+38 097 677 32 19polypro.help@gmail.com

1 EUR = 51,06 грн1 USD = 43,12 грн

  • UAH
  • EUR
  • USD
PolyPro - manufacturer of polyurethane silent blocks wholesale.
Login
overlay

Пильник напрямної супорта

Polyurethane Caliper Pin Boot

A caliper pin boot is the cover that seals the slide pin of a brake caliper. It keeps grease on the pin and keeps water, brake dust and road chemicals away from it. The part is small, but whether the caliper can move freely depends on it: a seized guide pin stops the bracket sliding back and the pads wear unevenly. PolyPro moulds polyurethane boots on its own tooling — see the sizes in the catalogue.

 

What a caliper pin boot is and how it works

A floating caliper is mounted to its bracket on two guide pins. The caliper body slides along them every time the pedal is pressed, squeezing both pads against the disc. To keep the pin moving freely it is greased and sealed with a boot: one end of the cover seats in the groove of the pin or in the bracket, the other in the bore of the caliper body.

The boot works in two ways at once. Mechanically it stretches and compresses with every stroke of the caliper and takes up pad wear as the friction material thins. Thermally it sits right next to a hot brake assembly. It also acts as an air cushion: while it is sealed, the pin does not push grease out, and air returns inside when the pedal is released. A torn boot is therefore not cosmetic damage but a direct route to a seized guide pin.

 

Signs of a worn slide pin boot

Check the condition when the pads are replaced: swing the caliper away, pull the pin out and inspect it. A serviceable cover is elastic, the grease under it is clean, and the pin comes out by hand and slides in the bore without binding.

  • tears and splits in the convolutions, especially on the disc side
  • a cover that has baked hard, turned brittle or stuck to the pin
  • rusty water and brake dust under the boot instead of grease
  • a pin that is tight or will not come out without a puller
  • uneven pad wear on one wheel: the outer pad worn, the inner one intact
  • one wheel running hot, binding, and the car pulling under braking

The last two signs mean the guide pin has already seized: a new boot alone is not enough, the bore must be cleaned, the pin checked for scoring and both covers on that wheel replaced.

 

Polyurethane or rubber

Factory guide pin boots are made of rubber — it stretches well and is cheap. Next to a brake assembly rubber works in hard conditions: constant heating and cooling cycles, water splashed onto a hot unit, brake dust and salt. It hardens, cracks along the folds and sometimes bakes onto the pin so firmly that it comes off in shreds.

Polyurethane resists abrasion, oils and road chemicals better, holds the geometry of the convolutions longer and copes better with brake dust. But this is a brake component, so the material is chosen from the data for the specific part rather than from general reasoning: the Shore hardness is stated on each product card, together with the seat the size is intended for. Rubber and polyurethane covers alike will die quickly on a dirty pin fitted without grease.

 

How to choose a caliper pin boot

Selection is by the dimensions of the pin and of the seats in the caliper body, not by the make of the car. The two guides on one wheel often differ, one with a bush and one without, so measure both.

By Pin and Bore Size

Measure the diameter of the pin where the cover seats, the diameter of the bore in the caliper body or bracket that takes the second bead, and the working length of the boot in its free state. Allow for travel: the cover must stretch freely by the distance the caliper moves once the pads are worn. Take the figures from the old part and from the pin itself — a stretched cover reads larger than it should. Half a millimetre of difference at the bead already means dirt being drawn in, so measure a clean part with the old grease wiped off. To match them against available sizes, use the boot selection page.

By Caliper Type and Number of Guides

Look at the design: most floating calipers have two guides per wheel, and they are not always identical — one plain, the other with a rubber compensating bush. The boots on them can differ in shape and length as well. Separate again are calipers where the cover is held by a shoulder in the body rather than by a groove. Do not confuse this part with the caliper piston boot, which seals the piston. Order covers for both guides of a wheel at once. If the pads are being changed on an axle, replace the covers on both wheels together: there is no sense in stripping the assembly twice.

By Durometer

The Shore hardness is stated on each product card and it is the main reference when choosing. A softer cover goes on more easily and follows the stroke of the caliper better, a harder one holds the shape of the convolutions longer and resists brake dust. For an assembly that heats up regularly, dimensional stability and an interference fit matter more, so read the description of the seat on the card and not only the figure. This shows up clearly on city cars with frequent short braking. Do not judge hardness by colour or by feel. If in doubt, tell us how the vehicle is used and we will suggest a size from stock.

By Retention and Fitting

The beads of the boot are held by an interference fit in the groove of the pin and in the seat of the caliper body; some designs add a circlip or a shoulder. Before assembly, clean the pin bore of old grease, rust and dust and check the pin for scoring. Use grease intended for caliper guide pins, in the quantity specified by the maker of the assembly: an excess builds pressure and pushes the cover off. Slide the cover on square and press the bead down evenly all round, then check that the pin still moves by hand. Non-standard sizes are made to a drawing, a sample or a worn part, from a single piece.

Why caliper pin boots are bought from PolyPro — retail and wholesale

PolyPro makes its polyurethane parts itself: in-house moulds, its own casting, dimensional control on every batch and sales without middlemen. For a small part that is what matters — the size is either exact or useless. Retail is by the piece: if you need one cover you take one, if you need four for an axle you take four. The products carry a warranty and international shipping is available.

Wholesale supply goes to garages, parts shops, vehicle fleets and resellers who need the common sizes on the shelf. For them there is a partner programme: bonuses for turnover or for the volume of a single order, access to prices and stock levels, and shipping under the partner's own brand.

 

Frequently asked questions

Can a new boot be fitted to a seized guide pin? 

No, the assembly has to be put right first. Pull the pin, clean the bore of rust and old grease, and check the pin for scoring and corrosion, replacing it if damaged. If a new cover goes onto a seized guide, the caliper still will not slide and the pads will keep wearing unevenly on that wheel.

How often should guide pin boots be checked? 

The sensible point is every pad replacement, since the caliper is apart anyway. At the same time assess the condition of the grease, how freely the pins move and how the pads have worn in pairs. An unscheduled check is due if the car pulls under braking, one wheel runs hotter than the others, or the pads on one caliper are worn differently.

What grease should be used on the guide pins? 

Only grease intended for brake caliper guide pins, compatible with the boot material and rated for the temperature of the assembly. Ordinary joint greases are not suitable here — they soften rubber and are driven out by heat. Use the quantity specified by the caliper manufacturer: an excess builds pressure and pushes the boot out of its seat.

How does a pin boot differ from a caliper piston boot? 

They are different parts of the same assembly. The guide pin boot is a small cover on the pin along which the caliper slides. The piston boot seals the piston in its bore: it is larger in diameter, works as the piston extends and seats in a groove in the cylinder. Sizes and seats do not match, so they are selected separately.

How many boots does one wheel need? 

Most floating calipers have two guides per wheel, so two covers, and four for an axle. They are not always identical: one guide may carry a bush while the other is plain, so measure both before ordering. Replace both covers on a wheel at the same time, even if only one of them is visibly torn.

Can a non-standard size be ordered? 

Yes. If the catalogue does not list the size you need, we will make it to a drawing, to a sample, or to a worn cover that you send us. The minimum is one piece. Send the measurements of the pin and of the seat in the caliper body, or the part itself, and we will say whether an existing mould fits or a new one is needed.

Do you sell boots individually? 

Yes, retail is by the piece, with no obligatory set. You can take two covers for one wheel or four for an axle, whatever the strip-down turns out to need. The products carry a warranty and international shipping is available. Items from different catalogue categories travel in one shipment.

What are the terms for garages and parts shops? 

Wholesale supply is for garages, parts shops, vehicle fleets and resellers. There is a partner programme: bonuses for turnover or for the volume of a single order, access to current prices and stock levels, and shipping under the partner's own brand. Send us the list of sizes you move regularly and we will work out terms.