Unable to delete second partition

I have the same problem

However, you can't delete the partition without formatiing the whole disk. I hope you have a backup.

I don't know whats wrong with this beta.

To resize (or delete) an existing partition without losing data, you will need to use, for example, iPartition:

http://www.coriolis-systems.com/iPartition.php

I had the same issue and fixed it like this.

1) Create a backup of your primary drive (typically named Macintosh HD)

2) Restart your computer and boot into Recovery Mode. To start your computer from Recovery, restart your Mac and hold down the Command key and the R key.

3) Go into Disk Utility and delete the Yosemite partition.

When you delete that partition, the main drive will automatically rename itself. At that point, you can resize your primary partition without suffering any loss of data on your Mavericks OSX installation.

I've been having the same exact problem! I do want to clarify a bit on the original instructions. Once you've rebooted into recovery mode, you'll want to go to this tab(see below). The very top one will still give you the greyed out minus sign. Go to this tab, then choose the erase button and reformat the drive. Once the drive is reformatted you can go to the very top tab (in the sidebar) and erase the 2nd partition. Once that is done you can reformat your main drive back to its' original capacity. I also ran a verify disk and permissions check after this. Everything was good, but it can't hurt! After this, reboot and your hard drive should be back to normal.

I get as far as brig able to click the minus sign with the Yosemite partition selected. However, when I click "Remove" in the dialog box, I receive a notification that the partition failed with the error "Couldn't in mount disk". This issue arises in both the CMD+R boot of Yosemite as well as the insude the OS 10.9 recovery partition. Please help! I just want to remove this partition. Even trying to reformat the entire drive returns the same error.

I just miraculously found a solution. I was able to delete the Yosemite partition inside 10.9 Disk Utility.

Did this return the storage to the main partition, or were you left with a blank partition where the Yosemite partition resided?

(A matter of curiosity, only.)

After removing the partition, I was able to resize the main 10.9 partition to take up all the space of the drive.

You were able to do this without losing data? Or did you have to erase the drive to repartition it?

Ok So the fix is this....

1. reboot to the recovery partition by restart with alt/option key pressed and choose recovery.

2. Choose disk utility

3. click on your Yosemite partition and erase this partition

4. Reboot to os x mavericks

5. open disk utility

6. click on full hard drive and choose the Yosemite hd and click the minus button on the bottom.

7. drag and resize the Macintosh HD to full space.

8. Click Apply

No data loss....

GOOD LUCK!

Thanks godsdisciple85

That did the trick!

Another thing to consider....

When Yosmite is installing, it asks you if you want to use FileVault encryption. If you agree then you can't delete the partition afterwards until you turn it off. You can do this in System Preferences>Security and Privacy/FileVault tab. Once it's turned off, it can be deleted via Disk Utilitiy with the usual pre-requisites.