City Girls' JT Dropped a Car's Worth on Yung Miami's Birthday Bling

City Girls rapper JT says she "spent a car" on Yung Miami's birthday gift, but clearly she was being modest -- it's easily the price of a house!!! Or maybe she drives really pricey cars.

JT surprised her partner with some shiny bling for her 26th birthday Tuesday ... leaving YM305 speechless. We're told the gift -- 2 months in the works -- was delivered Tuesday night.

The chain is a baller 130 carats ... and features everything YM's obsessed with -- diamonds, music notes, money, Chanel and her kids' names. Celeb jeweler Elliot Eliantte was the artist behind the masterpiece.

JT said on social media ... "Happy birthday to my EVERYTHING. I spent a car on this I F***ING LOVE YOU & if a b*tch ever think otherwise they crazy!!!! B*tch you love diamonds Chanel & your kids.... it's all there! Pop your sh*t!!!!"

YM's reaction can be summed up in 2 words. Speechless and tears.

As we first reported ... Miami hooked up JT with some serious jewels last year to celebrate JT's prison release.