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There are not too many 4-piston calipers by Shimano.

M640 Zee and M820 Saint are identical (calipers), and upon release Shimano claimed to have a 'slight difference in leverage' (i.e. a different brake lever) due to 'much bigger caliper'

It's my understanding that Shimano pistons are 2 x 22mm in 2-piston calipers, and 2x15mm + 2x17mm in 4-piston calipers.

That's a difference of around 6%, which doesn't seem too significant in displacement terms. However they said that things would not work well without the matching lever.

However, in 2017 Shimano released the M8020 caliper, which appears to be another paint job for the Zee/Saint caliper.

And they said it would work just fine with their existing M8000 brake levers (2015).

Then they decided more people would like 4-piston brakes and:

  • in 2018 they released XTR M9100, which had a new 4-piston caliper design (M9120) and matching lever
  • they updated (or renamed?) their MT500 brake lever (which was itself just a non-series version of the Deore M6000) and called it MT501, and supplied it either with their existing MT500 2-pot caliper, or the new MT520 caliper, which was a lower end 4-pot caliper with straight rather than banjo hose joint. It's possible that the new part name reflects new combinations of caliper, hose + lever and there is no change to the lever itself, but that I don't know.
  • the next year they released another 4-pot caliper, the MT420, which is lower-end than the MT520 in that it has resin pistons rather than ceramic. And again, they updated the paired levers, so that MT400 (old lever) was only for 2-pot MT400, while there was a new MT401 lever for both MT400 and MT420 calipers.
  • they have also released two other versions of M9120, that is M8120 and M7120, and another name for MT520, that is M6120
  • this year they have released a new version of their T8000 lever, the T8100. This appears almost identical to the old one, BUT they say that you can use the T8100 lever with the M8120 4-piston caliper (presumably this is intended for e-bikes)

Shimano specifically say in their compatibility guide that the MT400 lever is NOT for MT420, while the MT401 works with both MT420 & MT400.

However I'm not really ruling out that there is no difference between these levers after all. Because on the one hand they could update the specs of the XT M8000 levers with no change in the product to be ok with a new (to XT) 4-piston caliper, but on the other they have (subsequently) released new (?!) levers to go with the new 4-piston calipers on lower ranges.

There is one section in the Shimano Compatibility guide which has me wondering:

https://productinfo.shimano.com/#/com?cid=C-651&acid=C-672

Compatibility for DIN 79010:2020-02C-672 DIN 79010:2020-02 Fahrräder - Transport- und Lastenfahrrad - Anforderungen und Prüfverfahren für ein- und mehrspurige Fahrräder

This is a new German standard for cargo bikes, and it provides

"Brake lever reach adjustment might be required to follow Minimum braking force value of 5.5.1.3"

and then five groups with a weight multiplication factor:

  • Group 1 1.5x
  • Group 2 1.4x
  • Group 3 1.3x
  • Group 4 & 5 1.1x

All five groups use 4-piston brakes, but:

So it seems possible that:

  • the levers were updated in some way, and some levers do not work well with 4-piston calipers (though I don't really see why)

or

  • the levers weren't really updated but Shimano want to get their products certificated and would prefer to re-issue a 'certified' combination such as BL-MT401 + BR-MT420, rather than saying 'you can use this old lever with this new 4-piston caliper', even if nothing has changed.

Any thoughts?

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  • "Any thoughts?" - that's one well-researched question 👍 Reports of Shimano caliper/lever cross compatibility are numerous, I am yet to hear about incompatibility. This is not data backed or should be considered a proper answer, but I'd put whatever Shimano combo, probably wouldn't notice the difference, if there's any at all.
    – Klaster_1 Нет войне
    Commented Sep 25, 2020 at 17:20
  • Excellent question. I suspect but don't know that there are no meaningful differences in displacement.
    – Nathan Knutson
    Commented Sep 25, 2020 at 19:59
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    Gut feeling is legal, not engineering. Market size vs cost of testing and paperwork of old levers + new calipers to required standards makes testing not worth it. Stating 'not compatible' in the same doc that discusses DIN compliance removes ambiguity. However, given the cost of a MT401 brake lever, begs the question is the risk worth it?
    – mattnz
    Commented Sep 25, 2020 at 22:23
  • there are actually four levers: MT400 MT401 MT401-3a MT402-3a Anyway, the '3a' means that it's a longer lever (for trekking bikes), and the absence means that it's a shorter lever. So basically MT400 = not MT420 compatible, MT401 = MT420 compatible, and MT401-3a not MT420 compatible, MT402-3a = MT420 compatible. This compatibility information was first released the year before the stuff about DIN compliance was added, but that doesn't mean too much as obviously they might have been working on the compliance before the standard was finalised.
    – thelawnet
    Commented Sep 26, 2020 at 7:50
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    it's hard to say because the existence of two separate short lever and two separate long lever levers suggests that there IS a difference in the lever cylinder, but on the other hand it could just be for regulatory reasons....
    – thelawnet
    Commented Sep 26, 2020 at 8:47

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