| Author | Message | ||
| Mike Bennett (Mikehypercube)
Registered Member Username: Mikehypercube Post Number: 1 Registered: 8-2008 Posted From: 81.129.217.60 Rating: N/A |
Hi there, I've got a bus with what I think is called semi-automatic transmission, that is there is a gear selector but the transmission is like an automatic gearbox (no clutch etc.). It's a Leyland Atlantean, a British model of double decker bus from 1979. The transmission seems not to be working. The bus moves forward by about an inch, and when you disengage it rocks back, so the actual selection of the gear seems OK. It did work when the bus was last driven, but it has been standing for some months. Is there some fluid that might have leaked out or some such thing? Could a wheel have locked up? Are there any simple things I could look for or try, that anyone knows about, before I get to the point of calling in expensive mechanics to replace it. Any pointers gratefully received. Mike | ||
| Buswarrior (Buswarrior)
Registered Member Username: Buswarrior Post Number: 1332 Registered: 12-2000 Posted From: 76.68.132.17  Rating: N/A |
Sounds like the brakes aren't releasing. You did release the parking brake? happy coaching! buswarrior | ||
| Bruce Henderson (Oonrahnjay)
Registered Member Username: Oonrahnjay Post Number: 260 Registered: 8-2004 Posted From: 72.12.39.78  Rating: N/A |
Mike, there are three different systems on an Atlantean: 1) A semi-auto system where you move an electric selector from slots for 1 to 2 etc (and R) manually. There is a modular torque converter instead of a clutch. The transmission is very much like an "auto" with shifter bands, epicyclic gears, etc. The electrical signals from the shifter go to a module that has 5 solenoids -- when you select a gear, the solenoid servo opens air to tighten the appropriate transmission band. 2) A system which is very like 1) but has an added on "macro-processor" that takes a speed signal, engine rpm sensor signal, shifter command input and mixes it up to automatically select the gear. It's odd, it takes an auto transmission that's been converted to semi-auto and converts it back to full-auto by adding external stuff. (I call it a "macroprocessor" since it is very British 70's electronics -- about 1/5000th of the computing power of a $5 Walmart wristwatch in a box about the size of large cornflake box.) 3) A shift system with the same basic transmission but with air to a shifter mechanism near the steering wheel. That mechanism mechanically valves air pressure direct to the pistons in the transmission instead of using electrical switching to direct the air. Which do you have? There's a company in the UK that specializes in rebuilding/repairing these transmissions, called Queensbridge Transmissions (Google it) and they have a US rep. www.usbusco.com in Charlotte, NC. | ||
| Bruce Henderson (Oonrahnjay)
Registered Member Username: Oonrahnjay Post Number: 262 Registered: 8-2004 Posted From: 4.153.53.213 Rating: N/A |
Oh, one other thing, Mike. Your transmission won't work unless there's sufficient air pressure -- you'll probably need at least 80 psi in the aux tank. Does the engine seem to "pull hard and bog down a little" when you select first? So, since air pressure is needed to release the brakes (thanks BW, that's a good place to look) and engage the transmission and you don't seem to get either .... (Message edited by oonrahnjay on August 17, 2008) | ||
| Mike Bennett (Mikehypercube)
Registered Member Username: Mikehypercube Post Number: 2 Registered: 8-2008 Posted From: 81.129.217.60 Rating: N/A |
Thanks Bruce, that's a lot of great pointers. I think my system is the first kind - the gear selector is on the side panel rather than by the steering wheel, and I'm not aware of any computers though there are some unused data cables. The left hand compressed air reservoir does leak, I have to run it up for about 20 minutes before the alarm goes off, at which point it sits quite happily at about 100 psi. The engine does seem to bog down a little when I select the gear, though not much - it took me a while to notice the bus creeping forward, at first I thought it was a contact problem. However, I haven't yet learnt to drive such a thing (hence my not having done this experiment at all until quite recently) so I don't have anything to compare with. I've located the air leak, though I'm sure it existed when the bus was last driven as I was there. I'll see if I can patch it up by way of diagnostic. Thanks for the transmission link, there's a fall-back plan if I need it :-) (I am also in the UK). I didn't manage to get to the bus this weekend to try any of that, but I'll let you know what I find as soon as I do. Much appreciated! Mike PS Buswarrior: Yes, parking brake working fine and you can feel when it's released and when it's operated. | ||
| Mike Bennett (Mikehypercube)
Registered Member Username: Mikehypercube Post Number: 3 Registered: 8-2008 Posted From: 81.129.217.60 Rating: N/A |
Update: I've managed to get the bus moving by a couple of meters, but very slowly. It's on a slight incline and I think the brakes may have been sticking a bit, but now it rolls back fine (on a very slight incline). It feels as though there is very low traction. Would this be transmission fluid? If it hasn't leaked out it will be the only fluid that hasn't, only I don't know where to look or what to top it up with. Mike |