Re: Twin Ultramatic Transmission oil pan bolts
Posted by HH56 On 2023/4/11 8:53:29
Here is the original spec on pan bolts. 5/16-18 and 3/4 long is used with the 56 aluminum trans cases. Most of the threaded holes in the aluminum cases are thru holes and could possibly be drilled and retapped larger with a corresponding enlargement of pan holes if there is enough excess metal surrounding the hole. Others are closed end and would need a bottoming tap. Some at the front could also be very close to fluid passages inside the case.
Has your mechanic checked the straightness of the pan mating surface itself? That is a frequent cause of leaks because the pan is stamped from fairly thin sheetmetal. When the bolts are overtightened the metal around the holes is distorted and pushed upward as the relatively thick cork gasket compresses directly above the bolts. Even with a new gasket if the metal is distorted the bolts stop applying much pressure when they reach the gasket. When that happens there is not enough compression on the gasket in the relatively long spaces between holes so a leak is the usual result.
Check with a good straightedge laying across the lengths of the pan bolt hole mating surfaces. Use a small rounded end hammer and GENTLY tap down and flatten or even slightly depress any metal around the holes that is above the surface as shown by the straightedge. The same issue and check applies to the engine oil pan.
Attach file:
pan bolt.jpg (38.48 KB)
Has your mechanic checked the straightness of the pan mating surface itself? That is a frequent cause of leaks because the pan is stamped from fairly thin sheetmetal. When the bolts are overtightened the metal around the holes is distorted and pushed upward as the relatively thick cork gasket compresses directly above the bolts. Even with a new gasket if the metal is distorted the bolts stop applying much pressure when they reach the gasket. When that happens there is not enough compression on the gasket in the relatively long spaces between holes so a leak is the usual result.
Check with a good straightedge laying across the lengths of the pan bolt hole mating surfaces. Use a small rounded end hammer and GENTLY tap down and flatten or even slightly depress any metal around the holes that is above the surface as shown by the straightedge. The same issue and check applies to the engine oil pan.
Attach file:
pan bolt.jpg (38.48 KB)
This Post was from: https://packardinfo.com/xoops/html/modules/newbb/viewtopic.php?post_id=255765