General Chat for advice

[Robert 352]

Hello Gary

One of the other questions you asked at the beginning of this thread related to the throttle cable not remaining clipped into the bulkhead and in doing so inferred that the problem might be with the cable itself. It is not I believe a problem with the replacement throttle cable which you have fitted.

The reason it pops out was, in my car, because the area of bulkhead surrounding the throttle cable entry and clip had cracked. The bulkhead was flexing and that seemed to be the reason why the cable was not being retained in the bulkhead.

I did not repair the cracking when I did the restoration on my car for I did not spot the cracking until long after the bodywork restoration had been done and the engine and all the dash fittings had been refitted. All I could do was to make up some reinforcement plates which I bolted to each side of the bulkhead. (They can be seen on page 3 of my restoration thread.) However that did not stop the cable from falling out of position so I made up a light plate with a new hole through it (with the right diameter hole in it) which I sandwiched between the reinforcement plates and the bulkhead. That seems to be working very satisfactorily.

I have also experimented with the routing of the cable and it seems best to bring in out through the bulkhead and pass it over the top of the wiring harness on the engine side before looping it around to connect to the carburettors.

You made the comment that you had not heard back from Basis who supply a range of products for Vintage and Classic vehicles. I may get a chance sometime this summer to go up to Renwick which is very close to Blenheim and if that is the case I shall see what I can find out about the windscreen rubbers which are available here in New Zealand. If that happens I shall report back.

Robert

[AndyJ]

"Well yes, but don't forget it's the tires, not the brakes, that ultimatly limit how much deceleration you can get (ignoring aerodynamic down force, e.g. 1 g with tires with a CofF of 1, etc.). So someone with worse brakes, but a heavier foot (or better servo or more nearly perfect biasing) and better tires could still out brake you"

Surely the brakes work by changing the energy of forward motion into heat and it's the rate at which the discs take up that heat and then dissipate it back to the atmosphere that determines the rate at which they slow the car down. The problem with small un-vented brakes is that they do neither well but are especially bad at shedding heat. This is why vented brakes were invented; they can't and don't increase the rate at which the friction between the pad and the disc heats up the disc but they do ventilate and therefore shed that heat quicker. The big issue here being whilst fade is an inherent problem with small un-vented discs mixed with fast driving because heat builds up in the discs until they are too hot to work, but when in traffic most of the cars around you have better brakes. This means that they can stop faster than you and when the situation occurs that you have to do an emergency stop in order to try and stop as quickly as the car in front you the dolly brakes lock up with the effort. Grippier tyres will pull the disc through the pads better, but they won't do anything to improve the rate at which the disc can shed heat and with the Dolly set up that is the root of the problem.
The standard set up can be improved by buying high quality discs and pads. The twin caliper set up on my last Sprint made no difference to braking performance either subjectively in use or objectively on the rollers in a testing station, but the car I drove with vented discs was far superior; more heat in via bigger pads and more heat out via the bigger surface area and vented airflow. Ultimately whilst you will always need your tyres to perform in order to stop efficiently they don't do anything to improve the rate at which the brakes shed heat and surely that is the limiting factor on our cars.
Andy.

[rvfrc45]

Thanks for more replies.
I was interested about the throttle cable possible problem but sadly that is not the problem with mine.
I do agree though that when I re shelled the sprint all those years ago My wife fancied a auto so that's what I did.
On the auto they list a extra bracket to strengthen the bulk head as you are also pulling a kick down cable and
yes even on the manual cars the bulk head often crack by the throttle pedal bracket. So when I put it back to manual/od
I left the bracket on as I could see no reason to take it off. I honestly believe the cable and barb are to small
as the hole in the bulk head has not got bigger LOL.
As for Andy J comments he is spot on, the disc's can not get rid of heat and when I think about Leyland cars when I worked on them that there were not many modifications to the faster models, almost one fit, fits all mentality. Ok they did put a bigger rear axle in the sprint but the front brakes were the same as a std 1300 with harder pads.
Ok we move the clock forward 30 plus years and we can learn from it, Blimey my daughter Corsa has wider tyres than the sprint.
I don't want to do that so I have to improve the brakes and look forward to fitting a conversion.
I loved my time working on Leyland cars even on some of the other unpopular models but I think we all agree that there
was never much development spent/money on them. I hope this will make you smile but the official mod for water ingress/leaks into the boot area on certain models was drill small holes in the floor in certain places. But one thing for sure when the garage I worked for
became a French car dealer we almost cried. 2-3 years later we went Volvo and most of the guys I meet at Daventry at the training
place came from Leyland Funny that hey.

[GrahamFountain]

Actually I'm confused, what ARE you saying?

Well I'm not sure which part of it you're asking about. But what I'm saying about the test that Carledo proposed is that it's possible in theory. But as Mahesh points out, you need cars that are otherwise identical and are used in exactly the same way and conditions, which is too hard to do in practise.

But, in absolute terms of how quickly a car can be stopped, it's the coefficient of friction between the tires and the road that really limits what is possible. So, given two cars with different tires, on the same surface, the car with the better tires can be made to stop more quickly, even if its brakes are worse than the other's, if its driver can press the pedal hard enough.

The rest of it is just about the fact that if you get better tires and want to take the same advantage of them, i.e. lock the wheels for the same foot pressure as before the tire upgrade, you want more gain from the brakes. And about what you need to do if you get that increase in gain at the callipers and discs.

Graham

[AndyJ]

Graham, you are right about the tyres up to a point, but once the brakes are working as hard as they can to turn forward motion energy into heat energy the tyres stop making any difference. Think of the situation reversed i.e. acceleration. If you get wheelspin on acceleration you can fit grippier tyres until the wheelspin stops and you get max acceleration. After that if you fit even grippier tyres you get no benefit because you need more engine power to see further improvements in acceleration, not more grip from the tyres. Fitting better tyres will improve braking until the maximum performance of the brakes is reached but after that fitting grippier tyres won't make any difference, you need to upgrade the brakes to stop quicker.
Andy.

[Mahesh]

Could you please post the make and model of tyres which will grip at max std Sprint braking, and acceleration.

I could do with an upgrade.

[GrahamFountain]

Fitting better tyres will improve braking until the maximum performance of the brakes is reached but after that fitting grippier tyres won't make any difference, you need to upgrade the brakes to stop quicker.

Yes, exactly. If you upgrade the tires, you will get better braking just for pressing the pedal harder than would have locked the wheels before the tire upgrade. But the point is that if you don't want to have to press the peddle harder to access that improvment in braking when you've upgraded the tires, then you need to upgrade the brakes about eqaully at the same time.

So the question was (in a round about way), what do these kits give in comparison to the 15 to 20 percent upgrade in front brake effort that relates to the biggest change in grip that changing the tires for a road car is liable to give. And that's not been answered, because the dimensions are still unknown, yet the issue has digressed further into this testing issue.

Graham.

[GrahamFountain]

but once the brakes are working as hard as they can to turn forward motion energy into heat energy the tyres stop making any difference.

Yes.

But unless you know how the pad's temperature goes up with brake effort (or energy absorbed) and duration of effort; what the efforts and durations are, in various braking scenarios; and how the pad's CofF with the disc changes with their temperature, that thermodynamic approach isn't any use. And since I don't know any of those, and they differ from one pad material to another anyway...

But, as long as the brakes haven't overheated and faded, you can treat them as a relatively linear force amplifier – they take the force applied to the pedal, amplify it, and apply it to the road through the tires.

And, outside of the faded condition, they will do that job of amplifying any force on the pedal until one of the following: your leg runs out of force; something in the brake system, e.g. the pedal, or the servo, reaches the end of its travel; or the tires brake traction and the wheels lock at the limit determined by their CofF.

And, given that you aren't changing anything else as well, if you increase the effort gain in the front callipers by 10 percent, then you increase the force on the wheel by 10 percent as well. So, if you increase grip by 10 percent, and the overall brake effort by 10 percent, you don't change how much force it takes to lock the wheels.

Graham

[AndyJ]

Thanks Graham that's very clear.
Andy.

[Galileo]

Well I thought, should be easy to work this one out with a simple bunch of formulae. And so a little research later and Newton's second law reared it's head but I was keeping up, and then the whole question of how to calculate wheel lock occurred and the answer is Fa = MWdyn.g.µf and at that point I realised that I am a network engineer and not an automotive engineer... There's a little light reading over here http://www.engineeringinspiration.co.uk ... s.html#STV on the subject, which probably accounts for why car manufacturers employ teams of people to spend years on these kind of dynamics.

It also occurred to me whilst wandering to Sainsbury's through the car park earlier today and seeing some cars with the most complex headlight constructions you could imagine, that the team that designed them probably outnumbered the entire Triumph Dolomite design and engineering team, and had greater resources and financing!

[Karlos]

Ways to improve braking performance without having to push the pedal harder:
1. run the car as light as you can,
2. use tyres that offer enough grip to prevent wheel locking.
And....

3. make a longer pedal.

[Carledo]

Oh dear! I really didn't intend to present ANOTHER can of worms to be opened!

I was offering to pit my rather heavily modded and somewhat lighter Toledo against a stock Sprint, mainly cos it would be fun and also to see if there really is any measureable difference in performance of the braking systems. There really are so many variables that a true scientific test is not possible, but whilst accepting this, some of the measures i would take would include, 1) making sure the Sprint brakes were in optimum state (as mine are) 2) making sure the Sprint tyres are in good order (as mine are) 3) checking speedo accuracy on both cars to ensure both cars start from the same speed (otherwise the test is a total nonsense) 4) Driving them both myself to eliminate differences in driver style (better still do it twice with both owners driving both cars, also shares the fun!)

Having seen a similar test conducted by Top Gear in the last series (in the Aussie outback) the results of which (in admittedly state of the art modern cars) made a total farce of the highway code stopping distances, I thought it would be interesting to see how (or if) our cars measure up!

Steve

PS to Karlos, running the car as light as possible is a double edged sword, you reduce the inertia which makes stopping easier but reducing weight reduces tyre grip on the road so the brakes will lock earlier.

[Mahesh]

My car meets all the criteria Steve, next time we meet, the speedo we can use the app on my phone for consistency.

[Carledo]

I wondered if you were volunteering for the test Mahesh! I also have a speedo app on my phone but it seems a bit slow reacting so was going to use a satnav and check what speed is showing on the car speedo when the satnav says 60 and use that! In my case that will be roughly 36mph indicated!
Now all we need is a clear, dry, straight road and a flipping long tape measure!

Steve

[Carledo]

I would just like to thank Graham

Thanks for the thanks, but it's not really taken that much time, and I do enjoy this sort of stuff anyway. And if I was truly dedicated, I'd have taken the trouble to go and read all the relevant threads, and not make the silly mistake of getting data on the wrong Sierra calliper.

Also, if we're going to have a bash at working out the gains some specific callipers might give, would this be better moved to a new/different thread? It does seem to be digressing a bit.

Graham

Some data for you Graham:-

Standard Sprint, 220mm disc, 2x 48mm pistons, hub centre to piston centre distance 87mm

TJ conversion, 239mm disc, 1x 54mm piston, hub centre to piston centre distance 104 mm.

I couldn't think of any accurate way to measure the area of eccentrically shaped pads but if you lay a Sprint one on top of a Ford one, lining to lining, the Sprint one has the exact same footprint as the Ford one for its total area but the Ford one sticks out the sides by a considerable amount, I would say at least 50% more pad area on the Ford one and probably nearer 60%.

Steve