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"upgrade brakes to dual system"


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Hi All, Hope everyone is well, safe and playing with their cars.  I have searched for this idea but couldn't find anything so thought I post a new thread.  Has anyone upgraded a single brake system on a spitfire, to a dual system ?  Does anyone know the pros and cons of this modification (insurance issue's etc) etc ?  I think (that's the best of saying "I don't really know";) the only limiting factor is the need to cut the bulk head to fit the bigger master cylinder ?  Not sure if this is feasible on the pre dual system cars, mines a 76.

 

Cheers.

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There are two purposes to a dual brake system.    One is as an alleged safety factor, the other to allow the balance between the front and rear brakes to be altered, according to road and driving conditions.

The first is borrocks.     Lose the front brakes and you have only rear braking, which will precipitate a spin as soon as you turn the wheel.     Lose the back brakes, and on most cars you loose very little braking ability, certainly in an emergency stop when all the weight of the car is thrown forward.     Less dangerous, certainly than the first case, but ineffective.       The first production car with split brake system was the Austin Princess, which was even more bizarre as while it had four-pot front calipers, each pair of pistons was on a different circuit.      The two circuits went separately to the rear brakes, so if one failed, the rears failed on one side only, while the fronts were less effective on the diagonally opposite side!     Trumph used a simpler system with a 'tandem' master cylinder and a front-rear split.

The second demands two separate master brake cylinders, operated by a single pedal on an adjustable  'balance bar', so that the relative pressure in the front and rear circuits may be adjusted.    IMHO this is only for highly skilled drivers, which of course we all are, but on the track or rally stage.   On the road there should be no need for such adjustment, which can allow you to drive as near to the edge of disaster as possible, as no one should drive like that on the highway!

John

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i guess the simplest way is to copy the late 1500 spitty .which has split line tandem master and a PWDA valve as used on later cars incl midget 1500 

but its of little improvement more a sales gimmick in the day

moderns are a different kettle of fish

spitfire 1500 was just split front and rear 

 

one new 1500 owner locally expired on my  drive , the  rears leaked like a sieve  the pwda valve seized so it didnt cut the rears off and he thought a pedal

on the floor was normal for an old car   

if you need to buy a pdwa stag and late mini are far cheaper than spitfires 

Pete

 

 

 

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2 hours ago, RogerH said:

I thought a dual system operated diagonally opposite brakes.  FNS & ROS - FOS & RNS  so you have one front brake and one rear brake.

Modern ones are but the early ones (including anything Triumph fitted) weren't. The problem with the diagonal split is that if you do lose one circuit, you then have one front and one rear brake operational. The car still tends to spin, pulls REALLY badly, and yanks the steering wheel out of your hands. The only way this can be made safe is to adjust the suspension and steering geometry so that it's all wrong, giving horrid heavy steering with no feel. To compensate for that, modern cars all have power steering.

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12 hours ago, SpitFire6 said:

Single system is dangerous if you have a leak at any corner. Tandem is not.

Agree with that! Having had this happen to me on my (dual circuit) Spit, I would also choose a dual circuit over single any time. You only find out when you're actually braking that there's a problem and if it happens, having the presence of mind to go for the handbrake is one of those things that takes a second or two to percolate through the old grey cells. The brake pedal goes further down (because you have no pressure in half the MC) but you still have some retardation. If you're driving like the road is your personal race track then that won't be enough. If you're being a bit more leisurely it probably will.

I converted my 1977 Spit with bits from my '79 model when it went to that great scrap yard in the sky. You need the MC of course, plus the lower and steeper angle bracket (to hold the MC lower so it doesn't touch the bonnet) and you already know about the dish in the bulkhead so it clears there (like the one behind the battery for US models which had dual circuit years earlier). I simply declared the change to the insurance company - no problem there. Then the standard setup is front one circuit, rear the other. As has been said, less likely to spin when you panic and hit the pedal hard - which you will!!! I did not fit the PDWA (Pressure Differential Warning .... don't know what the last one is) as it only illuminates a silly little light on the dash - which you probably won't even notice. You'll know something's wrong because your foot WILL feel the difference!

Cheers, Richard

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Hi, thanks, I don’t suppose you have any pictures of your installation?  I did think that I would have to fit the PDW thingy does it do anything else other that light up the warning lamp, reason for asking is I remover years ago my mini (when it was a bloody mini) had a pressure reducing valve one the rear circuit on the rear subframe.  Only found out about it after spending days and days unsuccessfully trying to bleed the bloody thing.  Found out you have to go really slowly on the down stroke to stop it locking off 😏

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Alan, I believe it's only function is as a switch for a puny little light on the dash - someone please correct me if I'm wrong. Here are some photos which may help - blue things are off the dual MC donor car. I had forgotten that the strengthening web is also different (lower) on the dual MC cars. The siamesed brake strengthening web and clutch bracket is to accommodate the 6-cylinder PI plenum. Sorry about the flash rust - that shower really caught us on the hop!

Cheers, Richard

DSCF1690.JPG

Photo0549.jpg

Photo0551.jpgPhoto0552.jpg

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Alan,

My comments above were the result of fitting dual circuit to my race Vitesse, Silverback.

1167987863_Dualsystembrakemaster.jpg.f040caec338115cea8e0a87ad6f0377e.jpg

It only needed the recess in the bulkhead to fit.

I did it to enable me fitting a brake pressure valve, like this

OBPBV02-586x673.jpg

in the rear line, as an alternative way to balance the front and rear brakes.    In fact, I found that I'm not that highly skilled a driver, and either it made no difference, or I couldn't adjust it in the heat of competition.

The seperate rear circuit also made possible a hydraulic hand brake, which was great!    No need to faff with cable tensions, and while the cable is essetail for MoT, it's mere presence was enough to satisfy the examiner, as the handbrake worked anyway.

If you want to go as far as that, fine, but as I said above, there is little point in a dual system by itself.      Brake failure should never happen in a well-maintained car, and is rare as a cause of incidents in cars.   Tyres are far more common.     Commercials suffer from brake failure but they have different  brake systems.

JOhn

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If you have a single system; Fit a level switch. Mine would have given me plenty of warning if I had wired it up.
Bulkhead had to be modified to fit Tandem but need to figure out how to measure both levels as a warning as do not want a PDWA.

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1 hour ago, alan.gilbert_6384 said:

Cheers Pete, that was quick, did you have it in back pocket 😉

He and Lindsey know everything or car find it reckon they must be on commission , bet they wish they were! Ha

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Taking all into account. The fitting of a reservoir float, Is likely the the better option, that and Keeping on top of Brake maintenance?.

Speaking of brakes. I am "informed" that some L-R? master cylinders are a direct "swop" for the Triumph ones? Can anyone confirm. (part no`s would be nice too, especially if the L-R? part comes with a float?). I have just cleaned my extremely "grotty" O/E ones, but I am not happy with the results. Having changed the full brake pipework to Copper/Kunifer, and with New Calipers and Rear Slaves and hoses. I may as well go the "whole hog".

P.s. Replacing the clutch Master is on the cards too.

Pete

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I know that for Heralds they used to sell a similar-looking master cylinder but it was angled whereas the Herald versions were straight up when fitted - can't find any this morning, only the Clutch MCs which look the same but are listed with a 3/4 bore.

Some of the later ones, seems to be late Series 3 onwards, are dual-circuit but the bracket mounting is sideways in comparison to our cars. I've looked at the larger dual circuit reservoirs on a number of sites but don't see any with any kind of float-related warning.

On a slightly different point, I see a seller on eBay at present selling Triumph master cylinders with a '3/4 bore modification' but even the seller has a disclaimer to say they're sold as a modification and he cannot give any advice as to suitability.

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we got a Mcly and plastic reservoir form merlin motorsports  

larger reservoir , just change the pushrod over 

not angled but with far more capacity and see thro res  makes checks visual and easy . 

just lift bonnet and peek 

something like these 

gmc_rr_l_2.jpg?cachebreak=a73f1e3ebc9d553ff0fcd82c1129d7c1gmc_10_r.jpg?cachebreak=817bd23905973b91703b087fd3d5e3de

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I can go out and Measure. But anyone confirm the correct dia for the Herald?. (save me unlocking and getting cold). There are similar looking M/C on offer but with 0.7 and 0.75 dia bore?. thaones I have LOOK smaller?.

Pete

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1 hour ago, PeteH said:

I can go out and Measure. But anyone confirm the correct dia for the Herald?. (save me unlocking and getting cold). There are similar looking M/C on offer but with 0.7 and 0.75 dia bore?. thaones I have LOOK smaller?.

Pete

Do you mean bore? herald and spit are 5/8 or 0.625. A 0.7 will feel hard and a little wooden, a 0.75 rather more so. (25 and 44% respectively)

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