Brake Master Cylinder Replacement
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From: St. John's, NF, Canada
Brake Master Cylinder Replacement
Looks like I will be needing a master cylinder swap in the near future. My brake pedal ever so slowly sinks when pressure is applied. I have checked the MC, all calipers and the rest of the system components and there is no visable leak...fluid level is rock solid and I have had the complete system bleed twice just to be sure... so I guess the MC is bypassing.
Just wondering what the advice is on replacing the MC. Should I simply swap it for a same model year unit ('85) or upgrade it to 86.5+ spec? I have no plans to upgrade the other parts of the brake system at present, but who knows what the future holds? Is it worth the u/g to the MC, seeing I have to replace it anyway? Anyone been here before?
Regards,
SteveCo in St. John's
Just wondering what the advice is on replacing the MC. Should I simply swap it for a same model year unit ('85) or upgrade it to 86.5+ spec? I have no plans to upgrade the other parts of the brake system at present, but who knows what the future holds? Is it worth the u/g to the MC, seeing I have to replace it anyway? Anyone been here before?
Regards,
SteveCo in St. John's
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From: St. John's, NF, Canada
John;
Thanks for the suggestion...and no, I have not been messing with the vacuum system! I am blessed with what appears to be very well functioning vac system...everything seems to work as it should, so I have been leaving it alone.
I'll take a look all the same...the system was working fine just prior to a caliper rebuild and system bleed about 3 months ago. I'm thinking that the MC seal(s) were damaged at that time...assisted by age, as well.
Regards,
SteveCo
Thanks for the suggestion...and no, I have not been messing with the vacuum system! I am blessed with what appears to be very well functioning vac system...everything seems to work as it should, so I have been leaving it alone.
I'll take a look all the same...the system was working fine just prior to a caliper rebuild and system bleed about 3 months ago. I'm thinking that the MC seal(s) were damaged at that time...assisted by age, as well.
Regards,
SteveCo
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SteveCo,
If you are going to update to the larger brakes, then change to the later MC. If not, then I wouldn't recommend it as the MC is matched to the later model calipers - not the earlier units.
Dangerous? Probably not, but once again, I wouldn't recommend it.
Greg
If you are going to update to the larger brakes, then change to the later MC. If not, then I wouldn't recommend it as the MC is matched to the later model calipers - not the earlier units.
Dangerous? Probably not, but once again, I wouldn't recommend it.
Greg
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From: Walnut Creek, California
Steve,
When I had a brake problem earlier this year, it turned out to be the seals in the front calipers has leaks in them. Just enough to create a very spongy feeling pedal, but never enough to show a visible leak anywhere (except when the calipers were taken off). I eventually replaced everything in my brake system (because it was long due), but a rebuild of the calipers would have solved the spongy feeling in the pedal. Still, I learned a lot from doing everything else.
Rob
When I had a brake problem earlier this year, it turned out to be the seals in the front calipers has leaks in them. Just enough to create a very spongy feeling pedal, but never enough to show a visible leak anywhere (except when the calipers were taken off). I eventually replaced everything in my brake system (because it was long due), but a rebuild of the calipers would have solved the spongy feeling in the pedal. Still, I learned a lot from doing everything else.
Rob
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From: St. John's, NF, Canada
Thanks to all. I don't plan to upgrade the braking system, so I think I will stick with the stock MC setup.
Rob;
I read about your experience while doing research on my situation. I'll have another look at all the calipers, but there is no sign of a leak and my MC reservoir has been rock steady on fluid level for months. I do understand that it is possible that a very small caliper leak might be the culprit, but I have a feeling that my MC is in need of service.
As I mentioned before, this situation suspiciously started after a caliper seal rebuild to fix a stickly front caliper. I know the mechanic did not use a vacuum/speed bleeder on this job and I figure the MC seals were "exercised" when the system was bleed with the pedal.
I had all 4 corners bleed about a month ago to ensure that there was no air in the system (none found). This has not made any difference to the very small (but perceptable) pressure loss on the brake peddle.
I think I will take the time and rebuild the other three calipers and the MC just to ensure everything is OK...I am sure the brakes have been serviced over time, but I have no service records to note when and what.
Which brings up a related question...or two: Is the switch to silcone brake fluid advisable? If so, how do you ensure the old fluid is flushed from the system? Double fluid change? I have concerns about conventional fluid and moisture, as my car is garage stored 5 months on the year and the local weather is...well, typically cool and damp.
Regards,
SteveCo in St. John's
Rob;
I read about your experience while doing research on my situation. I'll have another look at all the calipers, but there is no sign of a leak and my MC reservoir has been rock steady on fluid level for months. I do understand that it is possible that a very small caliper leak might be the culprit, but I have a feeling that my MC is in need of service.
As I mentioned before, this situation suspiciously started after a caliper seal rebuild to fix a stickly front caliper. I know the mechanic did not use a vacuum/speed bleeder on this job and I figure the MC seals were "exercised" when the system was bleed with the pedal.
I had all 4 corners bleed about a month ago to ensure that there was no air in the system (none found). This has not made any difference to the very small (but perceptable) pressure loss on the brake peddle.
I think I will take the time and rebuild the other three calipers and the MC just to ensure everything is OK...I am sure the brakes have been serviced over time, but I have no service records to note when and what.
Which brings up a related question...or two: Is the switch to silcone brake fluid advisable? If so, how do you ensure the old fluid is flushed from the system? Double fluid change? I have concerns about conventional fluid and moisture, as my car is garage stored 5 months on the year and the local weather is...well, typically cool and damp.
Regards,
SteveCo in St. John's
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From: Ellsworth, Michigan
Steve I replaced the MC a year ago. I found one somewhere on-line for I think.... $160 or less. P.M. me and I will dig through my receipts. It was a OEM replacement. The change was easy and not too nerve racking. As for the fluid switch. I considered that also. After speaking to my mechanic (I was doing this myself with his advice). Only switch the fluid if you plan to make sure that all of the old is out. As you know the two are not compatable. It will turn to sludge.
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From: St. John's, NF, Canada
Thanks, Chucker...I'll PM you on the MC source you used. 928 Intl has them for $175, FYI.
On the fluid, some digging through the forum archives produced a definitive "No" on the switch to silicone and the "Yes" to synthetic glycol-type fluid. Based on this, I'll stick with DOT 3 or 4 spec standard fluid and plan to change it out every two years (just add it to the list...along with the coolant swap at the same interval).
Regards,
SteveCo in St. John's
On the fluid, some digging through the forum archives produced a definitive "No" on the switch to silicone and the "Yes" to synthetic glycol-type fluid. Based on this, I'll stick with DOT 3 or 4 spec standard fluid and plan to change it out every two years (just add it to the list...along with the coolant swap at the same interval).
Regards,
SteveCo in St. John's
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