Hello,

I've recently purchased a 1976 28' Barth on a P30 Chassis with a 454. At 70-75 mph, it sounds like the engine is turning too high of rpm. Is there an overdrive available on this chassis? I thought I read a discussion on this subject on this site, but I am unable to locate. PLEASE HELP.

70 to 75 is pretty fast for a 454. I prefer to drive under 60, at 2800 rpm. With all the idiots out there, and the weight and bad handling of most RVs, I get nervous over 60. If you drive that fast, I hope you have good tires and a good front end, Bilsteins, IPD, etc.

That said, you can install a Gear Vendors or US gear overdrive. It will cost a bit over 2000 dollars, plus installation. Either will slow the engine down in high as well as giving you second gear overdrive for hills. The other way is to install a 4L80E GM trans. It has four speeds, the top being overdrive, and a locking convertor. You will need a stand alone computer to make it work in your year coach. It will cost over 3 grand before you're done.

You just have a 3 speed tranny there, no overdrive. Mine is the same and when I first drive it I thought that it revved too high because it vibrated. Fact was, I had a bad wheel bearing and it almost killed us. So make sure you suspension in all that is ok.

As far as the overdrive is concerned, there is the over/underdrive stuff but you are talking $3,000.00 +.

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Shortcuts Always Take Longer

Just to reiterate what Bill and Dave said:

Your turbo 400 tranny is about the best unit for your motorhome, and most of these are geared towards acceleration and pulling up hills.

Sure, on a flat highway you will find the top end to be flat, but even if you gear it up, the drag coefficient would limit your top end to about 80-85. Bill is correct, that is really moving for this much mass, and most tires and brakes for these units are going to be overwhelmed if you try and stop fast from these speeds.

Unless you are willing to sacrifice acceleration and pulling ability, or spend $$$ to put a different top gear in your tranny, accepting your current situation is your only recourse.

The TH 400 is really rugged, much more so than the 4L80E. And much more reliable and easy to repair and find parts. I just bought a Gear Vendors gear splitter, and will be installing it soon. That will slow my cruising RPM down by 22%. That means I can cruise at a regal 2184 RPM.

Now, if I can manage to rig up a locking torque convertor...............