Radical upgrade/conversion of a GMC Motorhome

[Ian]

Now I am not sure where this one belongs so I will leave it here and Tom can work out what to do with it LOL

In the last month or so I have fallen in love with an Impossible Dream - the iconic GMC Motorhome. I just love it but chances of owning one and getting it Downunder and getting it converted to suit our roads. Nah, way too hard to even think about although quite a few others have brought them down our way... But gee, that is an awesome design and it was so far ahead of its day when it was produced.

So this gent has been working for the past 2 or so years on converting his GMC so it better suited their needs. What he has ended up with just took the wind right out of my sails.

Look in the comments for some more pictures of the changes and the work going on through the rebuilding process.

I think he has set a very high benchmark but that is just a personal impression.

https://www.facebook.com/groups/classicgmcmotorhomes/permalink/1943461265778401/

 

[SeilerBird]

People keep saying it was ahead of it's time. When is it's time? I certainly don't see any new front wheel drive under powered tiny RVs in my park.

 

[Ian]

From what I can find out it was considered to be ahead of its time though its time was 1973 - 78. Things have changed since then but at the time it was considered to be great. GMC produced over 12,000 of them and about 40% are still on the roads.
Not sure about the power of them. Most of them had the 455 engine which I thought might be good enough. At the end of their run, they went to a slightly smaller engine so maybe that was what lead to the call about power. I have never seen one though we apparently have several of them in our State.
Apparently the Front-wheel drive allowed them to have a lower and cleaner floor level but I guess that is all subjective.

 

[Gary RV_Wizard]

Spacious and elegant for the 1970's, but on the pricey side too.  They got passed by as RVs got larger and less expensive models dominated the growing market for family RVs from Winnebago, Fleetwood, etc.  The GMCs (and the similar Winnie Elandon) were more like mini versions of bus-type coaches, and you didn't see a lot of them around the local campgrounds either.

 

[Matt_C]

Ian,

If you contact the community (there is an actual Oz chapter), I am sure that one of them can tell you what it takes to get one to Australia and use it.  There are 25 of them there already.  Some of the owners write over at GMCnet <http://gmc.mybirdfeeder.net/GMCforum/> from time to time.  Rob, one of our members that lives in Paddington NSW, has two.  The one he keeps in Texas is almost a sequential serial number with the Oz Coach as both are Avion fits. 

Seilerburg,

If you keep an eye out, you will soon see a number of smaller front wheel drive coaches around you.  With numerous manufactures producing vans of such description.  And, those won't be anything like under powered either according to those that have driven them.  Many will have the high altitude advantage of being turbo-diesel. 
Oh, and your 40% number is wrong too.  It is over 60% and that is only those with current registration according to our organizational registry.  I think that isn't too bad for a unit that was last produced over 40 years ago.  Next time you are at an FMCA rally, look them up when you can and then count how many other 40+yo coaches you see there. 
As far as being underpowered, that is not really any issue.  They were geared for a 70mph highway speed and will still do that easily, When DW is driving, I have to remind her to not keep up with the interstate traffic.  It is easy to do, but 70+ gets up down to about 7.5 MPG.  Part of our problem is that GM put the wrong final drive (it isn't a rear end because it is not in the back) and cam in them because that was what they had.  This is easily corrected as better choices are now available.  Our '73 had no problem crossing the Bighorn and that is over 8000'MSL, I am told that the Eisenhower tunnel is a tough one.  But then only a few of us have converted to turbodiesel. 
I have always used  a standard GPS because I don't need to be advised of clearance or weight issues.  I can get to a normal fuel pump if I want to. 
Ours is a 23 and we never plan to throw parties in the coach, so it is a great size for the two of us and two dogs and we don't usually drag a towed because we carry a pair of bicycles that get us to the few places we can't park close to.

See you on the road

Matt

 

[Old_Crow]

People keep saying it was ahead of it's time. When is it's time? I certainly don't see any new front wheel drive under powered tiny RVs in my park.

Pretty sure a 25' GMC with a 455 olds motor in it wasn't under powered.  The several I have driven all had way more pickup than the 29' P30 with a 454 I used to own.
If I was still a weekend warrior instead of a full timer, I'd own one in a heartbeat.  In our travels this winter I shared campgrounds with more than one of those old GMC's(twice in Arkansas, once in New Mexico, and at a casino in Arizona).

Heck, I saw one of those old Argosy coaches that look real similar to the GMC parked out on the Arizona land grant just last week. 

 

[jubileee]

People keep saying it was ahead of it's time. When is it's time? I certainly don't see any new front wheel drive under powered tiny RVs in my park.

Definitely not under powered. Drove a 1973 model ( in 1973 before gas crunch and 55 mph limit) from Oklahoma to California. RV would run with car traffic easily and run off and hide from the truck/bus traffic of the day.

 

[Larry N.]

Definitely not under powered. Drove a 1973 model ( in 1973 before gas crunch and 55 mph limit) from Oklahoma to California. RV would run with car traffic easily and run off and hide from the truck/bus traffic of the day.

I agree it's not under powered. In 1973 I test drove one in Albuquerque (5,000 ft. elevation plus), and it was able to easily scoot up 9 Mile Hill* at 70 mph (with oomph left over).

* 9 Mile Hill is a stretch of I-40 going from about the Rio Grande (about 4,900 ft) up to around 6,000 or so 9 miles west. Here's a picture looking back to downtown from the top.

 

[Ian]

;D Thanks everybody for joining in. Such great interest in this kind of vehicle.

I found the Australian site for the GMC folks and there are at least 2 in my city, probably others too, most appear to be down south of me. Once we get back to travelling around safely I plan on contacting them just so I can see what they really are like.
Some good news I got from their site, IF the vehicle had been made in 88 it would have to be converted to Right-hand Drive and the entrance door swapped to the other side. As the last was made in 78 there isn't that kind of problem. That would leave the electricity that would have to be brought up to code for our 240V system and the gas/LPG/Propane would have to be brought up to our code. Probably also switched over to the individual bottles because our code doesn't let autogas (LPG) to be used for other stuff like heating and cooking and autogas would be the only way to fill that underfloor tank while on a run.

I like the idea of switching the engines and transmission for more modern alternatives but there is also the attraction of keeping it as original and historic as possible. We have a major historic run each year called the Bay-to-Birdwood Rally: http://baytobirdwood.com.au/  To be eligible to run in it your vehicle must be at least 30 years old and be nearly perfect original or restoration (See below). That would be a hoot dressing up in 70s gear (yes, I kept some flairs and wide ties to go with the paisley shirt) to roll up through the Hills for the Rally. So tempting to stay original just for that reason.

Now, this might get even more controversial. I have seen the original documentation and some of the views of various rigs. My favourite layout puts the bed at the rear and the bathroom to the side. I have zero interest in making a bed every night. Or am I being fussy?


The spirit of the Bay to Birdwood is centered around the following:
Ÿ The vehicle has not been modified from the original manufacturer?s specifications or original equipment manufacturer (OEM) options. Minor modifications aimed at ensuring roadworthiness and safety of the vehicle (eg electric starters, seatbelts) are permitted.
Ÿ The wheels on the vehicle are period correct and have not been changed to a wheel style not available at the time the vehicle was manufactured.
Ÿ All motor vehicles must be of a roadworthy standard in South Australia and of an acceptable standard of quality in the opinion of the Organisers.
Ÿ  Trailering or towing of any entrant vehicle from the Start to the Finish is not within the spirit of the Bay to Birdwood and therefore not allowed.

 

[Lou Schneider]

People keep saying it was ahead of it's time. When is it's time? I certainly don't see any new front wheel drive under powered tiny RVs in my park.

The Olds 455 definately isn't underpowered, the problem with a FWD motorhome is drive wheel traction.

A motorhome carries about 2/3 of it's weight on the rear axle and only about 1/3 on the front wheels.  Count the tires at each end to verify this.

This is different than a car which has about 60% of it's weight on it's front wheels, giving FWD a traction advantage over RWD.

 

[Ian]

The Olds 455 definately isn't underpowered, the problem with a FWD motorhome is drive wheel traction.
A motorhome carries about 2/3 of it's weight on the rear axle and only about 1/3 on the front wheels.  Count the tires at each end to verify this.
This is different than a car which has about 60% of it's weight on it's front wheels, giving FWD a traction advantage over RWD.

That is a good point that I had not considered. is it likely to make much of a difference in normal travel situations?

 

[Lou Schneider]

No, but it can be a factor in gravel or dirt/mud or in another slippery situation.

 

[Ian]

No, but it can be a factor in gravel or dirt/mud or in another slippery situation.

ROFL, not that Australia would have any roads like that... well, maybe some are

 

[Matt_C]

Ian,

I am glad that you found the locals. 

I have to suggest that you very thoroughly investigate changing anything in the driveline.  Such changes tend to be problematic and VERY expensive. 

There are two web forums you can follow.  http://gmc.mybirdfeeder.net/GMCforum/ Is the older one and the residents are older also.  Some are original first owners and many have grand experience.  (I am neither.) 
The other is largely a younger and more ambitious group.https://www.gmcmhforum.com/ It is a good read and there is a lot going on there, but less than that first still. 

Then, there are a number of pages of FaceBook that are GMC related, but the information there is best thought of as amusement. 

I will also stop here and lay out some cautions. 
As fun as these old girls are, they are seriously senior.  They do require all the maintenance and attention that everything did forty plus years ago.  Then add the age and mileage. 
While there is currently only one orphan part (the inner tie rod end), sometimes parts can have availability issues.  There are several good places that you can reliably get parts, but they are all on my side of the globe. 

There is amazing support available in North America, but when you make the new friends they will tell you more. 

Matt

 

[Ian]

Thanks, Matt, Gary and everybody for the interesting responses. I have now been part of the Facebook Forum "Classic GMC Motorhomes" for a couple of years and every day I find something new to convince me that these coaches are the way I want to go to get out onto the open road.
Amazing discovery for me, I started chatting with Tom and the originals back in 95-96 when this Forum (RVFOR?) was on CompuServe and I was the sysop (System Operator = Manager) for the Pacific Forum (PACFOR). Sigh. I knew I wanted a Motorhome to see our country, I never could find the $$ nor the right coach for me. Still don't have the $$ but found the coach.

I have learnt some things too. One of the first was that GMC stands for 'Get More Cash'. Who would have thought that was a factor?
Another classic was just the other day, it went something like this... 'GMC Motorhomes don't break down but their owners get very creative in finding places to take a break from driving' LOL
Have missed being a regular and more than likely missed the passing on of some of my old friends from when I was a more regular participant.
I will try to do better with following the posts and stories, you are all still my Framily.

 

[Tom]

I have learnt some things too. One of the first was that GMC stands for 'Get More Cash'.

Ian, I just noticed this one.

Just like BOAT used to mean Break Out Another Thousand. Nowadays, it's 'several thousand'.

 

[Lou Schneider]

Interesing factoid about the GMC motorhome development. When GM introduced the front wheel drive Oldsmobile Toronado in 1966, John Hull, the stepson of Airstream founder Wally Byam asked about buying the drivetrain to use in a motorhome he was developing. GM made him build a prototype and perform extensive tests to verify the Toronado drivetrain would stand up to motorhome use. It passed and starting in 1968 Hull got the drivetrains for his Revcon motorhome.

A few years later GM came out with their own motorhome using basically the same platform and construction as the Revcon.

What's a Revcon? - My Revcon Motorhome.

 

[John From Detroit]

That is a problem with FORD as well.. People design and even patent a product license it to FORD. Ford will make just a couple of minor changes and POOF. they now make it without paying the inventor.
Company my mother worked for designed a self tightening NO SPRINGS Fan belt pully. It was designed so it automatically put the proper tension on the belt adjusting for changes in conditions like temperature. I forget if they tried to sell it to ford or not. But I've never seen such a device in production.

 

[Daveinet]

Interesting observation about gearing. While getting on the freeway, I noticed it accelerated good up to about 48 mph. After that, it seemed to take a lot of peddle to get that last 8 to 10 mph. It got there fine, but took a lot of peddle. Seems maybe what the GMC needed was a overdrive or 4th gear. Could have lumbered along fine and gotten a significant mileage boost. Probably would have needed a lockup TC, which was not developed yet. At that point in time, no one was towing a car, so you didn't need the extra high gear roll on power.
The idea of it being ahead of its time really had the same issues the Revcon did, where no one was asking for an efficient motorhome. Revcon was using a lot of technology that is too expensive for the RV industry, so while innovative, the ideas never took root. Maybe these coaches are still ahead of their time, as if the industry turns electric, it will be critical to build a lightweight, aerodynamic highly efficient motorhome.

 

[Oldgator73]

Coming back. I thought the SR71 start cart used Olds 455 motors so I looked it and found I was mistaken. The start cart originally used 2 Buick 401’s and later went to Chevy 454’s. I saw an SR71 start up at Mt Home AFB in early 80’s.