How much is too much ?

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User1

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<TABLE cellSpacing=1 cellPadding=6 width="100%" border=0><TBODY><TR><TD colSpan=2><TABLE width="100%" border=0><TBODY><TR><TD style="PADDING-TOP: 4px" vAlign=top colSpan=2>[FONT=Trebuchet MS, Verdana, Tahoma, Arial]How much is too much ?<!-- google_ad_section_end -->

[/FONT][FONT=Trebuchet MS, Verdana, Tahoma, Arial]December 8 2000 at 9:57 PM[FONT=Trebuchet MS, Verdana, Tahoma, Arial][/FONT][/FONT]</TD><TD vAlign=top align=right>[FONT=Trebuchet MS, Verdana, Tahoma, Arial]lezesig [/FONT]</TD></TR><TR><TD vAlign=bottom colSpan=3><HR></TD></TR><TR><TD colSpan=3>[FONT=Trebuchet MS, Verdana, Tahoma, Arial]<!-- google_ad_section_start -->Subject ? Calipers. Specific area ? The piston guide or bore. We all know what happens when a bare corrodable metal is exposed to water right ? We also probably all know that brake fluid is hygroscopic meaning that it has the ability to pull moisture in from the air and combine with the fluid, right ? So basically we have an aluminum (unknown alloy) caliper that is operating with a fluid that contains varying amounts of water and will begin to corrode fresh out of the box in normal use on the car through no fault of our own. Even with frequent brake fluid replacement there will still be water present in the fluid since the reservoir is normally vented to the atmosphere.....and we all know what the atmosphere is typically like here in the Great Northwest ! There is also another possible way that water can be introduced into the caliper from the outside. A small rip or tear on the dust cover boot which surrounds the piston can allow water into the bore outboard of the piston seal. Since water is always slinging onto the entire assembly during normal driving operations in wet weather this is a good way to start the corrosion process on the bore from outside the hydraulic system. Man, this is getting kind of longwinded....but a little free time here...I'll plow forward.......I pulled the aft calipers and dismantled them and found corrosion in the bore. Not much but some. The piston glides smoothly without hangup. The piston does not have a blem on it much to my surprise. A testamant to the fact that Aluminum corrodes much faster than chromium under the same operating conditions. <Our vendors aren't gonna like this part> If money was not a concern I'd replace the caliper because of the slight sign of corrosion in the bore. Is this safety a concern ? You bet. Do I think that the piston has the potential to seize or gall in the bore. No, not really. There seems to be a good tolerance and coencentricty of the bore and has not been jeopardized through corrosion. Is the bore so rough that fluid will slip past the seal and render the assy inoperable during driving ? Definitely not ! I thought I had all of the fluid drained from the assembly prior to dismantling. Big Suprise ! When the piston was removed from the caliper about a quarter cup of fluid flew out drenching the workbench. A good reminder to wear safety glasses during this step as a precaution ! The bore to piston to seal arrangement was fluid tight. So.........it boils down to the question " How much corrosion is too much ? " It would be nice to replace the caliper everytime brake pads are replaced because of slight corrosion but this would be impractical from a costing standpoint. And certainly the calipers will need replaced once the wear limit is reached but it still points to the original question on limits (for bore surface roughness). Without a comparisn of a rejected caliper its hard to judge the permissable limits. The manuals and spec's certainly do not quantify this surface characteristic. The best these manual do is say something to the effect ...ah....if there is wear beyond normal then replace. That really defines the permissable limits of the surface doesn't it ? In the very least how about some pics of the go and no-go limits editors/publishers ? We're really only talking about one square inch of total surface area here but it's a pretty important surface and could make the difference between a proper brake rebuild job and one that's substandard. I'm leaning towards rebuilding the assembly by replacing all the seals and not replacing the piston. I noticed the the next more thorough kit also contains the piston. That is unwarranted for this job in my opinion. So how about it from a historical standpoint ? How much can the X endure on the calipers before they're considered shot, toast, kaput ! Seen any really bad still functioning caliper bores ? How bad ? Any stories on rebuilding ? Thanks much...and out for now, lezesig ('79 w/ tranny rebuild 100% complete) <!-- google_ad_section_end -->

[/FONT]</TD></TR></TBODY></TABLE><TABLE cellPadding=4 width="100%" border=0><TBODY><TR><TD vAlign=top noWrap align=left>[FONT=Trebuchet MS, Verdana, Tahoma, Arial] [/FONT]</TD><TD vAlign=top align=right>[FONT=Trebuchet MS, Verdana, Tahoma, Arial]
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[/FONT]</TD></TR></TBODY></TABLE></TD></TR><TR><TD>[FONT=Trebuchet MS, Verdana, Tahoma, Arial]Author[/FONT]</TD><TD>[FONT=Trebuchet MS, Verdana, Tahoma, Arial]Reply[/FONT]</TD></TR><TR><TD vAlign=top noWrap width="17.9%">[FONT=Trebuchet MS, Verdana, Tahoma, Arial]Steve Hoelscher[/FONT]
[FONT=Trebuchet MS, Verdana, Tahoma, Arial][/FONT]</TD><TD style="PADDING-LEFT: 15px" vAlign=top><TABLE cellSpacing=0 cellPadding=1 width="100%" border=0><TBODY><TR><TD align=left>[FONT=Trebuchet MS, Verdana, Tahoma, Arial]<!-- google_ad_section_start -->Caliper rebuilds<!-- google_ad_section_end -->

[/FONT][FONT=Trebuchet MS, Verdana, Tahoma, Arial][/FONT]</TD><TD vAlign=top align=right>[FONT=Trebuchet MS, Verdana, Tahoma, Arial]December 9 2000, 6:57 AM [/FONT]</TD></TR></TBODY></TABLE><TABLE cellSpacing=0 cellPadding=1 width="100%" border=0><TBODY><TR><TD style="PADDING-LEFT: 15px">
[FONT=Trebuchet MS, Verdana, Tahoma, Arial]<!-- google_ad_section_start -->The proper method of rebuilding the calipers is to chase the bores with a "brake hone". Similar in theory and operation to a cylinder hone, a brake hone will remove any surface corrosion that may foul the piston in the bore. Remember, that in this instance, the seal sits in the grove of the bore and rides on the chromium face of the piston, so the bore of the caliper should have only incidental contact with the piston, therefore there should be little if any wear in the bore.

Any corrosion should be limited to the surface, so the brake hone should leave a smooth and un-blemished finish in the bore. Any visual evidence of pitting or gauling after honeing should disqualify the caliper. I also fabricated a tool to clean the seal's grove in the bore as corrosion there will cause the seal not to seat properly. Finally, I also use a "scotch bright" pad to clean the piston before re-assembly (Scotch Bright will not damage the finish of the piston). It is rare that I find a piston that is gauled or otherwize damaged enough to require replacement.

As a side note, I also use a wire wheel to clean the caliper's sliding surfaces and shims and give each a light coating of anti-sieze before re-assembly.

I have found that the calipers I have rebuilt in this fashion perform as well and are as reliable as new units.

Congratulations on completing your transmission rebuild.

Steve
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[/FONT]</TD></TR></TBODY></TABLE></TD></TR><TR><TD vAlign=top noWrap width="17.9%">[FONT=Trebuchet MS, Verdana, Tahoma, Arial]lezesig[/FONT]
[FONT=Trebuchet MS, Verdana, Tahoma, Arial][/FONT]</TD><TD style="PADDING-LEFT: 30px" vAlign=top><TABLE cellSpacing=0 cellPadding=1 width="100%" border=0><TBODY><TR><TD align=left>[FONT=Trebuchet MS, Verdana, Tahoma, Arial]<!-- google_ad_section_start -->thanks<!-- google_ad_section_end -->

[/FONT][FONT=Trebuchet MS, Verdana, Tahoma, Arial][/FONT]</TD><TD vAlign=top align=right>[FONT=Trebuchet MS, Verdana, Tahoma, Arial]December 12 2000, 6:24 PM [/FONT]</TD></TR></TBODY></TABLE><TABLE cellSpacing=0 cellPadding=1 width="100%" border=0><TBODY><TR><TD style="PADDING-LEFT: 30px">
[FONT=Trebuchet MS, Verdana, Tahoma, Arial]<!-- google_ad_section_start -->Thanks Steve,
Good idea on the land cleaner. I did notice that the seal was starting to breach on the OD due to oxides. The removed seal looked like a lunarscape on the OD. I had my suspicions there. Bore is basically a guide like you said. Will dress it up with emery and hot soap and water. Out for now, lezesig '79<!-- google_ad_section_end -->

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[/FONT]</TD></TR></TBODY></TABLE></TD></TR><TR><TD vAlign=top noWrap width="17.9%">[FONT=Trebuchet MS, Verdana, Tahoma, Arial]<SCRIPT language=Javascript> <!-- var n54_em; n54_em = ""; n54_em = n54_em + "s";n54_em = n54_em + "e";n54_em = n54_em + "r";n54_em = n54_em + "v";n54_em = n54_em + "i";n54_em = n54_em + "c";n54_em = n54_em + "e";n54_em = n54_em + "@";n54_em = n54_em + "i";n54_em = n54_em + "m";n54_em = n54_em + "p";n54_em = n54_em + "o";n54_em = n54_em + "r";n54_em = n54_em + "t";n54_em = n54_em + "a";n54_em = n54_em + "u";n54_em = n54_em + "t";n54_em = n54_em + "o";n54_em = n54_em + "t";n54_em = n54_em + "e";n54_em = n54_em + "c";n54_em = n54_em + "h";n54_em = n54_em + ".";n54_em = n54_em + "c";n54_em = n54_em + "o";n54_em = n54_em + "m"; document.write("steve ambrose"); // --> </SCRIPT>steve ambrose <NOSCRIPT></NOSCRIPT>[/FONT]
[FONT=Trebuchet MS, Verdana, Tahoma, Arial][/FONT]</TD><TD style="PADDING-LEFT: 15px" vAlign=top><TABLE cellSpacing=0 cellPadding=1 width="100%" border=0><TBODY><TR><TD align=left>[FONT=Trebuchet MS, Verdana, Tahoma, Arial]<!-- google_ad_section_start -->Calipers....<!-- google_ad_section_end -->

[/FONT][FONT=Trebuchet MS, Verdana, Tahoma, Arial][/FONT]</TD><TD vAlign=top align=right>[FONT=Trebuchet MS, Verdana, Tahoma, Arial]December 9 2000, 9:03 AM [/FONT]</TD></TR></TBODY></TABLE><TABLE cellSpacing=0 cellPadding=1 width="100%" border=0><TBODY><TR><TD style="PADDING-LEFT: 15px">
[FONT=Trebuchet MS, Verdana, Tahoma, Arial]<!-- google_ad_section_start -->Hi there... It's been my experience that if the piston is in good shape, and moves freely in the bore, that just replacing the seals will work fine. I believe the main seal is between the piston and the rubber seal, and the bore just guides the piston.
Rear calipers tend to leak after the piston is retracted for pad replacement, and it would be wise to put in seals at that time. If the fronts retract easily when pads are replaced, I don't usually have any leaking or binding problems. In short, I think the piston condition and seal condition is far more important to sealing than the bore condition. Good luck,
Steve<!-- google_ad_section_end -->

[/FONT]</TD></TR></TBODY></TABLE><TABLE cellSpacing=0 cellPadding=4 width="100%" border=0><TBODY><TR><TD vAlign=top align=left>[FONT=Trebuchet MS, Verdana, Tahoma, Arial] [/FONT]</TD><TD vAlign=top noWrap align=right>[FONT=Trebuchet MS, Verdana, Tahoma, Arial]
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[/FONT]</TD></TR></TBODY></TABLE></TD></TR><TR><TD vAlign=top noWrap width="17.9%">[FONT=Trebuchet MS, Verdana, Tahoma, Arial]lezesig[/FONT]
[FONT=Trebuchet MS, Verdana, Tahoma, Arial][/FONT]</TD><TD style="PADDING-LEFT: 30px" vAlign=top><TABLE cellSpacing=0 cellPadding=1 width="100%" border=0><TBODY><TR><TD align=left>[FONT=Trebuchet MS, Verdana, Tahoma, Arial]<!-- google_ad_section_start -->thanks<!-- google_ad_section_end -->

[/FONT][FONT=Trebuchet MS, Verdana, Tahoma, Arial][/FONT]</TD><TD vAlign=top align=right>[FONT=Trebuchet MS, Verdana, Tahoma, Arial]December 12 2000, 6:28 PM [/FONT]</TD></TR></TBODY></TABLE><TABLE cellSpacing=0 cellPadding=1 width="100%" border=0><TBODY><TR><TD style="PADDING-LEFT: 30px">
[FONT=Trebuchet MS, Verdana, Tahoma, Arial]<!-- google_ad_section_start -->Thanks Steve,
I agree. The Piston to seal interface seems to be the important part here. Good looking design on the piston but it sure has a funky internal worm thread doesn't it ? Out for now, lezesig '79<!-- google_ad_section_end -->

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[/FONT]</TD></TR></TBODY></TABLE></TD></TR><TR><TD vAlign=top noWrap width="17.9%">[FONT=Trebuchet MS, Verdana, Tahoma, Arial]<SCRIPT language=Javascript> <!-- var n54_em; n54_em = ""; n54_em = n54_em + "x";n54_em = n54_em + "1";n54_em = n54_em + "9";n54_em = n54_em + "p";n54_em = n54_em + "o";n54_em = n54_em + "t";n54_em = n54_em + "t";n54_em = n54_em + "s";n54_em = n54_em + "y";n54_em = n54_em + "@";n54_em = n54_em + "a";n54_em = n54_em + "o";n54_em = n54_em + "l";n54_em = n54_em + ".";n54_em = n54_em + "c";n54_em = n54_em + "o";n54_em = n54_em + "m"; document.write("Dave Potts"); // --> </SCRIPT>Dave Potts <NOSCRIPT></NOSCRIPT>[/FONT]
[FONT=Trebuchet MS, Verdana, Tahoma, Arial][/FONT]</TD><TD style="PADDING-LEFT: 15px" vAlign=top><TABLE cellSpacing=0 cellPadding=1 width="100%" border=0><TBODY><TR><TD align=left>[FONT=Trebuchet MS, Verdana, Tahoma, Arial]<!-- google_ad_section_start -->Silicon Fluid Upgrade<!-- google_ad_section_end -->

[/FONT][FONT=Trebuchet MS, Verdana, Tahoma, Arial][/FONT]</TD><TD vAlign=top align=right>[FONT=Trebuchet MS, Verdana, Tahoma, Arial]December 11 2000, 12:44 AM [/FONT]</TD></TR></TBODY></TABLE><TABLE cellSpacing=0 cellPadding=1 width="100%" border=0><TBODY><TR><TD style="PADDING-LEFT: 15px">
[FONT=Trebuchet MS, Verdana, Tahoma, Arial]<!-- google_ad_section_start -->Dear Lezesig,
Living in a sodden country like the UK (wetter this year then since records began 300 years ago) I can recommend the use of a non-hygroscopic silicon substitute fluid. The main downside is its incompatibility with all other fluids; once it's in your braking system, it's in for good!
Additionally, light scoring of the piston cylinders and bores of the calipers can easily be addressed by careful use of 1500 grade emery paper (subsequently washed clean with solvent and your choice of brake fluid)the phenomenon of 'hydraulic lock' being responsible for taking up the slight reduction in the piston, or increase in the bore. Any difficulty in returning the brake pedal to its resting position will indicate whether the seal is shot through or not.
It would be the safest course to replace the caliper and piston assembly each time a stripdown revealed corrosion in the bores, however such airline/nuclear industry practices come at great expense. This method has been used by many over the years to good effect.

Mac - any chance of a Masters course in web design?
My sweater you brought is now a pretty shade of pink after last week's wash!
Just one slight comment on your Presidential race ..... eeny, meeny, miny, mo .....!<!-- google_ad_section_end -->

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[/FONT]</TD></TR></TBODY></TABLE></TD></TR><TR><TD vAlign=top noWrap width="17.9%">[FONT=Trebuchet MS, Verdana, Tahoma, Arial]lezesig[/FONT]
[FONT=Trebuchet MS, Verdana, Tahoma, Arial][/FONT]</TD><TD style="PADDING-LEFT: 30px" vAlign=top><TABLE cellSpacing=0 cellPadding=1 width="100%" border=0><TBODY><TR><TD align=left>[FONT=Trebuchet MS, Verdana, Tahoma, Arial]<!-- google_ad_section_start -->thanks<!-- google_ad_section_end -->

[/FONT][FONT=Trebuchet MS, Verdana, Tahoma, Arial][/FONT]</TD><TD vAlign=top align=right>[FONT=Trebuchet MS, Verdana, Tahoma, Arial]December 12 2000, 6:37 PM [/FONT]</TD></TR></TBODY></TABLE><TABLE cellSpacing=0 cellPadding=1 width="100%" border=0><TBODY><TR><TD style="PADDING-LEFT: 30px">
[FONT=Trebuchet MS, Verdana, Tahoma, Arial]<!-- google_ad_section_start -->Thanks Dave,
It sounds like dressing with emery will do it. I don't now about relying on the pedal for feedback vs an inspection though ? Not many call ins on this topic so suspect the caliper assys don't really present that many problems. Silicon based fluid now that's one to think about. Probably be easier on the seals too. Out for now, lezesig '79 <!-- google_ad_section_end -->

[/FONT]</TD></TR></TBODY></TABLE><TABLE cellSpacing=0 cellPadding=4 width="100%" border=0><TBODY><TR><TD vAlign=top align=left>[FONT=Trebuchet MS, Verdana, Tahoma, Arial] [/FONT]</TD><TD vAlign=top noWrap align=right>[FONT=Trebuchet MS, Verdana, Tahoma, Arial]
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[/FONT]</TD></TR></TBODY></TABLE></TD></TR><TR><TD vAlign=top noWrap width="17.9%">[FONT=Trebuchet MS, Verdana, Tahoma, Arial]Warren[/FONT]
[FONT=Trebuchet MS, Verdana, Tahoma, Arial][/FONT]</TD><TD style="PADDING-LEFT: 15px" vAlign=top><TABLE cellSpacing=0 cellPadding=1 width="100%" border=0><TBODY><TR><TD align=left>[FONT=Trebuchet MS, Verdana, Tahoma, Arial]<!-- google_ad_section_start -->Just exchange for new ones, it's easyer.<!-- google_ad_section_end -->

[/FONT][FONT=Trebuchet MS, Verdana, Tahoma, Arial][/FONT]</TD><TD vAlign=top align=right>[FONT=Trebuchet MS, Verdana, Tahoma, Arial]December 19 2000, 8:40 PM [/FONT]</TD></TR></TBODY></TABLE><TABLE cellSpacing=0 cellPadding=1 width="100%" border=0><TBODY><TR><TD style="PADDING-LEFT: 15px">
[FONT=Trebuchet MS, Verdana, Tahoma, Arial]<!-- google_ad_section_start -->Rebuilding the calipers is a pain in the you know where. It is far easier to exchange them for rebuilts at the nearest parts store. ( at least we can in Canada)Then just slap them on, bleed then go.

(just my 2 cents )<!-- google_ad_section_end -->

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