Brake master rebuild

ng_randolph

ng_randolph

Bjorn H
I received the rubber bits to rebuild my brake master cylinder, and was surprised to find that the three oval edge seals are not all the same size. Two of them are 4.15 mm thick and 19.5 mm OD, the last one is 4.35 mm thick and 20.1 mm OD. I no longer have the original seals, and did not notice if they were all the same or not when I disassembled the master. I took pictures of the internals of the master before I tore it down, and from the photos it looks like the seal towards the bottom of the cylinder (closest to the rear of the car) is a bit fatter than the other two. Is this correct, or should I chalk the difference up to manufacturing tolerances (that would be pretty sloppy tolerances)?
 
Hope This Helps

Page 117 from the 74-78 Fiat X 1/9 Shop Manual. Incase you don't have one.



Much easier to Read, if you just Print it out NORML Size.
 
The O ring seals I have listed are identical for all three (4115451).

(and the identical seal for the Clutch master and slave cylinder too)

Your going to have 'fun' squeezing a 20.1mm seal into a 19.05mm hole...

SteveC
 
Where did you get the kit?

If it was from one of our usual supportive vendors, could you call them in the morning and ask?
 
Getting that 20.1mm seal into the 19.05mm bore might be fun, the resulting friction is going to be fierce..

Cannot see how this could even begin to work.

Would it be possible this 20.1mm seal is for a over sized bore?


Bernice


fiatfactory said:
Your going to have 'fun' squeezing a 20.1mm seal into a 19.05mm hole...

SteveC
Click to expand...
 
Rupunzell said:
Getting that 20.1mm seal into the 19.05mm bore might be fun, the resulting friction is going to be fierce..

Cannot see how this could even begin to work.

Would it be possible this 20.1mm seal is for a over sized bore?


Bernice
Click to expand...

That certainly is possible, although they were bought as a kit. I have e-mailed the vendor about this.

I saw what I believe is your X1/9 today. Burgundy with bumperettes and Maserati wheels. Those wheels look nice on the X.
 
The vendor replied this morning, saying (like SteveC did above) that all three oval edge seals should be the same size. They are dropping a replacement set in the mail.
 
Yes, that is me, 74' exxe with those Maserati Biturbo wheels and it needs tires.

It is my sunny daily driver complete with original 1300cc, 4 speed driver line for now.


Bernice


ng_randolph said:
I saw what I believe is your X1/9 today. Burgundy with bumperettes and Maserati wheels. Those wheels look nice on the X.
Click to expand...
 
How did the rebuild work out for you?

Can you share a little more info?

I would like to have the rebuild seals on hand BEFORE I have to take mine apart. I cannot be sure from looking at the pics floating around EXACTLY what is required. Based on other topics regarding replacement cylinders, it seems rebuilding (with a possible resleeve) is a safer bet.

Looking at the pic RedBull linked (many thanks) it appears that one needs THREE identical seals for the main assembly, one different (double lip?) seal for the innermost end, and an external boot, and perhaps the 'gasket' for the elbow on top.

Looking on Obert's site, it doesn't indicate required quantity of the various seals listed for X1/9 application

Can you share the specific PN's & quantities for the items you purchased?
 
master cyls

the problem is probably is not a factory seal kit. fiat never listed nor supplied an oversize "seal" kit. the only size they offered was standard(original) size. if you look at book time on replacement (r&r)
there is no mention of honing, resizing, rebuild. it was more cost effective just to replace the assembly than to repair. in later years they switched to feed nipples that popped into grommets, instead of the ones that were held in by star washer lock rings, which the customers were bi##hing about. hence the new design. best to find a original seal kit and hopefully find a source to sleeve it back to original dimensions.
mikemo90*aol.com
 
I'm just looking for correct numbers and quantities of each appropriate seal for original replacements. There is no 'kit' that I can find...
 
lookforjoe said:
How did the rebuild work out for you?
Click to expand...

Not so good. I can't get a firm pedal. Somewhere between the sleeving and replacement rubber bits, I have an internal leak in the brake master. The master cylinders are coming out again this week for closer inspection.

lookforjoe said:
Can you share a little more info?

I would like to have the rebuild seals on hand BEFORE I have to take mine apart. I cannot be sure from looking at the pics floating around EXACTLY what is required. Based on other topics regarding replacement cylinders, it seems rebuilding (with a possible resleeve) is a safer bet.

Looking at the pic RedBull linked (many thanks) it appears that one needs THREE identical seals for the main assembly, one different (double lip?) seal for the innermost end, and an external boot, and perhaps the 'gasket' for the elbow on top.

Looking on Obert's site, it doesn't indicate required quantity of the various seals listed for X1/9 application

Can you share the specific PN's & quantities for the items you purchased?
Click to expand...

My brake master (which looked to be original to the car) had:

3 D-profile seals that look like Fiat part number 4115451
1 double lipped seal that looks like Fiat part number 792780

As it came out of the car, this is how it looked:

DSCN1235M.jpg



My Clutch master (Beck/Arnley) had:

1 D-profile seal that looks like Fiat part number 4115451
1 double lipped seal that looks like Fiat part number 792780

As it came out of the car, this is how it looked:

DSCN1236M.jpg



You will also need replacement copper crush washers for the the plugs at the end of each of the master cylinders. For the clutch master the ID is 24 mm and the OD is 30 mm. Search Amazon for "[ame="[URL]http://www.amazon.com/gp/product/B00HER9JEU/ref=oh_aui_detailpage_o01_s00?ie=UTF8&psc=1[/URL]"]M24X30 Metric Solid Copper Sealing Washer DIN 7603A[/ame]" For the brake master the old crush washers was 22 mm ID and ~28 mm OD (perhaps closer to 27 mm pre-crush?). I was able to find 27 mm OD which works well. Search Amazon for "[ame="[URL]http://www.amazon.com/gp/product/B00HER9IG4/ref=oh_aui_detailpage_o01_s00?ie=UTF8&psc=1[/URL]"]M22X27 Metric Solid Copper Sealing Washer DIN 7603A[/ame]"

I have not done anything to the clutch slave, but an old one from my parts pile had one of the D-profile seals like the master cylinders and one narrow two-lipped seal that looked like Fiat part number 4184521. From an earlier thread here I gather there are a few different types of clutch slave cylinders that take different seals. I don't have a photo of my clutch slave piston, but it looks like the first one in Jvandyke's post.
 
Last edited:
Thank you for the detailed (with pics) explanation. :)

My X still has the original masters, so I'll go with those seals.
 
Curious, was this cylinder sleeved in Brass or 304 Stainless Steel?

Brass sleeves cannot be honed and can corrode under specific conditions. The inability for a brass sleeve to be honed post installation is a significant negative as honing (proper cross hatch and finish surface) of the cylinder smooths out the lumps and bumps that happens during the sleeving process and helps the seals create a effective seal.

This is a patent related to what is required to sleeve a cylinder and have it function properly:

http://www.google.com.au/patents/US4227292


It is possible there is still air in the brake system resulting in a soft pedal. Those right angle brake fluid feeder fittings are air traps due their design. It was a problem to purge the air out of them even on the bench cylinder test rig. The solution is to use a fitting with a smooth radius bend in place of the hard right angle bend of the stock fitting.

It is possible Fiat changed from a 6mm - 1/4" ID feed hose to a 8mm - 5/16" ID feed hose due to this problem of air getting stuck at this fitting.

Another detail worth noting, the OEM Fiat fittings have a shoulder diameter of 13mm and the current aftermarket cylinders appear to have a shoulder diameter of 1/2" which is slightly smaller than the stock Fiat. The rubber fittings appear to be the same dimensions. The smaller 1/2" shoulder runs the risk of a small air leak. This can suck in a small amount of air into the system aggravating the problem of air in the system.

Years ago when one can walk into a Fiat dealer and get a OEM Fiat brake master off the shelf, these feeder fittings were very difficult to turn if they can be turned at all out of the box. Of the current aftermarket ones I have used, the fittings are supplied loose and DIY install. Post install, they can be easily rotated which implies a less than tight seal.

I'm going to re-design these fittings and post info about them later.

It is worth noting that early Fiat cylinders have a different brake fluid inlet design which uses an O-ring on a plastic fitting into a tapered seat that is held in place with a press to lock spring washer.


Bernice

ng_randolph said:
Not so good. I can't get a firm pedal. Somewhere between the sleeving and replacement rubber bits, I have an internal leak in the brake master. The master cylinders are coming out again this week for closer inspection.

My brake master (which looked to be original to the car) had:

3 D-profile seals that look like Fiat part number 4115451
1 double lipped seal that looks like Fiat part number 792780
Click to expand...
 
Brass Sleeves

"Brass sleeves cannot be honed and can corrode under specific conditions. The inability for a brass sleeve to be honed post installation is a significant negative as honing (proper cross hatch and finish surface) of the cylinder smooths out the lumps and bumps that happens during the sleeving process and helps the seals create a effective seal."

It's interesting to me that you say Brass inserts can't be honed. I have no experience sleeving hydraulic cylinders, but my profession is repairing Musical Instruments, and I'm pretty familiar with their manufacture. Nearly every piston-valved musical instrument (trumpets and the like) have brass valve casings that are honed-to-size then lapped to fit. Sometimes valves are repaired by honing the casing oversize, plating the pistons oversize, externally honing the pistons, then lapping to fit. Those casings are solid brass, not sleeved, but I'm not seeing how that would make it impossible to hone it. If you can explain what the problem is honing a brass sleeve, I'd appreciate it.

-Brian
 
Brass is honed all the time, lapped too. According to the folks at Apple Hydraulics who sleeves cylinders in brass, they have not had much success honing the cylinders and have stopped doing this.

Same was noted by Karps Brake who sleeves in stainless steel.

This is worth further research as it maybe that brass when honed with a residual pattern is too soft when subjected to polymer seals operating at a few thousands psi to properly retain a good seal over many cycles of piston operation.

This is quite different than musical instruments that operate at inches of water. Valves in brass musical instruments have a solid valve body that runs in a precision bore fitted to the valve body. A thin layer of oil keeps the valve body from contacting the bore and create a seal.


Bernice


Russe11 said:
"Brass sleeves cannot be honed and can corrode under specific conditions. The inability for a brass sleeve to be honed post installation is a significant negative as honing (proper cross hatch and finish surface) of the cylinder smooths out the lumps and bumps that happens during the sleeving process and helps the seals create a effective seal."

It's interesting to me that you say Brass inserts can't be honed. I have no experience sleeving hydraulic cylinders, but my profession is repairing Musical Instruments, and I'm pretty familiar with their manufacture. Nearly every piston-valved musical instrument (trumpets and the like) have brass valve casings that are honed-to-size then lapped to fit. Sometimes valves are repaired by honing the casing oversize, plating the pistons oversize, externally honing the pistons, then lapping to fit. Those casings are solid brass, not sleeved, but I'm not seeing how that would make it impossible to hone it. If you can explain what the problem is honing a brass sleeve, I'd appreciate it.

-Brian
Click to expand...
 
In the hundreds of hydraulic cylinders I have had sleeved I have had two failures due to incorrect installation of the sleeve....

one was bored and pressed in at an angle...the maunfacturer replaced that one FOC once I showed them the issue...

the other was too smooth and hadn't been honed after install, and I couldn't get the pedal firm until I pulled it back apart and ran a fine stone hone up the bore, it was all good after that.

SteveC
 
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