diff --git a/clocks/jumbo/README.md b/clocks/jumbo/README.md
index e04dfcd..d45fa33 100644
--- a/clocks/jumbo/README.md
+++ b/clocks/jumbo/README.md
@@ -10,4 +10,6 @@ The drivers are (in order):
 * DClock
 * Cricket!
 
-The installer is silent - no output is shown on either failure or success.
+By default, the installer logs on success so you can tell what clock was detected, but you can build with `LOG_SUCCESS=0` to prevent that.
+
+If ProDOS _already_ has a clock driver installed, the driver is checked for common Thunderclock year tables. If found, the table is updated in memory to cover 2023-2028.
diff --git a/clocks/jumbo/clock.system.s b/clocks/jumbo/clock.system.s
index ebfc36d..0a3819d 100644
--- a/clocks/jumbo/clock.system.s
+++ b/clocks/jumbo/clock.system.s
@@ -50,7 +50,7 @@
 .proc maybe_install_driver
         lda     MACHID
         and     #$01            ; existing clock card?
-        bne     ret
+        bne     check_thunderclock
 
         jsr     ns_clock::maybe_install_driver
         bcc     ret
@@ -70,6 +70,91 @@
 ret:    rts
 .endproc
 
+.proc check_thunderclock
+         ;; Look for Thunderclock year table
+        bit     RWRAM1
+        bit     RWRAM1
+
+        lda     #<table_1982
+        ldx     #>table_1982
+        jsr     check_sig
+        beq     update_table
+
+        lda     #<table_1986
+        ldx     #>table_1986
+        jsr     check_sig
+        beq     update_table
+
+        lda     #<table_1993
+        ldx     #>table_1993
+        jsr     check_sig
+        beq     update_table
+
+        lda     #<table_2018
+        ldx     #>table_2018
+        jsr     check_sig
+        beq     update_table
+
+        ;; Table not found - we have a clock but don't
+        ;; know what it is, so don't log anything.
+        bit     ROMIN2
+        rts
+
+        ;; ----------------------------------------
+
+        ;; Copy the latest table into place
+update_table:
+        ldx     #SIG_LEN-1
+:       lda     table_2023,x
+        sta     SIG_ADDR,x
+        dex
+        bpl     :-
+
+        bit     ROMIN2
+.if ::LOG_SUCCESS
+        ;; Display success message, to confirm table updates.
+        jsr     log_message
+        scrcode "ThunderClock - "
+        .byte   0
+
+        ;; Display the current date
+        jsr     cout_date
+.endif ; ::LOG_SUCCESS
+        rts
+
+        ;; ----------------------------------------
+
+check_sig:
+        ptr := $06
+        sta     ptr
+        stx     ptr+1
+        ldy     #SIG_LEN-1
+:       lda     (ptr),y
+        cmp     SIG_ADDR,y
+        bne     :+              ; Z=0 for no match
+        dey
+        bpl     :-
+        iny                     ; Z=1 for match
+:       rts
+
+SIG_LEN = 7
+SIG_ADDR := $D7B8
+
+table_1982:                     ; ProDOS 1.1.1
+        .byte   $54, $54, $53, $52, $57, $56, $55
+
+table_1986:                     ; ProDOS 1.3 - 1.9
+        .byte   $5A, $59, $58, $58, $57, $56, $5B
+
+table_1993:                     ; ProDOS 2.0.3
+        .byte   $60, $5F, $5E, $5D, $62, $61, $60
+
+table_2018:                     ; ProDOS 2.4.2
+        .byte   $12, $17, $16, $15, $14, $14, $13
+
+table_2023:
+        .byte   $18, $17, $1C, $1B, $1A, $19, $18
+.endproc
 
 ;;; ************************************************************
         .include "../../inc/driver_postamble.inc"