Just a heads up, I changed my original ATF the other day after reading everything I could here first, and was expecting a potential fight with the pan bolts based on other members' experience with their rigs. What I found was actually the opposite, as all of the 10mm pan bolts were loose enough to remove with a mere nut driver, and some even felt loose enough to have taken them out with fingers. My truck spent its first 101,000 miles in Houston, so no corrosion to speak of, but this was beyond not being stuck or breaking off as some have experienced. I've seen this before over years of working on cars and bikes, and I chalk it up to gasket shrinkage. The bolts were properly torqued 12 years ago against a brand new gasket, and it then shrank over the years effectively taking tension off the fasteners. I know most of you are avid vehicle maintenance freaks, but I have seen a few comments here and there about not messing with the transmission fluid per Toyota's lofty assertion that it is sealed and maintenance-free. If you are in the latter boat, at the very least have a look at the bolts and check their tightness with an inch/pound torque wrench. As sophisticated as vehicle sensors have become, nearly all still lack the ability to warn when the most vital of fluids are low until it's pretty much too late. Happy wrenching!
A public service announcement regarding shrinkage...
- Thread starter z00t3ch
- Start date
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Better check those valve cover gaskets/bolts while you're at it.... i'm sure you will again be surpirsed...... i would recommend replacing the gaskets vs over torqueing the bolts and potentially snapping one off.
- Thread starter
- #3
That is where I most often see this phenomenon, especially my old '95 ZJ, but it was weeping oil all over itself. This motor is dry as a bone, but I'll have a look here soon when I go to replace plugs.
i did my transmission strainer this past weekend and noticed the bolts were loose as well. Overtime itll happen.. like the valve cover gasket.
my bolts all came off easily... too easily... pretty much i could loosen them with just socket and finger. The plus side was that the pan literally dropped down as i unbolted the last bolt and the gasket came off CLEAN and in 1 piece... the bad was that once i removed the strainer i was greeted with more transmission fluid
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my bolts all came off easily... too easily... pretty much i could loosen them with just socket and finger. The plus side was that the pan literally dropped down as i unbolted the last bolt and the gasket came off CLEAN and in 1 piece... the bad was that once i removed the strainer i was greeted with more transmission fluid
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Rubber can shrink or swell in service but probably not the case here.
When put under a compression load, rubber and most other non-metallic materials experience physical changes. These include:
-- Permanent compression set - the rubber part in this case gasket becomes permanently thinner = loss of initial bolt torque.
-- Compression stress relaxation (CSR) - when first installed the rubber component is "pushing back" (sealing force) with 'X' lbs force. Slowly over time that sealing force will drop could be as low as 50% of initial load. Translates to loss of initial bolt torque.
These factors are well known by engineers who should build them into their designs.
Unless the manual tells you to do so it's probably not a good idea to re-torque a gasket joint to compensate for these factors. Reason being doing so will just create a new zero point for compression set and stress relaxation to start over. Eventually a rubber gasket or seal / o-ring can be compressed to the point the rubber will split.
The only way to get around this is to build a metal sleeve or "torque tube" into the gasket around the bolt hole. Say the designer wants the gasket to be compressed 25%. If the gasket is 10mm thick then the torque tube would be 7.5mm thick. The attachment bolts can be torqued to whatever they can handle, the gasket is compressed 25%. The rubber will still have permanent set and CSR but the bolts will stay tight.
When put under a compression load, rubber and most other non-metallic materials experience physical changes. These include:
-- Permanent compression set - the rubber part in this case gasket becomes permanently thinner = loss of initial bolt torque.
-- Compression stress relaxation (CSR) - when first installed the rubber component is "pushing back" (sealing force) with 'X' lbs force. Slowly over time that sealing force will drop could be as low as 50% of initial load. Translates to loss of initial bolt torque.
These factors are well known by engineers who should build them into their designs.
Unless the manual tells you to do so it's probably not a good idea to re-torque a gasket joint to compensate for these factors. Reason being doing so will just create a new zero point for compression set and stress relaxation to start over. Eventually a rubber gasket or seal / o-ring can be compressed to the point the rubber will split.
The only way to get around this is to build a metal sleeve or "torque tube" into the gasket around the bolt hole. Say the designer wants the gasket to be compressed 25%. If the gasket is 10mm thick then the torque tube would be 7.5mm thick. The attachment bolts can be torqued to whatever they can handle, the gasket is compressed 25%. The rubber will still have permanent set and CSR but the bolts will stay tight.
