Supercharged111
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What's your fuel pressure?
4L80E to TR400 Trans swap 1995 Chevy P30 chassis motorhome
- Thread starter Wulfdan
- Start date
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What's your fuel pressure?
Don't expect the new motor to run any different than the current one. You have a problem that needs cured. Then you can try out the 4l80 then swap motors. What is your fuel pressure?
A TH400 will run without the kickdown solenoid. My Jaguar doesn't have it hooked up and it shifts fine, but it won't downshift until the throttle pressure overcomes the governor pressure. In a lightweight vehicle like a 3500 lb race car with a 500 cid Caddy motor, it's not a serious problem. In an RV, you're going to be lugging the engine.
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Because the 4L80E isn't currently broke and it's a royal PITA to do the swap. A bird in the hand is worth two in the bush.
Then you don't have the skills to do this swap. I get it, your margins are tight and you've had a transmission leave you stranded before. Now you're paranoid about this one. Unfortunately you're not including the uncertainty of the TH400 into your calculus, nor all the work involved in getting it to integrate with everything else in your RV. It's not rocket science, but it's a lot of motivation-killing small hurdles.
Run that 4L80 until it poos the bed. The TH400 can still be a contingency plan.
Wulfdan
Newbie
iirc it was in the 20s
I will say that it was running pig rich before we started taking things apart. Oh and I redid the gasket/spring in the injector pressure regulator too, no change in operation. The prior owner did say he'd replaced the fuel pump, so if the swapped motor starts doing the same thing we'll drop the tank and check part numbers and whatnot, or maybe I just need to install a regulator on the supply side. I dunno, I gotta get the blocks swapped before I can chase that down again. I will try to find the pressure test kit in the garage and see if I can get a better number for you. I should be able to put 12v on it and roll the key and check pressure.
The reason I went with a "new" motor was the oil ring in #7 being shot.
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Yes, in a lighter weight vehicle like the above, it's not a big deal...Not the same as for a heavy motor home but more importantly, I was trying to impress upon him (as everyone else is) what a poor idea this 'TR 400' swap is...But he seems bound and determined to go ahead with it so who am I (or we) to stop him. Sometimes lessons have to be learned the hard way.
Wulfdan
Newbie
You've successfully beaten me almost all the way to the 4L80E. If you would though, lets perform a thought experiment. Forget about all the custom that has to happen for this swap for a moment, because my brother is handling all of that and could probably be a pro mechanic if he wasn't already a network engineer. But lets set all the custom aside and look at just the transmissions. Mechanically why would a TR400 be less reliable than a 4L80 with triple the miles? Nobody has explained that. Everyone is fixated on the fact that there's some custom fab, and wiring that has to take place, and the trans brace has to move and shortened driveshaft and so on. I'm really not trying to be a pain, I want to understand why. "it's newer" doesn't really explain anything
Why in the world do you keep calling it a 'TR400'?
There is such transmission as a 'TR400'....Its a Turbo Hydramatic 400 or TH400 for short (sometimes folks will refer to it as a 'Turbo 400').
I'm not performing any thought experiments, I've already provided my advice and not going any further with it - as I stated now three times, it's your vehicle, you are free to do whatever you would like with it. You have asked for advice and several of us have responded, largely in alignment with each other....I only came back to the thread because Erik quoted one of my prior posts about the TH400 detent solenoid, which if you want the TH400 to shift properly at all times as it was designed, a detent solenoid had to be installed and working correctly. He pointed out a nuanced exception to that statement, I responded.
Beyond that, I'm not in the business of twisting anyone's arm to do things they don't want to do, especially with their own personal property where there is no impact to me one way or another.
The TH400 is a 1960s transmission design that left production in 1990, when the 4L80E entered production. In the interim GM invested a lot of money improving their transmissions. The casting quality is better, the tolerances are better, the technology is better.
Keep in mind that in the 1960s cars were expected to last about 5 years, and a car with 100,000 miles was "wore out". By the 1990s cars were expected to go at least 200,000 miles. In use, 4L80s have proven to probably be GM's best transmission ever put in these trucks.
Keep in mind that in the 1960s cars were expected to last about 5 years, and a car with 100,000 miles was "wore out". By the 1990s cars were expected to go at least 200,000 miles. In use, 4L80s have proven to probably be GM's best transmission ever put in these trucks.
Wulfdan
Newbie
Brain fade
Here's my final bit of advice - FIRST install the 4L80E, assuming it has the manual lever position sensor which is necessary to start the vehicle if you are still using the factory ECM to control the engine and transmission in that motorhome. If it works, great - run it for as long as you can while you start putting money aside for a refresh if/when the time comes. Like you said, you won't be putting a lot of miles but will be installing a much better transmission..There is literally no risk involved for you...If it doesn't work, you have the TH400 laying around which you can swap if you want to do so. Erik summarized the differences well, which is fine without getting into the weeds...We have all suggested this at least twice.
In my humble opinion, the 4L80E is the best transmission GM has ever produced and I say that with the caveat that I have not gotten my hands on any of the 10-speed units as of yet.
