Slow 5ghz network via extended wireless network

[groovyf]

My current setup is as follows on a 3-floor house:

Lower floor: Airport express 1st gen (extending only 2.4ghz network)
Ground floor: Airport Express 2nd gen (acts as main wireless point connected to router - distributing wireless on 2.4ghz and 5ghz networks (SSIDs different for each band)
Upper floor: Time Capsule 3rd gen (extending both 2.4ghz and 5ghz)

When my MB Air is connected to the 2.4ghz network (being pushed out via the Time Capsule (transmit rate is 130, and verified it's the TC by looking at the Network Diags wireless utility), I get decent throughput, and speedtest.net download peaks at my current ADSL limit - approx 7mbps connection
However, whem I connect to the 5ghz network, again via the TC (transmit rate is 300, and again verified it's the TC), I get really poor download speed, approx under 1mbps connection.

I've performed a file copy from my Mac Mini server (connected to the TC via ethernet), and on the 2.4ghz network all is as expected speed-wise, but on the 5ghz network it's atrocious - only really noticed due to a Time Machine backup taking far longer than expected.

For reference, I disabled extending the 5ghz network on the TC, and made sure I was connected to the 5ghz coming out from the main Airport Express (transmit rate around 240 or so), and the download speeds/file transfer speeds were as I would expect.
Is this looking like an issue with my TC and it's 5ghz band? (given the fact on 2.4 it's OK).

Thanks in advance for any help/advice.

 

[Altemose]

My current setup is as follows on a 3-floor house:

Lower floor: Airport express 1st gen (extending only 2.4ghz network)
Ground floor: Airport Express 2nd gen (acts as main wireless point connected to router - distributing wireless on 2.4ghz and 5ghz networks (SSIDs different for each band)
Upper floor: Time Capsule 3rd gen (extending both 2.4ghz and 5ghz)

When my MB Air is connected to the 2.4ghz network (being pushed out via the Time Capsule (transmit rate is 130, and verified it's the TC by looking at the Network Diags wireless utility), I get decent throughput, and speedtest.net download peaks at my current ADSL limit - approx 7mbps connection
However, whem I connect to the 5ghz network, again via the TC (transmit rate is 300, and again verified it's the TC), I get really poor download speed, approx under 1mbps connection.

I've performed a file copy from my Mac Mini server (connected to the TC via ethernet), and on the 2.4ghz network all is as expected speed-wise, but on the 5ghz network it's atrocious - only really noticed due to a Time Machine backup taking far longer than expected.

For reference, I disabled extending the 5ghz network on the TC, and made sure I was connected to the 5ghz coming out from the main Airport Express (transmit rate around 240 or so), and the download speeds/file transfer speeds were as I would expect.
Is this looking like an issue with my TC and it's 5ghz band? (given the fact on 2.4 it's OK).

Thanks in advance for any help/advice.

First of all, ensure that you have everything connected via Cat 5 or later Ethernet cables. Begin by powering off the Expresses and reset the Time Capsule. Set it up using AirPort Utility 6.3 or later. Then you can make changes later on in 5.6 as necessary. Then reset both Expresses and configure them in AirPort Utility 6.3. Try leaving them as one SSID and separating them later if necessary.