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Weird problem with TH400 (see post #79)

andyblack

andyblack

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The stock TH700R4 in my '85 shortbed pickup went out this week. It had been sounding worse and kinda slipping for a couple of days and when I backed out of the driveway and put it in drive, I heard a loud BANG. I started driving down the street and when the trans shifted to second gear, I started hearing some awful grinding and ticking sounds.

I don't really want to repair that trans though because I've had it leak and burn fluid and stuff before. My dad says to go with a TH400. He's rebuilt literally hundreds of them and has all the stuff to build one up for me. What I don't know about though is all the stuff involved in a swap like this. I used the search function and found out that I should be able to use my old driveshaft (as long as I use another NP208 t-case) and that I would need a 32 spline NP208. I know it's possible to swap the input shaft on the case from the current 27 spline to the required 32 spline if I have to. What else do I need? Will my old crossmember work? I read that the TH400 is only 3/8" longer than the TH700R4, so I guess my driveshaft will work. What about shifting? I don't think the 400 will need the TV cable like the 700 does. So what does it need to shift? Is it electric or vacuum operated or what?

I guess my main concern is my engine. It's the stock 305. Will a TH400 bolt up? Or do I need a regular 350 engine? I have so many questions but I'm sure some of you guys know all about how to do this.
 
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Personally, I'd replace it with another/rebuilt 700R4.

The TH400 will bolt up to the 305 as long as the trans has the chevy bolt pattern instead of the BOP pattern, but IIRC all of those were 2wd. It's vacuum modulated and has an electric solenoid for kick down. You will lose OD and mileage.

What gears are in the axles? What size tires do you run or plan to run? How is the truck used?
 
I would stay with the 700R also. TH400 is a great double tough trans, but you may have to have your driveshaft length changed. Depending on gearing, you mileage will suffer quite a bit. 700s can be built to handle alot. Just takes someone who knows how to build em.
 
any other tranny than 700 combo you have now = money for drive shaft length diffrences and other mods to fit .

unless you do a th350 swap with a fitz-all spacer kit made for the 700r4 to th350 swap with no driveline mods.

and also a th400 is yes a great tranny but the unit eats 15-20 more hp to turn the bigger guts inside it than a th350 or 700r4 so this means less power to rear wheels.

and last with todays fuel prices why drop a non overdrive back in unless off road only truck. ? ? ?

i my self am getting ready to swap in a 4l80-e to my k30 were a th400 is now to get more fuel mileage.

lots of guys here run these 2 brands and no problems .

http://www.bowtieoverdrives.com/index.shtml

http://www.monstertrans.com/store/
 
My vote is keep the 700R4. I have 3 of them and one is behind my 462BB. I think that your 305 is going to feel really sluggish on acceleration with the 400 trans. Remember that the first gear ratio is deeper in the 700R4. Your truck may have tall gears in it that may lessen the loss of OD with the 400, but in town is where I think you will notice it more. I have a '87 TBI 305 truck with 3:42's and it seems more doggy than my '90 Jimmy with TBI 350, same gears and larger tires.
 
Just some of the questions I needed answered too for a '87 Silverado,..whether to go with whats already in it(TH700) or swap up to a TH400. But the mods is what I would be wondering about,...affordability,mechanic who is willing to work on it and initial use and intent of the upgrades,trailer hauling,4wheeling or bogging,etc.
 
Check out Raptor trans, Monster trans, Bowtie Overdrives. All of them have a wealth of info on what upgrades are needed/available, as well as complete trans.
 
imo if the truck is seeing any kind of highway driving, 700 or 4L80 all the way...

especially with the 305 factor.. nasty BB, sure I'd consider the 400.. but an anemic 305 and that first gear are gonna make it a pig...

BTO for me...... a well built one will last a long time...
 
Thanks for the feedback everyone. The main reasons I was looking at the 400 were strength (obviously I've done something to break mine, like bogging and stuff) and availability. There's a guy who wants to trade me a 400 and 208 out of a military Blazer (or truck-I don't know) for a gun. I'm sure the trans will need rebuilding because it's been sitting around for a long time, but like I said, my dad can rebuild it really fast. I've also decided that I'm going to go ahead and replace the tired old 305 with a stockish 350.

So I've about decided that the thing to do is try the TH400. So now I'd like to hear from someone who's actually did this swap. Is there anyone out there that can share some firsthand info please?
 
Oh by the way, I drive this truck about 10 miles a day usually and I seldom do long trips in it. I don't go off road much anymore, but when I do, it seems like something breaks (last time it was the stock transfer case). The truck has either 4.10s or 4.56s in the stock 10 bolts rolling on 35s. I plan on installing Lock Rites in both axles after I get this transmission dilemma solved. I do plan on taking it on trails and through the mud a lot more after that.

Just so y'all know.:D
 
plan on new drive shafts possible then with swap. and moveing crossmember and possible diffrent one .

also 4.10 or 4.56 in 85 10 bolts = not likly at all :whistle:

you best search here first on all the mods for the best pay out.

10 bolts dont like lunch box lockers in the rear like the lockright. weak carriers in them. and locked front 10 bolt hard to steer and severly hard on axles and u-joints .

all this stuff has been covered here a lot . so sit back and read up to get the best bang for the buck.
 
I vote 700, my buddy swapped a th400 into his, I just dont like how much doggier it feels off the line.
 
I went ahead and got me a TH400 and a 32 spline NP208 to use because the price was right and I just think the 400 is less likely to break on me again. So don't hate. :rolleyes:

Now maybe you good fellas can tell me a few things about this swap. I was able to get the electric kickdown switch and the plug that goes on it. Two wires come out of it. I think one is orange and the other is purple with a black stripe (I think). I saw where the orange wire goes to the trans, but what about the other wire? 12 volts? I got the bracket for the switch and the gas pedal too.

Another thing I don't know about is the torque converter. The 400 came out of a military Blazer that had a diesel engine. I'm going to be bolting it up to a gas engine, most likely a 350. I got the torque converter that was in the original diesel truck (at least I think that was it - it was lying out by the trans). Will that converter bolt up to my flywheel and all? I mean I'm just going to turn it in as a core and get a rebiult one if it's the type that works. If not I'll go back to the junkyard and get one that I can turn in of the type that will work.

What else do I need to know? Can anyone suggest any upgrades that I might be able to do while I have the trans apart for a rebuild? I got the linkage and the cross member and skidplate and all too.

Oh and those aren't the original gears in my (lame) 10 bolt axles either. The truck originally came with 3.08 gears. I would imagine that life would be pretty miserable if I still had them in there now considering that the truck came new with 235/75 tires originally.
 
I beleive it can be bolted up but stall is alot lower on a diesel. I know mill did on his, but i thought he had to do something with it. If just for a core it may not matter but im not sure sorry
 
andyblack said:
I went ahead and got me a TH400 and a 32 spline NP208 to use because the price was right and I just think the 400 is less likely to break on me again. So don't hate. :rolleyes:

Now maybe you good fellas can tell me a few things about this swap. I was able to get the electric kickdown switch and the plug that goes on it. Two wires come out of it. I think one is orange and the other is purple with a black stripe (I think). I saw where the orange wire goes to the trans, but what about the other wire? 12 volts? I got the bracket for the switch and the gas pedal too.

Another thing I don't know about is the torque converter. The 400 came out of a military Blazer that had a diesel engine. I'm going to be bolting it up to a gas engine, most likely a 350. I got the torque converter that was in the original diesel truck (at least I think that was it - it was lying out by the trans). Will that converter bolt up to my flywheel and all? I mean I'm just going to turn it in as a core and get a rebiult one if it's the type that works. If not I'll go back to the junkyard and get one that I can turn in of the type that will work.

What else do I need to know? Can anyone suggest any upgrades that I might be able to do while I have the trans apart for a rebuild? I got the linkage and the cross member and skidplate and all too.

Oh and those aren't the original gears in my (lame) 10 bolt axles either. The truck originally came with 3.08 gears. I would imagine that life would be pretty miserable if I still had them in there now considering that the truck came new with 235/75 tires originally.
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I wouldnt have wasted my money on a 700 either. Especially if you can get the 400 built by family for free or cheap.

I swapped a 700 out for a 400 out of a CUCV. The converter worked fine. The trans shop I called to buy a new converter told me the stall speeds are the same between diesel and gas, and I've yet to see otherwise, so I ran the diesel converter. It ran and drove fine. I believe the governor needs changed, but I'm not sure.

I think TCI or someone makes a kickdown switch for this swap, I did a reverse manual valve body, so I didnt mess with the kickdown.

I used the stock crossmember but had to modify it a bit. The mounting foot on the 208 adapter was longer than the stock one, so we cut the crossmember and dropped it down 2 inches or so. I think it was to make up the difference on the 1 ton frame, I remember the 1 ton crossmember being fairly flat.
 
If going auto I would have only considered a 400 or a 4l80e. 700/4l60/4l60es are OK but even built ones will only take so much.
 
I'm torn between replacing the dying 700r4 in my 85 diesel Suburban with another used one,or to go with a TH400 too--I have a TH400 out of a BB '74 Monte-Carlo I could use,and a NP208 T-case with the 32 spline input..................................................................................................I know the tranny will likely need a 4x4 output shaft swapped in ,and maybe a rebuild kit (it worked OK when pulled 15 years ago,but has sat in my dry shed since)....but I would likely need other parts to complete the swap,and I know putting anything other than what was in the truck in will be more work,expense,and possibly a headache...since my physical condition isn't the greatest,I might have to farm the job out to a friend too,something I dont have the cash for...I'd rather use parts I have,than buy a used tranny in unknown condition,as I cant afford to do it twice either!...............................................................................................In my instance,I wont be driving the truck far very often,if at all,and wont be going off road,I'd just use it locally and to plow my driveway (which is why I'd prefer a TH400 or a 700r4)...I feel the 5 mpg I might "lose" by not having overdrive and the slower take offs of a higher first gear might not be such a big deal,when I'd gain a beefier tranny in the end.....heck,up until 1980 or so,we had NO overdives,and we still managed to drive everywhere we wanted to go,towed our trailers,etc,with no troubles....................................overdrive is nice,but not a must,IMO---...............................................................I've seen way too many overdrive trannies go bad at fairly low mileage with NO abuse,so many,that I feel its not really a step "backwards" to go with the older,more durable automatics,and call the loss of a few MPG a "wash"...you can buy lots of fuel for what it costs to rebuild a tranny ,IMO...ask any tranny rebuilder which is stronger,an overdrive automatic or an "old" 3 speed one,and you'll get the same answer--"old" ones were much longer lived when used in harsh conditions...
 
When marty when from a 700 to a sm465 he actually gained mpgs.
 
diesel4me said:
I've seen way too many overdrive trannies go bad at fairly low mileage with NO abuse,so many,that I feel its not really a step "backwards" to go with the older,more durable automatics,and call the loss of a few MPG a "wash"...you can buy lots of fuel for what it costs to rebuild a tranny ,IMO...ask any tranny rebuilder which is stronger,an overdrive automatic or an "old" 3 speed one,and you'll get the same answer--"old" ones were much longer lived when used in harsh conditions...
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http://monstertrans.com/store/produ...,-Mega-Monster%2dIn%2dA%2dBox:-1985%2d86.html <--- Basic rebuild kit for 700r4 is $499.

http://monstertrans.com/store/produ...S-Mega-Monster%2dIn%2dA%2dBox:-1985%2d86.html <--- SS Mega Monster rebuild kit for 700r4 is $799

Local gas stations have regular gas at $3.63 per gallon as of this morning. I think I have a 32 gallon tank in my blazer. If it was completely empty and I filled it up it would be $116.16 to fill it up. So it would be roughly 5 tanks or 8 tanks depending on which rebuild kit you went with. Depending on my driving, how far I drive, if its in 4 wheel drive or not, etc. etc. I probably average a tank every week to week and a half. I wouldnt think about putting any tranny without an overdrive in mine. To me the rebuild kit is alot cheaper and most likely faster to get the vehicle back up and driving again than to do anything other than whats in it. I dont know about anybody else (and I'm assuming by the OP post about the noises that his tranny is no longer working) but I have been talking to the owner of a local salvage yard and he will let me have a 700r4 for free to rebuild, once I rebuild it and put it in my blazer I take the one I pulled out and give it to him. My blazer still runs and drives but I was just thinking about rebuilding it cause it has been in water, it has lost its fluid thanks to a busted line and I know it has been hot so its just a matter of time. I am however putting it off because I am looking for another vehicle so I can hopefully/finally swap all of these parts I have been collecting into the blazer. When I do that the blazer will get the 6.0 motor I have and I will be looking for a 4L80e.
 
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