The goal is to pull the Heater Case Assembly and to then pull and replace the Heater Core. Thanks to Tech2 the Heater Core was the problem.

An 89 Suburban 454 3/4 ton with AC has a Heater Case Assembly (whole unit that contains the Heater Core) that is fastened with 3 studs. The 3 studs are bolts which have no-grab-point-ability (circular and flat . . . not hex shaped nor slotted for a screw driver) on the passenger front compartment side, threads on the stud bolt shaft, and a washer-based-nut-combo on the engine side of the firewall. i.e. feed bolt thru Heater Case Assembly from the passenger compartment thru the firewall and fasten with the washer-based-nut-combo on the engine compartment side of the firewall.

After much patience and significant contorations, I managed to find (first challenge) and remove (second challenge) the stud washer-nuts. The stud positions were in an L shape relative to the Heater Case Assembly. Two were to the left, one above the other about 14 inches apart. The third was in line with the one on the bottom left, but instead to the bottom right side.

Now I am trying to pull the Heater Case Assembly (third challenge). While I attempt to pull the Heater Case Assembly, it is very clear that the bottom two studs can be completely pulled thru the firewall along with the bottom side of the Heater Case Assembling (showing me that I am almost able to remove the Heater Case Assembly). i.e. The bottom portion of the Heater Case Assembly is able to pull out two full inches. However, the top portion of the Heater Case Assembly does not want to pull away as did the bottom portion. So, I took a hammer on the top remaining stud and tried to pound light from the engine side toward the passenger compartment. It does not budge even slightly. So, I scanned the perimeter of the whole Heater Case Assembly looking for yet another fastener of some sort, but I could not find one.

So, something is keeping the top portion of the Heater Case Assembly from coming loose. My Chilton manual is really not specific enough to guide. There might be yet more fasteners of screws in some not-so-obvious place.

If anyone knows what Heater Case Assembly fasteners remain, then maybe you could guide relative to the L shaped stud pattern mentioned above (the reason why I described the L shaped studs as reference points). Also, after so may years the seal in combo may have become a form of glue on the top side (but I already tried the tapping hammer route mentioned above). Also, the bottom moves easily two full inches away from the flooring / firewall so I lean toward the extra fastener theory.

Perplexed.

-- Steve

 

Solved and here is why:
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1) When they put the tar around the studs on the engine side, there is a very thin flat tooth washer buried under the tar.
2) I took a 2 foot steel file with pointed ends and tapped until one thread popped. Then I knew to keep hammering.
3) Once the threads hammered thru the hidden tooth lock washer, the Heater Case Assembly popped out. I have know idea why the top stud had a buried tooth lock washer, while the bottom two had none. Go figure. Trust instincts.

 

The washer was probably put on to hold the assembly in place on the firewall so that the next guy on the assembly line could install the nuts.