Early and late sprint brakes

[PaulB]

We have two Sprints. One is very early with single line brakes. The other is very late with tandem brakes.

The early brakes are much better than the late ones. Considering the disc size etc, they are surprisingly good. Seems strange that Triumph 'improved' the brakes on the late cars to improve safety by making them tandem, but in fact made them worse at stopping the car.

The only difference is the master cylinder, but I think the bore size is the same.

Has anyone worked out why the late ones are so poor compared with early?

[sprint95m]

Late Sprints have dual circuit brakes not tandem brakes.

The Sprint dual master cylinder can be swapped for one from a Saab 900 (or 99) which will give a better pedal feel but not make the car actually stop any better.
The OE Saab BMCs are long lived. (They are 7/8" bore.)
There are two bore sizes of wheel cylinder available for Dolomites. If your Sprint has the bigger size it is possible to use the smaller bore version instead.
Again this will improve the pedal feel without actually making the car stop better.

The change from single to dual circuit was made to comply with new car legislation....




Over the years there has been quite a bit written in club magazines on improving the brakes,
fitting an upgrade such as a Trackerjack conversion is the way to go. You will also then need high level brake lighting...





Ian.

[PaulB]

Sprint95 thank you for your reply. However......

The factory referred to it as 'tandem' brakes not dual circuit.

IMG_1321.JPG (54.9 KiB) Viewed 1734 times

You did not answer the question about the route cause for the 'problem' on the late tandem brake system and why it is poor compared with the early single line brakes.The reason for the post was that I am curious as to why they are different, not what modifications there may be.

I am well aware that the change was caused by legislation, but Triumph could have introduced a different change which might not have had a detrimental effect.

The brake systems are fundamentally the same, so the discs and calipers are capable of stopping the car for normal road use. Our late Sprint is a very original concours winning car so I don't want to fit anything like a trackerjack conversion.

[xvivalve]

Is it not the simple fact that the later master cylinder shares its pedal pressure over the xsa of two pipe systems, rather than just the one on the single line system and the changes to the master cylinder don't quite compensate for this?

[soe8m]

The max stopping power depends on the friction of pads and shoes against their discs and drums. Not the size or bores or types of hydrolic components.

[GrahamFountain]

The max stopping power depends on the friction of pads and shoes against their discs and drums. Not the size or bores or types of hydrolic components.

I just don't see how you come to that conclusion.

I agree that the stopping power is determined by the force of friction between the pad/shoe and disc/drum. But surely that is determined by the pressure applied to the pedal multiplied by the mechanical advantage from the hydraulics and the servo? And, while I'm not entirely up on vacuum servos, the gain from a hydraulic system is almost all given by the ratio between the bores of the master and slave cylinders.


Graham

[soe8m]

No, your conclusion say's that someone with very strong legs can increase a cars stopping power.

The only way of having more max stopping power is to increase the pad/shoe area for more friction or have the same sizes and use different materials what have more friction.

Jeroen

[tony g]

Arent sprints supposed to have a different friction material from other Dolomites although the same physical size? Maybe one car has the correct pad material and the other doesnt? Swap them over from car to car and see if it makes any difference

Tony

[Magenta Auto Sprint]

Friction is not dependent on surface area.

http://zebu.uoregon.edu/1999/ph161/friction.html

[Dolly-Nut]

It could be possible that the rear brakes need adjusting on one of the cars. I find it can affect pedal feel a lot.

[DaltonBarham]

A value for Friction is usually found by multiplying the coefficient of friction (depends on how rough surfaces are etc) by the resultant force.

So therefore an increase in the force of shoes against drums would increase friction- thus stopping power.

So if you had a system that could put more force behind the shoes, in theory the friction should increase.

Just my interpretation- although this is a simplified model and there are probably other variables i haven't considered.

Dalton

[tony g]

Friction is not dependent on surface area.

http://zebu.uoregon.edu/1999/ph161/friction.html

No I'm not saying that. The same area and the same force can give different friction rates with different materials. If you make pads out of a rough material like emery paper it would stop quicker with the same force but would of course wear stuff away fast. The friction coefficient of materials is usually expressed in Mu. High Mu = high friction (for a given force and area)
Tony

[Carledo]

The ONLY difference between early and late Sprint braking systems is in the master cylinder and in my opinion there is no difference in performance between the two if they are in good order throughout.
So my thinking is that there is something not quite right about your tandem braked car. It is well known (to us at least) that there are distinct pads for Sprints but many factors and lots of ebay sellers will sell "ordinary" Dolomite pads as Sprint pads just because they are the same size and they don't know any better. So I'd go there first, try some proper Sprint pads and see if that helps!

Steve

[soe8m]

So therefore an increase in the force of shoes against drums would increase friction- thus stopping power.

So if you had a system that could put more force behind the shoes, in theory the friction should increase.

Dalton

So more muscles in your leg increases the cars stopping power? I think Steve is right on your car.

Jeroen

[Washdog]

Its just a thought....
Having used 1500's, 1850's and Sprints, both early and late, as daily drivers I can see where Paul is coming from. In my opinion I always found single systems much more user friendly. For me the tandem system lacks the 'feel' of the single which seems more in line with a modern car, i.e you press the pedal and it feels much more responsive. For me the pedal on the tandem system always felt heavier and braking effect didn't seem to start to take place until you were giving it a hefty shove. I first came across this when I had a late (in the last 2000) 1500HL and a friend had an early one, I always assumed something was wrong with my car, but having had examples of 1850's and Sprints, both single and tandem, I found these the same.
I guess if you drive examples of each back to back as Paul is doing then its far more noticeable as you probably adjust to whichever system you have.

Ian