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Old 03-30-2016, 11:18 AM   #1
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Need info on Chevy 454 and TH400...

I recently bought a 1987 Country Camper motorhome. It has the Chevy 454 and TH400. I bought it in Vancouver, Washington. When I bought it I was told by the PO that the original transmission lost reverse. So he bought a "Craigslist rebuild" (I know, I know). There was no pan gasket on the trans, and it again had NO REVERSE. This is how it was when I bought it. I put a pan gasket in the transmission and filled it with ATF and let it run in PARK for a while before driving it. It seemed to go forward fine but still had no reverse. I drove it to Welches, Oregon before it started bogging down really bad and backfiring. I pulled over, and then it would NOT MOVE. The motor just revs in any gear.

Thankfully, I had purchased AAA RV PREMIERE, and after spending a bitterly cold night atop Mt. Hood with no heat (batteries died) and no blankets, I got it towed home.

I got another TH400 given to me for free. It is a 1973 CJ model from a C30 or a motorhome. My mechanic friend said that if it ran when it was pulled, it should be good to go ( I am told it ran 5 years ago when pulled. It sat inside a woodshed with only 3 sides. I am planning to replace the front and rear seals, pan, filter, pan gasket, torque converter and replace fluid with new HIGH TEMP ATF. Also new 1350 stall 13" converter. It is full of fluid and the fluid looks good).

ANY ideas as to what else to do to the trans?

Also, I would like to get more torque and HP from the 454 and possibly improve mileage. Thinking a Lunatic cam, Aluminum RPM Air-gap or Torker-II intake, MSD distributor, stock oval-port heads (049?), headers and a good exhaust

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Old 03-30-2016, 01:30 PM   #2
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Have the trans rebuilt, don't go to the trouble of putting one in with just word of mouth that it's good. As far as the 454 having more power and torque, save your money the 454 will serve you well as is if it's a good engine. You'll get 7mpg perhaps a tad more but doing what you mentioned will not help you out no matter what you do. I've owned that engine and was completely happy with the performance and the coach was larger. My advice rebuild the trans. and enjoy the ride. Good luck with your choice.

Bruce & Nancy
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Old 03-30-2016, 02:11 PM   #3
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If you got the pan off, drill a hole in it and install a drain plug. The drain plug is a hollow 3/4" bolt, threaded on the outside and inside. The threaded outside is what holds it to the pan, with a gasket and a bolt on the inside of the pan. The threaded inside of the big bolt is the removable plug that the fluid drains thru. I drain my fluid every 25k and change the filter every 50k. I threw away the inner plug and installed a tranny temp sending unit. So now I can monitor the temp of the fluid in the pan, the hottest fluid in the tranny. When you remove the sending unit to drain the fluid, hold the larger bolt to keep it from rotating.
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Old 03-30-2016, 04:30 PM   #4
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Take that 400 trans and get it rebuilt cost around 750 to 1 gran but worth every dollar. For that 454 there like bullet proof
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Old 03-30-2016, 04:57 PM   #5
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As far as the engine itself . Headers are always an improvement , but do yourself a favor & spend the money on food quality heavy duty headers with heavy flanges or you'll regret it . An RV type cam such as the Edelbrock performer would be some imprint as well as a Performer Intake, ( not the Petformer RPM). A good investment is always a good tune up , & maybe an upgraded HEI distributer.
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Old 03-31-2016, 05:28 AM   #6
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A simple cam,intake & 650-750 carb will be night and day on a stock 454 truck/MH engine. A simple port, polish & gasket matching of the intake/exhaust runners will be more than sufficient for sub 4500rpm RV duty. Headers, cat delete & Flowmaster mufflers could come later on, but as mentioned don't cheap out on them. Cheap headers warp & leak every time, especially under hot HD use such as MH's.
This should get you +75hp relatively easily, in which I'd want a known good transmission to handle the hp/tq and weight of MH...... Biggest oil cooler you can fit as well😉👍
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Old 03-31-2016, 02:23 PM   #7
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I would not trust an auto trans that's been sitting around either. In fact I have a couple on my shed that I know for sure were fine when I took them out of vehicles I scrapped and I plan on rebuilds before I reuse them. Its just not worth getting stuck somewhere if something decides to fail. As for the 454, if it was me I'd give edelbrock a call and let them recommend cam, intake and carb as a set. When I rebuild I'm in the habit of also having .030 shaved off the heads for a little extra compression as well.
Just my 2 cents.
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Old 03-31-2016, 07:02 PM   #8
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I hope you mean your using Dextron 3/Mercon fluid not ATF
Paul & Kim Carillon
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Old 04-02-2016, 07:20 AM   #9
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Wow, just wow.
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Old 04-02-2016, 08:25 AM   #10
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I would say a rebuilt TH400 done by an experienced OH shop and a NEW torque converter is a must if you plan to keep the MH. A bulletproof addition to these TH400's is a Gear Vendor overdrive unit that bolts to the rear of your transmission. You will reduce your cruise engine rpm with this addition.

As far as the engine, I would keep it just like GM built it. Keep your cast iron headers, just be sure you have a 3" dia exhaust system with low resistence mufflers which is inexpensive. Be sure your plug wires are good and consider a HEI distributor. A good tune will go a long way to improve your engine performance rather than spending a bunch of money on aftermarket parts. This all assumes you have engine compression within spec.

My two cents!!

Rick and Lynda Smith
2004 NEWMAR DSDP M-4011-SPTN 8.9 Liter Cummins
2018 RAM 1500 4WD Laramie CREW toad
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454, chevy

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