Sapete che misura interna deve essere la pinza posteriore dunlop nella rallye 1,3 ? Sul cd viva.lancia sono riportate le quote dei freni girling e la misura che trovo sulla mia fulvia corrisponde alla 1,6 HF !!!!(1 5/16 pollici circa 33,34 mm) Sapete fino a che misura mi posso spingere nell'alesaggio senza perdere i gommini per la strada?
Grazie.
Stefano
PINZE POSTERIORI DUNLOP
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Stefano
Re: PINZE POSTERIORI DUNLOP
(chiedo scusa se è già la seconda volta che urlo nell'oggetto, spero di non venire messo all'indice!)
Stefano
Stefano
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Huib Geurink
Re: PINZE POSTERIORI DUNLOP
Sorry for replying in english. My Italian is not (yet) good enough.
If you just grind the cilinders to let's say +0,2mm, the problem will be back soon. The cilinders are blank bores in cast iron. Because of the temperature changes (as a result of braking as well as weather changes) there will be condensation in the gap between cilinder and piston. Where there is condensation, there is corrosion.
The way I repair the Dunlop wheel brake clinders is:
- sand blast or bead blast the cilinders till completely clean
- grind the clinders to 0,5mm oversize.
- have the cilinders nickle plated using the electroless process. 10 to 15 microns of nickle is ok.
- press the brass piston out of the saddle for the pad. It is a good idea to also nickle plate the saddle.
- make a new oversize brass piston with 0,2mm clearance between cilinder and piston
- transfer the internal parts from the old piston to the new piston
- press the saddle for the pad back onto the piston
Notes:
- the standard seal can be streched to the oversize, but you have to increase the diameter of the seat of the seal a bit more than the 0,5mm oversize. You have to calculate with surface area's here. If you go to 33,8mm the surface area of the cilinder is increased by 26mm2.
The diameter of the seat of the seal is 21,6mm. The surface area is thus 366mm2. Add the 26mm2 to the 366mm2 and calculate the new diameter for the seat of the seal.
I have a spreadsheet to calculate all the new piston diameters for any oversize of cilinder. If you do not want to do the calculations, mail me the new diameter of the cilinder.
- you can leave the pin in the cilinder
- it is a good idea to nickle plate all the parts of the calliper
- do not use galvanic plating processes. The thickness will vary too much. Only electroless nickle plating is good.
- do not heat treat the nickle plating
If you just grind the cilinders to let's say +0,2mm, the problem will be back soon. The cilinders are blank bores in cast iron. Because of the temperature changes (as a result of braking as well as weather changes) there will be condensation in the gap between cilinder and piston. Where there is condensation, there is corrosion.
The way I repair the Dunlop wheel brake clinders is:
- sand blast or bead blast the cilinders till completely clean
- grind the clinders to 0,5mm oversize.
- have the cilinders nickle plated using the electroless process. 10 to 15 microns of nickle is ok.
- press the brass piston out of the saddle for the pad. It is a good idea to also nickle plate the saddle.
- make a new oversize brass piston with 0,2mm clearance between cilinder and piston
- transfer the internal parts from the old piston to the new piston
- press the saddle for the pad back onto the piston
Notes:
- the standard seal can be streched to the oversize, but you have to increase the diameter of the seat of the seal a bit more than the 0,5mm oversize. You have to calculate with surface area's here. If you go to 33,8mm the surface area of the cilinder is increased by 26mm2.
The diameter of the seat of the seal is 21,6mm. The surface area is thus 366mm2. Add the 26mm2 to the 366mm2 and calculate the new diameter for the seat of the seal.
I have a spreadsheet to calculate all the new piston diameters for any oversize of cilinder. If you do not want to do the calculations, mail me the new diameter of the cilinder.
- you can leave the pin in the cilinder
- it is a good idea to nickle plate all the parts of the calliper
- do not use galvanic plating processes. The thickness will vary too much. Only electroless nickle plating is good.
- do not heat treat the nickle plating
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Stefano
Re: PINZE POSTERIORI DUNLOP
Dear Huib,
Your answer is a real help and a honour form me. As you can read my english is more bad than your italian. I've just made (after you give me the idea) a spreadsheet to calculate the new diametere of the seat of the seal. For a new diameter of 33,8 as you suggested, the new value of the seat is 22,31. Can you control this value please?
What kind of treatment is the "electroless nickle"? What chemical element is used, Ni, Cr or Zn? I'll plate all the part of the calliper in yellow Zn (zincatura a freddo). This treatment looks very well but i think it's no much resistant.
An other problem is to transfer the internal part of the piston...
Thanks in advance for your answer.
Stefano
Your answer is a real help and a honour form me. As you can read my english is more bad than your italian. I've just made (after you give me the idea) a spreadsheet to calculate the new diametere of the seat of the seal. For a new diameter of 33,8 as you suggested, the new value of the seat is 22,31. Can you control this value please?
What kind of treatment is the "electroless nickle"? What chemical element is used, Ni, Cr or Zn? I'll plate all the part of the calliper in yellow Zn (zincatura a freddo). This treatment looks very well but i think it's no much resistant.
An other problem is to transfer the internal part of the piston...
Thanks in advance for your answer.
Stefano
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Huib Geurink
Re: PINZE POSTERIORI DUNLOP
Your english is excellent and the 22,31 looks correct to me. So your mathematics is excellent too.
The element used is mainly Ni but also the layer includes a small percentage of phosphorus. In fact the more phosphorus, the better the corrosion resistance.
First you grind all the cilinders to the same oversize diameter which should be as small as possible. So you start with the worst one. Usually it is about +0,5mm. If you get by with less, so much the better
Make the right tools to ensure the grinding is done in a pure circle centered around the pin.
The yellow zinc plating is all right for the callipers, the bolts, the parts of the handbrake etc but not for the cilinders. I prefer to have all the parts nickle plated like the clinders.
New cilinders are (were) zinc plated. It comes off very very quickly.
Most plating processes are galvanic. It means they use electric voltage and current. The electric fields are strong at sharp edges and absent in cavities. This results in a thick layer on sharp edges and no layer in the inside of cilinders.
Fortunately for nickle plating it is possible to use a chemical process without electric current. It is called "electroless nickle plating" or "chemical nickle plating". The thickness of the layer is determined by the length of time the parts remain in the chemical solution. The thickness is very constant and even on all parts. If you specify 10 to 15 microns, you will be all right and all the bolts will still fit.
I assume you will go to a machine shop (like I do). They will have no problem transferring the inner parts of the piston.
I have just finished doing the rear brakes of the Fulvia of a friend. The result is excellent and looks very nice too.
I don't know what wheels you are using. If you already use 13" alloy's your brakes have been modified already. If you have 14" wheels and consider to change to 13" in the future it is a good idea to modify the brakes already before you have them plated.
I often find that the original bolts which fasten the callipers to the axle have been replaced by standard M10x1,25 bolts. This is not good. The upper parts of the bolt, where there is no thread, should have a diameter of 7/16". The easiest way to maken new bolts is to buy 7/16" 20 UNF bolts. 20 turns per inch is the same as 1,25 mm per turn. Lathe the part where the thread is down to 10mm and cut M10x1.25 thread. 7/16 UNF is the standard bolt size for seat belts, but I don't know if those bolts are 20 turns per inch.
The element used is mainly Ni but also the layer includes a small percentage of phosphorus. In fact the more phosphorus, the better the corrosion resistance.
First you grind all the cilinders to the same oversize diameter which should be as small as possible. So you start with the worst one. Usually it is about +0,5mm. If you get by with less, so much the better
Make the right tools to ensure the grinding is done in a pure circle centered around the pin.
The yellow zinc plating is all right for the callipers, the bolts, the parts of the handbrake etc but not for the cilinders. I prefer to have all the parts nickle plated like the clinders.
New cilinders are (were) zinc plated. It comes off very very quickly.
Most plating processes are galvanic. It means they use electric voltage and current. The electric fields are strong at sharp edges and absent in cavities. This results in a thick layer on sharp edges and no layer in the inside of cilinders.
Fortunately for nickle plating it is possible to use a chemical process without electric current. It is called "electroless nickle plating" or "chemical nickle plating". The thickness of the layer is determined by the length of time the parts remain in the chemical solution. The thickness is very constant and even on all parts. If you specify 10 to 15 microns, you will be all right and all the bolts will still fit.
I assume you will go to a machine shop (like I do). They will have no problem transferring the inner parts of the piston.
I have just finished doing the rear brakes of the Fulvia of a friend. The result is excellent and looks very nice too.
I don't know what wheels you are using. If you already use 13" alloy's your brakes have been modified already. If you have 14" wheels and consider to change to 13" in the future it is a good idea to modify the brakes already before you have them plated.
I often find that the original bolts which fasten the callipers to the axle have been replaced by standard M10x1,25 bolts. This is not good. The upper parts of the bolt, where there is no thread, should have a diameter of 7/16". The easiest way to maken new bolts is to buy 7/16" 20 UNF bolts. 20 turns per inch is the same as 1,25 mm per turn. Lathe the part where the thread is down to 10mm and cut M10x1.25 thread. 7/16 UNF is the standard bolt size for seat belts, but I don't know if those bolts are 20 turns per inch.
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totola
Re: PINZE POSTERIORI DUNLOP
ciao io possiedo dei gommini maggiorati se mi vuoi chiamare ti potrò spiegare molto bene come
fare un buon lavoro e non perdere nulla per strada.
348/5620444 Stefano ha scritto:
>
> Sapete che misura interna deve essere la pinza posteriore
> dunlop nella rallye 1,3 ? Sul cd viva.lancia sono riportate
> le quote dei freni girling e la misura che trovo sulla mia
> fulvia corrisponde alla 1,6 HF !!!!(1 5/16 pollici circa
> 33,34 mm) Sapete fino a che misura mi posso spingere
> nell'alesaggio senza perdere i gommini per la strada?
> Grazie.
> Stefano
fare un buon lavoro e non perdere nulla per strada.
348/5620444 Stefano ha scritto:
>
> Sapete che misura interna deve essere la pinza posteriore
> dunlop nella rallye 1,3 ? Sul cd viva.lancia sono riportate
> le quote dei freni girling e la misura che trovo sulla mia
> fulvia corrisponde alla 1,6 HF !!!!(1 5/16 pollici circa
> 33,34 mm) Sapete fino a che misura mi posso spingere
> nell'alesaggio senza perdere i gommini per la strada?
> Grazie.
> Stefano