GT6 brakes conversion & tandem system

[popeye]

Hi, I need help concerning the dual line brake system (tandem).

Indeed, I have the project to convert my spitfire 1500 to the GT6 big brakes.
I own a late 1500 with the dual line (tandem) master cylinder.

Concerning the front:
there is no problem, I know Iwill need all the complete uprights, calipers....

Concerning the rear:
I will the 8" drums, backplates and the correct type of wheel cylinders (I will have to source the correct bore size).

My question is concerning the dual line master cylinder. I had a look to the canley website and it seems the PDWA are the same for the spitfire and the GT6; am-I right ?

I think the simple solution, in my situation, will be to fit all the GT6 brake system. So, where can I source a dual line master cylinder for GT6 ( part n°: 213690 or 218947) ? it should the master cylinder of the GT6"+" or MKIII ?

I haven't found any information concerning the bore size of the dual line master cylinder from a GT6. I guess it is not the same as the 1500 tandem MC.
Can I still use the standard spitfire master cylinder ? or Have I to use the GT6  one ?

I have tried to find informations concerning the GT6 brakes conversion for a tandem system but I haven't find anything.

All the point of views and advices are very welcome ; many thanks by advance

[JohnD]

I fitted a dual circuit to the Sb, because:
I couldn't find a handbrake cable to fit (Vitesses never had long halfshafts)
so I made a hydraulic hand brake.
And the UK MoT regs demand a 'seperate' system for the hand brake.
It's pushing the regs a bit, but my MoT man says if you have the handbrake cable fitted, how is he to know if that or the hydraulics are working?

John

[popeye]

Many thanks GTEVO, JohnD & Davesideways for your help .

I thought the dual line system was an improvement by the factory.

But it seems you prefer the single line system: may you explain to me why this system is better than the dual line system ? I apologize if my question seems to be stupid, but I would be very happy to know.

One of the reason I would prefer use a dual line master cylinder is : with a single line system, I will have to change the metal pipes and I have no idea how to build the correct pipes needed for the single conversion.

Dave,
- you told "Use a 0.750 master cylinder on the GT6 setup": if I have the project to fit the 16 type calipers, 8" drums ;  I presume I can still use my dual line MC as its bore size is 0.7" ?
-  you told "you can use any size, just it changes the way it feels and length on the pedal etc...Any size will stop the car." To have less length on the pedal: I have to use a smaller or a bigger bore size ?

There is some usefull informations here: http://www.teglerizer.com/triumphstuff/brakecylspecs.htm

Many thanks again by advance to share with me your knowledge and experiences...

[popeye]

I am still searching informations to do the conversion and I have another question: where can I source a 0.single line master cylinder ?
If someone knows the girling part number of a such MC: I thank him very much by advance for letting me know.
Is it a MC with a plastic reservoir ? or a MC with a large alloy reservoir ?

[CharlieB]

The 0.7 master cylinder is GMC209 from the usual suppliers Canleys, James Paddocks etc. Doesn't matter if its plastic or aluminium.

Some people have used the cheaper Wilwood master cylinders from motorsport suppliers although they do have a smaller resevoir.

[popeye]

Many thanks for your help CharlieB.

I think I will go for a single line system: i had a discussion with a gt6"+" owner  (the car had a dual MC) who told me the brakes were very bad too, even if all the system checked and rebuilt with new parts...

By the way, I had a look on the competition preparation manual from the factory: on the race cars, a single line system was fitted instead of the dual one...


Thanks too concerning Wilwood: I will have a look on their catalog

[Deleted User]

Good choice unless you already had a twin mc there isnt much point, the only small benefit of running the twin system is the PWDA valve which gives you an added safety mechanism in that if one line fales power is diverted to the other system.
However should this fail in a single line system you always have the handbrake.
And also in a well maintained single system you shouldnt have a problem of failing brakes and not as much chance of it failing as a twin system.

[rotoflex]

The PDWA doesn't really shut off the side with the pressure loss, although 1st glance at its design seems like it would.

Basically, it turns on a switch to activate a warning light if there's a leak.  You will use the handbrake even if you have a PDWA & a hydraulic failure.

I have heard that it was originated to satisfy some US regs for a brake warning light.  You can see how they could do that using the PDWA & a 2-line system - the shuttle inside moves & stays where it is even when you take your foot off the pedal.  PDWA=Pressure Differential Warning Actuator

It's actually something of a pain.  If you have a leak, or are too vigorous in bleeding, the shuttle is decentralized causing the light to come on.  After the repair, it can often be time-consuming & frustrating to get the thing moved back to center so the light will go out.

It's one of those weird things that's more fun to have because it's weird than because it's very effective, like the SU auxilliary electric starting carburetor.

[Deleted User]

Actually the PWDA valve works exactly as you would think!

A PWDA switch works as you explained but a PWDA Valve works as you want it to.

Quote:

A brake pressure control valve consisting in a combined pressure differential warning actuator (PDWA) and pressure conscious reducing valve (PCRV) in which the PDWA consists of a piston exposed at each end to fluid pressure of one brake system acting in combination with an electric switch in such a manner that if the differential pressure between the ends exceeds a certain value the piston is moved to operate the switch and give a warning and in which the PCRV consists of a piston or a number of pistons arranged within the PDWA piston to provide for control of the fluid pressure supplied to rear brakes of a vehicle to assist in preventing locking up, such control not being exercised in the event that there is a failure of the front brake system of the vehicle.

You are right it includes a switch but it also includes a piston which should one side of the circuit fail the other will gain full control of the system. Hence why its called a valve and also Hence why when bleading the system you have to reset the pwda valve to get the brakes operating correctly.

I have experienced this in operation and it actually works very well, i lost all front brakes and gained more control on the rear.

[popeye]

Mattius,
do not hesitate to let me know when you will have test your brakes on the road/ I have seen the thread concerning your brake servo...it might be a solution for me too ...
Yes, I aldready have a the tandem brake master cylinder. I am wondering if I have a problem with my brakes as some people are happy with the tandem system.

Is it possible to have a worn MC, even if I have no leak, no air in the system. I think the pdwa valve works fine as the light has never turn on...

A solution, in a first time, would be to fit the GT6 front & rear brakes with the twin MC and let's go for a test... Once, this will be done and if the car still had bad brakes: I will fit the single 0,75" MC...

I have never drive a GT6 with the single MC: so I have no point of comparaison...

[Nick Moore]

So, Dave and Gareth, if you were designing a brake system from scratch for a souped-up Spittie or Herald, would you stick with single circuit brakes (with or without an inline booster according to taste) or go for tandem circuit (using Triumph or after-market parts) for safety? Single circuit is simpler to set up and maintain, tandem circuit is safer in the event of failure.

[popeye]

Many thanks Dave & GTevo to share with me your knowledge.
I will go for the complete GT6 brake system: I will have to source good second hand spares.
Yes, I agree with you GT when you said: " I have often worked on French Triumphs and they are RUBBISH". I think you will agree with me if I say there is something more rubbish in France concerning TRIUMPH: the false specialists" ...
By the way, GT: I will not hesitate to contact you when I will rebuild my engine ; I hope to start in december....

I have another question concerning the GT6 brakes:
What are the dimensions of the brake drums ?
I know they are 8" : but is it inside or outside diameter? How large are they?

[spitfire6-2500]

Hy all,

I am new on this forum.

I live in Belgium and I drive a spit 1500 (1977)

I have totally rebuild this car over 3  Years 2005 to 2008 and drove it for more than 100 000 km. (sorry in Europe we use km instead of miles :) )

Than I had a stupid accident in 2010 that demolished the front of the car.

 No worry, I had a spare engine in my mind and also in spare from a GT6 MK3.

I also bought a second hand engine hood and the left and right front axles with brakes from a vitesse.

While rebuild of the engine: this seemed to be a 'adepted" 2L to 2.5 L so the surch to the right carbs was needed.

2 Stromberghs CD175 were found with a vitesse intake and all off these stuff was placed under the bonnet with "zero" play :) .

Now I will try to place a servo booster with the tandem cilinder. 

After reading a lot off articles and books I go for the boost only on the front brakes.

Originally Triumph used this at the end of the gt6 history ... .

I figured out that they also used the biggest wheel cilinders at the back: 7/8 inch instead of the smaller onces in the past: when you figure out that the 7/8 have more than 50% more surface then the previous wheel cilinders than the equation front with 1.5/1 and the back surface with 50% more surface stays equal at the end.

Please give me your thoughts about this matter, i'm curious if my thoughts are ok ... 

[Gt6s]

Wow A post dragged through time all the way from 2007.

 

 

Laurence

[Gt6s]

I apologise for trolling a new poster. But I do feel that in twelve years the original poster has this issue well sorted or could even have died. 

[thescrapman]

Popeye is still about, though not about here lately. Disappeared about the time of the forum revamp.

[Nick Jones]

Quoted from spitfire6-2500-

Hy all,

I am new on this forum.

I live in Belgium and I drive a spit 1500 (1977)

I have totally rebuild this car over 3  Years 2005 to 2008 and drove it for more than 100 000 km. (sorry in Europe we use km instead of miles :) )

Than I had a stupid accident in 2010 that demolished the front of the car.

 No worry, I had a spare engine in my mind and also in spare from a GT6 MK3.

I also bought a second hand engine hood and the left and right front axles with brakes from a vitesse.

While rebuild of the engine: this seemed to be a 'adepted" 2L to 2.5 L so the surch to the right carbs was needed.

2 Stromberghs CD175 were found with a vitesse intake and all off these stuff was placed under the bonnet with "zero" play :) .

Now I will try to place a servo booster with the tandem cilinder. 

After reading a lot off articles and books I go for the boost only on the front brakes.

Originally Triumph used this at the end of the gt6 history ... .

I figured out that they also used the biggest wheel cilinders at the back: 7/8 inch instead of the smaller onces in the past: when you figure out that the 7/8 have more than 50% more surface then the previous wheel cilinders than the equation front with 1.5/1 and the back surface with 50% more surface stays equal at the end.

Please give me your thoughts about this matter, i'm curious if my thoughts are ok ... 

I think your thoughts are ok.  In fact, I think Triumph themselves did almost the same thing, but for a slightly different reason.

Late Mk3 GT6s had bigger rear brakes (wider drums) as part of the return to the swing axle design, apparently to give them self adjusters (don't work very well) and make them common parts with some Dolomites. In some markets at least, those cars had a brake servo that operated on the front brakes only.

Only sure thing to do is to test it once the car is complete.  Do this by braking hard from maybe 50 kph to a near-stop on a moderately slippery surface.  You need to discover whether the front or rear brakes lock first - and it wants to be the front.  If the rear locks first, you need smaller wheel cylinders

Cheers

Nick

[Nick Jones]

Quoted from spitfire6-2500-

Hy all,

I am new on this forum.

I live in Belgium and I drive a spit 1500 (1977)

I have totally rebuild this car over 3  Years 2005 to 2008 and drove it for more than 100 000 km. (sorry in Europe we use km instead of miles :) )

Than I had a stupid accident in 2010 that demolished the front of the car.

 No worry, I had a spare engine in my mind and also in spare from a GT6 MK3.

I also bought a second hand engine hood and the left and right front axles with brakes from a vitesse.

While rebuild of the engine: this seemed to be a 'adepted" 2L to 2.5 L so the surch to the right carbs was needed.

2 Stromberghs CD175 were found with a vitesse intake and all off these stuff was placed under the bonnet with "zero" play :) .

Now I will try to place a servo booster with the tandem cilinder. 

After reading a lot off articles and books I go for the boost only on the front brakes.

Originally Triumph used this at the end of the gt6 history ... .

I figured out that they also used the biggest wheel cilinders at the back: 7/8 inch instead of the smaller onces in the past: when you figure out that the 7/8 have more than 50% more surface then the previous wheel cilinders than the equation front with 1.5/1 and the back surface with 50% more surface stays equal at the end.

Please give me your thoughts about this matter, i'm curious if my thoughts are ok ... 

I think your thoughts are ok.  In fact, I think Triumph themselves did almost the same thing, but for a slightly different reason.

Late Mk3 GT6s had bigger rear brakes (wider drums) as part of the return to the swing axle design, apparently to give them self adjusters (don't work very well) and make them common parts with some Dolomites. In some markets at least, those cars had a brake servo that operated on the front brakes only.

Only sure thing to do is to test it once the car is complete.  Do this by braking hard from maybe 50 kph to a near-stop on a moderately slippery surface.  You need to discover whether the front or rear brakes lock first - and it wants to be the front.  If the rear locks first, you need smaller wheel cylinders

Cheers

Nick