SRAM Guide R Problem

Lever now goes to bar and doesn't retract.

The plastic piston in the levers expand/swell when they get warm/hot, had this happen a few times with Code and Guide R levers over the years, almost always when it's a warm sunny day. It's a known issue specifically with the R lever which uses different piston to the RS and RSC levers

I have had this and they would return + it's not particularly hot...The lever goes to the bar without the brake doing anything.  Lever piston looks like it isn't returning at all

I’ve had this too on a 3yr old Guide RS. Changing the lever pistons solved the problem. 30min job plus re bleed 

Eurgh

I'll whack a spare brake on and persevere with them

Are you using the bleed-a-ma-jig and two syringes.... (apologies I dont know if you have done this previously....)

Is the lever easy to return to normal position of needs a but of force? If easy I guess its not bled and air. Bit of force, sticky M/cyl issue. But strangely you don't mention it being a warm day.. 

The plastic piston in the levers expand/swell when they get warm/hot, had this happen a few times with Code and Guide R levers over the years, almost always when it's a warm sunny day. It's a known issue specifically with the R lever which uses different piston to the RS and RSC levers

Yep, it'll be this.

They all use a plastic piston that swells when exposed to DOT 4 / 5.1, warm weather makes it worse.  R's use a different piston because the levers aren't linked via a cam so just be careful which replacement you buy.

A company called RISK do 'titanium' pistons on Ali-Express (also available on ebay, but cost more and still ship from China).  Get the ones with seals already installed for about £1 more as they're not easy to fit without splitting them.  

You also need some very skinny circlip pliers. I had to buy some from screwefix then grind them right down to fit down the bore of the master cyclinder.  If you're near Reading you're welcome to borrow them.

Do both brakes at the same time because they all do it eventually.

It was a problem with a lot of the Guide R for a few years.  Normally a swollen piston in hot weather. I’d be tempted to chuck them and pick up some cheap replacement brakes on eBay unless you like a fiddly fix. 

Had this too. I replaced the plastic pistons with eBay Al ones from a Chinese manufacturer. Cheap. Effective. Edit - replacement was straightforward for me. Been fine ever since.  

my rear lever piston just wouldn’t return after a hot few days when the bike was stored in the garage. It had been fine the week before. 

Thanks all

This feels a bit different to the sticky piston as I've experienced that with these brakes before. Lever goes all way to bar with no braking, despite being bled to the letter of the instructions and having a firm lever beforehand...plus no evidence of leaks.  I'm a bit puzzled.

To be honest I'm fed up with poor quality and finicky SRAM brakes and I've put on a Tektro 4 pot for the summer with view to swapping to Magura in the future.  I just can't be arsed to fight with them 

This feels a bit different to the sticky piston as I've experienced that with these brakes before. Lever goes all way to bar with no braking, despite being bled to the letter of the instructions and having a firm lever beforehand...plus no evidence of leaks.  I'm a bit puzzled.

It's the piston in the master cylinder, it's pushed down, jammed, and not returning so when you pump the lever nothing is happening.

It's not 'sticky pistons' like lot's of 4-pot brakes get where one in the caliper doesn't want to move with the rest. 

To be honest I'm fed up with poor quality and finicky SRAM brakes and I've put on a Tektro 4 pot for the summer with view to swapping to Magura in the future.  I just can't be arsed to fight with them 

To be fair on them mine have  been 100% reliable since I replaced the master cylinder pistons.  It's a cheap, if slightly fiddly fix. 

They look like this, except the original is white plastic.  The seals sit in the grooves on it and the wider flanges keep it aligned with the cylinder, but when they swell it jams.

Obviously if you contact SRAM they will tell you it's just bled wrong and they've never had any issues with any brakes ever. Pisses me off that they cheeped out with a plastic part that they must know will fail after a few years. At the scale they're making them it would cost pennies to use a metal part, we're hardly talking making them Trickstuff prices.

I'll give it a go.

I had avids on a previous bike and they were hateful.  The quality of these seems about the same - e.g. crap

Apologies poor terminology on my behalf. When i said sticky piston I meant the slow lever return.  I've definitely had that in the hot weather on these brakes.

Cheers all.  I'll give those ti pistons a go...I just can't bring myself to fight with them at the mo after spending ages running lines and bleeding them a few days ago

Probably put them on a 2nd bike that isn't internally routed.  They are fairly crap anyway 😁