Quote:
Originally Posted by Mandinee1
I want to add, I think my real biggest concern at this point is the transmission. The mechanic seemed unworried, but I kept pressing him- couldn't this really be a problem? He said he doesn't know what the fluid is, which he said was "all over" the trans, that he spent 10 years rebuilding transmissions and didn't recognize this at all, and yet there was no leak during his entire inspection.
I'm posting a pic if anyone has any input
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Sorry, I'm a little late to the party here, couldn't find this pic in the post right away. I've not seen an Allison automatic up-close and personal before, but having seen a pic of the pan, this looks like the six-speed, at least, the pan looks right from what I can tell.
Let's take into account the symptoms (and lack thereof) here.
Inspecting mechanic states no visible leaks observed (I am assuming they checked with engine running / trans in gear), but states evidence of a leak with residue 'all over' the transmission. Transmission pan appears completely coated, but isn't dripping fluid, at least not at an obvious rate. Pan gasket leaks would drip straight down, or blow backward along the underbody – NOT straight up and over the transmission case.
Also, a leaking transmission pan gasket is likely to drip non-stop until the fluid level drops below the mating surfaces and gasket, whether the transmission is turning or not, so if the transmission is not dripping constantly or slipping due to low fluid, we can rule that out, I think. The transmission output shaft seal could be a possibility here, but I should think that would stand a fair chance of leaking while stationary. I also think residue from such a leak would have inconsistent coverage as well.
Having seen the pic (Angle isn't the best but gives an idea), taking into account that an RE's inverted setup would put the trans pan rearward of the differential, I would say this kind of looks like a differential pinion or possible transmission output shaft seal leaking and blowing back under (and over) the transmission.
Such leaks would not be likely to be evident unless driving, as the differential is under no pressure until moving. However, I'm not sure how likely the transmission is to lose fluid unless it is in gear, and the output shaft might not even leak then unless it starts moving.
But quite simply, a transmission leak is not likely to coat the entire unit, while anything leaking ahead of it is, in this case, the differential. And the pinion input shaft seal is in a good position to blow gear oil over both the engine and the transmission, coating them completely.
And, is not likely to leak when stationary. Combined with the inspecting mechanic's statements of the mess being all over the transmission, and that they observed no visible leak with it running, I would have to lean toward the pinion input seal on the differential leaking, MAYBE the transmission output shaft seal. However, the residue kind of looks like gear oil to me, which would also indicate the pinion input shaft seal.
Whatever it is, it appears to have been leaking for awhile, maybe years. Source of the leak could have already been repaired with no clean-up done after the fact, as a DIYer might not clean the trans pan off after replacing a pinion seal, but I wouldn't bet on it without evidence of a new seal in that area. I wouldn't rule out power steering or transmission fluid / oil cooler lines or fittings, as they could still have slow leaks that might not be obvious. But what I see, at least in my mind, points to the pinion input shaft seal leaking.
Normally, I wouldn't say a pinion seal would be a huge concern if it's a small leak, but there's no way to tell, given the age of the bus (I'm under the impression this is an '03 model?). It depends on how much fluid is leaking. If it's a severe leak that requires topping off the gear oil / fluid frequently, then it needs to be repaired. If not, then it can wait, I suppose. But you never know when an existing leak can get worse, either.
On the surface, it appears to be a small leak that's been there a long time, which would beg the question of how much fluid is in the trans and / or differential. Have they been running low for awhile as a result? A differential has to get pretty low on oil to really damage it, however. I would have the levels checked, as well as for evidence the pinion input seal or transmission output seal is leaking.
If the fluid level isn't that low, and the leak isn't severe, might be able to just put a new seal in it, clean things up, and have at it. And then again, the bus might well make it the entire 1,650-mile trip to its destination without an issue. But given the cost of towing, I think I'd rather fix it before it gets worse, and causes a bigger problem.
I hate to encourage someone to spend more money on a contingency, but an ounce of prevention is worth a pound of cure -- and given that towing a bus is $100 hookup and $10 / mile, BEFORE you spend $1000 repairing or replacing a differential... Especially when this could be used to negotiate the price to offset the cost of repair.
That being said, a pinion seal by itself requires removing the axle shafts, draining the center section of oil, and removing the pinion before the seal can be replaced. In some rare instances, the seal could have worn a groove into the pinion shaft, causing the leak, in which case the shaft might require replacement, or perhaps an upgraded thicker seal to make up the difference could be used, if such a seal is available.
A transmission output shaft seal may or may not require partial disassembly of the transmission. While I'm not totally familiar with servicing Allison units, output shaft seal replacement might be possible without disassembling the transmission, but I can't say for sure from the pics I have seen.
Something that could help in distinguishing where the leak is coming from is to look at the driveshaft, if this bus has one. If there's residue on the driveshaft, that points to the differential pinion seal. If it's dry, then that would point to the transmission output shaft seal.
If there is no driveshaft and the mechanical connection between the trans and differential is nothing more than U-joints, look closely at the area in which they join. Fluid on the entire connection would indicate the pinion seal, fluid on only one side or not at all would indicate the transmission output seal.
Couple other things to check would be the fill /drain plugs for the differential -- if they are loose, the differential could be pushing fluid around the threads. Not likely, but possible.
Also, if the differential assembly has a vent port or tube of some sort, the differential could have been overfilled at some point (still overfilled, perhaps?) and have been spitting gear oil all over through the vent until the level dropped sufficiently. An automatic trans will generally have a similar vent system for the same purpose, and neither would be likely to manifest themselves when stationary.
I've read the OP has persuaded the seller to have a shop look at it. If I'm right about the source of the leak (it would make sense), perhaps they could use this issue to negotiate the price. But I would hardly call it a deal-breaker just yet.
I don't know what the cost of repairing such an issue would be, but I would say it could be pricey -- $1000 maybe? Especially if both seals I mentioned are leaking. Could be a good opportunity to get the sixth gear unlocked while they're at it though, as well as set any speed limiter / governor to a speed of your choosing. And such a leak could be used as leverage to bring the price down -- $1000-$1500 to offset the repair, maybe?
My advice to the OP, if one or both of these seals are leaking, and you can buy the bus for $1500-2500 with the leak and have it repaired for $1000-$1500, it might still be a good buy, if all other systems are good to go. Depends on the scope of the rust I've seen in the pics. If it's just wheel wells, that can be managed. Just my $0.02.
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