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rick lohrey
Active Member
27 Posts |
 Posted - 09/05/2011 : 1:40:28 PM
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| Sorry if I'm in wrong forum, however, ou are the experts. New to this forum, it's great. I'm looking to buy a bus for rv conversion. Which is the best drive train? Whether front engine, or pusher, there are quite a few types, which ones perform and last the longest? Most importantly: which ones to avoid? Things such as 'cavitation' can ruin one's day. I've heard of engines 'eating' trannies. I'm leaning toward front engine, leaving the rear for bike storage. We hope to go anywhere an rv can, flat interstates to the Rockies. I've never worked diesels and the hp ratings seem low for that much weight, but the must perform well, or there would not be many out there. I understand gearing and rearend ratios, just have no experience with which is best? Is 70mph on flat surface as a cruising speed unrealistic? I know there will be differing opinions on this, but I'll read them all. I suppose dependability is top priority. Appreciate all help! |
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08 Thomas EF
Top Member
533 Posts |
Posted - 09/05/2011 : 3:08:27 PM
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I'm not an expert, but just to echo some highlights that have been mentioned already --
Generally the inline 6 engines are considered more durable and stronger than V8s. Go for a DT466 instead of a 7.3L / T444E, if it's AmTran we're talking about. Mechanical engines (mid '90s and earlier) are more desired than the newer electronic ones. So go for a DT466 rather than a DT466E (beware that some DT466Es were labeled as DT466s on the badges on the hoods of conventionals). From what I've seen the DT466E is a good engine (so is the T444E, just not as rugged), but most people say non-electronic is better. The DT360 is a great engine, too.
Also accompany it with a transmission like an MD-3060 or MT-643 or manual. DT466s do not like 545s... that's likely the "eating" combination you've heard about. We have 6 '01 AmTran FEs with DT466Es and 545s and 2 or 3 of them have had transmission replacements in the past couple years.
Blue Bird and Thomas transits are considered more durable than AmTrans. If you are going with one of these, the engines I mentioned earlier won't come with them. Instead they'll have Cummins 5.9 or Cat 3126 or 3116 or... whatever they had before that (I haven't been around for that long  ). I think Detroit might have gone in the Thomas ERs, not totally sure about that though.
My personal opinion here -- air suspension would be desirable so everything inside doesn't get shaken up as badly, like stuff in cabinets and the woodwork and plumbing itself.
Here's some information on Allison automatics:
http://www.schoolbusfleet.com/forum/topic.asp?TOPIC_ID=21674
Here's some gearing information:
http://www.schoolbusfleet.com/forum/topic.asp?TOPIC_ID=21556
A speed / engine RPM calculator to toy around with (for tire revs, use 504 for the 11R22.5 tires, most buses come with those if you weren't already aware of that):
http://www.cwis.net/~mallie/page12.html |
Edited by - 08 Thomas EF on 09/05/2011 3:09:08 PM |
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JustinB
Advanced Member
United States
490 Posts |
Posted - 09/06/2011 : 06:13:22 AM
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I will echo the in-line 6 (L6) configuration.
DT466
DT466E (make sure that ther is no combustion "miss" & that the overhhead valve adjustments have been done as prescribed.)
DT360
Cummins B5.9L Mechanincal
Cummins ISB (5.9L & 6.4L Electronic)
Cat 3116 mechanical
Cat 3126 Electronic
Cat C7 Electronic
Mercedes MBE906/904
Transmissions
Allison MT640 series (642, 643 etc)
Allison MD3060 series
Allison 2000 series
Allison AT545 caveats:have a rebuilder put in a full lock-up torque converter. The continual slop-along of the original generates the heat that kills this model. Torque input is limited & thus the engine hp/torque ratings will be too. Too much torque input & they explode internally.)
Gearing: Play with the tire size & rear end ratio for the bus to cruise comfortably at 60-65mph. Most older buses are geared to be beating their head against the rev-limiter at 58-60mph. Not a good combination for fuel economy or longevity in an RV.
Cummins B5.9L Mech is happiest cruising at 1800-2100rpm
Cummins ISB is happiest cruising at 1800-2000rpm
Cat 3116 Mech is happiest cruising at 1800-2000rpm
Cat 3126/C7 is happiest cruising at 1700-1900rpm
Mercedes MBE904 L4 is happy from 1600-2100rpm
Mercedes MBE906 L6 is happy from 1300-1900rpm |
I may not know the answer but I can usually find who does. |
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rick lohrey
Active Member
27 Posts |
Posted - 09/06/2011 : 1:40:13 PM
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| Wow, this is exactly the info I'm looking for and I thank you, very much. I appreciate your time and experience. |
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bwest
Administrator
United States
3820 Posts |
Posted - 09/07/2011 : 05:41:12 AM
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| It's really interesting to hear what people think is a good combination when you ask. The problem with most school bus guys is we don't see that much over the road running on our units. The reason I mention this is because you should be cautious when changing the application of these units. Yes I know there are many out there doing this and I'm sure it works. That being said I think one transmission I would stay away from is the AT545 Allison. This is a trusty route tranny but I have a feeling it would not last up and down the rockies. I live in a flat area and really don't have a clue as to what would hold up in those conditions. Also I would caution you on the 3116 cat. One situation I ran into was when a church camp bought one of our buses. They ran it for a couple of years with no problems. Then they started taking it on long trips (200-300 miles) All was well until the old trusty 3116 Cat gave out. I can't remember what exactly happened but to say the least I was surprised. So the moral of the story is what will work in one application may not work in another. Good luck in you adventures! |
Bryan |
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JustinB
Advanced Member
United States
490 Posts |
Posted - 09/07/2011 : 08:05:49 AM
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I will give points regarding the reliability of an AT545 in a linehaul application. The biggest killer of the AT545 in steady-state operation is heat. The heat is generated because there is no full-lock-up feature on the torque converter. Slopping along & motorboatiing for hours on end will create the severe overheating issue that kills transmissions.
Two things can assist in preventing heat related failure in a line-haul application for an AT545. #1 is a full lockup tor converter. #2 is an additional air-to-oil fluid cooler.
Every engine has its foibles and failure points. The keys are to verify that these issues have been consistantly addressed prior to major progressive damage and how to address/manage/minimize these issues under your ownership.
When it comes to used equipment, verification of proper service and qualified visual inspection are the next best things to mechanical prophecy. I have yet to see the spiritual gift of mechanical prohecy listed in the scriptures. Stick to verification and visual inspection.
Used equipment always carries risk. Sometimes the expense of new equipment minimizes that risk... |
I may not know the answer but I can usually find who does. |
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bwest
Administrator
United States
3820 Posts |
Posted - 09/07/2011 : 09:58:47 AM
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| LOL, I like your comment on "spiritual gift of mechanical prophecy"! And probably equally as funny is the comment about "sometimes" the expense of new equipment minimizes the risk. Without a doubt that is a true statement! "Sometimes" can't stop laughing! |
Bryan |
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JustinB
Advanced Member
United States
490 Posts |
Posted - 09/07/2011 : 10:10:29 AM
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I may not know the answer but I can usually find who does. |
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rick lohrey
Active Member
27 Posts |
Posted - 09/07/2011 : 6:32:44 PM
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Great info! I thought city vs highway would make a difference. I may be oversimplifying it, but I relate mountain driving to city, or a lower gear ratio needed. But, I'd rather not gear so low that top speed is 55-60mph. Is there a compromise?
On a more specifice note: I've found a 1968 GMC equiped with a Detroit 6v92 and 4speed manual trans. I've heard the 92 series did not come out until '89. No one listed a DD 6v92 here, does this mean it should not be considered? What is the power band of these engines? I DID say I was leaning toward a front engine, but it seems that all front engined buses would be geared for city. There are pluses to a pusher chasis and I am condsidering it an option. Best I've been able to tell, this bus is either a 4503, or a 5303. It may be a 'suburban' as it has no 'standup windows'. These buses came with either manual or, auto trans. My question here, is will an auto trans fit? I think the old (original) auto trans were 2speeds. How much larger would an auto 3 or 4speed be? and would it fit? Also, that brings up linkages...more headaches? Might be better to stick with the manual 4speed. Are transmissions in pusher buses actually transaxles and if so, can the gear ratios be changed, again...how much headache.
I also got a chuckle out of 'spiritual gift of mechanical prophecy'! Lacking that, where in NE Texas could I take this bus for a shakedown, or expert checkout, if there is such a thing? The owner claims and I quote, "It drives great and being air-ride on the ft. and rear, it just floats down the highway and man is it fast." The owner hauls otr in his truck. I plan to 'test drive' this bus this week or, early next week. Unless a 6v92 is a bad risk?
Thanks again guys, I apreciate the advice.
Rick |
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eddo
Advanced Member
USA
311 Posts |
Posted - 09/08/2011 : 10:11:06 AM
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my experience: a well maintained DT466c can easily last 500,000 miles. Non-electronic engine, full load, not too many hills, had a AT643 behind it. It was an 1987 IHC, and was solid for many years. The re-man engine however, was a pile of junk and only lasted 250,000 miles.
the DT360s are a very nice engine (mine are 1990's.) I have seen these go 500,000 over the road miles as well. Not as loaded as the DT466c was, but still a god performer.
The DT466E's tend to be a whole lot less reliable, in my experience. I have a truck (98 IHC) with 600,000 miles on it now, and it's on it's 3rd engine (although the last one was replaced under warranty.)
I have one AT545 that went 600,000 miles, and one pushing 550,000 now with no issues on them. again, all over the road driving, and both behind DT466E's but doing well.
My actual experience is with IHC's, so I can;'t help ya much with the GMC. Good luck to ya! :) |
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JustinB
Advanced Member
United States
490 Posts |
Posted - 09/10/2011 : 1:19:41 PM
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| You are looking at some vintage erquipment on that equipment. My experience is deliberately limited on 6-71 & 6V92 Detroit Diesel product. If you are looking at old transit product, it is likely gear bound and it has a lot of potentials to go wrong. Transit buses are not a K.I.S.S. concept of engineering. |
I may not know the answer but I can usually find who does. |
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bus724
Top Member
USA
1609 Posts |
Posted - 09/11/2011 : 06:49:47 AM
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The GMC you're looking at is a transit bus, and doesn't have much in common with the school buses that most on this forum are familiar with. You might have better luck contacting people who work for a transit museum. The Seashore Trolley Museum in Maine has a collection of buses including several from that vintage. I know a few of the people who work there and they can probably give you some good advice. Their website is http://www.trolleymuseum.org/
The engines in those were set up in a "V-drive" configuration, with the engine mounted sideways on the left side of the bus and a transmission with an angled output mounted at the right side. 3-speed automatics were available to fit this configuration, but you're probably not going to find one outside of a transit/coach bus application. Transit museum people would probably be able to help you there too. A V-730 would pair up nicely with that 6V92, it was very popular with 6v71s, 8v71s, and 6v92s in the 80s (and later evolved into the electronic V-731). The 92 was probably a repower. If you can find a V-730 and want to avoid a linkage, there was an air-solenoid shifter mechanism available for those, but the ones I've seen haven't always been reliable.
Since it's a 68, I'm assuming you're looking at one with the "Fishbowl" styling (6-piece windshield)? Great buses, and if it's in good shape and mechanically sound, I'd definitely recommend it for a conversion. I toyed with the idea of saving up for one of those for my own RV conversion instead of a school bus, but I got a great deal on a rear-engine skoolie at auction. The only thing I don't like about my bus is that she has the dreaded AT545 mentioned above, but now that Justin tells me it's possible to retrofit a lockup converter on that, I may look into doing so. |
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rick lohrey
Active Member
27 Posts |
Posted - 09/11/2011 : 2:08:08 PM
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Wow, you guys are a great help, thanks. The bus in question bothers me due to the age. New engine, or not lots of miles mean lots of $ in repair/refurb. It seems I should go back to my original idea, a school bus. I'm slowly working through your info along with other forums concerning the actual conversion. It occurred to me that transits are probably only shut off once per day, unless it's 'broke', or a pm is scheduled. School buses, on the other hand, being 'pick up and deliver' are generally operated twice a day. Obviously, the overall miles the bus has made is important in other areas, too. Drive trains are my first question, I'd rather be rolling with no a/c than broke down w/ac. Still, in ya'll's opinion and considering pm schedules, ease(or, lack) of maint being considered as well as realiability issues, which would be your choice: front or rear engines? The aestetics(sp?) of the transits offer a much wider variety of style, but style doesn't offer help when on the side of the road. I understand sensors...well, to the point that they are needed to appease EPA as their main asset; mph increase, if any is secondary to getting it legally on the road. For my intended application an fe offers area in the rear to carry a motorcycle accesible from side or rear and generally fit in better with any floorplan that would carry a bike. A friend has a bike trailer behind his rv and I would like to avoid that...just more mechanicals and basically another vehicle to buy tags and tires for. The re on the other hand could have a platform fitted on rear for a bike, but would need to be easily removed for engine access. The bike is not a must either, but it beats towing a second vehicle, hands down. I will muddle thru all the pros and cons after I've gotten enough info on engine/trans first and general bus second. If I haven't said it before, I'm not stupid, I'm ignorant concering these topics. Ask me about repairing any machine in today's industry and I'll likely have a correct answer as I've spent the 26yrs since my 4yrs in the Marines doing industrial maint. And the Corps trained me (right out of high school) for 'automotive electric' tech). Your input is not being wasted. Thanks.
Rick |
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bus724
Top Member
USA
1609 Posts |
Posted - 09/11/2011 : 3:19:19 PM
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Don't let high miles scare you. While most school buses are only expected to last for 10-12 years and 200k miles (expected, I know there are plenty out there that have far surpassed this), with transits I've heard of 500,000 in a 12 year life cycle. Tractor trailers and coach buses can go for millions. I've seen plenty of transits from the 60s with only 2 or 300K, which are still structurally and mechanically sound.
As for a school bus conversion, FE versus RE depends on your own needs. I would (and did) go for RE because the ride is quieter up front, and the longer wheelbase gives you a smoother ride. REs are also easier to work on, as they usually have a large, open engine compartment the full width of the bus. FEs are loud and hot in the front, and a pain to work on because they have to cram everything under the "doghouse" while still allowing room for the driver's seat and entry. FEs have a shorter wheelbase (rougher ride, but better maneuverability), and access from the rear as you mentioned. |
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JustinB
Advanced Member
United States
490 Posts |
Posted - 09/11/2011 : 5:09:17 PM
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I would be choosing between an RE and a convnetional in a school bus. An FE transit has always impressed me as the worst of both worlds. If you do go with an FE, find a great case quantity seal on kneepads, you'll need 'em every time you work on it.
Keep an eye out for structural corosion on anything that you buy. The old transits were built with less steel & more SS & aluminum. Wiring will likely be your greatest challenge on older equipment. When it comes to vintage equipment I tend to prefer western, desert or non-coastal southern domiciled equipment. Get underneath and check out the structural x-members, body framing and wheel well support structure. Don't be afraid to walk away from polished turds that may soon become basket cases. Remember, old RE city transit buses are essentially unibodies. |
I may not know the answer but I can usually find who does. |
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bwest
Administrator
United States
3820 Posts |
Posted - 09/12/2011 : 10:02:39 AM
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| Bus 724, thanks for the Trolly Museum link. It was quite interesting. Didn't have may pictues of their bus collection though. |
Bryan |
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IBTMech
Top Member
USA
973 Posts |
Posted - 09/12/2011 : 4:02:27 PM
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If you're ever in the Northeast, a visit to the Trolley Museum is worth your time.
A friend of mine spent many years there rebuilding those big DC motors for the trolleys.
As far as those old 2 cycle Detroits go, the 6V92s are pretty tough, giving you up to 300 HP. |
If it doesn't fit, FORCE it.
If it breaks, well, it needed replacing anyway.
Pullin' wrenches for 45 years. |
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bwest
Administrator
United States
3820 Posts |
Posted - 09/13/2011 : 11:31:33 AM
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| Not much of a chance of me going that far from home. Suposed to go to DC this comming summer but time will tell. I have a soft spot for historical machines specifically & history in general. If those things could talk! |
Bryan |
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Wolf0r
Top Member
USA
2181 Posts |
Posted - 09/14/2011 : 07:56:11 AM
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6V-92  |
“The good thing about science is that it's true whether or not you believe in it.”
Neil deGrasse Tyson |
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Best drivetrain
