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My front GRX calipers is badly corroded and one of the pistons is seized due to poor storage so needs replaced. You can get front and rear calipers that are different prices but the only difference I can tell is that the front ones come with an adaptor for rotor sizes - which I already have.
Would I be ok to just buy a rear and reattach the old mount and save myself a tenner or is there something I'm missing?
Thanks in advance
Flat mount will usually differ front to rear
Thanks - in what way?
Go to the shimano web site, e.g.
and look at the part numbers
Have seen that document already which has made me think my above post is correct but wanted to see if anyone else had further insight
Could you test fit your existing rear on the front? Or even the faulty front on the rear.
The flat mount calipers themselves are the same but the adapters are different front and rear. Most frames will bolt a flat mount caliper directly to the stay for 140mm rotors but need a rear specific adapter for 160mm.
The front usually requires an adapter for both sizes, you just rotate it 180degrees for whichever size you need.
The bolts that mount the rear caliper to the frame are a specific length for the frame (I think Shimano supply one length with the caliper) and you must use the correct length for your frame.
Assuming that you have the adapters from your current setup and both them and the bolts (if needed) are all still serviceable then the caliper itself is the same.
I did a massive deep dive for a customer with a similar query.
I discovered that there were very subtle differences between the front and rear caliper that were only noticeable when both calipers were laid out together. As someone has already commented-part numbers are different.
I also discovered that Shimano updated the calipers (without press comment anywhere) after initial GRX production started.
So in summary: there are different versions of GRX calipers, F+R have different part numbers and although you may be able to hack the fit, a few extra quid for peace of mind related to a serious safety issue wouldn't be worth it to me.
The Hope ones aren’t that much more I think- £80?
I’ve got a couple of ultegra ones I took off that I thought had the leaky calliper thing.
You can have them if you want- see if they can be cleaned up.
I had a rear Shimano 105 ish level flat mount caliper get the micro leak issue. I just got the Hope RX4 replacement and so far it’s been fit and forget. I broadly like Shimano brakes when they’re working but wouldn’t buy any that didn’t come on a bike as I’ve had a few micro leak scenarios now. Also had a go on a few bikes that have had inconsistent bite point on Shimano brakes.
I did a massive deep dive for a customer with a similar query.
Thats very interesting information, are you able to detail what the differences are and even more interesting, are these F/R differences specific to GRX.?
As far as I’ve been able to tell there is no difference on the Ultegra callipers I have or the 105 ones I’ve had a good look at.
🙄From memory.....the angle of hose attachment was slightly different and the two halves of the caliper had different shaped cast marks in the base (one round, one square). If you put both calipers together on the base plates, they sat at slightly different angles. I vaguely recall a smaller hole where a clip/pin was factory inserted being in a different place F to R. Tended to suggest that the calipers were slightly differently mounted to get full pad contact front to rear.
During the pandemic there was a massive shortage of calipers and we looked at all ways around it hence the research.
The fact there were differences ruled out any sale of bikes to customers with bodged brake calipers!
Not so up on the 105/Ultegra side but they are interchangeable with GRX.
Again (purely personal) but Shimano spend a lot of time and effort getting things right so I would always stick to their advice especially when safety is concerned.
Thanks for your insight @ginsterdrz - will get a front specific one for the extra tenner.
Although now you all reminded me of the rx4...
Although now you all reminded me of the rx4…
And of course you can’t have one Hope and one Shimano, so better safe than sorry get a pair of Hopes.
The calipers themselves are identical, and have the same part no printed on them.
The front adaptor that comes included with the packaged front caliper is the only difference. Ft and rear are interchangeable bar the required front adaptor (apart from a handful of forks that use the closer spacing mount) and the optional +20mm rear adaptor.
As you already have the front adaptor, you can use the cheaper rear that comes without an adaptor
.
The calipers themselves are identical, and have the same part no printed on them.
The front adaptor that comes included with the packaged front caliper is the only difference. Ft and rear are interchangeable bar the required front adaptor (apart from a handful of forks that use the closer spacing mount) and the optional +20mm rear adaptor.
As you already have the front adaptor, you can use the cheaper rear that comes without an adaptor
😂 We seem to be going round in circles a wee bit here!!
Sorry - missed your post! Just correcting the incorrect info that followed.
From memory…..the angle of hose attachment was slightly different and the two halves of the caliper had different shaped cast marks in the base (one round, one square). If you put both calipers together on the base plates, they sat at slightly different angles. I vaguely recall a smaller hole where a clip/pin was factory inserted being in a different place F to R. Tended to suggest that the calipers were slightly differently mounted to get full pad contact front to rear.
The calipers themselves are identical, and have the same part no printed on them.
The front adaptor that comes included with the packaged front caliper is the only difference. Ft and rear are interchangeable bar the required front adaptor (apart from a handful of forks that use the closer spacing mount) and the optional +20mm rear adaptor.
As you already have the front adaptor, you can use the cheaper rear that comes without an adaptor
So there seems to be a couple of strongly held differences of opinion here.? I was going off of my own observations and brief research so was more than willing to be told otherwise but it seems I wasn't alone in my belief.... Is there any way of getting a definitive answer one way or the other.??
And before anyone asks, no I have no idea why I've gotten so invested in the answer as if I ever change my calipers I'll be putting RX4+ ones on, already sitting in the spares box waiting.!!
Same part no on caliper means same part.
My front GRX caliper failed also. Replaced with a Hope. Much better so far 🤞
This small differences between front and rear callipers seems very un-Shimano to me. Every other brake they make is universal. Why would GRX be different? From a manufacturing point of view why would you make two products almost the same when they could be the same?
As far as I’ve been able to tell there is no difference on the Ultegra callipers I have or the 105 ones I’ve had a good look at.
Yep, I got a seized piston in a 105 rear calliper mid lockdown. Couldn't get a new one but did have an old 600 calliper with a seized piston lying about, so I took the working half of the 600 and my 105 and bolted them together - got another year out of that. Then I replaced the bastardised calliper with a GRX (as that was all I could find online to buy). They all seem identical. GRX is working fine with the 105 lever.
From memory…..the angle of hose attachment was slightly different and the two halves of the caliper had different shaped cast marks in the base (one round, one square). If you put both calipers together on the base plates, they sat at slightly different angles. I vaguely recall a smaller hole where a clip/pin was factory inserted being in a different place F to R
I also discovered that Shimano updated the calipers (without press comment anywhere) after initial GRX production started.
So given that the emerging consensus from practical experience is that they are the same (part no., combining different caliper halves, etc.) is it possible that the experience quoted above was due to an inline production change to the caliper that just so happened to reveal itself when comparing a front and rear.? (i.e updated front, original rear or vise versa.?)
That's possible - Shimano tend to refine existing products with running changes, but front and rear would remain the same when comparing product produced around the same time, and it remains true that beyond their respective adaptors, there's no difference between front and rear calipers.
another vote for Hope RX4+ here - they are amazing.