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Old 12-02-2005, 02:19 PM   #1
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Question "Overdrive" for 370

(I suspect this topic has been covered in another thread, and if so, please just direct me to it.) Has anyone had any experience with places like Gear Vendors who sell "Overdrive" gears for 3-speed trannies? I have a 1989 370LE, new to me, and the Gillig axle ratio is right at 5:1, which means the 460 with the C6 Ford tranmission is screaming at anything above 60 mph. The coach has less than 17,000 original miles, so it's no where near needing work that could justify doing this to repair and maintain the present system. I can live with it, but there are times when you need to be able to run faster than that on the interstates just to stop from holding people up. Is adding an "overdrive" worth the money? About how much would that cost? Has anyone done that who could give me advice? Thanks in advance for any help with this.

Noiva
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Old 12-02-2005, 03:12 PM   #2
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Novia, I'm not sure about the price for the Gear Vendors setup but one thing for sure I do know is that a lower turning engine is better in a lot of respects. I'm blessed with a 3.73 in the AS I've got. You will likely spend in the area of $2500 to $3200 if memory serves. That's a lot of cash if you don't do much mileage. If you intend to do a lot of traveling you may well justify the expense. Less fuel, less wear, quieter....
Another less costly way is to change the rear end ratio. I know that the 460's have lots of power and other than burning exhaust valves are pretty stout. You are much longer so I'm not sure the ramifications of this on your chassis.
I'd still love to have just one more gear, or 500 rpms of releif at highway speeds. I don't like to get up over 3000 rpms so limit my speed to about 65-70. Would love to do that at 2400-2500 rpms.
BTW I broke 10mpg last night on a fill up!! 10.1 in fact.
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Old 12-02-2005, 11:07 PM   #3
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Glen,
I was pretty sure the cost would be prohibitive. The axle gear is another issue. Since Gillig made the chassis I've been led to believe the gear is theirs, but I think I'll try to find out. As much as I love this unit, the mixture of Airstream, Gillig, Ford, and Chevrolet all in one vehicle makes for some strange issues. It all seems to work well enough, and the interior/exterior are as beautiful as I've seen, but these mechanical issues can be a killer. There are some things that aren't covered under the Airstream manual nor the Gillig manual. There's even a note to call for assistance if you can't figure out who is responsible for a given item. Of course, that was for 1989. No one wants to take the responsibility now. I could live with this for many years, but I agree the real answer would be a true overdrive 4th gear. Anyway, I'll try to see if there's any realistic chance of changing the axle gears, but I'm not very optimistic. I guess I'll adopt the motto that "Slower is better." Thanks for responding.

Noiva
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Old 12-02-2005, 11:09 PM   #4
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By the way, congratulations on the mileage. I get about 8, and I'm told that's pretty good for this rig.

Noiva
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Old 12-04-2005, 09:41 AM   #5
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novia,
Have you looked at the Gear Vendors website? I am most likely going to get one for my Ford PSD monster truck. I have a relative that installed one on his older gas MoHo and loves it. I like the idea of being able to split gears on the diesel. I would give them a call and see what they have to say. From best guess I would say it is going to run you close to $4k or a bit under. They do list pricing on their website. What Chevy parts do you have on your Gillig Chassis? That C-6 tranny is a beast, I have had them go over 100k under heavy use with nothing more than a heavy duty clutch kit and program kit installed.

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Old 12-04-2005, 10:51 AM   #6
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Aaron,

Thanks for the tips, and the assurance of the C-6 tranny. I just studied the Gear Vendors site, and it certainly looks like they have what I would need. Now I just have to figure out the money angle. I'm giving this MH a year of use to be absolutely sure I want to stay with it. In the meantime I'm hanging on to my 30' Avion(sorry) trailer and 2500 Suburban. Ultimately, something's going to go, and if it's the trailer that's when I could conceivably do the gear thing. Thanks so much for the help. If you think of anything else, please let me know.

Noiva
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Old 12-04-2005, 11:04 AM   #7
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Novia, my mind went numb when you said angle drive. It never ocurred to me that the Gilligs had angle as I thought that only came into play with rear engine setups like the old highway buses.(edit, oops I misread it and thought you had said angle instead of axle.) never mind
Your mileage is pretty good for the length/weight of the coach. Has it had any modifications done to exhaust or ignition? I believe the carb/headers/exhaust redo on my rig have helped me obtain the great fuel economy I have.
I love my vacum guage. It lets me know when I'm being too agressive on the throttle. I've been looking at digital flow meters from Navman as another monitor of fuel consumption.
I'm still on my way to a new Mallory ignition setup but just the electronic box and distributor, not the manual timing deal. But now with a new coil in my old distributor I'm going to wait till spring likely.
The next big job is likely a repaint of the topside of the bus. I'm very seriously looking at chrome paint for the topside. I have no desire to maintain a polish job but would like it to be bright.
The bottom line is that this is a business expense for me and as I'm running up the miles it all seems to work out.
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Old 12-04-2005, 12:09 PM   #8
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Glen,
Boy, you had me worried I had written ANGLE instead of AXLE. Anyway, I have a vacuum Gage on the dash, and I use it faithfully. I towed in the pre-electronics days, and I learned to use a vacuum Gage as the key measure of strain on the engine. Mileage is definitely better when I keep it above 10, and around 12 is even better, but harder to get. I have no modifications to the stock setup, but there are several things I have discovered. Headers won't go in the engine compartment. I tried to switch to them when the stock ones started leaking, but the clearance and heat problems made after-market ones impossible. The exhaust is stock except the new one from several years ago has no crossover pipe. Not a fatal error, but I intend to get it put on. The carb is original also. Since I use the vehicle for travel (camping) only, changing these kinds of things probably isn't cost effective until they need replacement. The engine/drive train are fine, run well, and are in excellent condition. The low mileage means I probably have some years before replacement things will be cost efficient. I am going to investigate an overdrive as discussed above once I determine to sell the Avion trailer. The low rear axle gearing is great in town and climbing mountains, but I desperately need a higher gear for cruising at highway speeds. I have to make myself run about 60 mph or the engine starts to go over 3000 rpms - where it is obviously not supposed to be. The manual says you can run at up to 4500 rpms at steady speeds, but that's just not correct. No big block should rev that fast.

Roof - I don't know what I'm going to do with mine. The whole unit was redone outside at Jackson Center in 2002, and the plasticoat on the roof is already falling off in sheets. Sides don't appear affected. What do you think? I'm thinking of just waxing the roof areas more than the rest of the body, and leaving the plasticoat alone. It looks good, but up close you can tell it's peeling.

Please let me know if you have any ideas or suggestions. I have enjoyed reading about your adventures with the funeral coach. Thanks for the help.

Noiva
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Old 12-07-2005, 07:19 PM   #9
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Novia, it sounds like you've likely got 456 rears. Most moho's of our vintage had these. My old Champion came with 410's and did better but the 373's in the funeral coach give me a solid 69mph at 3000 rpms.
It might be more economical to look into dropping the ring and pinion for a lower number.
One could only hope that your G frame has a Dana rear end. Have you researched that part of it yet?
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Old 12-07-2005, 08:53 PM   #10
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Glen,

The info on the rear axle ratio is in my Gillig manual. I have not gotten around to locating whether it belongs to Gillig or Ford - since it's a Ford engine and tranny maybe the whole driveline is Ford. The Gillig manual lists 2 ratios for this coach, but gives no help in how you determine which you have. Bad news is that one is like 5.33 and the other is almost that. Lowest gears I've ever dealt with. My Suburban has a 4.10, but of course it doesn't weigh over 17,000 lbs. It does, however, have an overdrive, of course, and that makes all the difference. I'll do some more research and see if I can determine for certain who made the differential. That may(?)help, I'll keep you posted. By the way I get exactly 3000 rpms at 60 mph. Anything over that and things get dicy. To may revs, too hot, too much strain on all the rotating stuff.

Thanks for taking the time to write. Always helpful.

Noiva
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Old 12-08-2005, 08:41 AM   #11
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Quote:
Originally Posted by GlenCoombe
Novia, it sounds like you've likely got 456 rears. Most moho's of our vintage had these. My old Champion came with 410's and did better but the 373's in the funeral coach give me a solid 69mph at 3000 rpms.
It might be more economical to look into dropping the ring and pinion for a lower number.
One could only hope that your G frame has a Dana rear end. Have you researched that part of it yet?
Glen - any idea if 3.73's are available (and where?) for my '77 Argosy 20'? I'd LOVE to drop down from the 4.10 slugs that are in there now! That thing pulls like a mountain goat right now, and I'll never tow anything but about 100 pounds of bicycles, so the 3.73's might allow me to keep a TH400 in there. . .
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Old 12-08-2005, 09:25 AM   #12
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Quote:
Originally Posted by noiva
...The info on the rear axle ratio is in my Gillig manual. I have not gotten around to locating whether it belongs to Gillig or Ford - ...
If you're lucky, it may by attached to the differential...
Crawl under the MoHo, there should be a tag secured by one of the differential cover bolts that looks like this (Picture 1).

The tag can be intrepreted as

41 teeth on the main ring, 9 on the pinion.

41/9 = 4.555556 (4.56)

The second pic is of the one ton Dana 10 bolt dually (4.56) axle under the '87 345 Motor Home.
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Old 12-08-2005, 10:51 AM   #13
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Ganzman, Dana parts are NAPA or Chevy or Summit Racing. Finding someone to do the swap is the key. It's not just slip one out and slip in the new. They often require shimming to mesh just right. Unless you've done it before and have the right equipment it is best left to the pro wrench.
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Old 12-08-2005, 05:18 PM   #14
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Novia, just got back from the local Wal-Mart and filled up after my drive home last night. I moved quicker than usual trying to stay ahead of a trucker pulling a FEMA trailer and was running the generator. Ran about 3100 rpms at times, speed around 70 mph. When I put the calculator to work it said 8.7 mpg including the generator running. The savings being able to run at more conservative RPM while not getting run over my be worth reducing the rear axle ratio on your chassis. Even if you manage to get down into the 4:10 ratio the savings could more than pay for the work in a couple of years.
One consideration I did not mention in my earlier post was that a drastic change in ratio sometimes demands replacement of axle shafts as the splines may not match the new ring and pinion.
One way or the other reducing the RPM's is key to enjoying the coach more and for longer.
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