Shimano Mineral Oil vs SRAM DOT: the Brake Fluid Mistakes That Ruin Your Seals

Shimano uses mineral oil; SRAM uses DOT 5.1. The two are chemically incompatible and must never meet in the same brake. L'Atelier's brake fluid guide says DOT fluid in a Shimano brake makes the seals swell and disintegrate within 24 to 48 hours, and mineral oil in a SRAM brake fails in the same way. Magura and Tektro sit on the mineral side; Hope (DOT 5.1), Hayes and Formula (DOT 4) on the DOT side. And whatever the label suggests, DOT 5 is silicone-based and never belongs in a bike brake.

Whether you are bleeding your own brakes for the first time or servicing a customer's bike with brakes you don't recognise, this comparison sets out what L'Atelier's brake guides say (la-telier.com). When a manufacturer's manual names a fluid for a specific lever, that instruction prevails.

Side by side: mineral oil vs DOT

The fluid is not the only difference. L'Atelier's SRAM/Shimano compatibility guide makes it an absolute rule never to pair a SRAM lever with a Shimano calliper or the reverse: piston, lever travel and mechanical compatibility differ, so even the correct fluid would not make a SRAM lever drive a Shimano calliper properly. Within Shimano, keep lever and calliper from the same series too: the lever ratio changed between series, and a BL-M8100 lever is not optimised for an older-generation calliper.

Brand by brand: which fluid goes in?

• Shimano (Deore, SLX, XT, XTR, 105, Ultegra): mineral oil.
• Magura (MT5, MT7, MT8): mineral oil.
• Tektro: listed under mineral oil in L'Atelier's table; confirm with your model's documentation.
• SRAM / Avid (Guide, Code, Level, G2): DOT 5.1.
• Hope (Tech 3, Tech 4): DOT 5.1.
• Hayes and Formula: DOT 4.

DOT 4, DOT 5 and DOT 5.1 are not a sequence

The numbering invites a mistake. DOT 4 and DOT 5.1 are both glycol-based. L'Atelier states they are compatible and mixable, and that DOT 5.1 can be used in a system designed for DOT 4. DOT 5.1's advantage is a higher dry boiling point: 270°C against 230°C. DOT 5 is a different product altogether: silicone-based rather than glycol. It is not a better DOT 5.1, and L'Atelier's instruction is unambiguous: never use DOT 5.

Workshop mistakes that ruin seals and pads

1. The wrong bottle. DOT in a Shimano system destroys the internal seals irreversibly; L'Atelier's bleeding guide says both lever and calliper then need replacing. Keep mineral oil and DOT on separate shelves, clearly labelled.
2. Buying DOT 5 by mistake because it looks like the newer version of 5.1.
3. Leaving the pads in. A single drop of mineral oil on the pads ruins them. Remove them before bleeding.
4. Bleeding with the lever tilted. Set the lever horizontal so the bleed port is the highest point, or bubbles stay trapped in the hose bends.
5. A syringe full of bubbles. Fill it slowly and tap it so bubbles rise; otherwise you inject the air you are trying to remove.
6. Careless spills. Mineral oil attacks paint. Use a drip tray, a clean rag and isopropyl alcohol.

For a Shimano bleed, L'Atelier lists the TL-BT03 syringe (or TL-BT03-S), Shimano mineral oil, a 2.5 mm Allen key for the lever bleed port and a 7 mm spanner for the calliper fitting. The fluid is pushed from the calliper up to the lever until it comes out perfectly clear, the lever is cycled to free trapped bubbles, then everything is closed and wiped down. If the pads were contaminated, clean the rotor with isopropyl alcohol before fitting new pads, and bed them in with 20 to 30 progressive stops.

1. Bike in a workstand, lever horizontal, wheel and pads out.
2. Remove the lever bleed screw with the 2.5 mm Allen key, then the rubber diaphragm.
3. Fill the syringe with fresh oil, free of bubbles, connect it to the calliper bleed fitting and open the fitting a quarter turn with the 7 mm spanner.
4. Push the oil slowly from the calliper to the lever until it runs perfectly clear.
5. Squeeze the lever several times; if bubbles still rise into the reservoir, push more oil until the lever is firm.
6. Close the calliper fitting, refit the diaphragm and bleed screw, and wipe off every trace of oil.

After a contamination: choosing replacement pads

If fluid did reach the pads, new pads are the only fix, and it is a chance to pick the right compound. Clean the rotor with isopropyl alcohol first: new pads on a contaminated rotor will not bed in. Then bed them with 20 to 30 progressive stops from about 20 km/h, and avoid a hard first descent that glazes the compound.

• Shape code first: buying "Shimano pads" is not enough. B (B01S/B03S/B05S) fits Deore, Alivio, Acera and MT200-MT420; D fits 4-piston XT, SLX and XTR; J fits 2-piston XTR, XT and SLX; K fits road hydraulic Dura-Ace, Ultegra and 105; L fits GRX, Tiagra and some flat-mount road models.
• SRAM pads follow the calliper family (Guide/G2/Code, Level/Level T/Level TL), each with its own reference.
• Organic (resin): smoother, quieter, better cold bite, wears faster in the wet; road, gravel, light XC.
• Metallic (sintered): more power and heat resistance, lasts longer, noisier when wet and slightly harder on rotors; enduro, DH, aggressive MTB.
• Wear limit: new pads have about 3 to 4 mm of compound; the limit is 0.5 mm.

How often to bleed, and how to tell it's due

The five tell-tale signs: a spongy lever before the bite, long lever travel close to the bar (rule out worn pads first), inconsistent braking from one pull to the next, a small clicking in the lever when pulled slowly, and bubbles visible in the open reservoir. A lever that firms up after pumping and then softens again points to air; a low fluid level, a sticking piston or, rarely, a worn master cylinder are the other causes to rule out. Air gets in through fittings, seal wear, condensation, or simply transporting the bike upside down.

To check a specific brake, the L'Atelier bike mechanics base answers questions such as "Can I mix mineral oil and DOT fluid in a hydraulic bike brake?" or "How often should I bleed Shimano hydraulic brakes?" with the source passage.