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PostPosted: Sun May 26, 2024 4:04 pm 
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I have just bled the brakes on my dolly. I have fitted mk5 escort calipers (they were brand new, ford, cw pads and carriers for £60/pr!) along with VW 256mm discs.
And having kept an eye on this forum, I have found a few things.
1. The std dolly calipers are 48mm, and my ford ones are 54mm. That is a substantial 26.5% increase in area, and therefore pedal movement.
2. The servo on my car could well be a sprint type, as I saw it mentioned that the sprint servo was used on late 1850s.
3. The brake pedal has more movement that I would ideally like, and that is without starting the engine.
4. The sprint servo has a delicate bakelite disc, and that breaks if the pedal moves too far.

So my questions are
1. How much is too much on the brake pedal for the sprint servo? (is there a visible tell tale to confirm it is a sprint type??)
2. Any pointers on a suitable larger bore master cylinder?

Ta

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Brighton


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PostPosted: Sun May 26, 2024 7:35 pm 
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The 54 mm dia piston on the Escort caliper is exactly the same as the Sierra/Ka/Puma caliper used by me and many others on the "normal" TJ conversion. My Sprint also uses 254mm Passat discs with it's Puma 54mm calipers and coupled with a dual circuit standard master cylinder, stock Sprint servo, all braided S/S hoses and 5/8" bore rear wheel cylinders, all is well. There is a little more pedal travel than I expect from a well set up standard Sprint, but it's not "excessive" in any way, my MOT tester has never even mentioned it, not even in passing.

My assumption here is that the basic setup you have contrived is fine, conforms to the normal "Trackerjack" pattern and should work as advertised.

The travel issue IS real, one that has bothered some people and not others! From the dozen or more TJ conversions i've done so far, a tandem master cylinder gives a lower pedal than a single circuit one, but in neither case has it ever been, IMO, cause for concern (and i'm fanatical about brakes)

How much travel is TOO much? It's a bit hard to quantify, But I have 3 TJ converted cars on the premises here, a more or less standard tandem circuit Sprint, my own Vauxhall converted Sprint auto (spec as above, it also has PDWA delete, LSV delete and my equal length rear axle pipe conversion) and the ex FWD car which has a similar setup to my Sprint but has 239mm discs, Sierra 54mm calipers and the 1500FWD servo. If it's not pouring with rain tomorrow, i'll do some measurements, running and stationary and get back to you.

But my provisional conclusion is that if you HAVE got too much travel, something else is responsible, not the design. One thing I have noticed over the years is that the TJ system is more critical of poor rear shoe (self :lol: ) adjustment, so that's worth checking.

On bigger master cylinders, I gather there is a 22mm bore Jag master available, also one from a Saab (don't know which model) and possible a Volvo one too (340/360?) But, as far as I'm concerned, you're on your own with these, I've never NEEDED to find out!

Steve

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'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.


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PostPosted: Sun May 26, 2024 7:57 pm 
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In the late eighties/early nineties it was popular to fit a a Ford P100 master cylinder, which was a slightly bigger bore, to reduce pedal travel. I did this back then and it seemed to reduce travel and give a better feel with the standard Sprint brakes.

I've got a Saab Classic 900 master cylinder to go with my TJ conversion, which I read years ago was a good option for a larger bore, but I haven't got it fitted yet, so I can't confirm that it works. I only have the original 1500 servo in my car, which might be a bit undersized, so I am now considering an LDV 400 servo and master cylinder swap, which is another one that is supposed to work well.


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PostPosted: Sun May 26, 2024 8:49 pm 
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The location of the one way valve can tell you if it is a Sprint servo; if it is at 11 o'clock, you could be in luck. 1850 fitted with these also have the remote reservoir clutch master cylinder.

The problem with servo pistons suffering shear damage seems to be predominantly with single line systems when empty as the push rod can then travel too far. Because of the internal design of the tandem cylinder, resistance is met before the pushrod can do any damage.

I can get an OE master cylinder sleeved to any bore size you choose (so long as sufficient side wall thickness remains. I've had one done to 13/16" without issue


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PostPosted: Mon May 27, 2024 5:13 pm 
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Quote:
The location of the one way valve can tell you if it is a Sprint servo; if it is at 11 o'clock, you could be in luck. 1850 fitted with these also have the remote reservoir clutch master cylinder.

The problem with servo pistons suffering shear damage seems to be predominantly with single line systems when empty as the push rod can then travel too far. Because of the internal design of the tandem cylinder, resistance is met before the pushrod can do any damage.

I can get an OE master cylinder sleeved to any bore size you choose (so long as sufficient side wall thickness remains. I've had one done to 13/16" without issue
The valve is indeed at 11 o'clock, and it does have a remote resevoir for the clutch (I guess the sprint has a larger diameter servo?)
If I am safe from breaking that bakelite part I will stick with the std cylinder for now. I did have a look, but most of the alternative recommendations are tricky to find new. What I did stumble across was the MGB dual circuit cylinder, which has a 20.6mm bore. So would almost compensate for the bigger caliper pistons. (17% bigger, but still down about 10%) Just a thought in case I really don't like the pedal travel.
Info on the servo etc VERY much appreciated.

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Clive Senior
Brighton


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 Post subject: Aye….
PostPosted: Tue May 28, 2024 10:38 am 
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There are quite a few BMCs that will fit (thinks 80s European )
They ideally need to be 22.2mm (7/8”) bore.
Saab 99/900 are ideal because they are mounted horizontally in original applications….

Ian

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PostPosted: Tue May 28, 2024 7:45 pm 
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One thing that has occurred to me, is the car late enough to be tandem master cylinder and carry a PDWA valve?

Don't want to climb too far onto my hobby horse but the PDWA can cause untold bleeding problems.

With that in mind I have recently managed to source a supply of brass Tee pieces in 7/16" UNF so can now offer an improved 2 piece PDWA delete kit which is a direct and reversible replacement for the PDWA. It's cheaper too, at only £20 including UK postage!

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.


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PostPosted: Tue May 28, 2024 8:27 pm 
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Location: Highley, Shropshire
Some numbers from the fleet

Standard dual circuit Sprint (TJs, 239mm discs 54mm calipers)

Stationary engine 2" travel from rest till hard
Initial bite point running 2.25"
Pedal hard running 3"

Dolomega Sprint (with all my mods and 256mm discs)

Stationary engine 2" travel from rest to hard
No further numbers for this car as not running ATM

Vauxhall converted 1500FWD (TJs, 239mm discs, 54mm calipers dual circuit)

Stationary engine 1,75" travel from rest to hard
Initial bite point running 2"
Pedal hard running 3"

On all 3 cars, distance from floorboards/carpet to top of pedal in rest position is close to 7"

The numbers are actually bigger than I expected them to be, having frequently driven all 3 cars, it doesn't FEEL like that much.
Additionally and again from driving the cars, the "pedal hard, running" number is probably a bit misleading as achieving that much pressure whilst driving would lead to locked wheels and flat spotted tyres! What you get in the shed/garage/workshop does not reflect too much how the car behaves on the road, there's no substitute for trying it in real road conditions!

HTH, 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.


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