Girling 3 Piston Brake Caliper Rebuild
Nov 2020 R. Kwas (Comments Added)
These notes document the rebuilding of three-piston Girling Calipers, as part of the complete refurbishment of an Amazon single hydraulic brake system.
The subject Calipers had previously been rebuilt by me...about 25 years ago(!), with new OE (chromed) pistons, Girling OE Seals, Dust-boots, and reassembled with Dow-Corning 200 Silicon lube. The System was then filled, bled and subsequently operated and stored with DOT5 Silicon brake fluid.
After removal from vehicle, at which time the fittings of both lines into the calipers were twisted off () by my assistant, it came to me that I probably should have used the huge and irresistible brake pressure that can be built by a foot on the pedal, to move the pistons from their rest position of years and prepare them for removal from the castings. The often heard advice of using (the measly!) 100 or (maybe!) 150 PSI of shop air is IMO not nearly adequate when trying to motivate sluggish, possibly corroded pistons. BUT...all's well that ends well...since I had rebuild these calipers (a mere) 25 years before, and the system was using DOT5 fluid, shop air was indeed persuasive enough to move, and REMOVE(!) the pistons in preparation for extraction! [...said NO one EVER who was using moisture absorbing, non-silicon DOT3, 4, or 5.1 Brake Fluid!].
Reiterating from elsewhere on the SW-EM site: Although multiple fitting styles are used on the car. All fitting threads are 3/8" 24TPI. ...this includes Bleeders, Unions, and Nuts on both Bubble and (Double)-Flare fittings.
Removal, Inspection, Clean-up, and Preparation for
Preparing Pistons for Reassembly
Preparation of Calipers for Reassembly
Different Length Tube-nuts
Experience and Tests with CuNiFer Brakeline
Using the Snap-On Flaring Tool
Stainless Steel Caliper Pistons
Compression of Caliper-half Seals
DC-200 Silicon Lube and Preservative
DC-200/DOT5 Compatibility Test
AC Cobra Brakes!
Removal, Inspection, Clean-up, and Preparation for Reassembly:
Calipers are removed from the vehicle. Plenty of surface rust is evident (these Calipers were not painted at last installation).
Although Anti-Seize was applied during last assembly, lines are spun off at the Caliper fittings, so these hardlines will need to be replaced. This is not a major issue, as the plan is to replace ALL hardlines with (non-corroding!) CuNiFer alloy lines, and all flex-lines with (non-occluding!) SS overbraid Teflon lines.
Calipers are inspected. Bleeder fitting is a conical fitting, and the Bleeder itself is an extended one in order to clear the two (of the 4 total) bolts which secure Caliper halves together:
Pressure line into the calipers should have a bubble flare, and a long tube-nut (to assure flare is secured into seat...a short nut does not reach to apply clamping force to the back of flare! See also below: Different Length Tube-nuts
In preparation of final removal of Pistons from casting, rubber dust boot (found to be in perfectly pliable condition!) is moved out of retaining groove in piston.
Two strategically sized wooden blocks are used as fulcrums on opposite sides of pistons, and flatblade screwdrivers, whose blades just fit into the boot retaining groove, are used to simultaneously apply lifting force for the final extraction of pistons. The lifting force must be straight out...one-sided and the piston will surely cock in the bore, and that will be the end of any removal attempts, and possibly result in breaking away the retaining lip of the boot retaining groove! "Care and feeling" are called for during this operation!
After Pistons have been removed, Boots are removed, and Seals are picked out of their retaining grove in the casting, with a dental pick. They are also still nicely pliable!
Inspection of Pistons upon removal. Back side of Pistons have plenty of rusty particulate munge, wet with Brake Fluid, but Piston sides as well as casting inside walls, are absolutely free of corrosion! I attribute the rusty particulate to having come from upstream (inside of lines etc), and deposited at the Caliper end-station, and I attribute the clean inner surfaces to the use of non-hygroscopic DOT5 fluid. I am not at all unhappy with these findings...in-fact, rather thrilled!
The plan is to get these calipers media-blasted in preparation for painting. I will be using the same high temp engine red which I use on the Alt Kit brackets (I frankly don't think paint qualified for anything hotter is necessary, and previous experience has confirmed this also). This paint has shown itself to last well at elevated temps which might occur at Calipers. It may be a bit flashy, but that's where my quest for flashiness ends...I will not be installing blue neon lights in the fenders any time soon!
Using used Piston Seals as a size-guide, rubber protective discs are cut of 1/8" thick gasket material stock. A drywall screw is threaded into the center to aid in manipulation of the discs. Update: This is less than optimum. Paint masking should be in Dustboot groove if possible. See below! Dustboot-groove Masking
Discs are inserted into seal grooves.
Screws are run in, to contact wall behind disc and keep blasting force from dislodging them. As can be seen, the Dustboot groove is open accessible for the blasting operation, but the Seal groove is protected.
Piston bores, which are clean and free of corrosion so don't need blasting anyway, protected and ready for media blasting.
Calipers get a degreasing before first derusting treatment.
24Hr submersion in Evaporust (a "Super Safe Rust Remover"!) [...I'll be the judge of that!]...and I'll see where this new (for me!) product makes it into the SW-EM Products Review Page!
After 48 hours of submersion in the Evaporust, the results are impressive. The magic potion has combined with all of the rust, either putting it into suspension in the liquid or turning the remaining products black like a surface coating (the coating can be easily scraped off, so is not a permanent coating). I would call the rust removal/transformation fairly effective. Since I do not know how this surface plays with paint coatings, I will still have the Calipers media blasted in prep for paint, but for its first test, it does look like it may have its place!
The two threaded ports are blocked off with sacrificial fittings in order to spare the threads from damage.
Calipers return from media blasting looking nice and clean with the typical "thirsty" rough metal surface just asking to be painted! The Rubber discs have had the desired results of protecting from the seal-pocket inward.
Rubber protective discs and port thread protectors are removed, the Calipers are hung, plumbing ports high, in preparation for a first thorough rinse and flush with acetone (OUTSIDE!) to remove any particulate or fluid residue. If the paint plays as poorly with silicon brake fluid and grease, a good rinse is definitely called for!
Generous flushing with acetone!
There is some local, very new slight surface rust evident in some areas of the Piston bores (once exposed to air, there's no stopping mother nature!).
Note to self: First flush of Evaporust should have been before installing rubber protective discs and trapping it internally where it can continue to react. Local cleaning and a second flushing return the bores to a clean condition.
The Rubber protective discs are replaced with cardboard paint mask discs in prep for painting with two heavy coats of Plastikote Ford #206 Red engine enamel from a rattle can. It is the writer's considered opinion, and experience, that unless calipers are on a racing car where they would potentially be exposed to extreme heat, that this paint is perfectly capable of enduring the (only somewhat elevated!) thermal conditions they will be exposed to in normal road service. Indeed, the Calipers installed in my 1800 have done just fine with it!
Engine paint is rated to 500ļF...that also happens to be the Boiling Point of DOT5 brake fluid!
It's November, so Calipers are hung in the SWedish-EMbassy - Paint Drying Department (SW-EM-PDD, next to the heating plant Exhaust stack!).
Preparing Pistons for reassembly:
Pistons are soaked in Evaporust for 48 hours in preparation for cleaning. There is some rust evident on the surface which contacts Brake Pads, but otherwise, there is fortunately no rust on the seal contact areas, and pistons are able to be cleaned up well.
Piston surfaces including Dustboot groove, are cleaned with Scotchbrite (which I much prefer as a non-rusting, much less likely to fall apart, alternative over steelwool).
OE Pistons are in very good shape after 25+ years of service since last rebuild of the Caliper. I believe I painted the inside of pistons (with not even high-heat paint!) at last rebuild, having seen extensive rusting on some others I have run across...even this seems to also have held up well.
These Pistons are perfectly capable of being returned to duty, but they will be replaced with new pistons of 316 Stainless Steel! See below: Stainless Steel Caliper Pistons
Preparation of Calipers for Reassembly:
A chop stick is split to make an internal plumbing fitting cleaning tool using a piece of Scotchbrite.
Threads and conical end of Bleeding fitting are now clean and ready again for service.
Calipers also get offset black paint in the casting depressions identifying them as the original castings...just because I can!
Bleeder and Plumbing fittings are test fit and inspected one more time at the bench.
Different Length Tube-nuts! BEWARE!
Part of the inspection process reveals an important point which must not be overlooked by an inexperienced mechanic, or even an experienced one who might be rushing! [Not that its advisable to be rushing on a braking system anyway!] This is less of an issue when existing brakelines are reused, and fittings are not being changed, but is very important not to be overlooked when making and installing new brakelines and fittings as part of the caliper installation process!
It is crucial the Long tube-nut be used at caliper junctions in order for flare of tube to reach, and be clamped to, its mating seat in down the caliper. Failure to notice this during installation into the vehicle and using a Short tube-nut will result in no hydraulic seal as the flare will not be seated deep enough...and that would surely be a BAAAD Thing!
Notice a 1/4" difference in length between Short (3/8") and Long (5/8") tube-nuts, and how deep the nut is threaded in, in order to secure, clamp and seal the line. The mating seat for the tube (bubble)flare is deep in the hole in caliper, and a short tube-nut would not reach!
New components from Vintage Imports are laid out on a clean work surface in preparation...[...I just love that 316 Stainless Steel!]
Pistons are dimensionally checked one last time against those removed...
...and also into the bores...but they only fit into their respective bores with difficulty and a bit more manipulation than expected...what the...???...a close inspection determines the paint (which I applied somewhat generously), presents enough of a bore decrease to cause this...
A bit of scraping with a sharp-edged block, and cleanup, removes the impediment. Note to self: In the future, mask for painting, not in inner Seal-groove, but in outer Dustboot-groove, to prevent this minor but needless setback!
Machined edge of a scraper removes paint, and clears the way for precision fit of new Piston(s)...there is not a lot of extra room!
After the paint cleaning operation, and general cleanup, the new Pistons all fit nicely.
Sample ID/OD measurement and
clearance calculation (Big Piston): Bore ID: 54.1mm, Piston OD: 59.998mm, Clearance: ID - OD =
...that's only about 0.004"...not very much indeed, but it also assures concentric movement, and minimizes the tendency of the Piston to cock in the Bore, during normal Piston operation in service...that wouldn't be good either!
Pistons are trial fit (dry and without lube, Seal or Dustboot).
Beyond this point, gloves and careful handling of the DC-200 Silicon Lube are advised, since all Rubber Parts and Pistons will need to be generously anointed with it. The lube also holds on to any particulate contamination...from rust particles to (fabulous) moustache hairs...work cleanly!
CAUTION and WARNING: Silicon lube film is EXTREMELY LONG-LIVED which is good in terms of its function, but it will also cause excruciating pain if the slightest amount is inadvertently gotten into the eyes, especially under contact lenses. Work carefully to prevent such an occurrence! This warning is thankfully not from personal experience, but I remember it from a Dow-Corning product literature where it was stressed in no uncertain terms!
Seal for Piston 1 is generously coated the lube and installed into its groove. The Bore area above Seal-groove and below Dustboot-groove can be seen to have been freed of paint.
Piston 1 (big) is lubed and checked once more for fit since this is the first piston to be installed and I wanted to get a good impression of fit and sealing force before continuing with the rest of the installations. I DO NOT insert it fully into the seal in the bore!...I still need to fully withdraw and removed it before the Dustboot is installed, and removal is difficult once it is snugly held by the seal!
First Piston is lubed and trial-fit.
Dustboot is lubed and installed...manipulating the super-slippery rubber is a tricky as wrestling a greased pig...patience and use of a blunt-tipped pick tool help...but I just know that I am giving the rubber parts the very best start to what will I expect will once again be a looong service life
Dustboot is lubed and placed.
Lubed Piston 1 is next to be wrestled in...
Piston 1 is manipulated...and manipulated some more...then manipulated some more...and finally manipulated into place...assuring concentricity of Piston with Bore is the goal and helps...precision manipulation is exceedingly tricky when Piston and Dustboot are lubed with silicon lube...possibly THE most slippery thing known to man (not counting CGG, see Reference)!
When Piston finally finds its way into bore and Seal, it will need additional CONCENTRIC(!) persuasion to stretch/compress Seal slightly and make it past the point of contact, but this not a bad thing, as it is an indication that the Seal is snug on the Piston and will seal the fluid behind it in service well...do not push the Piston much further after making it past the Seal, to allow more room for the next step...
Inner diameter edge of Dustboot can next be "helped" to get seated in its groove in Piston. After Dustboot has found its final position in Piston groove, can Piston be pressed home fully and the rest of the way, to give maximum room for wrestling with the small Pistons next.
The installation is pretty much similar for little Pistons 2 and 3...
Seals for Pistons 2 and 3 are lubed and placed.
Then Dustboot lubed and placed...
...then Pistons 2 and 3...
Pistons number 2 and 3 are manipulated into place, making sure they pass through the hole in Dustboot, I like to assure the lip of Dustboot seats correctly in its groove in the Pistons, and doesn't punch out a sliver of rubber because of the precision Bore to Piston clearance. Here Piston 3 is being manipulated with a blunt-tipped stick. [A chop-stick, of course!]
Dustboot is in its proper place, and both small Pistons are pushed fully back, giving full clearance for new Brake Pads during installation.
Caliper 1 reassembly is complete...more fun than wrestling with a greased pig, but (only slightly less) squealing!... and its ready for installation!
Caliper 2 ...lather, rinse, repeat!
SW-EM - BPRaED:
The SWedish-EMbassy - Brake Plumbing Restoration and Engineering Department (SW-EM - BPRaED):
Experience and Tests with CuNiFer Brakeline:
See also: CuNiFer Brake Line
It cuts no differently that steel line.
Minor burs and debris are present after cutting (nothing new!).
Burs and cutting debris are the arch-enemy of hydraulic systems with rubber seals!...they should be removed before flaring. A drill-bit serves the purpose well, and a flush and wipe with some brake system cleaner can't hurt!
Deburred and ready for flaring.
A 1/8" drillbit opens the distortion from cutting, back up to the nominal ID of 3/16" Brakeline.
Using the Snap-On Flaring Tool:
Stainless Steel Caliper Pistons:
Components consisting of six custom machined 316 Stainless Steel pistons, protectively packaged and Rubber Items Rebuild Kit, arrives from Vintage Imports.
Stainless Caliper Pistons....OOOOOHH....AAAAAAHH! [I MAY have a problem with Stainless Steel...I'm seeking help!...I don't think it's working!]
Matt there is highly experienced, having provided caliper rebuild services in the past...he was pleasant to speak with, giving intelligent answers regarding options and his experience removing the pistons from the caliper, and he was forthcoming with this information from his experience. He notes that the piston material is 316 marine SS, and that their Rebuild Kit is made in England by a company which took over the original Girling tooling. The rubber used is EDPM synthetic. Ref: https://en.wikipedia.org/wiki/EPDM_rubber
I am happy to send my money to support this reputable outfit, with which I can generate a rebuild of known providence, where I know what I have that I am trusting my life to, instead of installing inexpensive, noname chinashit "exact replacement" (but not really!) clone calipers...some of which apparently aren't exact enough that they even fit, as Lars Rengersen recently experienced.....but that's just my opinion...!
Lars R. picture used with his kind permission.
Another example of china's finest..."exact replacement": Negative clearance!
Compression of Caliper-half Seals:
For removal of Pistons, it was not necessary to split the Calipers above, but here seems to be a good place to show what Art Benstein found when he split some 240 calipers to satisfy his curiosity. The general recommendation is not to split calipers, and Art any I have been discussing why this might be from the objective engineering standpoint of what jeopardy and risk one might incur (and also the liability if this was done as a part of a business' rebuild)...
From Art Benstein's site: http://cleanflametrap.com/calipers/ ...and reposted here with his kind permission.
Measuring Sealing Washer. The Seal sits in a counterbore on one side, and interfaces with the machined surface on the other.
From Art's measurements, 0.013" compression occurs on the "elastomeric; rectangular cross-section O rings" (some sort of rubber compound), he found in the 240 caliper.
[Anyone splitting Amazon or 1800 Calipers and finding anything significantly different is invited to contact the author with findings and pix!]
Canada Goose producing one of the slipperiest materials known to science...and (barefoot) man: CGG!
Note: CGG is not a preferred lube for hydraulic components!
Canada Goose Guano production!
DC-200 Silicon Lube and Preservative:
Since the System will be using DOT5 Silicon Brake Fluid, it must be reassembled with a compatible lube product. Compatibility of DC-200 and DOT5 was confirmed at that last rebuild, and the outstanding state in which caliper pistons and rubber parts were found after 25 years, is enough of a successful long-term test result for me, but I thought I'd document a bit of a compatibility test...see below!
Dow Corning DC-200 Silicon Lube will (once again!) be used on all rubber parts during the rebuild process documented here.
DC-200/DOT5 Compatibility Test:
DC-200 was checked for compatibility with DOT5 fluid. The test was performed on a clean mirrored surface under a strong light which would allow seeing any parting line between the liquids. The premise is that if they readily mix there will be no discernable parting line...
See also: SW-EM Product Reviews: Product Reviews DC-200
A drop of the super thick and viscose DC-200 is applied to the mirror.
The bead (~0.5" dia.) has very low surface tension and starts a relentless spread, but the solubility test will/should be complete long before it might make it to the edge of the 4"x4" mirror.
Several drops of DOT5 are added next to the drop of DC-200. Before the DOT5 has even crept around the far side of the drop, the initial line of contact has disappeared, and the contact line around the far side is fast disappearing...
A chop-stick is used to intentionally but gently (not trying to entrap any air bubbles) to try and mix the two liquids at their point of contact, and observe if any indications of separation become visible.
Condition after 1 minute of mixing. There is already little doubt the two liquids are capable of mixing.
Condition after about 2 minutes. I would declare the DC-200 as soluble in DOT5 and fully compatible!
Condition after 90 minutes the DOT5 has almost completely united with and leveled the DC-200. Material borders are all but gone as the two liquids have effectively merged, and I'm certain would continue to do so until totally leveled. Graph paper (1/4" squares) behind the mirror still allows seeing some optical refraction of borders (more correctly: Areas of application) of the two samples because of the density differences.
Conclusion: DC-200 is absolutely compatible with DOT5 fluid!
This a fairly new product at the SW-EM - Rust Elimination Department (SW-EM - RED)...but in initial use tests on sheetmetal and cast components which could be placed in a bucket of the water soluble rust-fighting-cocktail, results are encouraging. It may yet make it onto the Most Favorite Products List on the SW-EM - Product Reviews Page, pending further research and tests.
Vintage Imports / European Parts Company (937) 550-4509
(Note: I have no relationship with this outfit, but this is where I procured the 316 SS pistons and Seal Kits shown here):
Excerpt from an e-mail contact with them:
...Regarding the question of material, the kits are made from a blend of EPDM and PVC. Repair kits have not been made of classic British Rubber for over 25 years. Matt Matthew Moore [Matt's name published with his permission.] Vintage Imports Inc
Excerpt from: https://europeanpartscompany.com/a-c-cobra-1963-1964-1965-new-front-stainless-caliper-piston-seal-kit/
Matt at VI / EPC was highly experienced and very informative in matters of Girling calipers, but had no answer for why the pistons are nominal metric sizes...maybe it was just Metric-Day at Girling when this size was specified. [...well OK...after running some calculations, 38mm works out to a nice round 1.5" (wonder of wonders...!), but 54mm is 2.12", and that's still two places behind the decimal point...well OK again...maybe its 2 and an eighth!]
AC Cobra Brakes: I do also find it telling and rather interesting that the very same Calipers were also fitted on the AC Cobras, who BTW had twice as many cylinders supplying power, and who also were high on the list of record holders for 0 to 100mph, and back to 0!! Source: https://www.roadandtrack.com/new-cars/car-comparison-tests/reviews/a18862/power-trip-0-100-0-history/ )...you don't think they fitted marginal brakes on those cars, so you might keep that in mind next time you think about wanting to "upgrade" the brakes on your Amazon or P1800 Volvo!
External sources attributed. Otherwise this information is Copyright © 2020-2023. Ronald Kwas. The terms Volvo, Girling, Dow-Corning, Evaporust and Vintage Imports are used for reference only. I have no affiliation with any of these companies other than to try to keep their products working for me, help other enthusiasts do the same, and also present my highly opinionated results of the use of their products here. The information presented comes from my own experience and carefully considered opinion, and can be used (or not!), or ridiculed and laughed at, or worshipped, at the readers discretion. Warning: Don't muck around with brakes if you don't know what you're doing! As with any recipe, your results may vary, and you are, and will always be, in charge of your own knuckles, and future!
You are welcome to use the information here in good health, and for your own non-commercial purposes, but if you reprint or otherwise republish this article, you must give credit to the author or link back to the SwEm site as the source. If you donít, youíre just a lazy, scum sucking plagiarist, and the Boston Globe wants you! As always, if you can supply corrections, or additional objective information or experience, I will always consider it, and consider working it into the next revision of this article...along with likely the odd metaphor, or analogy (see: CGG!) and probably wise-a** comment.