Early and late sprint brakes

[trackerjack]

Its true Sprint brakes are fantastic things and perfect for a fast saloon of the early 70,s.

Fact is the brakes can stop the car once or twice in quick succession and then the extra friction that big muscles and or a big servo exert on those tiny little pads on those tiny little discs that were originally designed to stop a limp wristed 1300, but by now the discs are glowing and the pads are fading.

Alright on a garage potato as it wends its way slowly from one classic car show to another to spend a day with the owner sitting by it in a sun hat, but not a car that will use its performance.

[gmsclassics]

I must admit having also had Sprints (at the same time) with single and tandem/dual master cylinders, I failed to detect any difference of note on the road. Certainly none I could attribute to anything other than pad type and wear of pads and discs. The latter affecting brake fade - less material to heat up.

If you haven't flushed the system with new, good quality brake fluid in the last couple of years, then that is the first step. Nothing better than compressing water vapour in the brake lines to give the pedal a sloppy feel.

There is one significant difference though between the factory set ups for cars using single or tandem/dual master cylinders. The bore diameter of the rear cylinders is smaller with the dual m/c and needs to be as there is not enough fluid in the rear circuit for the master cylinder to fully operate only the rear brakes if the larger diamenter wheel cylinders are fitted. So if you convert / upgrade, then these need to be changed as well.

Unfortunately I know this from experience.

Given the age of our cars along with the dubious quality of some parts on offer, my view is converting to a tandem / dual system is a wise move. With good quality discs, pads and shoes there is nothing wrong with standard brakes in normal use. But if you want to thrash the car a bit, then the Trackerjack conversion is a wise move. If you want to race, then if regulation allow, bigger wheels, vented rotors, willwod 4 pot calipers, Ferodo DS3000 pads and high boiling point fluid are essential.

Geoff

[GrahamFountain]

So more muscles in your leg increases the cars stopping power?

From simple physics, it can't work any other way: More force on the pedal = more force on the pads = more braking effort. That may be complicated a bit by the force multiplying effect of the servo, which I suspect will have non-linearties in its transfer function, but it's still true.

But only up to the point where the force between the tire and the road exceeds the limit of rolling friction, when the wheels begin to slide and any more force on the pedal only bends it.

[GrahamFountain]

What's the differenced between the single and tandem servos, and does it affect performance?

Graham

[mahony]

What's the differenced between the single and tandem servos, and does it affect performance?

Graham

No difference there both the same part number

[GrahamFountain]

Its true Sprint brakes are fantastic things and perfect for a fast saloon of the early 70,s.

But if you can reach the point where the brakes break traction and lock the wheels with the standard set, then using bigger, vented disks, multi-pot callipers, and Kevlar pads, etc., only gets you there quicker and lets you do it more often.

So don't you also have to use softer compound tires if you want to actually stop sooner?

The possible problem with that is that it moves you into a part of the curve where balance of braking is more to the front, and the back wheels more likely to lock first. Which might be a bit more "fun" than many of us want.

Graham

[GrahamFountain]

No difference there both the same part number

DOH! Sorry, I looked at the Rimmers list, and saw they are listed separatly, but didn't see they're the same PN. I should know to check, Rimmers being the only place you can get inlet rocker arms for the sprint.

So the differences between single and dual systems (in equal states of maintainance) can only be in the ratio between foot pressure and stopping force?

Graham

[Jon Tilson]

I too would strongly suspect the difference in feel between the single and dual cars that started this thread
is down to the different pad material.

When I used my sprint at around 25 k per year I was horrified at the variation between pads from various
manufactures. One set lasted sub 5k miles!!!

Now I choose them carefully...hopefully have enough to see me out...

Aeroquip hoses are a good fit. Old hoses do balloon...

Jonners

[PaulB]

I really don't believe there to be any faults with the braking system on our late Sprint.

I am using EBC greenstuff pads, water absorption cannot be an issue as I am using silicon brake fluid. Before you say the problem is silicon brake fluid, I had a Stag and I also used silicon fluid and that was fine.

The calipers have been reconditioned, new master cylider, new ish brake lines throughout, including stainless braided hoses......

I am completely convinced that the late Sprint brakes are inferior to the early ones.They do work but not as well, you have to stamp harder on the pedal to stop the car.

The hydraulic arrangement is different. On the early car a single piston operates all 4 slave cylinders in parallel. On the late car one piston operates the OSF caliper and the second operates the NSF caliper and both rears.

[Carledo]

The hydraulic arrangement is different. On the early car a single piston operates all 4 slave cylinders in parallel. On the late car one piston operates the OSF caliper and the second operates the NSF caliper and both rears.

If your car is plumbed up like this it's not correct, 1 circuit for front and 1 for rear is the proper way. there is some debate about which end of the master cylinder feeds which circuit, with the parts list showing one way and most peoples cars (when still original) being the other way. As near as I can tell, if you are looking at the pressure sensing valve from the front of the car, the pipe from the front circuit of the master feeds the right hand or inboard section of the PSV which in turn feeds both front calipers. Ergo the rear master circuit feeds the left or outboard section of the psv and thence to the LSV and the rear brakes.
This is how I have plumbed my car and is copied from the 1980 W reg Sprint from which all my brake parts were originally liberated. Said Sprint was still carrying all its original steel pipes so one can fairly safely assume that is how it left the factory.
My brake system now bears very little resemblance to the original, I have deleted the PSV and the LSV, replacing the PSV with a 3 way for the fronts and a pressure limiter valve for the rear brakes plus i've added a line lock above the 3 way and a TJ conversion below it, the plumbing, however still follows the original plan and the brakes are finally fit for serious use!

Steve

[Jon Tilson]

Aside from the plumbing issue, this is your problem...

"I am using EBC greenstuff pads"

I'd take them out and chuck them in the bin before they kill you and maybe someone else too....like they nearly did my wife once.

Never again....

Jonners

[PaulB]

My car is plumbed as original. I have replaced all the pipes, but they are as original. I have just checked and you are correct, the NSF and OSF are connected in parallel and the rears are feed by the second circuit. My memory wasn't as good as I thought!

Whats wrong with Green stuff pads? What alternative would you recommend?

[sprint95m]

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

I did answer the question surely?
Triumph, instead of specifying a small bore alternative, could have used the same BMC as Saab (and Audi, Volvo, etc).
Aside from the numbers on the casting, these all look the same externally (for the same production period).



From my experience, I think the brake pad material argument is a bit of a red herring....
in the 90s, when you could still buy OE pads, I tried both types on my Sprint. The much dearer Sprint ones (60% dearer) lasted longer but the brakes were no different.
Similarly we used to swap between Ford, Hillman, etc and feel no difference even though some had larger friction pad surfaces.

Re the EBC pads, I had these on a T2500 which had XJ12 calipers. I tried Unipart (non asbestos) pads and found no difference in braking.

With brake pads, what I have seen a couple of times is the linings detaching (on a Maestro and an Opel Manta). I think the main wear nowadays is to brake discs rather than pads.
If I need to replace discs, this is always done in conjunction with new pads.




Ian.

[PaulB]

Thanks Ian,

Would you know whether any of the alternative master cylinders with larger bore size have the brake pipes exit i=on the same side and the Sprint?

The saab 99 seem to exit on the other side. Which volvo and audi models might be suitable?

[sprint95m]

Which side of your Sprint's BMC has the outlets Paul?
The parts book shows the LHS but the illustration for the brake pipes shows RHS .



The Saab 900 (79-85) has two outlets on the LHS but I think that the slightly older 99 has four outlets (two per side).
So, thinking out aloud, if the Sprint has RHS outlets then the 99 BMC would be suitable (with its two LHS outlets blanked off)?
Saab used metric unions.
I am thinking Audi 80 or late Volvo 300 (not the early ones as these had little calipers) are alternatives? It used to be possible
to explore breakers' yards to gauge possible contenders....


It is possible to cross reference a lot of the braking system components using a Lockheed/Girling parts book......
about 12 years I did just that when looking for a 7/8" bore BMC to fit to a T2500, which was necessary after fitting XJ12 calipers.
(I found a Sherpa/LDV one to do the job.) Alas, the local shop that had these catalogues has now closed ,
but I looked on ebay and found this
http://www.ebay.co.uk/itm/GIRLING-LUCAS ... 35ce5f1c84
which is Windows only.





Ian.