First, in response to RVDude, I would love to DIY this maintenance but I'm still full time employed for at least another 8 years and don't have time to do this work. Paying the shop to to the work is worth my time. In fact I sit in a shops lounge and telecommute via wi-fi which is ultra geek efficient
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Okay..here's the summary on the maintenance cycle and how things might be approached differently for some of us.
Went to Pacific Power Products
http://www.pacificdda.com/ for Allison MH 3000 36 service months maintenance. They are the biggest, and by all accounts the best, Allison distributor and service centers in the Pacific Northwest.
The service manager walked me through Allison Service Information Letter 10-TR-99-rev_F (full page
http://pacifier.com/~jcp/Allison-SIL...Rev_F_full.jpg) which on the surface mirrors what we have all read and understood about initial Gold Filter replacement at 36 months and Transynd fluid changed at 48 months as applies to most of our rigs as they came from the factory . So far no surprises.
BUT! There is a note in the letter which says the preferred method for determining when you should change fluid is based on fluid analysis and the 48 month/4000 hours/150K miles is to be used when fluid analysis isn't available (enlargement of note
http://pacifier.com/~jcp/Allison-SIL...lysis_note.jpg). The intent here is to say the fluid should be changed when it needs to be changed which could be more or less than 48 months.
The service manager continued to say that even for lightly used motor homes the big deal is moisture but Transynd has turned out to be so resilient they have a lot of customers at 5-6 years and 100K miles and the fluid is still good.
So I went with their process (yes I got the High Cap filters) and saved myself $350 (for now). Allison uses Horizon 3 for fluid analysis. My results will be posted at
http://www.trackmysample.com in 2-3 weeks using a tracking number supplied by the shop (see
http://pacifier.com/~jcp/Allilson_fl...s_tracking.jpg if you want to look at my results when they are available).
My summarized interpretation of this alternative as presented to me is analyze the fluid starting at 36 months when the filters are changed and then every year until it's changed, then start again when the filters are changed again (48 months in my case since now I have the High Cap filters). The analysis is about $45 with shop labor and $25 if DIY. In theory for the first fluid change you would probably save $$ by deferring to later.
One improvement to this alternate approach I'm thinking about when it comes time to change the filters again in another 48 months I'll pull enough fluid to send it in for analysis on my own BEFORE the filters are changed.
Putting on the devil advocate hat what if they change the filters and do the analysis and then find you need to change the fluid immediately. Then you have to pay for and change the filters a second time. So to RVDudes point with the High Cap filters putting fluid and filters on the same 48 month cycle you can consider paying for the extra 8 gallons of Transynd @ $40/gal (plus tax) and replace all the fluid as a simpler approach with less to remember with every thing on the same 48 month cycle?
NOTE: While compiling this post I notice the Allison Service Information Letter is for transmissions prior to specific serial numbers which can be seen at the top of the letter. My guess is the units after these serial numbers came with High Cap filters from the factory and have filter/fluid baseline cycles that are identical (e.g. 48 months) as they come from the factory. Next time I have a chance I'll go back to Pacific Power Products and ask for the SIL for the newer transmissions.
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