Hi,

I have 2 pairs of xt brakes with wandering bite point.

The m8000 have been relegated to a seldom used bike. They wandered badly

The m757 have been put in the spares box. They very occasionally wander

Some posters on pink bike suggested using fork oil as it’s less viscous and stop.

Before I actually put the fork oil in my brakes, will it kill them?

What is Shimano brake oil? I know it’s a mineral oil, is that the same as a fork oil?

Yours warily…

Source of dubious info?

In an emergency it would do – but 3 in 1 oil without all the additives would be better. No advantage to doing it at all. Don’t mess with brakes

I know someone who ran XT brakes for a year on washing up liquid.

Martin – I’ve got some mineral oil (can’t remember exact brand – power steering fluid) that I’ve used for Deore brakes for years and they’ve been fine. Don’t know if it’ll fix the bite point issues.

You’re welcome to try some if you want – you’re not that far from me.

fork oik – as in suspension oil of a known weight?

It definitely wont do any damage as it is a form of mineral oil , but I would go for quite a light WT number, like 2.5, definitely not 20wt etc.

I used rockshoc reverb seatpost oil in mine, it worked pretty well

I’ve got a bottle of Shimano brake fluid that I’ve been using for years. It’s not about having the right stuff.

I’ve bled both sets repeatedly and very carefully. They still wander in bite point.

The link doesn’t work it’s this

http://bicycles.stackexchange.com/questions/65337/what-causes-and-how-to-fix-wandering-bite-point-on-shimano-hydraulic-brakes

It’s 2.5 weight they suggest.

The key bit being

high Shimano mineral oil viscosity at low temperatures (viscosity being, in layman’s terms, the resistance of fluids to flow freely; water has very low viscosity and flows easily, while e.g. honey has high viscosity and oozes slowly), combined with the small orrifices of the Shimano levers’ inlet and compenstaing ports through which oil flows between the master cylinder and the brake fluid reservoir. Namely, instead of the oil flowing to the reservoir through the compensating port as the pistons are retracted after braking, the oil stays in the main line, so as the lever returns the pistons do not yet retract fully, meaning that on the next braking they are extended closer to the disc and therefore bite sooner, with lever further from the handlebar. If given more time, the oil slowly flows back in the reservoir, the pistons retract fully, and the bite point returns to its usual position. Hence, the bite point wanders to the outside by amount dependant on how often you engage the brake; at low temperatures, you can pump up the lever so that there is almost no free stroke before engaging

If those other fluids work I might give it a go.

@StuF thanks for the offer, I’ll give this ago and see if it works 🙂

Used the Halfords mineral oil (green stuff) in my older XT brakes for a few years and also my Zees
Never had any issues,It’s used on BMW cars allegedly so if it’s good enough for them then hey who am I to argue
Plus £10 a litre

I would say the issue with high viscosity is plausible.

I had some xt8000 brakes that also suffered this wandering bite point. I bled them, then bled them again, then bled them a further two times. They then worked absolutely perfect. And I do mean perfect; no more weirdness.

Mine came as a set already bled etc. And were shite. There was literally nothing in them that made me think they should suffer this mystery wandering bite point, yet I kept reading about it all over the internet.

In the end I went through the whole bleed rigmarole and it worked perfectly. I think they must have a trillion nooks and crannies that air can get trapped in, which means they just never feel right for some folk. Once I’d done a good bleed they were mint.

I think we’re so used to shimano products just working that it throws us when something isn’t quite right. The problem with these brakes is that they can feel fine… until they don’t. They then feel fine in the shop and any bike workshop really pushed for time will get them to feel ok, and that’s it – they won’t spend hours faffing as it’s just not economical. So if you’re ok with bleeding them and have a shimano bleed kit I would persevere for a while until you’ve purged every bit of air from them. It took me hours (actually two days).

This was using the pink shimano mineral oil.

Thanks @mildred.

I have bought hopes for the two main bikes. However, one set have been awesome for 2 years and now have sticky pistons so the xt are back on while they get fixed.

I’ve given up on riding the xt as main brakes, but would rather have them working well as spares.

It took me hours (actually two days).

You have more patience than me 🙂

I bought a litre of LHF+ Brake fluid off amazon the other day for something like £8, turned up within 24hrs…

TBH I’d just buy a fresh bottle of brake fluid and be done with it…
It almost took me longer to faff about searching for and buying it than doing the first bleed with it….

The key bit being

high Shimano mineral oil viscosity at low temperatures (viscosity being, in layman’s terms, the resistance of fluids to flow freely; water has very low viscosity and flows easily, while e.g. honey has high viscosity and oozes slowly), combined with the small orrifices of the Shimano levers’ inlet and compenstaing ports through which oil flows between the master cylinder and the brake fluid reservoir. Namely, instead of the oil flowing to the reservoir through the compensating port as the pistons are retracted after braking, the oil stays in the main line, so as the lever returns the pistons do not yet retract fully, meaning that on the next braking they are extended closer to the disc and therefore bite sooner, with lever further from the handlebar. If given more time, the oil slowly flows back in the reservoir, the pistons retract fully, and the bite point returns to its usual position. Hence, the bite point wanders to the outside by amount dependant on how often you engage the brake; at low temperatures, you can pump up the lever so that there is almost no free stroke before engaging

This is really interesting – I’m seeing exactly that scenario with my Ultegra discs on the cross/winter bike. Never had the problem across my Shimano MTB brakes over the years though and they’ve been used in some proper cold weather.

Try bleeding using the “Syndicate Bleed” method if you haven’t already https://www.youtube.com/watch?v=piWBVDh1pTE

Seems to sort a lot of the wandering bite point issues out, which I do believe are caused by air getting trapped in some weird cavity in the caliper.

I’ve been dealing with this issue on one set of my xt brakes. I went through that thread and considered it. I even stripped an rebuilt the whole lever assembly.

So far I think I’ve fixed it by lining the pistons with a bit of silicon grease. I think the whole wandering bite point issue is around the callipers not self adjusting for pad wear correctly.

That combined with a poorly aligned calliper in my experience leads to strange bite point issues.

I think the whole wandering bite point issue is around the callipers not self adjusting for pad wear correctly.

This, plus an underfilled reservoir seem the most likely causes to me. I’d be very surprised if the viscosity of the fluid was enough to prevent it flowing through the compensating port. However, in cold weather, the piston seals will be much stiffer and this may affect their ability to self adjust. Or, if the system is underfilled, the fluid expands when the brakes heat up on a descent and this fills the master cylinder properly so the bite point wanders.

now have sticky pistons so the xt are back on while they get fixed.

Put them back on the bike. All you need to do with sticky pistons is get each piston to pop out independently, and pop a little silicon grease or dot fluid around them.

*Don’t* clean them with IPA, it’ll swell the seals.

Just use a tyre lever to hold the side back that isn’t sticky, and pop the pistons a little way out. Grease up, push back in, repeat.

Should take no more than 15 minutes.

All you need to do with sticky pistons is get each piston to pop out independently, and pop a little silicon grease or dot fluid around them.

In the case of Shimano brakes, use mineral oil based brake fluid, not DOT fluid. Basically, lube the seals with the correct type of brake fluid for the brakes and you won’t have problems.

I don’t buy into that theory about oil viscosity. I can’t believe the shimano engineers would design a system so badly.

you can pump up the lever so that there is almost no free stroke before engaging

This however, is a classic symptom of air in any hydraulic braking system.

isn’t sticky, and pop the pistons a little way out. Grease up, push back in, repeat.

Should take no more than 15 minutes.

My hopes are currently going through this. Based on that I will take me alot longer than 15min!

underfilled reservoir seem the most likely causes to me.

They are as full as I can get them 😜

I don’t buy into that theory about oil viscosity. I can’t believe the shimano engineers would design a system so badly.

Me neither! However I can’t get them to work consistently and two sets have been replaced after a load of faffing.

you can pump up the lever so that there is almost no free stroke before engaging

This however, is a classic symptom of air in any hydraulic braking system.

Yep

How about (just ‘whatabouting’ now) a double syringe bleed?

Bleed bottom up but into a syringe at the lever port, then shunt back and fourth a couple of times to try and displace any entrapped air, tap the line and finish with a bottom up push. Do not pull either syringe you’re not doing a vacuum bleed.

I’ve got some mineral oil (can’t remember exact brand – power steering fluid) that I’ve used for Deore brakes for years and they’ve been fine

I’ve got some fluid that I’ve been using in 3 pairs of M785s, one pair of M8000s and a set of RS685s for years with no wondering bite points. I do remember the brand: Shimano

fork oil like 2.5, definitely not 20wt etc.

I used rockshoc reverb seatpost oil in mine

Reverb oil is exactly the same as RS sell as 2.5wt fork oil – some of my reverbs came with oil bottles labelled fork oil, some reverb oil.

@cookeaa

How about (just ‘whatabouting’ now) a double syringe bleed?

Tried that. Got lots of bubbles out, brake get great for 40 miles. Didn’t solve the wandering bite point as the wander came back.

Hence the interest in and internet suggestion!

Maybe it’s not my skills! Maybe its the oil!

At least if I try it it doesn’t sound like it will kill the breaks.

Flush through with fresh oil?
Micro leak at piston seals?

instead of the oil flowing to the reservoir through the compensating port as the pistons are retracted after braking, the oil stays in the main line, so as the lever returns the pistons do not yet retract fully, meaning that on the next braking they are extended closer to the disc and therefore bite sooner, with lever further from the handlebar.

This explanation doesn’t make sense to me. If the fluid doesn’t go back into the reservoir, then you have the same amount of fluid in the brake line and master cylinder and the bite point will be the same. For the bite point to be higher, you need more fluid to somehow get into the line.

Variable bite point on my XTs has always been down to air in the system. You can test if this is the cause of the problem that you’re seeing very easily. Lean the bike over to the side with the misbehaving lever and apply the brake a few times. If the bite point drops, it’s air.

My theory is that the size of the reservoir is not much bigger than volume needed to accommodate pad wear, so even a pretty good bleed on new pads will lead to whatever small bubbles are present getting into the lines once the pads have worn a bit.

Maybe it’s not my skills! Maybe its the oil!

If it’s old fluid then that’s entirely possible, it takes on water over time even with just variation in ambient temperature.
A lovely new bottle of brake fluid should eliminate that potential variable.

Not sure what else to suggest it sounds like you’ve tried all the things most people would in trying to tackle this issue…

If it’s old fluid then that’s entirely possible, it takes on water over time even with just variation in ambient temperature.

Mineral oil is supposed to not do this. DOT fluid absorbs moisture from the air.

I know someone who ran XT brakes for a year on washing up liquid.

And given how much they squeaked it must have been Fairy washing up liquid as it cleans to a squeak!