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

More sporting gear ratios

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  #1 (permalink)  
Old 28-08-12, 11:20 AM
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Default More sporting gear ratios

My car is the HRG 2 Litre, an experimental chassis built in 1948/9 for a Bristol engine (a privateer had previously tried out a pre-war BMW engine
for hill climbing) which went as far as a rolling chassis before HRG realised they were going to be a small player among many others using the Bristol engine for racing. The bits came out to Oz and eventually became a car in about 1995.

The engine is a very early Bristol 400 and I have already sought the views
of this forum about its origin, stamped on the rocker cover as a 75 HP. My problem is the gear box, contemporary with the engine and utterly unsuited to a little car weighing around 600 KGs. First gear takes me out of the garage, second 20 yards further. Third is fine but fourth is really too low, I have had the little car up to an easy 95 mph with plenty more to come if I hadn't run out of road free of cameras and radar - my license usually hangs by a thread.

I need some better, broader, more widely spaced gear ratios. A Toyota Celica five speed box was suggested, but would not fit in the short chassis
and neither would my first hope of a 405 overdrive box.

Any suggestions? What ratios did Bristol 6 cylinders engines use for racing?
Is there available a better set of cogs that will fit my early Bristol gearbox casing?

Best regards,

Lewis Luxton
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Old 28-08-12, 11:39 AM
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Derek Hughes sells an overdrive upgrade as does this company Sheffield Yorkshire providers of overdrive units

Or I have instructions for fitting a 5 speed Ford type 9 from a Sierra etc -- a popular upgrade with a lot of classics and I know one Bristol 400 owner that is delighted with the results.

I would have thought that Brian Marelli could advise at Bristol Cars

Come to think of it - this company look after more racing Bristol's than anyone else so would be best to advise https://www.inracing.co.uk/ Ian Nuthall

The Ford option would be the cheapest..

Last edited by GREG; 28-08-12 at 11:46 AM.
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Old 28-08-12, 11:54 AM
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Id suggest a higher final drive ratio if you are not hillclimbing with it.The o/d conversions work well and fit inside the existing footprint of the Bristol gearbox without chassis cutting, and a later Bristol gearbox (B/W model)has better spaced ratios.
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Old 28-08-12, 12:47 PM
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I think that once you have fitted a Ford or Mazda box used to work in classics and kit cars, the options on ratio's are almost limitless due to the amount of people using and racing with them. There are lot's of specialists around like this one

ford type 9 gearbox reconditioned sierra first motion transmissions - Ford Type 9 Gearboxes

I'm sure that In Racing can supply a Bristol bell housing to start with, or I may have one if needed ( shame to break up a good box ) I don't think you would get as many ratio options with the overdrive route.

In Racing make new Bristol engines and support a lot of race cars so probably best for advise due to the knowledge of the engine characteristics. Although if it's down to budget and race ware maintenance, I think the Ford / Mazda box route will win.

Good luck
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Old 28-08-12, 02:02 PM
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I think it would be worth looking at your rear axle ratio and the diameter of your tires. You can then calculate speeds ( in each gear) based on the various gearbox options.
I find it strange that your first 2 gears only get you 20 yds yet you can do well over 95.
I still do a fair number of hill climbs, and I can't immagine a box like yours being much use, maybe for wall climbing. LOL
Dorien







Quote:
Originally Posted by Lewis View Post
My car is the HRG 2 Litre, an experimental chassis built in 1948/9 for a Bristol engine (a privateer had previously tried out a pre-war BMW engine
for hill climbing) which went as far as a rolling chassis before HRG realised they were going to be a small player among many others using the Bristol engine for racing. The bits came out to Oz and eventually became a car in about 1995.

The engine is a very early Bristol 400 and I have already sought the views
of this forum about its origin, stamped on the rocker cover as a 75 HP. My problem is the gear box, contemporary with the engine and utterly unsuited to a little car weighing around 600 KGs. First gear takes me out of the garage, second 20 yards further. Third is fine but fourth is really too low, I have had the little car up to an easy 95 mph with plenty more to come if I hadn't run out of road free of cameras and radar - my license usually hangs by a thread.

I need some better, broader, more widely spaced gear ratios. A Toyota Celica five speed box was suggested, but would not fit in the short chassis
and neither would my first hope of a 405 overdrive box.

Any suggestions? What ratios did Bristol 6 cylinders engines use for racing?
Is there available a better set of cogs that will fit my early Bristol gearbox casing?

Best regards,

Lewis Luxton
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  #6 (permalink)  
Old 28-08-12, 08:07 PM
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Default gearbox

I used a BWCR 12 when I raced an Arnolt Bristol. First was gear to start the car in motion only. I used the ring and pinion from a BMW 328 to help acceleration. Final ratio was 4.2 and good for 110 to 120 mph. If you are racing you must use ATF in the transmission, the transmission overheats and you will lose your synchros if you don't.
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Old 28-08-12, 11:54 PM
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Lewis

Bristol made a number of close ratio boxes (all with higher first gear) for racing. Early Frazer Nash boxes (to go with FNS engnes, contemporary with the 85/85A/85B/85C engines) were CR3 type.
Later (Borg Warner synchro type) were BWCR6, BWCR9 and the BWCR12 mentioned below. they all have closer ratios (which will sort out your large gap between 1st and second and third) and a higher first gear (with no synchro)

the other implied problem in your question is your overall highest ratio. this could be dealt with by either and overdrive (use the adaptor kit and more modern overdrive to fit inside the footprint of the normal Bristol gearbox plus extension) or a higher final drive (a 3.66 ratio was used on some cars - normal 400/401/403 ratio is 3.9, 405 final drive is 4.2 with overdrive giving an effective 3.3ish ratio)

none of these options would be cheap, but they would be historically 'correct'. Rob McDermott can probably help you if you want to go the CR gearbox route

the ford option could be cheaper

cheers

Julian
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Old 29-08-12, 12:41 AM
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Found the actual ratios for you

400 gearbox (for 85A engine)
1st 4.3:1
2nd 2.172:1
3rd 1.295:1 (box for 85C has lower third gear 1.41:1)
4th 1.0:1

CR3 (also BWCR 6, 9 & 12)
1st 2.92:1
2nd 1.825:1
3rd 1.292:1
4th 1.0:1

BWCR 5 (403)
1st 3.16:1
2nd 1.825:1
3rd 1.292:1
4th 1.0:1

my 403 runs a CR5 box with a higher 1st (2.92:1) no freewheel (so essentially a CR3/6/9/12 set of ratios. i think they are nicely spaced for my car (3.9 diff) your lighter car could probably easily pull a higher diff without too much loss of acceleration in the intermediates

if you go to the CR3 ratios, you will essentially have a first gear just below your current second ratio, a better spaced second gear and third and top essentially the same (well third is fractionally higher in the CR3 ratios)

hope that helps

Julian

Last edited by Julian Caples; 29-08-12 at 09:30 AM. Reason: simple corrections
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Old 29-08-12, 01:37 AM
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a correction

for the BWCR5 box the service manual (and handbook) gives the ratio as 3.16:1 (which i put in the table below), if you actually calculate the ratio using gear teeth ratios it is actually 3.61:1 (which gives the correctly quoted 14:1 overall ratio with a 3.9 diff) - a simple typo that seems to have been perpetuated in a number of sources

so a straight CR5 box will still have a first gear that is too low for you - you will need the 2.92:1 ratio of the sports boxes

Julian

Last edited by Julian Caples; 29-08-12 at 09:33 AM. Reason: improved phrasing to remove ambiguity
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Old 31-08-12, 01:55 AM
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Default Gearbox Cure

Lewis,

I don’t think that it is a good idea to fit any other gearbox to your HRG, in particular a box of modern non-British make. It is not in the “spirit” of the whole concept of an historic sports car.
Furthermore, a Bristol gearbox properly set up can be an absolute delight.
I have been building special Bristol gearboxes all my life. I have in recent times created a separate division of my restoration business specializing in developing the Bristol gearbox, and I can produce you any ratio that you desire. I am only too willing to give you advice as to what you need. Below is a copy of an article that I wrote in the Bristol Owners Club Newsletter earlier this year titled “The Bristol Gearbox Cure” which explains some of the story.
For your information, it sounds like you have a Type 400/85A gearbox which, with a 3.9 diff and 600x16 tyres will give speeds at 5,000 RPM of approx. 23, 46, 77 and 100 MPH.
The standard Bristol sports/racing gearbox, CR3 – BWCR6, 9 and 12 will give speeds of 34, 55, 77 and 100 MPH.
The Derek Hughes’ overdrive is a very good conversion without altering the chassis, and will fit exactly where the standard Bristol gearbox will fit. There are several ratios from which to choose.

THE BRISTOL GEARBOX CURE ARTICLE:
For more than 50 years I have been involved in the restoration of specialist and collectable cars. One of my favorite marques is the 2 litre Bristol and its derivatives. I have been working on and developing their components for more than 45 years, and now provide a service which is of great interest to many Bristol owners. The rebuilding of Bristol gearboxes.
The First Gearboxes – Bristol Type Synchromesh
One of the few disappointing features of the 400, early 401’s and 402’s is their gearbox.
Marginal when new, most now have no effective synchronization on second gear, and have very slow synchromesh action on third and top. Many cars now drop out of third gear on overrun, and some have even worse problems. The introduction of the Borg-Warner synchromesh system and a change of ratio on later cars made an enormous improvement.

I have developed and manufactured the necessary components to convert and rebuild the early Bristol gearbox to the Borg-Warner system. The free wheel can also be replaced with synchromesh on first gear if required, and the ratio can also be altered for a much closer and more drivable combination. These modifications will totally transform the way your car changes gear, accelerates through the gears, and handles traffic conditions generally.

If you would like your beloved 400 and 401 to change gears like a 405, or better, and still retain its original gearbox, then this is the solution. By the way, the fitting of a remote control mechanism does not make a Bristol type gearbox into a Borg-Warner type. The improved qualities of the later cars come purely from the internal components of the gearbox.

The gearboxes that are relevant to this Borg-Warner style development are: 400/85A, 400/85C, CR2 & CR3 types. The CR3 type gearbox was only used on sports and racing cars such as the Frazer Nash. This gearbox does not have a free wheel and its ratios do not require alteration. Apart from the first gear synchromesh, the parts used in these modifications are identical to, and interchangeable with the original Borg-Warner style components used in the later gearbox.

The Borg-Warner Type Gearboxes
The later Bristol gearbox built with Borg-Warner style synchromesh, although excellent when new, is now about 60 years old, and many high mileage cars, alas suffer from slow synchromesh and gear drop-out. Simply rebuilding these gearboxes with new bearings and synchro rings will not necessarily restore their superb original drivability and feel, and will not cure gearbox drop out for more than a very few kilometres.

As with the early “Bristol” type gearbox, the cars fitted with the BWCR5, 7 & 11 gearbox can be further and greatly improved with a change to first gear ratio. These gearboxes are fitted as standard to the 401 from Chassis 1006, and 403, 404 and 405 cars. The inclusion of synchromesh on first gear is far more robust than the free wheel, and also provides the driver with a much more useful facility in traffic and it’s also a lot more fun. Gearbox types BWCR6, 9 & 12 are used for racing and sports cars such as Cooper Bristols, Arnolt and AC cars. The ratios are the same as CR3 and without a free wheel. However synchromesh on first will make all of these cars easier to drive and faster in gymkhana events. The CR3, 6, 9, or 12 are not suitable for the saloon cars with the standard 3.9 differential.

I have in stock all the components to correctly overhaul the Borg-Warner type gearbox to ‘as new’ condition, and if desired, to carry out the modifications. For those who are interested in enjoying driving their Bristols, you won’t be disappointed. If you are having gearbox problems, I am happy to speak with you. My phone number is: 03 9362 0291 or (m) 0416 074 120.

Robert McDermott.
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Old 31-08-12, 12:57 PM
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[quote=Robert McDermott;6144]Lewis,

I don’t think that it is a good idea to fit any other gearbox to your HRG, in particular a box of modern non-British make. It is not in the “spirit” of the whole concept of an historic sports car.

I would agree in a good Concours standard car, but with racing a lot of non standard things are fitted and increased wear and tear demands parts that can be replaced as economically as possible. I don't see how sticking an overdrive box from a Triumph or Volvo is any more acceptable than using a Ford box. However the upgrades that McDermott engineering offer sound fantastic ! I wish I knew someone in the UK that could do these upgrades on two 85 engine boxes I have.
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Old 02-09-12, 07:48 AM
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Default More sporting gear ratios

Very impressed with the number and quality of replies. Thank you all. Despite the fact that engineering runs in my family - and a distant cousin, Harry Varley,
worked with Burgess and WO to design the first 3 Litre Bentley, my fascination with old cars is founded on aesthetics rather than mechanical ability. I have a
3 Litre Bentley and its appeal lies in the fun of trailing a sonic boom behind a
gothic cathedral with wheels. The HRG's silencer was carefully designed to be
impressive but empty, the twin exhausts issuing raucously below my right ear.
I am Mr Toad well into his second childhood.

I think Robert McDermott's first comment is what I needed to hear. The HRG
2 Litre (as the HRG Association calls it) or the HRG Bristol (BOCA) is unique and
deserves better than a modern gearbox. Geoff Dowdle was of the same opinion
and I will seek guidance from him.

Robert, we have met, some years ago and I recall lusting after your 404; you are now near enough to my route to Melbourne from the south coast and I shall
consider my options and make a time to call in.

Again, thank you all for your interest, you may be pleased (along with my wife) to learn that the 3 Litre's days are numbered while the HRG Bristol, which was my
baby from its arrival resembling something from an archeological dig, will remain
in the family. My youngest son has recognised its potential as a chick magnet.

Kind regards,

Lewis
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Old 02-09-12, 09:37 AM
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Any chance of a picture of the HRG ?
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Old 02-09-12, 03:17 PM
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Default More sporting gear ratios

Greg,

I would be delighted to send photographs of the HRG, but I was born about the time Alan Turing was building his computer at Bletchley Park. I've managed to transfer some images into the "Manage Attachments" window but there I bog down. Be patient, I shall ask one of my younger sons for help and, after the
usual tedious quips about senility and declining IQ, I may succeed.

Regards,

Lewis
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Old 02-09-12, 03:44 PM
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I understand :-)

I have a son in I.T. that rescues me from thoughts of smashing computers to bits that fail to comply. Unlike classic car drum brakes, computers don't respond well to a big hammer :-)

Got four broken lap tops to prove it if anyone wants one !
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Old 10-09-12, 11:58 AM
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Default HRG Bristol Photos

Posted by KevinH on behalf of Lewis - see attached
Attached Images
File Type: jpg DSCN1938.jpg (65.9 KB, 36 views)
File Type: jpg DSCN1932.jpg (95.2 KB, 31 views)
File Type: jpg DSCN1936.jpg (99.5 KB, 31 views)
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Old 05-11-16, 01:11 PM
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Dear Greg.
My Name is Peter Stellwag from München, and I am also a BOC member, since 2003.
As my old std. 400 gearbox has the same usual problems, I would like to go for the Ford box.
Can you, please tell me who has it in his 400? And, possibly, who can do that work needed, please?
I thank you very much for your efforts and help.
With best regards
Peter
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Old 05-11-16, 09:58 PM
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20160923_114937.jpgPeter,
Hello , I have fitted a Ford Type 9 gearbox to my other 400 chassis 650 .
It has only been registered a few weeks and I have only covered a few hundred miles in it so far.
Compared to a standard 400 box that not in good condition ( these often jump out of third gear ) the Ford box is a major improvement . The ratios and syncro action are far better .

The basic steps involved in doing the conversion are as follows

Purchased reconditioned Ford Capri 2.8 litre Type 9 gearbox (the other Type 9 boxes have a shorter input shaft and the ratios are not as suitable)
New clutch plate to suit gearbox shaft
Modify bellhousing
Make adapter between bellhousing to gearbox
Fabricate bracket to fit to rear gearbox mounts
Make new tail shaft
Make new main gearbox cover
Modify rear gearbox cover
Buy right angle speedo drive
Make new speedo cable
Fit new gearbox carpet as gear lever is in different position
Shorten the handbrake lever
plus a few other small items

The Ford gearbox is not as a good in the shift as a remote shift Bristol Borg Warner box, the 1st gear is higher, 2,3&4 are almost the same , plus 5th is the bonus.

Interestingly on secondary roads at up to about 65 mph I did not use the 5th gear . But on the expressways at 70 - 80 mph I was in 5th but it would have happily cruised at those speeds in 4th with a standard gearbox.

In retrospect ,my recommendation is try to purchase a Bristol Borg Warner gearbox , it will fit without any major modification . But if you decide to fit a Type 9 I can help with further details and photos .

Attached are a few photos
Regards
Geoff
Attached Images
File Type: jpg 20160923_121257.jpg (433.9 KB, 21 views)
File Type: jpg 20160923_120222b.jpg (454.7 KB, 24 views)
File Type: jpg 20160923_121423.jpg (461.4 KB, 22 views)
File Type: jpg 20160923_120025.jpg (285.4 KB, 22 views)
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Old 06-11-16, 10:37 AM
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Dear Geoff.
I thank you very much for your quick and detailed answer. That sounds not to be a simple way. Maybe the better Option is a CR 5 box plus overdrive? And that would also be the more original way.
And. your 400 Convertible looks fantastic.
best regards
Peter
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Old 06-11-16, 10:43 AM
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Dear Robert.
My 400 has the usual gearbox Trouble. At first I thought to transform into a Ford Type 9. But it seems to be not easy to make, and is far away from originality. The gearlever is much more back. I therefore want to instal a CR 5 box, maybe with an overdrive for the German Autobahn. Do you possibly have on overhauled CR5 for me for sale, please?
I thank you very much for youe efforts.
With best regards
Peter
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