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Old 08-12-2019, 12:14 PM
Kestas Kestas is offline
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Why are transmission pan bolts included in trans service kit?

In my opinion, the only time a transmission pan bolt is needed for purchase is if you lose one or horribly mangle it. So why are transmission bolts routinely sold with the service kits? It seems like a waste. My 2015 320i is new to me; I haven't dropped the transmission pan yet.

Last edited by Kestas; 08-12-2019 at 12:18 PM.
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Old 08-12-2019, 12:27 PM
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Originally Posted by Kestas View Post
In my opinion, the only time a transmission pan bolt is needed for purchase is if you lose one or horribly mangle it. So why are transmission bolts routinely sold with the service kits? It seems like a waste. My 2015 320i is new to me; I haven't dropped the transmission pan yet.


One time use due to being made of aluminum I believe. Not made to be accurately torqued a second time.


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Old 08-12-2019, 12:48 PM
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+1

A second torqued use will be as accurate, but the screw may break.
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Old 08-12-2019, 12:49 PM
Kestas Kestas is offline
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Okay, that would make sense. Weird though... why not use steel? Using this logic, why doesn't BMW make all fasteners from aluminum?
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Old 08-12-2019, 01:35 PM
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Okay, that would make sense. Weird though... why not use steel? Using this logic, why doesn't BMW make all fasteners from aluminum?


Might be a corrosion issue. Aluminum resists corrosion and does not get rusty. Steel bolts would. I wouldn’t want anything rusty on my transmission pan.




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Old 08-12-2019, 02:02 PM
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Aluminum is anodic to steel. May I remind everyone of the problem with aluminum fasteners on the power steering unit.

Last edited by Kestas; 08-12-2019 at 03:52 PM.
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Old 08-13-2019, 06:55 AM
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Originally Posted by Kestas View Post
Aluminum is anodic to steel.
Indeed it is. Do you think the the 8HP's housing is made of steel?
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Old 08-13-2019, 07:42 AM
Kestas Kestas is offline
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What is the 8HP? Is that the steering unit? If it was made of steel, the problem for aluminum corrosion would be even worse.
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Old 08-13-2019, 07:56 AM
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Interesting info here. Based on this article it may very well be a case of a BMW engineer deciding “better safe than sorry” to replace a $2 bolt vs a $4000 transmission.

https://www.portlandbolt.com/technic...reusing-bolts/

Can a bolt be reused? If so, what grades and in what scenarios?
A bolt that has already been used in a given application may or may not be reused, depending on the grade, application, and recommendation of the “Engineer of Record”. There are a tremendous number of conflicting opinions on this subject, but the only definitive published information we can find on this issue from a reputable source is in regards to ASTM A325 and A490 structural bolts.

According to the Research Council on Structural Connections, Section 2.3.3:

“Reuse: ASTM A490 bolts and galvanized ASTM A325 bolts shall not be reused. When approved by the Engineer of Record, plain finish ASTM A325 bolts are permitted to be reused. Touching up or re-tightening bolts that may have been loosened by the installation of adjacent bolts shall not be considered to be a reuse.”

“Pretensioned installation involves the inelastic elongation of the portion of the threaded length between the nut and the thread run-out. ASTM A490 bolts and galvanized ASTM A325 bolts possess sufficient ductility to undergo one pretensioned installation, but are not consistently ductile enough to undergo a second pretensioned installation. Plain ASTM A325 bolts, however, possess sufficient ductility to undergo more than one pretensioned installation as suggested in the Guide (Kulak et al., 1987). As a simple rule of thumb, a plain ASTM A325 bolt is suitable for reuse if the nut can be run up the threads by hand.”

When reusing bolts, it is critical to involve an engineer since the reuse of the fastener depends on a variety of factors including bolt type, application, grade, finish, installation method, etc. If the bolts have been tensioned beyond their yield point, they enter the “plastic zone” (where they elongate and do not contract once the load is removed), which means they may be subject to premature failure. Since it is virtually impossible to determine visually if a specific fastener has entered its plastic zone when previously used, the decision to reuse a fastener will be determined by the price to replace it versus the potential cost and/or liability of that fastener failing.

Spending a few hundred dollars replacing structural bolts supporting an overhead sign structure on the freeway makes sense when evaluating the potentially devastating consequences and liability involved in reusing bolts that may ultimately fail. On the other hand, attempting to reuse a few hundred dollars worth of bolts instead of replacing those fasteners on a noncritical pump or other piece of equipment might make sense when a failure would only result in the piece of equipment not working.
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Old 08-13-2019, 08:10 AM
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Quote:
Originally Posted by Kestas View Post
What is the 8HP? Is that the steering unit? If it was made of steel, the problem for aluminum corrosion would be even worse.
Sorry for the jargon: 8HP is the family model number of the ZF 8-speed transmissions. The 8HP has an aluminum housing; hence, aluminum screws to attach the pan.
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Old 08-13-2019, 08:11 AM
Kestas Kestas is offline
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No, no, no. Though a good article, chiefneil, it plays strawman and doesn't address the question of why aluminum and not steel. For many decades, the motoring public has been just fine using steel bolts into aluminum housings for transmission pans, which were reusable for the life of the vehicle and beyond. For some reason BMW went with aluminum. If they really wanted to be safe and not sorry, use steel bolts for the sake of a $4000 transmission.

Last edited by Kestas; 08-13-2019 at 08:19 AM.
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