Stirling and XKC 005
Discussion
This month's Motor Sport mag is a must if you are a fan of the above driver or car. He can still pull 120 MPH at Silverstone in the pouring rain, and that approaching his 80th birthday!!
What a pity they didn't fit those six pot calipers to the production cars.
Has to be one of the most beautiful sports cars ever.
What a pity they didn't fit those six pot calipers to the production cars.
Has to be one of the most beautiful sports cars ever.
Some production cars did get them, just not when they were originally made.
Even when they were fitted to the 1953 Le Mans cars they were still very much prototypes. They were still suffering from knock off with the rear callipers. Even with the Plessy pump powered rears, Norman Dewis comments that you could still sometimes put your foot on the pedal and it would go straight to the floor, you might need to pump the brakes to get any braking. That's fine when the car is being driven by the likes of the Sir Stirling and he's be warned about it and he's on the track. But even then the brakes were still very much in development. Even in 54 with the Ds Moss had a failure of the brake assistance at the end of the Mulsanne.
Many of the production Cs were driven on the road and they really didn't get the road disc brakes sorted till the 150 came out in 57. The race and road brakes each had very different problems to overcome.
Was a good article in Motor Sport though
As you say stunning cars
Hopefully I'll win a jaunt around the track with Stirling Moss in a couple of weeks time
Even when they were fitted to the 1953 Le Mans cars they were still very much prototypes. They were still suffering from knock off with the rear callipers. Even with the Plessy pump powered rears, Norman Dewis comments that you could still sometimes put your foot on the pedal and it would go straight to the floor, you might need to pump the brakes to get any braking. That's fine when the car is being driven by the likes of the Sir Stirling and he's be warned about it and he's on the track. But even then the brakes were still very much in development. Even in 54 with the Ds Moss had a failure of the brake assistance at the end of the Mulsanne.
Many of the production Cs were driven on the road and they really didn't get the road disc brakes sorted till the 150 came out in 57. The race and road brakes each had very different problems to overcome.
Was a good article in Motor Sport though
As you say stunning cars
Hopefully I'll win a jaunt around the track with Stirling Moss in a couple of weeks time
The reason the rear brakes failed was locking up the wheels! The Plessy pump drives off the gearbox to power the rear brakes so braking too hard locked up the transmission and so - no power. Didn't affect the fronts though.
Sad news: the original Montlehry XK120 coupé, LWK 707, was until recently in totally original condition. It was wrecked at the Nurburgring a couple of weeks back though and will now have to be rebuilt losing all that patina. Hope the radio and instruments survived.
Sad news: the original Montlehry XK120 coupé, LWK 707, was until recently in totally original condition. It was wrecked at the Nurburgring a couple of weeks back though and will now have to be rebuilt losing all that patina. Hope the radio and instruments survived.
lowdrag said:
The reason the rear brakes failed was locking up the wheels! The Plessy pump drives off the gearbox to power the rear brakes so braking too hard locked up the transmission and so - no power. Didn't affect the fronts though.
Sad news: the original Montlehry XK120 coupé, LWK 707, was until recently in totally original condition. It was wrecked at the Nurburgring a couple of weeks back though and will now have to be rebuilt losing all that patina. Hope the radio and instruments survived.
Two interesting points here Lowdrag. I used to do quite a lot with RR and Bentley models, and they had a similar brake boost system also driven from the transmission. One of the problems with this that you did not get on the track was that, if the pressure accumulator was not up to scratch, you would lose all assistance at crawling speed in heavy traffic say, and slowly and gracefully glide into the back of the vehicle in front of you!! This was simply because the pump was not turning fast enough to generate any assistance and the vehicle was so heavy it was almost impossible to stop without. The effect you describe is most likely the opposite of this after a high speed run: it just takes the development of a proper control medium in the system to eliminate these sort of problems.Sad news: the original Montlehry XK120 coupé, LWK 707, was until recently in totally original condition. It was wrecked at the Nurburgring a couple of weeks back though and will now have to be rebuilt losing all that patina. Hope the radio and instruments survived.
Knock off on the calipers, whether it be front or rear was doubtless caused by the assumption that once the pads had contacted the discs they would simply retain their own running clearance, but in a system like the six pot calipers there is so much potential for lost travel that a method of maintaining running clearance had to be found. In modern calipers you have neoprene seals that have a ratchet effect preventing the pistons from retracting in the bores and all sorts of anti-rattle clips and slides that do the same thing. In those days it was all about development by trial and error, usually more error than trial!!!
But a lot of fun.
jith said:
Knock off on the calipers, whether it be front or rear was doubtless caused by the assumption that once the pads had contacted the discs they would simply retain their own running clearance,
...
In those days it was all about development by trial and error, usually more error than trial!!!
But a lot of fun.
The problem with the rear knock off was lateral movement of the wheels. The rear axles were not developed for the disc brake cars, a bit of movement in and out wasn't a problem with drum breaks, but for the discs the callipers are located with respect to the outside casing of the rear axle, but the discs themselves are connected to the shafts. Salisbury couldn't make the axles with a fine enough tolerance. As a result the shafts and the discs wobbled around a bit and knocked the brake pads back into their cylinders. The pump arrangement was intended to give enough capacity to the braking circuit to allow the pistons to move far enough to reach the discs again without the driver having to keep pumping the pedal....
In those days it was all about development by trial and error, usually more error than trial!!!
But a lot of fun.
Moss was renowed for liking a soft peddle on his brakes! I recall hearing Maserati fitted a larger servo unit to his 250F to provide a bit more travel, and a lighter feel to the peddle - so perhaps the longer peddle suited him!
Mind you there is a considerable difference between the peddle giving 'feel' and going to the floor!!
Mind you there is a considerable difference between the peddle giving 'feel' and going to the floor!!
TimCrighton said:
Moss was renowed for liking a soft peddle on his brakes! I recall hearing Maserati fitted a larger servo unit to his 250F to provide a bit more travel, and a lighter feel to the peddle - so perhaps the longer peddle suited him!
Mind you there is a considerable difference between the peddle giving 'feel' and going to the floor!!
The problem at the end of the Mulsanne was that he had no rear brakes and no assistance and so was having to pretty much stand on the pedal. Not surprisingly after the experience he retired the car from the race.Mind you there is a considerable difference between the peddle giving 'feel' and going to the floor!!
a8hex said:
jith said:
Knock off on the calipers, whether it be front or rear was doubtless caused by the assumption that once the pads had contacted the discs they would simply retain their own running clearance,
...
In those days it was all about development by trial and error, usually more error than trial!!!
But a lot of fun.
The problem with the rear knock off was lateral movement of the wheels. The rear axles were not developed for the disc brake cars, a bit of movement in and out wasn't a problem with drum breaks, but for the discs the callipers are located with respect to the outside casing of the rear axle, but the discs themselves are connected to the shafts. Salisbury couldn't make the axles with a fine enough tolerance. As a result the shafts and the discs wobbled around a bit and knocked the brake pads back into their cylinders. The pump arrangement was intended to give enough capacity to the braking circuit to allow the pistons to move far enough to reach the discs again without the driver having to keep pumping the pedal....
In those days it was all about development by trial and error, usually more error than trial!!!
But a lot of fun.
They are quite a devil to set up and involve using a stretching jig to fit the diff into the central casing. Tolerances are very finite, and the outer hubs are no exception.
The half-shafts are splined into the planet gears in the diff, but at the other end are fitted with either roller bearing or tapers. These are held onto the shaft by interference fit collars and the outer part of the bearing is harnessed to the end of the axle tube with a steel thrust plate, shimmed for pre-load. The lateral movement of these should be set at only 1 or 2 thou. When the shaft passes through the bearing it terminates in a Morse taper, and it is on to this that, in the case of the C Type, is fitted a splined hub to take a wire wheel. The brake disc is bolted directly on to this hub. Now whilst I would agree that the wheel itself is subject to quite a bit of lateral flexing, particularly when racing, the hub that the disc is mounted on is most definitely not; unless that is, they fitted different hubs and bearings to the C, but I can see no reason for them doing so. The idea of the discs "wobbling about a bit" is utterly terrifying and should not happen.
Incidentally, the outer bearings are fitted with oil seals and are lubricated along the axle tube with the same oil that the diff runs in. This means that they are constantly, and very thoroughly lubricated. I could count on one hand the number of times I have had to renew rear wheel bearings on a Salisbury equipped Jag axle.
Where did you get this information from, if you don't mind me asking?
jith said:
Where did you get this information from, if you don't mind me asking?
Hi Jith, you clearly know a lot more about Salisbury axles than I.My source is "Developing the Legend" the biography of Normal Dewis.
On pages 90 & 91 they discuss the problems with the loss of braking. The 2 main problems early on were boiling the brake fluid and knock back.
It goes on to say that for the front discs, by tightening up the tolerance on the bearings and disks they were able to limit knock back, but were still getting some due to stub axle bending.
It's then fairly blunt about the Salisbury Axle, it then comments that when cornering hard nearly all the load in on one wheel and that this would deflect the shaft and knock the pad back.
On Page 123, there is a quote from Harold Hodkinson that they made Salisbury sweat a bit, as they like the rear axle to be really sloppy.
I'm sure there were some more references in the book as well.
Incidentally, this book list the problems with Moss' D-Type in 54 as the serrate drive on the end of the plessy pump having come loose, so loosing drive to the pump and therefore brake assistance.
lowdrag said:
Sad news: the original Montlehry XK120 coupé, LWK 707, was until recently in totally original condition. It was wrecked at the Nurburgring a couple of weeks back though and will now have to be rebuilt losing all that patina. Hope the radio and instruments survived.
O my god, Tony, do you have anymore info on this. Last year I was lucky enough to blag a "run up the Goodwood Hill" in this car. such a shame to hear this news.lowdrag said:
CORRECTION
Spoke to "someone in the know" today. The XK120 LWK 707 was wrecked at Goodwood when it slammed sideways into the straw bales at Molecombe. Er - it was being driven by a Jaguar sales director apparently. Do we say ta-ta to this director?
There is picture on page 33 of the latest Octane, haven't read the article yet.Spoke to "someone in the know" today. The XK120 LWK 707 was wrecked at Goodwood when it slammed sideways into the straw bales at Molecombe. Er - it was being driven by a Jaguar sales director apparently. Do we say ta-ta to this director?
Le Mans Visitor said:
Any more news on the state of the Montelery XK120 yet, I have been looking out for a copy of "Octane" but no luck.
Has anyone seen this car yet, there must be pictures out there somewhere of it.just to recap it (a Gold Jaguar XK 120 FHC) was stuffed hard at the Festival of Speed this year by one of the Jaguar Directors.
I am amazed that the factory and in particular the JDHT allow these fools anywhere near such an important car(120 FHC) without their own driving skills being assesed first. A prime example of this attitude was the 53 C ruined by Top gear. busted half shaft, tyres ruined, body damage etc.
This seems to me that it is all about image and egos and for me, if this Director has the same beligerant attitude to his his position, then he should be sacked without a second chance. Why do we offer so much tolerance to these fools ?
This seems to me that it is all about image and egos and for me, if this Director has the same beligerant attitude to his his position, then he should be sacked without a second chance. Why do we offer so much tolerance to these fools ?
The current state of the Montlhéry XK120 FHC LWK 7070 is that t is very poorly, with substantial damage to the off side where it hit the bales at speed. The restorer isn't keen on doing it but since he has worked on the car before is rather having his arm twisted on the matter. There is a lot of work to do, not least of which will be trying to replicate the paint. Don't expect to see this car for some time.
Such a shame because a year ago I was lucky enough the "blag" a ride in this car up the Goodwood Hill (ironic) just before my wedding.
Pics.....
There is a picture of the car in Practical Classics about a nano second before the crash, going very sideways with the driver having a "brown" moment
Pics.....
There is a picture of the car in Practical Classics about a nano second before the crash, going very sideways with the driver having a "brown" moment
Edited by Le Mans Visitor on Thursday 25th September 00:44
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