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Old 08-04-2020, 03:28 PM   #1
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1981 28' Airstream 280
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Cruising speed?

Curious what a 1981 Excella 280 with the 6 cylinder Isuzu diesel / Th400 will comfortably cruise at on the highway? Is something like the Gear Vendors overdrive necessary for todayís speeds? Thanks in advanced, Ken
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Old 08-04-2020, 05:04 PM   #2
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I drive our 1984 310 at about 55-60 mph turning about 3,000 rpm. Our 1990 345 with a Gear Vendors unit will go freeway speeds at 3,000 rpm, but I keep both coaches off the freeway as much as possible. The 310 is a traffic hazard on the freeway, and state highways are just more interesting to drive. I have seen some discussion here about diesel engines being hard on Gear Vendors units.
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Old 08-04-2020, 05:50 PM   #3
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1982 28' Airstream 280
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We have a 1982 280 Isuzu with TH 400 and Gear Vendors. We did 16,000 miles in 4 months wandering to the east coast and back and 9,000 miles in 3 months to Alaska and many shorter trips in between. We average 62 to 65 mph at 2200 to 2400 rpm. Before the GV max speed was 65 to 67 at 3300 rpm. The noise level was less than desirable. I usually kept it below 55 mph.

I don't like the idea of driving much faster than 65 mph because it is a 38 year old truck and the suspension, brakes, tires and stuff were not really designed for high speed travel. Also because I use it as a recreational vehicle, I like to experience my recreation at a slower pace. I also stay to the right so interstates are not a problem. Most state laws require staying right except to pass anyway.

I did have the GV rebuilt after about 7 years but I did buy it used from a guy who ran it in a Camaro so I can't complain.
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Old 08-05-2020, 08:33 AM   #4
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1981 28' Airstream 280
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Quote:
Originally Posted by Waipio Rim View Post
I drive our 1984 310 at about 55-60 mph turning about 3,000 rpm. Our 1990 345 with a Gear Vendors unit will go freeway speeds at 3,000 rpm, but I keep both coaches off the freeway as much as possible. The 310 is a traffic hazard on the freeway, and state highways are just more interesting to drive. I have seen some discussion here about diesel engines being hard on Gear Vendors units.
it

Thanks for your time and the information, Ken
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Old 08-05-2020, 08:40 AM   #5
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Why hurry? We are retired... took some adjusting to that pace, and more time to relax instead of fixing rattled stuff. Fuel mileage, 2017 2500 HD with Mjolnir in tow, @ 50 MPH, 16-18.. at 60 MPH, 12-14.. But math has never been my winning hand...
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Old 08-05-2020, 08:42 AM   #6
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1981 28' Airstream 280
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We have a 1982 280 Isuzu with TH 400 and Gear Vendors. We did 16,000 miles in 4 months wandering to the east coast and back and 9,000 miles in 3 months to Alaska and many shorter trips in between. We average 62 to 65 mph at 2200 to 2400 rpm. Before the GV max speed was 65 to 67 at 3300 rpm. The noise level was less than desirable. I usually kept it below 55 mph.

I don't like the idea of driving much faster than 65 mph because it is a 38 year old truck and the suspension, brakes, tires and stuff were not really designed for high speed travel. Also because I use it as a recreational vehicle, I like to experience my recreation at a slower pace. I also stay to the right so interstates are not a problem. Most state laws require staying right except to pass anyway.

I did have the GV rebuilt after about 7 years but I did buy it used from a guy who ran it in a Camaro so I can't complain.
Thanks for the information, Iím not looking to set any land speed records! I would just like to cruise 65 to 70 without r the motor screaming next to me. Based on your information I think the addition of a GV would be perfect. Thanks again, Ken
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Old 08-05-2020, 12:12 PM   #7
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The GV is one option, however it is not cheap. You can change the differential gears to gain top speed for a much cheaper price tag however you give up acceleration at lower speeds.

One thing nobody is talking about is power. These old Isuzu's are not known as any kind of powerhouse. They are naturally aspirated diesels that Airstream added a low pressure turbo. It gains a few ponies without destroying the engine.

I can get the 280 up to 73-74 mph, without a lock up torque converter it varies, but the slightest little grade or head wind will slow it dramatically. You are running at WOT ,wide open throttle, but will never reach governed rpm. You are simply asking more than the engine can give. Adding a GV or changing rear axle gears will bring the rpms down and make it much nicer to drive up to about 65 mph but above that it you need to find more power.

I suggest you try to get a ride in a 280 with an Isuzu and GV just to see the limitation before you spend a bunch of bucks and end up unhappy. You are welcome to drive mine but I'm not exactly around the corner.
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Old 08-05-2020, 01:36 PM   #8
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I see on Bob Millerís thread that he plans to install a two speed differential in his 370. He has a Gillis chassis, but is that a realistic option for a P30 chassis?
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Old 08-05-2020, 06:32 PM   #9
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A two speed diff would be great but I don't believe they ever made one. It certainly would be possible to mount one from something else but then you have to deal with the conversion headaches. They are common on the next heavier class trucks but they are physically larger in size and it does get crowded back there especially with a tag axle. Drive line and brakes are easy to connect however the axle might have to be narrowed to clear the wheel well. The wheels won't match the P 30 but I suppose you could cut off the spindles and fabricate and install spindles to fit the P 30 hubs.

Anything is possible, it's just a question of how much time, effort and money you want to put into it. Because of liability it would be tough to find somebody to do it for you making it a self built and installed project. I do agree it would be a great solution.

Just for thought, two speed diffs usually provide a direct and underdrive so you need to find something with a gearset available to provide the highway speed you desire. That is always the challenge in medium duty sized trucks.
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Old 08-06-2020, 09:51 AM   #10
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1981 28' Airstream 280
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Thanks, really great information. I haven’t purchased yet and want to go into this somewhat educated. Could I trouble you for a phone conversation? Since the test drive is a bit far. I really like this old rig and think she should be saved. Thanks Ken kolzewski@comcast.net
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Old 08-06-2020, 08:51 PM   #11
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Email sent, check in case it winds up as junk or spam.
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