The RV Forum Community

RVing message boards => Motorhomes => Topic started by: IBTripping on February 24, 2020, 10:11:01 PM

Title: GMC MH - Ahead of Its Time
Post by: IBTripping on February 24, 2020, 10:11:01 PM
Saw this link on another forum about an interesting front wheel drive GMC Motorhome built in the 70's. It was innovative and unique for even today.
Title: Re: GMC MH - Ahead of Its Time
Post by: Gizmo100 on February 24, 2020, 10:30:09 PM
Some great ideas..
Title: Re: GMC MH - Ahead of Its Time
Post by: jubileee on February 25, 2020, 12:57:12 AM
 My brother had one, I believe it was a 1973. It was brand new and we drove it to California to pick up a new truck. I drove the truck back.
  Very nice unit and it seemed to me very expensive at the time. Fun to drive. My brother lived in Oklahoma and the motorhome was destroyed in a tornado a couple of months after California trip.
Title: Re: GMC MH - Ahead of Its Time
Post by: Lou Schneider on February 25, 2020, 02:15:32 AM
Most of the GM motorhome's design actually came from the Revcon front wheel drive motorhome that started production in 1971, two years before GM started to make their own motorhome.

Shortly after Oldsmobile created the front wheel drive Toronado in the late 1960s, Revcon approached GM and asked to purchase the Toronado drivetrain to use in their motorhome.  GM insisted Revcon build a prototype and do extensive stress testing at Revcon's expense to prove the drivetrain would stand up to motorhome use before they would agree to sell them.

The testing was eventually successful and Revcon started motorhome production in 1971 using the Oldsmobile drivetrain on a low, flat floor chassis.  The body used the same aluminum semi-monococque construction as the Airstream trailers.  Not too surprising since Revcon founder John Hall was Airstream founder Wally Byam's stepson and worked for Airstream for 20 years.

Two years later in 1973, GM came out with their own motorhome using the same drivetrain and chassis layout as the Revcon.

Both companies produced their respective motorhomes for several years.  When GM discontinued their motorhome and the Oldsmobile Toronado drivetrain in 1978, Revcon designed their own front wheel drive powertrain using the Chevy 454 engine and gave their motorhome a slanted front end similar to what GM had used.  It stayed in production until 1990.

Early Forum member John Wilson had a mid-1970s Revcon and except for the flat nose it was a close match to the GMC motorhome.
Title: Re: GMC MH - Ahead of Its Time
Post by: Old_Crow on February 25, 2020, 03:43:24 AM
In the 80's I was a motor home service tech at a Chevy dealership.  Did this for about 8 years.  The two worst jobs I had in 8 years were both on the GMC motor homes.
One was an engine replacement.  The factory service manual called for removing the windshields and taking the motor out the top.  Neither the customer or my boss wanted to take the responsibility for removing and replacing the windshields(not that I blamed them)so I was forced to remove the motor through the bottom, the same as I did with the P30's.  That big old transmission got in the way and I ended up with the entire powertrain on the floor and the front of the motor home jacked about 4' in the air on cribbing.
The second horror job was repairing the leaks in the air suspension.  It took over 3 weeks to find all the air leaks to the point that the suspension would hold air overnight. 

All that being said, I still love those coaches, and would have loved to have owned one, but I never saw one big enough I thought I could live in it.  There was a nice one parked in the same park I stayed in last month in Little Rock.
Title: Re: GMC MH - Ahead of Its Time
Post by: edjunior on February 25, 2020, 07:48:48 AM
I saw one of these for sale not too awful long ago...I just can't remember where.  It looked to be in pretty good shape.  Of course that was just a drive-by, and like I said, I don't even remember where now.  I have seen them occasionally over the years though sitting in someone's yard with a for sale sign in front of it.
Title: Re: GMC MH - Ahead of Its Time
Post by: Larry N. on February 25, 2020, 08:01:15 AM
I test drove a GMC in about 1973, though I couldn't quite afford it then. It was a sweet driving machine, and would very comfortably hold 70 mph up Albuquerque's 9 mile hill on I-40, as easily as a car. If memory serves, they wanted something a bit over $13,000 for the 23' model, which was out of my reach.
Title: Re: GMC MH - Ahead of Its Time
Post by: House Husband on February 25, 2020, 11:30:53 AM
Cute toy but not very practical. Small holding tanks. No basement storage. Note storage container on roof. Front hub bearings overloaded. As already noted, hard to maintain.
Out coaches today fit our needs much better.

Title: Re: GMC MH - Ahead of Its Time
Post by: TomJF on February 25, 2020, 11:46:28 AM
I always loved the looks of the GMC motorhome, just as I liked the styles of most GM products.  As a mechanic, though, I hated working on them.  I think the GMC motorhome was famous in it's role as the Uban Assault Vehicle in the movie "Stripes", with Bill Murray.  Now, if I owned that motorhome, I'd feel safe driving anywhere!
Title: Re: GMC MH - Ahead of Its Time
Post by: Utclmjmpr on February 26, 2020, 06:18:08 PM
 This motorhome has a large cult like following with many sources for parts and upgrades,, the front bearing problem is now being
  handled by replacing the front upper and lower "A" arms ,,spindles and bearings from the late model GMC one ton four wheel drive front end,, really a nifty upgrade..  Rear boggie air bags are still being produced,, the old 455 Olds engine is being replaced with the late 454 Chevy's,, electronic ignition systems work great,,new drive gear sets are being made to give lower ratio's for towing,, front wheel spacers are being made to widen the the width 4 inches so the front now matches the rear width at the boggies.. In the 5 year run from 1973 to 1978,, two models were made,, a 23 and a 26 footer...
  The ride and handling is very smooth.. All impressive for the small money needed to get into one of these classics..>>>>Dan
Title: Re: GMC MH - Ahead of Its Time
Post by: Tom on February 26, 2020, 09:33:49 PM
Quote from: Lou Schneider
Early Forum member John Wilson had a mid-1970s Revcon ...
And proud of it he was. When he invited me aboard, he said "come see what a REAL motorhome looks like"  :)   
BTW John was also on our original forum staff - he was our forum Librarian.
Title: Re: GMC MH - Ahead of Its Time
Post by: Lou Schneider on February 27, 2020, 12:25:33 AM
Legendary Top 40 radio station KFRC in San Francisco converted a 1975 GMC motorhome into a mobile radio studio.  They completely stripped out the interior and built a complete control room and stuidio in it.  On very short notice they could drive it to a parking lot or other location so people could see their favorite DJs in action along with what happens behind the scenes.

It was a tremendous hit as a promotional vehicle, but the real reason they built it was their studios were in a non-reinforced building that wasn't expected to survive a major earthquake.   The motorhome would let them stay on the air if their building became uninhabitable.

Here's a story about it with several photos including the on-board studio. (
Title: Re: GMC MH - Ahead of Its Time
Post by: Larry N. on February 27, 2020, 07:14:49 AM
That's neat, Lou -- thanks.
Title: Re: GMC MH - Ahead of Its Time
Post by: Matt_C on February 27, 2020, 09:38:41 AM
Very little of what Dan "Utclmjmpr" wrote is accurate. 
Yes, there is an almost cult like following.  Of close to 13000 built, about 9000 are still in use.
But the front wheel bearings are not a problem as they are not overloaded, but GM took the cheap way to make the knuckles.  We have a guy that fixes them and we do only know that his fix is good for more than 140K as that is the highest to date. 
The one ton front end has a new an different set of problems.  The one that bothers me most is that I can feel the camber problem in a hard corner. 
The rear airsprings (airbags) are out of production and one supplier was bringing in parts made offshore, but there were issues.  That is little consequence as  there are multiple kits available to use current production parts.
They were all shipped with a 3.07 final drive (rear end) that came from the Toronado towing package.  It was (is) wrong with the reduced speed limits.  Others are available with greater ratios. 
The front wheel spacers are not required if one takes the time to set the front end up the may the service manual directs.  The problem was that most shops do not understand the different steering box.
The 455s only go about 180K before needing an overhaul.  A 454 will not fit without major work because the it will only bolt to the 425 transmission with 2 of four bolts.  Some of the later coaches were shipped with the 403 with no loss of performance.

Yes, the ride is very smooth.  So smooth that when we used to have to "Push" travel and off duty driver could sleep in the back.

There are three good ways to get the engine out. 
You can take it out the top, but the interior was at risk.  You can borrow the hoist and gantry from many of the local chapters.
You can take it out the bottom and it is simple if you take it down with the transmission attached. 
You can break the frame at it joint and pull the entire assembled drive line (ready to run) out the front.  (I have had to do this to do an engine overhaul and a year later to repair crash damage.)  With small effort, you can then test run the engine before re-installing.

The leaks in the rear suspension were largely a direct result of the cheap-assed plastic air fittings that GM used.  If you replace them with real air fittings, the suspension will stay up for weeks.

The design and development actually started in 1970.  While driveline is based on the Toronado, there are many important parts that were revised for the motorhome production and some were revised even more during the production run.
If you want one, you can acquire one at small cost, but beware.  We have a saying: "A reliable and ready to travel GMC will cost you ~30k$us.  That is all at once or as a kit."  They unsaid thing is that sweat gets billed in at full shop rate. 

There is still amazing support for the old girls.  We have three companies that can supply most any part needed and about a dozen good shops to do work if you don't want to.

Want to look at a few, there are local rallies all the time and most have an open house on the schedule (usually a Sunday).
If you want to know more? ( 

Matt Colie -   
Title: Re: GMC MH - Ahead of Its Time
Post by: Tom on February 27, 2020, 09:45:05 AM
Thanks Lou. Great story.
Title: Re: GMC MH - Ahead of Its Time
Post by: Old_Crow on February 27, 2020, 05:07:34 PM
Matt, yes, I ended up changing just about every air fitting in the system and one bag.  Got to the point that I'd come to work and it was flat.  I'd air it up, find and fix another small leak, air it up at the end of the day to sit overnight.  Rinse and repeat until I used up a whole bottle of Dawn finding leaks.
I totally did a happy dance the first day I came to work and the suspension was still aired up.

As far as the engine, started out with blown head gaskets, got the engine torn apart in-frame.  Then the decision was made to yank it and do a complete rebuild.  Took the block and the trans out in one piece.  Reassembled the motor and installed the complete motor and trans as a unit.
Big problem was, I was set up to drop 454's through the bottom of P30 chassis, did not have a table or cart that would support the 455/trans unit.  Building that was half the fun.
Title: Re: GMC MH - Ahead of Its Time
Post by: catblaster on February 28, 2020, 02:36:44 AM
  The cadillac 472/500 cu in engines have the same BOP bolt pattern and a swap is much easier, the only problem is the motor mounts are forward on the caddy in stat of centered as on the olds. The eldorado trans will also swap, there the difference in some models is the caddy lacks one friction disk. Not sure which cluster it is but if it will take the torque from a 500 I doubt that is much concern.
   I sold two trans to a company in Orlando that rebuilds the GMC's, one of his upgrades is to replace the quadrajunk carb with a fuel injection system.
Title: Re: GMC MH - Ahead of Its Time
Post by: Matt_C on February 28, 2020, 12:44:32 PM

In the community, there are more than a few that have been refit with 500's.  Most of those have used the 7747 ECU with an addition that makes both real time monitoring and reconfiguring the engine map very simple with a laptop. 

If you want to read about some very involved private development programs, this is where they are.  Not just the engine, but we have numerous brake systems and suspension control.  the one thing that has not been offered as a kit is anti-lock.  There are two running, but the builders do not believe that they can field an effective kit. 

I don't have much of that stuff, I have enough trouble affording to travel as it is (that is a direct result of the abrogation).  I have upgraded the ignition (not to HEI), have a different cooling fan and a modification to the rear brakes that is like the floating backing plate of a dirt bike racer. 

If you ever get near a rally, stop in and talk to owners.  A GMC owner that does not want to talk about his coach is a rarity.

Title: Re: GMC MH - Ahead of Its Time
Post by: Utclmjmpr on February 28, 2020, 01:53:12 PM
 Matt,, I have a close Friend that has a 26 and has had the upgrades I listed installed except engine .. He is in Mexico now having it painted and will return to his home on Bainbridge Island Wa. soon,, he has been to several rallies in the northwest.>>>Dan
Title: Re: GMC MH - Ahead of Its Time
Post by: decaturbob on February 29, 2020, 08:21:10 AM
Saw this link on another forum about an interesting front wheel drive GMC Motorhome built in the 70's. It was innovative and unique for even today.

If I was smart I would have bought one 35 years ago
Title: Re: GMC MH - Ahead of Its Time
Post by: hra on March 01, 2020, 08:11:58 AM
I had a 1976 26 GMC for 12 years, my dad had owned it for 20 prior to that. Great driving and riding coach, parts were easy to come by. I still miss it, should have kept it. The hardest thing to fix for me was the radiator hose to water heater. Loved it, only downside was no made up bed....