4L80E to TR400 Trans swap 1995 Chevy P30 chassis motorhome

[Wulfdan]

No, and you don't need me to do so as you already have one...Since you bought the th400 used, do you have proof of the mileage on it and/or it's source vehicle?

250k vs 70k is nearly the equivalent of 6 in one hand, half a dozen in the other since the newer 4L80E will last longer all things equal to the older TH400 but either can go south at any time. It would be different if the Th400 was either freshly rebuilt or had less then 5K on it...

I'd price out the cost of refreshing your 4L80E (new filter, paper/rubber, bushings, clutches, harness/solenoids) against the cost/risk/benefit of integrating the TH400 as-is into your powertrain and make a decison on a best-value basis.

If you determine the th400 is your best route the go for it. Likewise for the 4L80E...

Thank you for the advice but I don't have the skills, tools, or a clean work area to mess with an auto trans. My options are stay with the 4L80E with a quarter million miles, that I don't know works, because it's only ever rolled around the yard at idle. Or, I have the TH400 that drove itself home before it was parked. I don't want to spend any money that isn't coming back to me which means I don't want to throw a bunch of parts at a high miles trans. This RV will go from my brother's property to my home, and from home to the septic service and back.

So let's see. High mileage, heavy duty, desirable overdrive transmission, stock to the vehicle: Means tranny x-member is properly located, wiring harness is plug & play, cooler lines are properly sized, routed and designed specifically. Drive shafts are directly usable too.

Or, lower mileage, unknown/untested, non OD tranny, possible non lockup torque converter: Means relocate x-member, rebuild/redesign driveshafts, cooler lines, vacuum shift modulator vacuum line & port on intake, burn a specific chip for an OBD1 ECM.

How about sell the 400 and OE big block, then send the OE 4L80 to a quality tranny rebuilder?

Because I'm not spending thousands on a ragged out clapped out RV. The OE big block doesn't run right, so it's a core at best. Are you interested in the TH400?

I get that you guys are pros or very experienced hobbyists and want things done the "right" way. I don't have the funding for that. I'm scraping together a place to live and most of the money I do have is targeted toward getting a decent piece of land. If I stay with the 4L80E and it blows up, I'm out good money to fix. It sounds like ya'll like that better than going to the th400 that I know works.

 

[95burban]

Swapping in the th400 will cost MORE than keeping 4l80e. There is a lot more that goes into it than nuts and bolts. If the fluid doesn’t smell burnt in the 80 run it.

 

[NickTransmissions]

Thank you for the advice but I don't have the skills, tools, or a clean work area to mess with an auto trans. My options are stay with the 4L80E with a quarter million miles, that I don't know works, because it's only ever rolled around the yard at idle. Or, I have the TH400 that drove itself home before it was parked. I don't want to spend any money that isn't coming back to me which means I don't want to throw a bunch of parts at a high miles trans. This RV will go from my brother's property to my home, and from home to the septic service and back.

I never suggested that you rebuild the transmission, please re-read the advice I gave you and if you were serious about being diligent, you'd price out the cost of a refresh for the 4L80E and cost to integrate the TH400 and compare them side by side. Some of the folks posting above you have forgotten more about this stuff then you will ever know and are all basically telling you the same thing. I'm merely suggesting you do some research into the costs associated with the two options in front of you and make an informed decision instead of one based on one trip of unknown duration in a TH400 with 70K + miles on it.

At very minimum, pop the pan off of both transmissions to see what the bottom looks like. Cut open each filter to see if any kibbles and bit have gotten caught up, and if so, determine what they might be/where they came from within the trans. Replace the filter and gasket on whichever trans you plan on running. For the TH400, I'd also replace the detent solenoid and its little metal gasket (two 3/8" bolts, one new little gasket, two minutes worth of work and about $20). The 4L80E will likely need a new harness and shift solenoids, about $100 total which can be put towards a refresh which is likely to cost you about $1200 or so if you can find a transmission shop willing to do it.

It's going to cost X dollars to have that driveline modified and it's not a simple one-piece deal like what's in a small truck or passenger car. Plus you need to move the X member forward and do other things that you may not currently be aware of. Plus you need to wire up a circuit for the TH400's detent solenoid so it can function, as someone else mentioned (hint: If that solenoid isn't active and working correctly your TH400 may not shift at all). And imagine, after all that friggin work, the TH400's intermediate sprag takes a dump (you lose 2nd gear if this happens) and you now need to pull it out and have it gone through ($1200+) which is roughly the same amount of money to have the 4L80E refreshed (CAL kit which is all new clutches, seals, o-rings, gaskets, pump bushings, filter, front band + electrical parts) while keeping everything else as it is.

None of us know how far you're going to be traveling with this thing or how often as it was never specified...Everyone is putting themselves in your shoes but with their knowledge, to help you make a decision with the information you provided.

I'd at least install the 4L80E to see if it works as it's meant for your vehicle...If it doesn't then consider your options.

But like I said earlier, you do what you think is best.

 

[NickTransmissions]

Thank you for the advice but I don't have the skills, tools, or a clean work area to mess with an auto trans. My options are stay with the 4L80E with a quarter million miles, that I don't know works, because it's only ever rolled around the yard at idle. Or, I have the TH400 that drove itself home before it was parked. I don't want to spend any money that isn't coming back to me which means I don't want to throw a bunch of parts at a high miles trans. This RV will go from my brother's property to my home, and from home to the septic service and back.

Because I'm not spending thousands on a ragged out clapped out RV. The OE big block doesn't run right, so it's a core at best. Are you interested in the TH400?

I just remembered one other thing: the Manual Lever Position Sensor (MLPS) - 1995 was the first year of the MLPS for the 4L80E which means your motor home's transmission, if it's also a 4L80E, should have had one as well.

If you put a TH400 into that thing, how are you going deal with the MLPS, which the computer needs to see to enable you to start the vehicle?

Have you already accounted for this as well?

 

[Wulfdan]

I never suggested that you rebuild the transmission, please re-read the advice I gave you and if you were serious about being diligent, you'd price out the cost of a refresh for the 4L80E and cost to integrate the TH400 and compare them side by side. Some of the folks posting above you have forgotten more about this stuff then you will ever know and are all basically telling you the same thing. I'm merely suggesting you do some research into the costs associated with the two options in front of you and make an informed decision instead of one based on one trip of unknown duration in a TH400 with 70K + miles on it.

At very minimum, pop the pan off of both transmissions to see what the bottom looks like. Cut open each filter to see if any kibbles and bit have gotten caught up, and if so, determine what they might be/where they came from within the trans. Replace the filter and gasket on whichever trans you plan on running. For the TH400, I'd also replace the detent solenoid and its little metal gasket (two 3/8" bolts, one new little gasket, two minutes worth of work and about $20). The 4L80E will likely need a new harness and shift solenoids, about $100 total which can be put towards a refresh which is likely to cost you about $1200 or so if you can find a transmission shop willing to do it.

It's going to cost X dollars to have that driveline modified and it's not a simple one-piece deal like what's in a small truck or passenger car. Plus you need to move the X member forward and do other things that you may not currently be aware of. Plus you need to wire up a circuit for the TH400's detent solenoid so it can function, as someone else mentioned (hint: If that solenoid isn't active and working correctly your TH400 may not shift at all). And imagine, after all that friggin work, the TH400's intermediate sprag takes a dump (you lose 2nd gear if this happens) and you now need to pull it out and have it gone through ($1200+) which is roughly the same amount of money to have the 4L80E refreshed (CAL kit which is all new clutches, seals, o-rings, gaskets, pump bushings, filter, front band + electrical parts) while keeping everything else as it is.

None of us know how far you're going to be traveling with this thing or how often as it was never specified...Everyone is putting themselves in your shoes but with their knowledge, to help you make a decision with the information you provided.

I'd at least install the 4L80E to see if it works as it's meant for your vehicle...If it doesn't then consider your options.

But like I said earlier, you do what you think is best.

I posted a couple times that it's not going to be traveling far. maybe 30 miles to RV service and back home.

local driveshaft shop quoted me $200 to extend the driveshaft and rebalance.

Kickdown solenoid is wired to a switch engaged by throttle linkage

I have the tone wheel to drive the speedometer

I will check the filters as suggested and make a final decision. Thank you for your help and advice. I don't have $1200 to burn right now, so refreshing or rebuilding the 4L80E is not a valid option for me. Either I use as is, or I swap.

oh, for the guy that was asking about the tailshaft. it's going to be moot. Both trans have bolt-on yoke, and once the trans is bolted in, the measurement for the new driveshaft length will be taken and provided to the driveline shop. (if I go with TH400)


If someone could explain why a TH400 with a lot less miles is a worse idea than the 4L80E with 250k from a purely mechanical perspective, that would be great. My current understanding of the two trans is that the 4L80E is a TH400 with overdrive and electronics. I don't understand how that would make it overwhelmingly better? Everyone seems to hold that opinion but I haven't seen any justification.

 

[NickTransmissions]

If someone could explain why a TH400 with a lot less miles is a worse idea than the 4L80E with 250k from a purely mechanical perspective, that would be great. My current understanding of the two trans is that the 4L80E is a TH400 with overdrive and electronics. I don't understand how that would make it overwhelmingly better? Everyone seems to hold that opinion but I haven't seen any justification.

See post 14...You don't know what you don't know and frankly I don't have the energy to delve into it as you've already made up your mind...Good luck on the project, I hope it turns out well.

 

[Wulfdan]

See post 14...You don't know what you don't know and frankly I don't have the energy to delve into it as you've already made up your mind...Good luck on the project, I hope it turns out well.

I haven't completely made up my mind but 250K that I haven't seen shift going down the road scares me. My concern is that I listen to the guys on the internet and end up with a blown trans and I have to deal with that.

 

[Supercharged111]

I haven't completely made up my mind but 250K that I haven't seen shift going down the road scares me. My concern is that I listen to the guys on the internet and end up with a blown trans and I have to deal with that.

And if that happens what are you out? It costs nothing to find out. For all you know the thing has a rebuild at some point in its life. My plow truck was purchased with 240,000 miles, 454/4L80. Engine runs perfect, trans smooth as silk. All original. Not a motorhome, but still.

 

[Moofus02]

I'm assuming the donar is carburetor. If the motor home runs and idles but all you can do is idle around which is why you want to swap and why you don't know if the 4l80 is any good. If you can't make the current tbi 454 run right i wouldn't expect the replacement to run right either. Either diagnose the fuel injected setup or convert to a carb and non electronic transmission. I'm not afraid of a 300k mile drive line and if you are always close to home I wouldn't worry a bit. It sounds like this entire swap nightmare is predicated on a drivable issue. Wouldn't it be easier to fix that? You can swap motors and likely have the drivable thing follow plus be amplified by a computer looking for a transmission that doesn't exist after the swap. Let us help with the drivable issue or swap to a non computerized driveline

 

[Wulfdan]

I'm assuming the donar is carburetor. If the motor home runs and idles but all you can do is idle around which is why you want to swap and why you don't know if the 4l80 is any good. If you can't make the current tbi 454 run right i wouldn't expect the replacement to run right either. Either diagnose the fuel injected setup or convert to a carb and non electronic transmission. I'm not afraid of a 300k mile drive line and if you are always close to home I wouldn't worry a bit. It sounds like this entire swap nightmare is predicated on a drivable issue. Wouldn't it be easier to fix that? You can swap motors and likely have the drivable thing follow plus be amplified by a computer looking for a transmission that doesn't exist after the swap. Let us help with the drivable issue or swap to a non computerized driveline

Went through the entire motor and got it to where it'll start with the bump of a key and idle fine, but no matter what I did, try to give it gas and it bogs. New distributor, new map, new plugs and wires, new O2 sensor, new ECT sensor, new injectors all AC Delco. Cylinder #7 becomes a dead miss because the oil control ring isn't controlling oil, so quickly fouls out. It's clapped out.

Donor motor is a carb, but I'm using trans dapt adapter plate to go carb to tbi.