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Josvin1 · 05-28-2012, 06:20 AM

Hi everyone, I'm the new owner of a '79 Airstream RV ''28.
It's a bit of a project so I have manny questions....
First of all is that the previous owner put a 6,2 diesel engine in and did not change the ratio of the rear axle. Does someone can tell what make the rear axle is and what the gear ratio is?

thanks in advance.

Jos den Ouden

CanoeStream · 05-28-2012, 07:35 AM

Hello Josvin1 -- Welcome to the forums!

Let me change the title of your thread and see if that helps grab the attention of knowledgeable members.

Hang in there -- somebody knows...

Mike Leary · 05-28-2012, 08:58 AM

Quote:

Originally Posted by Josvin1

Hi everyone, I'm the new owner of a '79 Airstream RV ''28.
It's a bit of a project so I have manny questions....
First of all is that the previous owner put a 6,2 diesel engine in and did not change the ratio of the rear axle. Does someone can tell what make the rear axle is and what the gear ratio is?

That's all Chevrolet/GM back there. What is the problem with the coach?

Smartstream · 05-28-2012, 09:59 AM

My 1982 280 has a Dana 70 rear axle with a 4:56 to 1 gear ratio. The rear disc brake axle has larger axle tubes than the drum brake version. These coaches were built back when there was a 55 mph national speed limit so top speed was not an issue. I have the Isuzu diesel which is goverened at 3300 rpm which is less than the 6.2 if I remember correctly. I like many other owners added a Gear Vendors overdrive unit to get the rpm's down a bit and gain some top speed. I might add that previous owners drove the coach for 25 years on the factory ratio with no problem.

Good luck, Dan

Mike Leary · 05-28-2012, 12:36 PM

Our first mo/ho (a 28' diesel) had had a higher ratio rear end installed, which gave it highway speeds, but was a complete mess getting up to speed. The overdrive in our current coach, as Dan suggested, is perfect. With a higher-powered engine, it very well could be a change-out for the differential would work. I have a Dana 70 rear axle w/ disks, as well.

Josvin1 · 05-28-2012, 02:47 PM

What is wrong? I think that because the diesel makes less rpm then a 5,7l gas engine it's a bit slow, about 50mph. It is a 6,2l GM engine and no overdrive on the gearbox.
Other problem is that the wiring is a mess, I need to sortern that out before I go on a trip... The family loves it thou!
Is there a wiring drawing on this site somewhere?
Thanks for all the quick reply

Mike Leary · 05-28-2012, 02:57 PM

Err, umm (an American term for "I'm thinking"). What sort of diesel is it? The new ones are very complicated as far as shift points go. Seems to me, the GMC transmission was re-programmed for the different power curve of the diesel. What kind of RPMs do you show at 50? The wiring on Airstream Motor homes was a mess straight from the factory! Where are you having problems?

Gregsch · 05-28-2012, 06:26 PM

My 1979 24' Argosy has a standard 10" Gm axle. If that is what you have it should be easy find a replacement ring and pipion. They are very common. FYI my MH has a 4.11 ratio. Does it look like this?

Mike Leary · 05-28-2012, 07:19 PM

The Airstream used 10-1/2" ring gears on both the Chev. and Dana.

Smartstream · 05-28-2012, 07:36 PM

Quote:

Originally Posted by Josvin1

What is wrong? I think that because the diesel makes less rpm then a 5,7l gas engine it's a bit slow, about 50mph. It is a 6,2l GM engine and no overdrive on the gearbox.
Other problem is that the wiring is a mess, I need to sortern that out before I go on a trip... The family loves it thou!
Is there a wiring drawing on this site somewhere?
Thanks for all the quick reply

The 6.2 makes 3600 rpm while the Isuzu that Airstream used only make 3300 rpm. The 6.2, the Isuzu, and the TH400 transmission are all mechanical not electronic like the newer versions. Your coach will be slow because of the speed limits in effect when these coaches were built. When driving a motor home you are supposed to be on vacation and not in a hurry.

The wiring on the chassis is made by GM and fairly normal for a truck. The wiring in the coach was made by Airstream. The main connection between the two systems is made to the left of the engine under the drivers seat. It does not seem to be very clearly documented anywhere that I have found.

Good luck,
Dan

Mike Leary · 05-28-2012, 07:59 PM

I think is was the 454 gas engine that was removed, am I right? Otherwise, the transmission is at fault if it had a diesel in it originally.

Keyair · 05-28-2012, 09:03 PM

Getting the rear end regeared should be easy and cost effective.

Talk to these guys?

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Kota · 05-29-2012, 06:33 AM

I've done several engine transplants in 4X4s and classic vehicles. Most have been with complete modern drivetrains. It's a huge project! Especially to do it right. More so if a computer (ECU, PCM, ...) is involved. You really need to put the effort into understanding, designing, installing, and documenting the wire harness to have a reliable and maintainable vehicle. I bothers me that the previous owner went through the effort and expense to do the conversion and sold it. I would suspect that things didn't work out as he hoped.

Here's what I would do. Look at the OEM drivetrain that came behind that engine. Basically, the transmission gear ratios, rear end ratio, and tire size. You can come up with the final drive ratio that GM designed for that engine with any one of several online final drive ratio calculators. I generally try to match that closely with adjustments for intended use. You might find that transmission gear ratios are totally different for the diesel that produces more torque at lower rpms. At this point a transmission swap might be realativly easy and inexpensive way to take advantage of the engine. Possible one with overdrive which might avoid a couple of grand in regearing the rear end.

I'd go through the installation one system at a time and clean up the installation. If the guy used cheap (parts store) crimp on connectors, I'd replace them commercial quality crimp ons with a professional crimping die designed the type of terminal you use. I really like shrink tubing and split looming. The good news is that bull work is done and a little finess and craftsmanship will make it the fun and reliable vehicle you are looking for. You will also gain the understanding to maintain it.

My Cummins powered 36 footer gets 13 MPG. I would think that 6.2 in a 28 footer would do significantly better with lots of get up and go.

Mike Leary · 05-29-2012, 09:22 AM

Fooling around with the trans is not for the timid. (triple click on the picture)

Josvin1 · 05-30-2012, 01:31 AM

Thanks for all the info, I hope to make it reliable as it is and go on holiday with the family
after that I have to decide what to do with engine and gearbox.
O and I have to get my truck divers license first, it's to heavy for a standard license in Holland...I have my test on 12 of june.

jos

ScrapIrony-2 · 05-31-2012, 06:49 AM

Do you have Gear Vendors Overdrive? Might make a difference...

ScrapIrony-2 · 05-31-2012, 06:56 AM

OOPS sorry...the button to shift should be located on the floor to the left of the bright/dim button...it took me awhile ton figure this out...the engine kept shifting to a different speed when I tried to dim the lights...thought I had killed it, for sure...m