Question about the 5500's, 4400's, 5800's

[sw4400]

This is a two part question. First, given the fact that these buses never underwent a mid-life rehab and there is still about I'd say 6+ months of service left for these buses, what happens if one of these buses develops a major problem(transmission failure, engine blowing a piston, etc...), do they just retire those buses that require too much work to put money into? I've noted that several 5500's have been retired according to the Chicago Transit and Railfan page as well as some 4400's and some 5800's. 2nd part: the 4400's and 5800's underwent a mid-life rehab, so why are some of these buses retired?

[trainman8119]

I cannot answer the entire question, but I am sure that part of the answer about premature retirements is that there were buses that were in wrecks that put them out of commission for good.

[Busjack]

You can go by the 77-Perry yard and see some burned hulks, etc. Also, there are about 60 more 7500s than the 4000s and 7300s they replace, so some 5300s (and anything else more than 12 years old) can go.