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Overdrive Transmission Conversion Eric 4-22-09  
I am looking at putting an overdrive transmission in my 1989 29' Coachmen Catalina A Class. It's running a Chevy 454, more then likely with a Turbo 400 3-speed. This thing revs at around 4200 rpm at 60mph!!! Not sure who the genius was behind this drive train. It must have a 4:56 or lower gear ratio too. What would be the best O/D tranny, or would it be better to change out the diff. gears for something higher? From some of the research I've done on-line, the 4L80E sounds the most durable option except the electronics may pose some issues.

Any takers on this one would be greatly appreciated.

Re: Overdrive Transmission Conversion BUBBA THE BUS TECH 4-22-09  
4L80E a pain to instal but solid and trouble free once the computor electronics are sorted out. The aftermarket computors I have used take some real sorting and can damage the trans if not set correctly and carefully. 4L60 (700R4) We have run these sucsesfully in several big block motor home conversions, but they can be a little under strength if you have a strong or modified engine. The stock 454 is really more than a stock 700 will handle. You need to have these built by some one that knows them well and will warranty in this application. The 400 with a higher diff ratio can be a problem because many of these unit simply won't pull away on a steep grade as it is, more gear will make this much much worse and stress the everliving heck out of the trans. Have you looked into an add on over drive for the setup you already have? They are genrally a trans mounted box that will give a slight under drive or over drive. Used to be Richmond gear? building them I think. Haven't installed one in a long time but they worked well as long as the engine was run over 2500 under heavy load, the trans will over heat and burn up under that. Good Luck
Re: Overdrive Transmission Conversion tom 3-19-13  
I have a 1982 23 ft motorhome on a c30 chassy. it has a 350 with a 400 3 speed. i am looking for a add on overdrive with a cost under 3000. can you help. thanks tom
Re: Overdrive Transmission Conversion Eric 4-24-09  
Thanks Bubba, this is helpful information. I had thought about a bolt on O/D unit, but so far the only one I saw was from Gear Vendors out of El Cajon CA. They retail theirs for about $3,200, which I think is still more then a rebuilt, or lightly used 4L80E + after market electronic controller. At any rate I will take a look at the option of a properly built 700R4, or a Richmond, or other bolt-on type O/D unit.

Again, many thanks.

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