TH400 took a dump, replacing with a TH350 and have questions.

[handloader90]

TH400 lost gears this morning. Somehow I was able to get into 1st and limp the truck home very slowly. Tow company was wanting $75 to move the truck about 2.5 miles. Fortunately I kept my $75 lol.

The TH400 in the truck is mated to an NP203.

I have a good TH350/NP205 in the garage and the driveshafts to go along with it. It was pulled out of a longbed truck and it's going into a long bed truck.

My questions are related to hooking the vacuum modulator up.

What size hose does it use?

Does it need steel tube in the middle and just a few inches of tube one each end to prevent collapsing the line?

Where is the best place to hook it up in the manifold?

Can I pull vacuum from one of the vac ports on my carb?

With the detent/TV cable does it have to be set in a fashion similar to a 700r4?

Also, how do I go about PROPERLY filling the trans? I've heard to fill the torque converter first, attach the torque converter install the trans and start the truck.... how long do I let it run to circulate the fluid prior to checking fluid?

I'm trying to avoid doing any kind of damage to this TH350 lol.

The reason I asked the last question is because I know if you dont properly fill/bleed a power steering system the pump will be trash as soon a you fire the engine up.

Anything else I need to know that you guys might be able to think of? I'm guessing its gonna be pretty straight forward.

Planning on starting the swap tomorrow and hopefully I'll be mobile again by the end of the day.

 

[skunked]

Manifold vacuum for the th350, usually right on the manifold port. Rubber line is fine and I think it's 1/4" or 5/16", steel hardline handles the heat long term obviously.

Th350 has a kickdown cable, it's not like the 700.

Some say to fill the converter, others have said otherwise. If it's used it probably has some fluid in it.

 

[toomany]

Your Th400 should have vacuum going to its modulator, can just re-bend the line. Or trace where it goes and tap in there.

 

[diesel4me]

When I put a NP-205 in a 77 GMC that had a TH350/NP-203,the rear drive shaft fit ok,but the front one had to be shorter..
You may find both shafts could end up being different,the TH400 is a bit longer than a TH350..

 

[handloader90]

When I put a NP-205 in a 77 GMC that had a TH350/NP-203,the rear drive shaft fit ok,but the front one had to be shorter..
You may find both shafts could end up being different,the TH400 is a bit longer than a TH350..

I still have the original driveshafts from the TH350/NP205.

 

[Fastereddie]

I pre-fill the converter with as much fluid as it will hold without spilling when held standing up. Install the converter into the trans spinning it while inserting. Should get three clunks. Make sure it is all the way in.

 

[diesel4me]

I still have the original driveshafts from the TH350/NP205.

Pays to keep everything!..

I've installed torque converters by pouring a quart of ATF in the snout first if its "dry",then install as suggested above making sure it clicks into all 3 detents while turning it--its easier to get it in properly if the trans it standing up facing you--then once you get the transmission bolted up you can add 3-4 quarts,start it up and let it run about 20 seconds,and add a few more,then it'll be safe to let it run without harming it,and add more until it reads a bit over the 1 pint low mark on the dipstick..

 

[handloader90]

So you spin the converter while putting pressure on it and there will be 3 audible clicks/clunks.

Thanks for that!!

 

[Justin V]

More importantly, the converter is all the way in if you can get the bellhousing seated against to block:

(a) without using bolts to "pull" the trans to the engine. Don't do that...

(b) the torque converter should spin freely after belhousing is bolted up. There should be approx 3/16" between the converter and the flexplate. As you install the converter bolts, the converter will migrate toward the flexplate, closing the gap.

 

[sweetk30]

my only point is i hear people all the time the tow guy wants $$$ to go a short distance . . . . .

its a show up fee / hook up fee / and first few miles all in 1 price .

you cant expect us to do this for free or dirt cheep . the tow truck insurance these days is CRAZY money . . .

rant off .

glad you limped it home . glad your able to get it going again .

 

[diesel4me]

I had to wait a day for a friend to tow my truck home with his ramp truck-15 miles,he charged me $100--thought that was pretty steep till I called a few legit towing companies and was quoted $150-$200,plus they wouldn't tow it to my house after dark,it had to go in their impound yard for the night,that would be an additional $25,then if I had to get it towed to my house a few miles the next day,it would be another $50..

And people wonder why I don't like going anywhere!..

Even if you have towing insurance like AAA,use it a few times,and your shut off for the year,unless you shell out more for the "unlimited" plan..I've been lucky to have been able to limp home after some roadside jerry-rigging most of the time,I think I've only had to be towed like twice since I got my license in 1976..

I shudder when I think of how far I went in some old vehicles with well over 100K on them,like to Nashville,NY,and all over the New England area,and made it there and back,without so much as a flat tire..I'd be terrified to try that now..

 

[handloader90]

my only point is i hear people all the time the tow guy wants $$$ to go a short distance . . . . .

its a show up fee / hook up fee / and first few miles all in 1 price .

you cant expect us to do this for free or dirt cheep . the tow truck insurance these days is CRAZY money . . .

rant off .

glad you limped it home . glad your able to get it going again .

It's probably a reasonable price, I know the time money and labor of moving a vehicle from 1 spot to another equates to something.

I was just glad I could limp the truck home vs. pay $75 to have it moved.

 

[handloader90]

Cleaned the TH350 up with oven cleaner and a hose. Made sure I plugged all holes that water could potentially enter into.

I found two cracks on the bellhousing. One down near the material where the dust cover bolts up and one at the 1 o'clock position between to of the holes for making it to the engine...

Called up the shop that I use for TIG work and he said he can fix it up and have it back to me today for $40

I've gotta make some kind of platform for my floor jack to lower the TH400/203 and lift the TH350/205.

I've got some 3/16" plate in the garage that I'm about to go mess around with.

 

[diesel4me]

I've used one of these before to swap a transmission,but the suck pill is you have to lift the trans up onto the jack,then the truck needs to be up on jack stands high enough to slide the jack & tranny under it,then hope it isn't so high the floor jack runs out of travel before the bell housing lines up with the engine..you almost have to have two floor jacks..

I'm not sure if they sell these at Harbor Freight or not..I got mine used at a swap meet for $25,guy used it only twice,then he bought a "real" transmission jack instead.. (HF sells those I think)....I've read this wont fit a HF floor jack though,the saddle hole is too small..

 

[Kain]

^^ I got one of these off amazon i think

 

[handloader90]

I've used one of these before to swap a transmission,but the suck pill is you have to lift the trans up onto the jack,then the truck needs to be up on jack stands high enough to slide the jack & tranny under it,then hope it isn't so high the floor jack runs out of travel before the bell housing lines up with the engine..you almost have to have two floor jacks..

I'm not sure if they sell these at Harbor Freight or not..I got mine used at a swap meet for $25,guy used it only twice,then he bought a "real" transmission jack instead.. (HF sells those I think)....I've read this wont fit a HF floor jack though,the saddle hole is too small..

View attachment 268107

The plan is to get the trans in this weekend. I'm sure I can come up with something stable enough to keep the trans from falling off and killing me to death.

 

[handloader90]

Here's the bellhousing after repairs.

Not the most beautiful welds but the ones on the inside of the bellhousing were at weird angles. Not complaining for $45 and a 2 hour turn around time.

The welder said that someone had threw JB weld into both cracks...

 

[handloader90]

Anyone have any special tricks for getting to and un-doong the bellhousing bilts besides a crescent wrench and a lot of patience?

 

[tenderfoot]

Man you need an engine hoist. I replaced my th350 a little bit ago. Someone, or a couple people posted here to use one with the chain through the shifter hole. It's the bees knees. The only way. Put the hoist arm through the passenger side door, drop chain through shifter, wrap around trany/TC mount, unbolt cross member. Eazy peezy. It's worth finding one. Borrow if you can't afford one at harbor freight. Was real easy to dismount/remount my 203 on the floor too. Id imagine that would be really tough up in the truck. Even with 205. Its just a win win. The only thing that was a B was getting the chain to hook to itself with my fingers in the shifter hole.

 

[tenderfoot]

Oh, maybe this will help with the vacuum location?