Sprint brake upgrades

[Mahesh]

I may take you up on that Ian, my Sprint will be running std front and rear brakes, it would be interesting to see what can be achieved in a 60 to 0 mph in metres.

Comparisons, discussion and experience will hopefully put a few definitive options that anyone looking on the forum can make a decision on, the Trackerjack conversion would seem the likely choice due to sheer recommendation from all I speak to and a proven record as per word of mouth and forum.

However I would still like to compare whilst using the std setup and see the differences.

[Carledo]

Nice pic Jon, the tuck under of that n/s/r tyre is amazing! Probably a Skyline for sale the next day!

Ian, you NEED to be at Coombe next April!

Steve

[trackerjack]

Thanks for that............yes a bit of tuck in

The input from probably the only person on here who really knows his stuff (Dolly Racer 33) is very interesting.
The reason I chose to use a setup from Ford was because the Sierra was a well designed purpose built car (as opposed to a parts bin lashup) that weighed slightly more than a Sprint and as such I trust Ford far more than BL.

So far heat has been ignored (apart from my telling of a road trip on Dartmoor).
Dolomite brakes work fine when used once or twice but after repeated use they simply fail and ask any one who has genuinely driven one in anger they will confirm that this is so. The more inexperienced the driver the more they use the brake pedal.
Putting two calipers on the front has been suggested and tried but the skinny little disc cannot lose the heat generated.

Back brakes on a sprint are as big as a 3 litre Capri and was simply used by Triumph because they had them on the TR range so no science used there! because the 1850' drums were much smaller with the weak axle that was not up to the sprints power.
I love Sprints but am also aware that they were flawed in so many ways.
One thing I have not mentioned is the fact that I fitted a Sierra load sensor to my Sprint on a bracket that could swivel to adjust it as these units use a ball and tube to achieve what Triumph did with levers etc. But having never had the rears lock up even in the wet it was not needed.

[AndyJ]

Chris,
This old thread always throws up lots of debate. Whilst you wrestle with the other responses I'd advise a couple of things:

1. Standard brakes can be optimised by buying good quality discs, pads and tyres. I've found Rossini grooved discs and Mintex pads to be very good, but even so you still can't match the emergency braking performance of a modern car so beware!
2. Whilst the modded brake set ups spoken about on here obviously serve a lot of users well you need to declare this to your insurers and get their approval. In particular removing the Load Sensor Valve which was (for better or worse) designed into the system might be frowned upon. If anyone got hurt in the event of an accident and made a claim against you, you could find yourself in trouble. Uprating the front brakes doesn't remove the logic of increasing the rear braking effort as the load in the car increases as the brakes won't lock up as easily with the increase in traction.

Andy.

[sprint95m]

Back brakes on a sprint are as big as a 3 litre Capri.

Furthermore Jon,
Ford mark 2 Cortina 1600GT and E also used they back brakes. Their front calipers are slightly different to a Dolomite's but the pads are interchangeable.
(If Wikipedia is reliable as a source here) a 1600E is about 10% lighter than a Dolomite Sprint, but the brakes are just as bad .
Capris had the luxury of a brake servo, but still the brakes are bad.

A lot of brake components (and indeed other parts too) are interchangeable across a variety of makes from this era.




Ian.

[trackerjack]

Good point well made Ian.
A 1600E was a product of the 60's and barely able to exceed 100 mph or in other words a lot slower than a Dolomite Sprint!
As with all things they evolve by the demands of the market place, so a TR3 that predates a 1600E by 20 years had no servo no antiroll bar no suspension( ) no power steering etc.
The Sprint came along a full 20 years later than the 1600E but had not evolved in the brake department, it came with the extra grunt but not the extra stop.
My wife had a 1600 Rover made in the early nineties and yes another 20 years on and her brakes were vented 280 mm together with a decent servo so what is quite clear to me but seems lost on some is the pace of development.
The back brakes I think you will find dont actually do a great deal as their most important roll is not locking and a handbrake.
It is also a fact that the lap records set by Sprints were beaten by a humble 1600 in the form of a Golf GTI and by coincidence these little hatchbacks are donors of the vented discs that I use to mod the Dolomite,s brakes

[Galileo]

...It is also a fact that the lap records set by Sprints were beaten by a humble 1600 in the form of a Golf GTI and by coincidence these little hatchbacks are donors of the vented discs that I use to mod the Dolomite,s brakes

That's because the 'Sport Golf', as it was called, is a car built by engineers and not accountants, business analysts, project managers, marketing executives etc. Sure, they came later, but the die was set by the small bunch of engineers taking a small economical hatchback and rodding it up. Each subsequent Golf GTi mark just became a more diluted form of that original, with the MK3 and 4 (2L 115bhp?!) being nothing short of an embarrassment to the name, though the MK3 ABF 2L with only minor fettling would sing a great chorus up to an easy 175bhp. I've digressed more than a bit here, I think what I'm trying to say is that the Sprint, like a lot of Triumphs, was put together by a team of engineers who had an idea, but an extremely limited budget and toolset, indifferent management, outdated manufacturing facilities and a disgruntled workforce, and all considered I think they did a pretty good job. Though maybe those brakes were designed after a Friday lunchtime sesh down at The Farmhouse... In saying that, they stop my Sprint in the same distance as my Fourtrak though that does weigh 1780 kilos.

I feel better for that, I've added absolutely nothing to this debate, clearly my work here is done.

[trackerjack]

Lets carry on with the thread digression Galileo!
I loved your spot on assessment (its a shame though that just one Red Robbo managed to bring down that rubbish management all on his own )

At the time of the Golf GTI launch Diane and I were a TR5 owner and I clearly remember a burn up with a GTI round Southampton with speeds in excess of 115 and stopping at a set of traffic lights and the grinning driver of the Golf looking over and saying "its not clapped like most TR's is it?" These were far off days before speed camera's and not nose to tail people carriers.

We used to sprint at Goodwood and the Golfs could achieve a standing lap of 1min 52 sec to the TR's best of 1min 49sec, occasionaly however I could only manage a 1min 52sec myself.

I have never owned a car that locked its back brakes and would loath one if it did though my current special will slide its tail if I trail brake into a sharp corner.

I would also point out that my mad road burnups are a past activity especially as Diane is now a driving instructor and I have a clean licence.

[iandollysprint]

Nice pic Jon, the tuck under of that n/s/r tyre is amazing! Probably a Skyline for sale the next day!

Ian, you NEED to be at Coombe next April!

Steve

Sounds like a plan, let me know when in April and i'll get it in my diary.

Ian

[Karlos]

I owned a Mini 850, my second car, totally un-modified, apart from advanced corrosion. If I stood on the brakes, I do mean literally standing on the pedal: bum out of seat while pulling on the steering wheel, one front wheel would lock up, just a bit.

How dangerous is that? Should I have been concerned? I wasn't, being only 19 at the time, come to think of it I'm not too bothered now either.

However it was no where near as dangerous as getting the needle almost off the scale thrashing the Mini down Iveshead Road toward Shepshed. That would be the needle hovering above the IGN light. My aim was to bend the needle - get it so far round it hit the resting pin at 0 mph. Never did manage it.

If only I still had that car, it could be worth 10k now.

[trackerjack]

Ha ha my first car was an 850 Austin Mini and the drum brakes were terrible especially in reverse because they were twin leading shoe type so no use backwards

I used to have to plan an overtake carefully because the power was non existant.

I would NOT want it back now.

[GrahamFountain]

Can you answer my question on what, with all your input, you would suggest as being the best set up?

Yes, though I'm not sure that question was entirely clear in its original context ("So whats your point."). And I'm sorry about the delay, it's not a trivial issue, and warrants some thought: which was my original point, I think, i.e. that you must think carefully before you substantially upgrade the effort from the rear brakes. And I wasn't intending to advise what anyone should do, just what to think about if you do upgrade the brakes, and why it matters. So it took a while to try to write about what I would do in such a way that it doesn't appear as a recommendation.

My take is this: I have no current intentions of upgrading or changing the brakes on my Dolomite Sprint. So, I suppose that means I suggest the best setup for me is standard. I'm certainly happy that I can use all the grip of the tires I have fitted, which are, admittedly, only Firestone F590 Fuel Saver tires, so perhaps a bit hard. I could fit tires with more grip than that, but don't see the point when it's just the daily drive and, more importantly, used for the school run: too much grip would only encourage me to excesses in driving; I know this about me.

But I have upgraded all the TR7's I've owned, except the factory TR7 Sprint. Usually that's just been to TR8 callipers, which is factory spec for the TR7 Sprint, and thus needs no thought. But where I've gone further – like with A TR7 16V the second, which had a bit of a cam, Dellorto 45s, some porting through, etc., to give (according to Dave Bogg) about 180 bhp, and (more importantly) wider wheels with grippier tires; and the TR7V8, which had SD1 heads over P6B pistons, etc., to give about 200 bhp (also on the Bogg standard) – I've use the big princess four pots and 4 speed TR7 rear slave cylinders to de-rate the rear brakes, as recommended by TriumphTune. Mind you, I think I worked out that the big princess brakes are something over 20 percent up on the piddling little HA Viva callipers fitted to the TR7 – though I've lost the envelope and, as a bachelor at the time, I had no children to speak of.

If I did want more effort from the brakes on the Dolomite, as far as I'm concerned, that would only be worthwhile if I upgraded the tires as well. And the straight-line braking model tells me exactly the maximum percentage change in brake effort when moving from one maximum CofF to another. So, if I've got a reasonable estimate of the grip figures for those I've got, and those I'm upgrading to, I can tell what brake upgrade is worthwhile, i.e. that would let me lock those grippier tires with the same brake pressure on the same surface. Even a reasonable estimate for the ratio of the grip factors, e.g. 0.9:1, or 0.8:0.9 (0.88:1) would let me get some good, ball-park figures for the range of upgrades that make sense.

For example (and only as an example), I can use some CofF data off the net (http://hpwizard.com/tire-friction-coefficient.html), to work out the percentage change in brake efforts I would need if I were to replace "tourism" tires with a maximum possible CofF of about 0.9 with "hi-performance" at 1.0.

Using the same guess for the CofG as before, I would need about 14.5 percent more effort at the front, and about 3.4 less at the back. But the results vary for other guesses of the location of the CofG. Hence, if I were doing this job and were trying to do it in anything like a proper manner, and still couldn't get the actual location for the CofG (with just me in it), I'd have to use values at all four limits of the position I believe reasonable, and take the worst of those. Doing that at the four corners, I get about 15 percent as the most I might need at the front and 5 percent more at the back. It also gives the least that I might want as 14 percent more at the front and about -3.6 percent at the back.

Since I would do this upgrade with more than half an eye to safety, I would probably look for a front brake upgrade that would give me no more than 14 or 15 percent, and look at the possibility of reducing the rears by 3 or 4 percent. But if that's too expensive for the relatively small reduction involved, I mightn't be too bothered about the small reduction in the safety margin. But I would want to test the braking, without the mod to the rear brakes, with tires worn to the limits on the front and new ones on the back, and somewhere dry (so not Lancashire then), as that should give me the greatest and worst imbalance in grip between the two ends.

It is a bit of a problem that the upgrade you get from changing to a different calliper, etc., isn't generally given as a percentage. However, all you need to work that out are the percentage change in the distance between the centre of the hub and the centroid (geometric centre) of the pad, and the percentage change in the areas of the pistons. Add those together, and you have a pretty good estimate for the upgrade as a percentage. I know that those specs have been got for an upgrade to the Vitesse front brakes.

I could do the same upgrade requirement calculations for slicks, e.g. with a grip of 1.1 or so. But I don't think my assumptions about the position of the CofG remain valid for a car that could use slicks effectively, I wouldn't have a clue where to set it, and I aren't interested in doing it. But if someone did want to offer a range of values for how far back and how high off the road such a car's CofG might be, I'll willing put those numbers in. I also think slicks imply a manual balance adjustment, and that means upgrading the rear brakes isn't a problem any longer, presupposing that money is no issue.

So that's what I would do if I wanted to do anything. But it does depend on doing these calculations in the very simple situation of braking in a straight line at the limits of grip, front and rear. However, simple though it may be, that situation is a rather special case, at least from the perspective of the physics: it identifies the maximum brake force it can ever take to lock the wheels. That's because for any other case, where there must be additional side forces and sideways weight transfers, the wheels must lock at a lower brake force than predicted by the model of straight line braking.

I would also limit the upgrade to what is sensible for the change in type of tire. That's because if you upgrade the brakes sufficiently far beyond what the tires will support, you will have other problems. I believe Dolly racer 33 was commenting on the more extreme effects of the brakes overpowering the grip from the tires in writing this: "If I run Toyo 888's or slicks I can brake very late and controlled into a corner. If I run a tyre with less grip, the brakes are a nightmare with no feedback, they lock up as soon as you apply any pressure to the pedal, I have to use a much softer pad to overcome this."

I also accept the point about some aspects of Triumph's production engineering being a bit shoddy, which I've always put down to penny-pinching by management (though I may be biased by personal experiences with production management; I'm not that impressed with research management to be honest). I assume the flaws in production are cited to suggest the safety margin is arbitrary and that attempting not to erode it is a waste of time. But if I thought that Triumph's design engineering, as opposed to production engineering, was that bad, I'd avoid all Triumphs like the plague and drive something where the engineering design was done by the Germans. But obviously, I don't believe that.

I also think that an understanding of the how the car responds to braking forces, how and why the limits change with grip, and what that means to where you can apply what force, is important if you are going to think about upgrading a safety critical aspect of the car, like brakes (and I do think it's important to think first). I therefore do think that explaining some aspects of that science in regard to a road car actually is constructive – and I think there are other responses that bear me out in that regard.

Graham

[landypoint]

Hallo Jon and the others
I am new here , come from germany. have a professional landrover restauration job,
but now i bought a RHD sprint that is converted to v8 in GB for me privat

However, the body is relatively dead, so the project is to buy a rust free lhd car and to change the subframe incl. V8 engine.

for this project I am looking for better brakes. All I read is the very best jons convrion to Golf disc and sierra calipper.

but Jon , how can I get contact to you? email? what is the price for your adapters,

if anyone knows a bit more about this car blue v8 dolly please give me information.
does somone know something more about the engine?

best Urs

[Toledo Man]

Welcome to the forum Urs.

I suggest that you send Jon a PM (private message) if you want to get in touch with him.