[williamsji]

What size impact are you using? If a decent 1/2" (so, not one of those that comes in a generic air compressor starter kit) with a 3/8" adapter isn't taking it off, I'd head to the dealer. Yes, you can do all sorts of crazy things to add leverage, but paying the dealer one time isn't likely to break the bank, and is less likely to end with broken tools, stripped bolts, and flying metal.

I agree.

I seem to recall another member posting recently that they actually stripped the threads on their CRV.

This is one of those... take it to the dealer this time around and have the differential serviced moments. Honda drive systems are pretty complex yet elegant these days.. and messing up one thing could result in compounding issues. Better to let a dealer mess something up and have to correct it than you. Think of it as money well spent as insurance against a major damage event to the differential.

 

[williamsji]

Waiting to see someone put up a photo of a 10 foot breaker bar, complete with leverage inducing lockable pivot points in the shaft of the bar, and a self fastening magnetic socket so the owner does not even have to crawl under the vehicle to apply torgue.. only under long enough to insert the socket to bolt and lock it in place.

 

[williamsji]

Thanks for the suggestions guys! I guess the dealer may be a good idea here. Although, the other ideas given here are pretty good, and may be worth a shot. The impact I was using was a 1/2 inch electric Ridgid impact, I'll throw a link for it down below. Its crazy, I have been able to remove any other fill bolt I've tried, but this one is something else! And then with the silicone being so close, heat doesn't seem to be an option unfortunately. If I do take it to the dealer this time around, then should I crack the fill bolt off when I get the car back home and do something to make it easier for the next time so I don't have to take it to the dealer again? From my experience, dealers usually torque things down with a few ugga duggas making it difficult next time I try to DIY.

RIDGID 18V OCTANE Brushless Cordless 1/2 in. Impact Wrench (Tool Only) with Belt Clip R86011B - The Home Depot

RIDGID introduces the 18V OCTANE Brushless Cordless 1/2 in. Impact Wrench (Tool-Only) with Belt Clip. OCTANE Tools feature high performance brushless motors and advanced electronics, providing best-in-class

www.homedepot.com

I bet the core issue here is two fold:

1) zealous torque down at the factory when assembled.

2) dis-similar metals between bolt and casing that over time cause either temperature or chemical (or both) induced freeze-up of the threads. I believe the casing is an aluminum alloy and the bolt is of course some alloy of steel.

I bet Honda dealers have a method to deal with these pesky hard to remove differential bolts

 

[williamsji]

I had my rear diff fill bolt lock up too. Changed the fluid at 15K and realized a mere 2,000 miles later that I changed the fluid without the car level, so I decided to simply double check the fluid level. No go. Only hand tightened the fill bolt cause I could not fit the torque wrench under the car. Ended up going to the dealer to fix the problem. Fortunately he reported that the fill bolt threads were not stripped. Still wondering why that happened.

Could be caused by thermal cycling of the differential from day to day use. Aggravated by dissimilar metals between bolt and casing. Not properly applying proper torque to the bolt after hand tightening might also have set up a contributing factor.

These are speculations, not known fact ... since you are seeking cause.

 

[williamsji]

Yep you got that right

Yeah, a soft porous aluminum washer will protect the bolt and casing, but I can totally see it binding hard with the bolt and casing as the bolt is torqued down.

The good news though is when you go to work that stuck bolt loose.. the weak link is the crush washer, so.. I bet it disintegrates before the bolt or casing gets damaged in most cases.

This does given more possible benefit to applying a little penetrating oil to the bolt/washer/casing and trying it in a few days.

 

[williamsji]

So guys, after procrastinating for a couple months, I finally got around to doing this again. The floor jack idea worked great! Turns out the fill bolt head wasn't really stripping, I just had to hammer the extension in further for it to grab; my mistake. That fill bolt is in a bit of a tight spot for people with big hands.

Thank you so much for coming back and telling us how you solved your issue.

It really helps all forum members when fellow members take time to do this. So, on behalf of the forum members... much appreciated!