I have a 2011 Thor Chateau (31R) on the Ford 450 chassis and started to notice a rear differential leak. The motorhome when sitting will have a small puddle (dollar size after 3-5 days). I am having a hard time finding a repair place in my town or within 100 miles. Does anyone have a DIY for changing the differential fluid to see how big of a job this is IF I attempt to replace the seal/RTV myself?Thank you in advance!

If it's just leaking around the cover, it's pretty easy to fix. Remove all the bolts around the cover, pop the cover off catching the oil in pan, clean off the old RTV, clean the sealing surfaces, apply new RTV, reinstall the cover, torque the bolts to spec, fill pumpkin with the correct gear oil. Might as well switch to synthetic gear oil while you're at it. I use a wire wheel to clean the RTV off of the cover. You can use a razor blade to clean RTV off of the housing and then use a solvent to clean any oil from the surfaces before applying fresh RTV.

From what I can tell, it is the cover that is leaking. It isn't overly bad but it is coming from the bottom end of the rear cover. I have put a wrench and all bolts are tight. I am trying to see if there is an actual seal or just RTV. I can see Grey RTV on the cover now, but trying to make 100% certain.Does anyone know how much fluid would be required to complete the job? Any recommendation on a fluid spec? I was thinking Mobil1 Synthetic Gear Lubricant LS 75W-140. Would that be a good choice?Thank you in advance!

Be careful undoing the bolts. On one of the bolts you might have what looks like a small metal tab with some numbers stamped on it. That is the "axle tag" and comes in handy for looking up info on diff.as example see http://www.fordification.com/tech/rearends_ford01.htm but you'll have to find newer site that covers your year model. google "ford axle tag decoder" Come in handy to know what you have (type and amount of oil, torque etc)

Should be a plug on the side , just unscrew it and put fluid in untill it starts coming out .

Yes, the MObile1 Full Syn 75w140 is good stuff. That's what I run as well. Keeps temps about 30F cooler than other synthetic lubes (I have a diff temp gauge because I run so heavy, up to 25k pounds combined).

Ford 450 Rear Differential Leak Help | Good Sam Community

JayBuchanan
Explorer
Aug 13, 2014
From what I can tell, it is the cover that is leaking. It isn't overly bad but it is coming from the bottom end of the rear cover. I have put a wrench and all bolts are tight. I am trying to see if there is an actual seal or just RTV. I can see Grey RTV on the cover now, but trying to make 100% certain.

Does anyone know how much fluid would be required to complete the job? Any recommendation on a fluid spec? I was thinking Mobil1 Synthetic Gear Lubricant LS 75W-140. Would that be a good choice?

Thank you in advance!
pauldub
Explorer
Aug 13, 2014
If it's just leaking around the cover, it's pretty easy to fix. Remove all the bolts around the cover, pop the cover off catching the oil in pan, clean off the old RTV, clean the sealing surfaces, apply new RTV, reinstall the cover, torque the bolts to spec, fill pumpkin with the correct gear oil. Might as well switch to synthetic gear oil while you're at it. I use a wire wheel to clean the RTV off of the cover. You can use a razor blade to clean RTV off of the housing and then use a solvent to clean any oil from the surfaces before applying fresh RTV.

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Ford 450 Rear Differential Leak Help

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