 411 (same chassis as the 412) and it was going to need modifications to the floor of the car plus a shorter prop shaft, so decided against it. I also embarked on modification and injection of the original engine, which I now regret.

With hindsight I would go with a modern injected Chrysler engine with associated box. I believe this is what Bristol has done this numerous times so you would be doing something that the factory has already done. Take a look at the 411 "S6".

[peasantslife]

Thank you both, I think next time home I'll grovel and see if there is a ratio tag...and in the meantime keep eyes and ears open for an XJS HE 2.88, (the simple option) and in parrallel search out more detail on 4/6/8 speed auto's and which engines drive them! Nothing like a challenge!

[peasantslife]

Today I had a very interesting discussion with a firm who import and factor from the US. Their suggestion is the Torqueflite 518 4 speed which is a straight bolt on to the LA engine. 3.5 inch longer, so shorten the prop and a bit of tunnel panelwork....brackets etc, use the Hydraulic control version (it went electric control mid '90's.) Ratios are same as the 3 speed +0.69 o/d in 4th which can be a manual switch or easily pedal/vac controlled. Delivered in gwo for under £500. So now I have two 'simple' starting options, Diff or gearbox? Maybe both, but that would take me to over 40mph/1000rpm! That could be too much for the stock engine, but they make a very persuasive argument for sticking with the carb 360 engine and with a simple 'modernisation' rebuild deliver oodles more torque and no (direct comparisons) economy loss.... Anyone with experience out there?

[GREG]

And this is how to do it properly

Dodge 727 Transmission Swap to 518 Transmission from PATC, 46RE 47RE 48RE


But will future owners want all these mod's or wish we had left our cars standard ?

[peasantslife]

Greg, yes thank you for the link. There seem to be numerous threads out there describing what has been done before. It really does inspire me to go this way as launch and intermediate tractability is unaffected. I think I will ask my stateside bloodhounds to start a junk-yard search, but I wont be doing this work this year I suspect - too many other projects on the go and a working car is worth a garage full of unuseable projects!

You ask an interesting philosophical question. My take is - that it is my car for the moment, and I intend to keep it, and use it. A car for Life! So, if I change it to make it a more satisfying drive (for me), I may well use it more often. Accepting I will (undoubtedly) have to modify some bracketry to hang the box by, and cut the tunnel to clear, then providing it is clear what has been done, then reversal would potentially be possible, and fairly simple. Remember my car was not that far from being a breaker when I got it. I'm sure there are far more original 412's which have had a lifetime of cossetted ownership, where 'mods' may be less appropriate. And so to the future owner, they buy into the contract with the car 'as is' at point of sale, and will no doubt immediately launch into their own series of 'improvements'. People buy cars for the 'Image' not often for the engineering of function...

Am I out of step with this forum, in being prepared to suggest we can do better today than those who engineered our cars 30 something years ago? If so I apologise now.

[Kevin H]

Originally Posted by peasantslife

Am I out of step with this forum, in being prepared to suggest we can do better today than those who engineered our cars 30 something years ago? If so I apologise now.

Not at all, so no apology needed. With 900 members you will find many different views on this forum, in fact there is rarely any consensus on anything

Besides, it's not like you are doing something the Bristol factory has not already done, or at least something very similar.

Personally I don't see any point in worrying what future owners might think as there are no guarantees they won't make changes that you wouldn't make.

I sold a V8 Aston a few years ago which despite being a 1982 car had only done 34,000 km. The original leather upholstery was in very good condition. The rear seats had hardly ever been used and the front seats had some patina which was totally in keeping with the car.

Unbeknown to me, the car had surreptitiously been purchased by a dealer to whom I had already refused to sell the car. The first thing he did was have it re-upholstered, immediately destroying it's originality.

Getting back to Bristols, if you owned a tatty 6 cylinder Bristol there's a good chance that any future owner would scrap it and sell the power train, which in many cases would be more valuable than the car as a whole in an unrestored state.

[GREG]

And I didn't mean the question as a criticism ! I probably do more non standard upgrades than most to make a car easier to live with, although I do like to see a nice original car and a Bristol V8 doesn't need much doing to it to make it easy to live with

Maybe just..

sound proofing
intermittent wipers
better gearbox
economy upgrades
modern air con
central locking

A philosophical question was all it was, and as Kevin says, Bristol's have always been upgraded even from new and it doesn't seem to be frowned upon as much as other marques.

I was really just wondering if an original car would command more value in years to come -- probably not !

I would love a modern common rail diesel in a 411 to use as an every day car ! -- I just don't have the know how - yet. Thor on this forum does, so maybe when I have some money spare and the timing is right. ! I just love my Merc 320 CDI's power delivery,economy and reliability -- and that engine is used in some Chryslers ! :-) so almost standard.

[peasantslife]

Wow, it did not take the stateside bloodhounds long at all! $500 buys me a box with lock up converter out of a moderate miles early 90's Dodge Ram (this is the 'perfect' match). 400k units per anum sold so the pick is easy....Or $1100 for a fresh 'reconditioned unit'. Now, ball back in my court. Buy now or wait until I actually start this adventure...

Greg, yes I agree with your improvement list. I wonder if the gearbox (am I fixated?) is the root to 25% economy improvement (so the yanks suggest), better gearbox (what characteristics are you critical of?), much improved refinement as engine speed drops by 30% when cruising. So that is at least part way to 3 off your list...Then wipers would be a fairly simple Lucas parts bin raid and wire up, A/C - buy everything salvage out of a fiesta and re engineer to fit!
Actually the older gasses are more 'efficient' than the latest so pumping energy consumption is on its way up, so just ditch that great York compressor for a more modern scroll unit and accept the hazards of gas/seals compatability (I've not researched this but I bet you can get modern compressors which cope with old gasses!). Then latching with Central Locking, I'd be looking at what suits from salvage and re engineer it into the car. Call me a butcher, but mine wont ever be a concours contender!!

[GREG]

Be careful with the gear box / torque converter swap ! even swapping like for like isn't that easy !! ( Just done one ) I would call Martin at ACCS and get an opinion - I know modern GM boxes fit with adapters as another option -- and it's a myth that all 727 boxes and torque converters are the same ! they are often adapted for the car that they go in, so just putting one in from anything could make your car run crap with harsh or lumpy gear changes. -- get advice from someone that has done a lot of gearbox upgrades on BRISTOLS , ( Brabazon, Bristol, SLJ or ACCS or you may be spending $500 dollars a few times :-) The same people can advise on all the other stuff.

[peasantslife]

Greg, yes thank you, I am aware that there are detail differences in spec's across derivatives and years within ostensibly a common case. the good news is that there appear to be just two interchangeable gear sets for 727 and 518, several valve bodies and everything else is tuneable - solenoids, clutch pac's and bands. Also there is a thriving US home rebuild/upgrade market for these things, so I'm not at all concerned for proving the concept with a less than perfect example, though I'm inclined to buy 'good working order' and then at whatever stage rebuild the trans to my own requirements. I confess I am impressed with the very soft shifting my current box delivers at part throttle, if it were'nt for the tacho and nvh one would hardly know the shift had occurred at all. I dont recall the AMV8's shifting so imperceptibly when new....And a soft shift is not ideal for overall longevity, as it puts friction materials into suspension.
As I've previously mentioned, the firm I'm in converstion with are specialist US factors, and they have already told me they supply several of the well known 'Bristol' specialists - the mentioned names probably known to us all. They also supply engines/trans/anything for the 'Yank' custom performance markets in UK and Europe so build or just supply with lashings of knowledgeable experienced advice. The bit I dont know is of anyone who has actually done the installation work at home, or who owns a car with a 518 lockup in it to comment on how it changed the characteristics which frustrate me. I think I've probably gone far enough now to put this on the back burner til ready to start. In the meantime out to the garage now to build a new axle for the Winnebago, and then take the skin off an aston...and that will be this year gone!