So, what have I personally learned from this whole experience?
1. My drivetrain is indeed a 1978 UPP FWD system, which, as you know, is based on the Oldsmobile Toronado passenger car. Therefore, basically all the parts from the 1978 Toronado or Eldorado fit (with some minor modifications, such as to the power steering pump mounts).
With one caveat: The openings in the steering knuckles are larger than those in the Oldsmobile Toronado passenger car to accommodate the more robust lower ball joint of the Revcon suspension. The motorhome has a curb weight of 5.7 tons, while the Toronado passenger car weighs only around 2 tons.
2. The technical components of my Revcon drivetrain are about 95 percent identical to those of the GMC motorhome, since John Hall (founder of the Revcon brand) famously conducted the first UPP stress tests with GM's permission, which were then used for the Revcon motorhomes. The GMC motorhome didn't come onto the market until a few years later, at which point GM ultimately drew on John Hall's data collection.
However:
For example, the drive axles from the 1978 Oldsmobile Toronado fit my Revcon perfectly, while those of the 1978 GMC motorhome are longer because the frame is wider at the front.
The torsion bars on my Revcon are shorter than those of the GMC motorhome, but with some modification, they can still be used in my Revcon. Original, functional torsion bars for my Revcon are practically impossible to find.
For comparison:
Revcon motorhomes produced approximately 2,000 units, while GMC motorhomes produced around 12,000, two-thirds of which are still running today.
3. I remain very happy with my UPP drive and its use in the GMC motorhome, because from 1981 onward, only newly and more robustly designed Revcons were produced. While parts for these are still available in the U.S., identifying them would be even more difficult for me, as the Revcon community—compared to the GMC motorhome fanbase in the various forums—is significantly smaller and essentially only active on Facebook.
4. I already knew beforehand that my car had a 1978 UPP FWD engine, based on the engine number. However, the steering system, which had been botched over the decades with its undersized, haphazardly fitted tie rods, caused a huge amount of confusion. This led to damage (a crack) to one of my wishbones and the drilling out of the tie rod mounting points on both steering knuckles, as the parts I bought by part number simply didn't fit.
To make matters worse, last summer the new, correct tie rods were installed backwards on one side, with the shorter tie rod on the outside instead of the inside, because the mechanics had used the incorrect, old, and too-short tie rod as a guide. Naturally, this one also didn't fit.
So, I was at my wit's end and, admittedly, quite desperate. I was "saved" by an unsolicited photo from the Facebook Revcon group, to which I described my problem: This showed the correct installation on a 1979 (!) Revcon, with the long tie rod pointing outwards.
It's possible that the steering is now, for the first time in over 30 years, working correctly and in its original condition. The TÜV (German vehicle inspection agency) and anyone else never noticed, which is understandable, since all the parts looked fine and always passed the shake test. It was only the damage (crack) to the wishbone that finally revealed something was wrong with the steering angle. A closer inspection then uncovered further problems.
Luckily, I was able to acquire the only drag link available on eBay for a 1978 Toronado from Canada; the old one had been drilled into multiple times to somehow attach the wrong tie rods with countless bolts.
5. When it comes to sourcing the correct spare parts for my Revcon, I can only rely on myself. In this area, I now have the upper hand even over seasoned motorhome professionals in Germany. Of course, this is only possible with the help and support of the U.S. Revcon community on Facebook and the helpful members of the GMC Motorhome Forum.
Together we archieved a "victory" over the Revcon's steering problem.
My thanks goes to you, without a doubt, because without the help of incredibly dedicated people, it would have been over (once again).
For my part, however, dear friends, I have to agree with King Pyrrhus I of Epirus:
"One more such victory and I'm finally lost."
Because the whole thing was starting to take its toll. But: No pain, no gain. That's my motto.
1. My drivetrain is indeed a 1978 UPP FWD system, which, as you know, is based on the Oldsmobile Toronado passenger car. Therefore, basically all the parts from the 1978 Toronado or Eldorado fit (with some minor modifications, such as to the power steering pump mounts).
With one caveat: The openings in the steering knuckles are larger than those in the Oldsmobile Toronado passenger car to accommodate the more robust lower ball joint of the Revcon suspension. The motorhome has a curb weight of 5.7 tons, while the Toronado passenger car weighs only around 2 tons.
2. The technical components of my Revcon drivetrain are about 95 percent identical to those of the GMC motorhome, since John Hall (founder of the Revcon brand) famously conducted the first UPP stress tests with GM's permission, which were then used for the Revcon motorhomes. The GMC motorhome didn't come onto the market until a few years later, at which point GM ultimately drew on John Hall's data collection.
However:
For example, the drive axles from the 1978 Oldsmobile Toronado fit my Revcon perfectly, while those of the 1978 GMC motorhome are longer because the frame is wider at the front.
The torsion bars on my Revcon are shorter than those of the GMC motorhome, but with some modification, they can still be used in my Revcon. Original, functional torsion bars for my Revcon are practically impossible to find.
For comparison:
Revcon motorhomes produced approximately 2,000 units, while GMC motorhomes produced around 12,000, two-thirds of which are still running today.
3. I remain very happy with my UPP drive and its use in the GMC motorhome, because from 1981 onward, only newly and more robustly designed Revcons were produced. While parts for these are still available in the U.S., identifying them would be even more difficult for me, as the Revcon community—compared to the GMC motorhome fanbase in the various forums—is significantly smaller and essentially only active on Facebook.
4. I already knew beforehand that my car had a 1978 UPP FWD engine, based on the engine number. However, the steering system, which had been botched over the decades with its undersized, haphazardly fitted tie rods, caused a huge amount of confusion. This led to damage (a crack) to one of my wishbones and the drilling out of the tie rod mounting points on both steering knuckles, as the parts I bought by part number simply didn't fit.
To make matters worse, last summer the new, correct tie rods were installed backwards on one side, with the shorter tie rod on the outside instead of the inside, because the mechanics had used the incorrect, old, and too-short tie rod as a guide. Naturally, this one also didn't fit.
So, I was at my wit's end and, admittedly, quite desperate. I was "saved" by an unsolicited photo from the Facebook Revcon group, to which I described my problem: This showed the correct installation on a 1979 (!) Revcon, with the long tie rod pointing outwards.
It's possible that the steering is now, for the first time in over 30 years, working correctly and in its original condition. The TÜV (German vehicle inspection agency) and anyone else never noticed, which is understandable, since all the parts looked fine and always passed the shake test. It was only the damage (crack) to the wishbone that finally revealed something was wrong with the steering angle. A closer inspection then uncovered further problems.
Luckily, I was able to acquire the only drag link available on eBay for a 1978 Toronado from Canada; the old one had been drilled into multiple times to somehow attach the wrong tie rods with countless bolts.
5. When it comes to sourcing the correct spare parts for my Revcon, I can only rely on myself. In this area, I now have the upper hand even over seasoned motorhome professionals in Germany. Of course, this is only possible with the help and support of the U.S. Revcon community on Facebook and the helpful members of the GMC Motorhome Forum.
Together we archieved a "victory" over the Revcon's steering problem.
My thanks goes to you, without a doubt, because without the help of incredibly dedicated people, it would have been over (once again).
For my part, however, dear friends, I have to agree with King Pyrrhus I of Epirus:
"One more such victory and I'm finally lost."
Because the whole thing was starting to take its toll. But: No pain, no gain. That's my motto.
