The Triumph Dolomite Club - Discussion Forum

Well I'M personally happy with the figures now. Especially as the original calculation of 54% for the TJs (based on erroneous data - not your fault) is pretty close to the 57% of my uprated TJs! My upgrade is definitely not for everyone, it was never meant to be. The original intention was to provide an easier drive for SWMBO who can't match my pedal pressures, driving a powerful and torquey fully auto trans car which, by definition, has no engine braking to help the driver scrub off speed. The spin off is a possible advantage with extremely modified high power/high grip cars. Even I would say it's probably too much for a stock-ish street car. Though at least, it's effectively free, the bigger discs and Puma calipers are the same price as the smaller ones.

The pedal length is the same for my upgrade as for the stock TJ setup as the pistons are the same (54mm) diameter, the dual purpose cure of using the smaller (0.625") 1850 rear cylinders works just as well on both designs.

I agree there's little likelihood of you actually being able to exploit a 40-50% increase in braking power, you'll not generate enough extra grip, even with the benefit of soft and sticky, bigger footprint 195/50 Toyos such as I have. However, I don't really look at it that way, as I reckon you are using at least half of that increase to get the brakes from "barely adequate" to "acceptable". The rest is a bonus! If they were good enough in the first place, there'd be no need to upgrade!

So far, i'm happy with the brake balance i've got. I may have erred a little too much on the forward side on the Carledo, which has the Vauxhall pressure limiter on the rear brakes as well as smaller cylinders against standard size TJ front brakes. The limiter is a hangover from before I fitted the TJs and had to find something to do duty for my non existent LSV and which i've never got around to removing. While the rear brakes are still powerful enough to give good readings at MOT time, it's not possible to lock the rear wheels at all on the road, even when I persuade the fronts to lock solid, something I personally find reassuring! So OK, if you want to be pedantic, my brake balance is NOT "ideal", but it suits ME!

However, the Carledo is, in many ways, a special case. In my pursuit of lightness, I have used a short tail 2 door shell and most of the dietary benefit has been at the rear, no back doors, no back seat, spare wheel, bumper, tools etc and only an 8 gallon fuel tank. To redress this imbalance I have a GRP front end, i've relocated the (bigger) battery to the boot, the engine and gearbox is 4" further back and I top up the tank when it gets down to 1/2 full. Still the back end of the car is extremely light compared to a stock 4 door causing me the weird problem of not being able (for quite some time, fixed now) to get the rear suspension SOFT enough! This will also have an effect on brake balance so i'm gonna leave the PLV in place for now!

I've not fitted a PLV on the much heavier Dolomega. time and testing i've not done yet will tell if I need one. If it turns out I DO need one, I have one in stock, so no worries. Whilst the LSV is a better technical solution (being "self adjusting" for conditions) my distrust of the standard design and high seizure rate (100% IME) means i'm happy to use a "second best" solution that IS reliable.

A couple of other points, there ARE 48mm calipers available for Fiesta, KA and other small Fords, but AFAIK, these are ALL for solid disc cars and miss fitting the vents (with new pads) by about 1/4", so near and yet so far! (Ask me how I know!) I suspect YOU would be much happier with TJs that had only 48mm pistons, decreasing their advantage considerably, but still curing the fade problem! I suppose it would be possible to fit these, if one was to deliberately shave 1/8" or so off each of the new pads.

The other point concerns LSVs in general, there are loads of types and designs for LSVs, many of them fitted to estates and light commercials (think Astra van) in the 80s and 90s (maybe still) So you'd think that, being unhappy with the Triumph one, I could just adapt someone elses to fit. Except for one small point, they ALL suffer from the same malady, i've lost count of how many i've had to free off or replace on non Triumphs for MOT over the years, it's a REALLY common fail. The ONLY thing that surprises me is how most testers (including my own tame one) seem to ignore or not notice the Sprint one is seized!

Steve

_________________
'73 2 door Toledo with Vauxhall Carlton 2.0 8v engine (The Carledo)
'78 Sprint Auto with Vauxhall Omega 2.2 16v engine (The Dolomega)
'72 Triumph 1500FWD in Slate Grey, Now with RWD and Carledo powertrain!

Maverick Triumph, Servicing, Repairs, Electrical, Recomissioning, MOT prep, Trackerjack brake fitting service.
Apprentice served Triumph Specialist for 50 years. PM for more info or quotes.

Consider the case of a caliper with two pistons and a hydraulic pressure that gives 1000kg force (9.81kN) on the area of the piston. There are two forces each of 1000kgf applied to each side of a disc that is fixed in the direction of these forces to the suspension (through the bearing, etc.) from a caliper that is also fixed to the suspension. Because of the fixings, each of these two forces is applied and reacted to independently. So, there are two 1000kgf forces acting in oposite directions on the disc and . These two forces (mostly) cancel out their effect on pushing the disc in or out. The combination of these two 1000kgf forces is then a total of 2000kgf through the two pads.

That one force is not a reaction to the other is shown simply by what happens when one piston is seized. In that case, the free one still applies it's 1000kg force and the brake gives half the stopping force it should - though it will tend to push the wheel bearing in or out as the result of the force from the working piston is returned though the suspension. If there's enough float in the bearing, it may push the disc up against the pad on the seized piston. But there's still only 1000kgf of compression force on the disk from the one piston through two pads, and it can't do more than give half the brake effort it should. If the other piston is freed, there's two pushing at 1000kg each, and the compressive force on the disc is 2000kgf.

The single piston case is more complicated, and I think more confusing (since it confused me). But with the same hydraulic pressure, there's a force of 1000kgf from the hydraulic pressure on the back of the piston through the piston on to one pad. There is also an equal an opposite force from the hydraulic pressure on the cylinder in the caliper that the piston is in. This second force is applied through the caliper, which is free in that direction, to the other pad. So, again, there are two separate 1000kgf forces acting in opposition on the disk fixed to the suspension, with no net effect relative to the bearing, and the total force on the disc from the two pads is 2000kgf.

I assume the equivalent fault with the single piston is when the slider that lets the caliper pull on the pad remote from the piston is seized. In which case, only the pad directly acted on by the piston can apply its 1000kgf force and again the brake operates exactly like the two piston one with one seized, and gives only half the effort it should.

Graham

_________________
The 16v Slant 4 engine is more fun than the 3.5 V8, because you mostly drive it on the upslope of the torque curve.

Factory 1977 TR7 Sprint FHC VVC 697S (Now all of, but still needs putting together)
B&Y 73 Dolomite Sprint UVB 274M (kids!)
1970 Maroon 13/60 Herald Convertable (wife's fun car).

They aren't additive forces, they only exist because of each other , 1000kg one way only exists because there is 1000kg acting back against it, so 1000kg of compression exists, i can visual force systems zero problem, just i can't translate it to language all that brilliantly.

The reaction is between each pad and the disc. That there's two forces only means there's no net resultant force on the bearing, not that one exists only because of the other.

Explain the situation when one of the two pistons is seized or when the slider on the single piston caliper is seized then, and there is only one force.

Graham

_________________
The 16v Slant 4 engine is more fun than the 3.5 V8, because you mostly drive it on the upslope of the torque curve.

Factory 1977 TR7 Sprint FHC VVC 697S (Now all of, but still needs putting together)
B&Y 73 Dolomite Sprint UVB 274M (kids!)
1970 Maroon 13/60 Herald Convertable (wife's fun car).

If it helps with visualisation, you can think of a single piston caliper like a G clamp. The forces work in exactly the same way. You only put energy into 1 side but both sides react equally in opposite directions.

A year or so ago, I met a Dolomite (I won't say whose) where 1 piston in each caliper had seized. The car had passed a legit MOT like this because the forces were equal (no imbalance issue) and, presumably, the tester was built like the Hulk and could put enough pressure in to make the numbers. The brakes were still total crap on the road, scary it was! On a damp road the fully operational rear brakes could and did overwhelm the only half working front brakes with predictable results in the underwear dept.

And yes, seized sliders are, to a single piston floating caliper, what a seized piston is to a fixed dual piston caliper. Fortunately for us, the Ford caliper has one of the best design sliders in the business, the rubber sleeve over a stainless steel pin means a seizure is almost unheard of.

Steve

_________________
'73 2 door Toledo with Vauxhall Carlton 2.0 8v engine (The Carledo)
'78 Sprint Auto with Vauxhall Omega 2.2 16v engine (The Dolomega)
'72 Triumph 1500FWD in Slate Grey, Now with RWD and Carledo powertrain!

Maverick Triumph, Servicing, Repairs, Electrical, Recomissioning, MOT prep, Trackerjack brake fitting service.
Apprentice served Triumph Specialist for 50 years. PM for more info or quotes.

If one piston is siezed then the free piston will not apply full force untill it meets resistance, either via bending of the disc or the caliper mount till it meets the other piston which although siezed will then provide the reactive force to cause the arbitrary 1000kg compression.

How do you get hold of a TJ kit, they don't seem to advertise anywhere. What do they supply, what do I need to supply, cost?

_________________
2009 Mini Clubman Cooper S Daily Driver.
1980 Dolomite Sprint with a touch of BLTS
Balanced Lightened and Tweaked 13B Rotary and SuperCharged.
Back in my possession 22 September 2019.
Rebuilding the Sprint time taken so far, 111Hrs@15/12/2020
212Hrs @31/12/2021
352 @ 28/11/2022
455Hrs @ 20/10/2023
480Hrs @ 14/03/2024
This is time taken at the Sprint not necessary time worked.

Working on a ratio of just 7Hrs a day not including driving to the Sprint.
That equals to 68 days that doesn’t include weekends.
Member TDC no 0471

Project 13B Sprint now back on.

Thank you.

So one piston alone gives 9.81kN force (1000kg is a mass) against the resistance of the bearing or the pad on the seized piston. But if the other piston is working, then together they still only give the same 9.81kN force, not (as me and Newton would have it) 9.81kN each and 19.82kN in total?

Graham

_________________
The 16v Slant 4 engine is more fun than the 3.5 V8, because you mostly drive it on the upslope of the torque curve.

Factory 1977 TR7 Sprint FHC VVC 697S (Now all of, but still needs putting together)
B&Y 73 Dolomite Sprint UVB 274M (kids!)
1970 Maroon 13/60 Herald Convertable (wife's fun car).

Yes precisely, a situation where the force can be compounded is if the cylinders are in tandem like a 2 piston sliding caliper or a 4 pot fixed caliper.

Also I forgot to add that in a scenario where there is seizure, the force absorbed in bending moments reduces the compression force by the amount taken to distort the brake components, say in the example it takes 300kg before it meets the siezed side, then there would be 700kg of compression available to the disc and imbalance of course.

Please stop using kg as a unit of force. It is a unit of mass and force is mass times acceleration, as in weight equals mass times the acceleration due to gravity M.g, or 9.81 Newtons from a mass of 1 kg in the direction of down.

Two opposed pistons in a fixed calliper give twice the force of one piston in the same fixed caliper. Where there is only one piston, e.g. because the other is seized, it does not matter how the reaction is generated (as long as the disc holds a fixed position against it) or how it is transmitted to the mounting to which the calliper is fixed. There is still half the force on the pads of the two piston case. In the case where both pistons work the same, the net force on the disc as a whole is zero because the two forces (and their two separate reactions) are opposite to one another.

One piston in a sliding calipers gives the same force as two opposed pistons in a fixed caliper, i.e. twice that of a single piston in that fixed caliper. That's because the sliding caliper itself acts in the same way as a second piston (I admit I missed that initially). If the slider is seized, then the system is equivalent to the fixed caliper with one piston seized - the force from the caliper acting as a second piston and normally applying an additional force on the second pad is lost in tensioning the components of the caliper up to the seized bearing of the slider, and cannot propagate to apply to the second pad. How the reaction to the force of the single piston is generated in that case is again irrelevant. Where the slider is free, the net force on the disc as a whole is again zero because the force from the piston is equal and opposite to the force from the sliding caliper, as are the two separate reactions to these two separate forces.

Graham

_________________
The 16v Slant 4 engine is more fun than the 3.5 V8, because you mostly drive it on the upslope of the torque curve.

Factory 1977 TR7 Sprint FHC VVC 697S (Now all of, but still needs putting together)
B&Y 73 Dolomite Sprint UVB 274M (kids!)
1970 Maroon 13/60 Herald Convertable (wife's fun car).

Going back to the original question.

You could always fit a adjustable brake bias valve.
This can then be adjusted to suit your own driving style.

_________________
2009 Mini Clubman Cooper S Daily Driver.
1980 Dolomite Sprint with a touch of BLTS
Balanced Lightened and Tweaked 13B Rotary and SuperCharged.
Back in my possession 22 September 2019.
Rebuilding the Sprint time taken so far, 111Hrs@15/12/2020
212Hrs @31/12/2021
352 @ 28/11/2022
455Hrs @ 20/10/2023
480Hrs @ 14/03/2024
This is time taken at the Sprint not necessary time worked.

Working on a ratio of just 7Hrs a day not including driving to the Sprint.
That equals to 68 days that doesn’t include weekends.
Member TDC no 0471

Project 13B Sprint now back on.

We basically overall agree, except the question of force multiplication, a force of 1N one way is held in static
equilibrium by a force of 1N in the opposite direction , which means a compression of 1N , not 2N.

No we are not in agreement.

It is true that "a force of 1N one way is held in static equilibrium by a force of 1N in the opposite direction, which means a compression of 1N". That is, it is true if the force is applied to an object, i.e. the disc, fixed in the direction in which the force is applied. In which case, that reaction is supplied by whatever fixes the disc in the direction the force is applied. If it is the other pad, that does not multiply the force and that total is 1N, and the area it's applied to never mattered anyway.

But two separate forces each of 1N acting in opposite directions, e.g. from two independent pistons(even if driven by the same hydraulic fluid), and holding one another in static equilibrium, give a total compression of 2N. And that does not rely on the object being fixed.

That there are two separate forces in opposition in the case of the two piston fixed caliper seems bleeding obvious to me. It's not so obvious with the 1 piston sliding caliper. In that case, one force is applied to one side of the disc by the piston The second force is applied by the same hydraulic fluid to the back of the cylinder, just as the fluid pushes on all surfaces, as pressure is a scalar - that's why the calipers need to be so robust. This second force is then taken to the other pad by the slider acting like a hook. It's exactly the same as the situation with two pistons, it just looks different.

Graham

_________________
The 16v Slant 4 engine is more fun than the 3.5 V8, because you mostly drive it on the upslope of the torque curve.

Factory 1977 TR7 Sprint FHC VVC 697S (Now all of, but still needs putting together)
B&Y 73 Dolomite Sprint UVB 274M (kids!)
1970 Maroon 13/60 Herald Convertable (wife's fun car).