Hi, has anyone got any tips for doing lots of thirds really fast and getting them together? I'ts just I'm doing Mozart's Sonata in F on the Grade 8 syllabus, and at the end of the 2nd and 6th pages come some tricky thirds and I just can't play them without seperating them.

Thanks

play them really slowly until they're completely together, then speed them up

As noodle has said, slow legato practice. Two ideas you can employ whilst doing this:

1) Learn it backwards as well as forwards. Keep the fingering the same, obviously.
2) Play them in rhythms; for instance [dotted-quaver, semiquaver] or [semiquaver, dotted-quaver] pairs. Importantly, when doing this, don't allow any split notes or roughness to creep in - have a pedantic attention to detail
3) Once you can play it backwards, take groups of thirds and play them back and forth; for instance, if the sequence of thirds has the upper notes going G-F-E-D-C then practice them in groups of three:

G-F-E-F-G-F....
F-E-D-E-F-E....
E-D-C-D-E-D....

and once you can do that, groups of four:

G-F-E-D-E-F-G-F.... and so on

Really, it's all to do with breaking it down into easily repetitive chunks and working it into your hands. These sorts of repetitive exercises are quite good for that - one can sit there all day going G-F-E-F-G.... gradually notching up the speed. To spice things up a bit, play the back-and-forth chunks in rhythms too. And, once you're in groups of four use a long-short-short rhythm - that'll really highlight the weak spots. Tedium and slog, but it does pay off .

I'm doing this for my Grade 8 too.
Try taking the bottom note of the lowest third ( ie B ) with the left hand. This lets you play the right hand for 3 bars in one position. (ie 5/3, 4/2, 3/1, 2, 3/1 etc).
I got this from 'Mozart and the Pianist' by M. Davidson - very good book with performance suggestions for all the sonatas and other works.
NB he suggests taking all the 'C's with the left also, but I find this unnessacery.
There is a Video of a professional teacher called Bar-Niv playing this movement on Youtube, where he does this.

Very ingenious. For where this isn't possible I find it also helps to put clearer-than-necessary accents on main beats to keep the playing rhythmic, and to get quite 'deep' into the keys for all the beats. You can gradually remove the accents in your practice once the passage is nicely in your fingers.

I have them marked as 1/2 4/2 (fingers) on my score, I don't have the ABRSM edition though. I have seen the Bar-Niv video but I think playing them with your left-hand is a bad practice for whats to come. You will have pieces where you have to play thirds with a left-hand accompaniment, if you do that you will probably be stuck anyway.

Best advice probably, play them slowly and try to get a shape of the thirds with your hand i.e. where the upper melody is going. That failing play the parts with the fingering you have marked separately then join them up. THAT failing I don't know. Usually a good way of playing thirds is to practice the movement even when you are not at the piano, i.e. alternating 1/3 2/4 repeatedly until the hand just does it automatically.