The 5-speed manual tranny in my 1990 F-150 works ok, but doesn't shift into gears as easily as it once did. I guess the synchonizers are wearing out. It also makes a "whirring" or light "howling" noise that's noticeable when the truck is not moving and I let out the clutch with the tranny in neutral. I'm sure it's just some worn input shaft bearings. It doesn't do anything else more severe than that (such as popping out of gear or grinding gears, etc).
How difficult would it be to rebuild it myself? I am a fairly skilled mechanic, capable of rebuilding and installing engines, but I don't have a feel for how difficult it is to rebuild a manual tranny. My garage is equipped with calipers, micrometers, dial indicators, feeler gages etc., but I don't know how delicate an operation it is, what I should expect to find wrong with it, etc.
Also, what range of costs should I expect to incur? How about the cost if I just hire it done?
If the shifts feel stiff, but there is no "crunch" as it goes into gear, the synchros are probably OK. Check to ensure that the clutch is not low on fluid and is fully disengaging. If the trans fluid has a lot of miles on it, consider a fluid change to Mercon V. The M5OD in my Explorer shifts a lot nicer with Mercon V than with the 80000 mile fluid that was in it.
If you are determined to go ahead with the rebuild, you can probably do it. You will need a clean, organized place to work. You absolutely must have the documentation on how to do it. An exploded view of the trans, as from some parts manuals, is also handy, as sometimes the overhaul manual isn't so clear on the positioning of shims, thrust washers, etc.
I haven't done an M5OD, but have done a GM trans. You may need some special tools and a press. Typically, none of the assembly/disassembly operations are particularly delicate, but there are a lot of parts -- more total internal parts than an engine if you count all the teeny little needle bearings.
The M5R2 is fairly straight-forward to rebuild. I'm doing the ol' 4x4 conversion and recently rebuilt an 'out of truck' tranny for the swap. This part's funny... I took it all apart in about 3 days, but after inspecting it all I realized i needed a new counter shaft/cluster gear. A year later, I finally get the shaft, get it all put back together in about 3 days. That's no more than 4-8 hours a day. More like 4 hours/day.
There are 2 bearings to press on, and one sleeve/bearing race that also needs to be pressed on the counter shaft. There are 2 ball bearings on the 2wd version (one on the 4wd), that will go running off on ya if you're not ready for them to pop loose. The nut on the end of the output shaft, as well as the counter shaft, both have a detent 'lock' to keep them in place, so you'll want to get new ones of those. However, I only got a new one on the output shaft, and was able to reuse the one on the counter shaft. All bolts are into the aluminum (ie soft crap) case, so not a lot of torque is used to tighten them down. The two nuts on the shafts I snugged until I had a nice preload on the bearings, but I don't have a manual giving specific torque numbers, so I'll admit I was guessing there.
I have some exploded view diagrams from the dealership, as well as a link to a website with a detailed view of it.
PM me if you'd like those.
Overall, I'd say it was a great rebuild on my end. Hope it goes the same for you.
Well, thanks to all for the great replies. I think I may just pass up rebuilding the tranny myself. I'm sure I could do it, but I don't really have the time to do it. Of course, it's not really urgent right now anyway. I'm confident it can be driven for quite some time as is, as long as I just take it easy on it when I shift.
I know the trouble it's having is not the clutch, as the clutch, pressure plate, throwout bearing, pilot bushing, slave cylinder are all new. And the tranny acted the same with the old clutch parts before I replaced them.