1. Door Latch Mechanism:
* Worn or Broken Latch: The most common cause. Over time, the latch mechanism (the part the inside handle operates) can wear down, making it stiff and difficult to release. The outside handle often uses a different linkage, explaining the easier external operation. This might require replacing the entire latch assembly.
* Binding Latch: Dirt, debris, or corrosion can build up in the latch mechanism, causing it to bind. Disassembly, cleaning, and lubrication (with a light silicone-based lubricant, *not* WD-40) might resolve this.
2. Door Handle Mechanism (Inside):
* Worn or Broken Internal Handle: The internal door handle itself may be worn, broken, or have a broken linkage connecting it to the latch. Inspect the handle carefully for cracks or play. Replacement might be necessary.
* Broken or Disconnected Linkage: The linkage connecting the inside handle to the latch can break or become disconnected. This requires careful inspection and likely repair or replacement of the linkage.
3. Regulator (Power Windows):
* Interference: If the door has power windows, the window regulator mechanism could potentially interfere with the door latch, especially if it's misaligned or damaged. Check for anything binding in the window mechanism.
4. Door Strike:
* Misalignment: While less likely to cause the specific problem you describe, a misaligned door strike (the metal part the latch engages with on the door frame) can add resistance. Check if the door aligns properly with the strike plate when closed.
Troubleshooting and Repair Steps:
1. Visual Inspection: Start by carefully inspecting the inside door handle and surrounding area. Look for any obvious damage, broken parts, or signs of binding. Remove the inside door panel (plenty of online tutorials show how; search for "1999 Chevy Suburban door panel removal").
2. Lubrication: After removing the panel, lubricate all moving parts of the latch mechanism and handle linkage with a silicone-based lubricant. Work the mechanism several times to distribute the lubricant.
3. Check Linkage: Inspect the linkage connecting the inside handle to the latch. Look for broken or bent parts. You might need to carefully trace the linkage's route.
4. Test the Latch: With the door panel off, try manipulating the latch mechanism directly. This helps isolate whether the problem lies within the latch itself or further upstream in the linkage.
5. Replace Parts: If lubrication and linkage inspection don't resolve the issue, you'll likely need to replace the faulty component (latch, handle, or linkage). Parts can often be found at auto parts stores or online.
Important Note: Working on car doors involves some mechanical skills. If you are not comfortable working on car parts, it's best to take your Suburban to a qualified mechanic. Improper repair can lead to further damage.
