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help with transmission.

what transmission should i get formy truck

  • TH350

    Votes: 0 0.0%

  • TH35o stage 2

    Votes: 0 0.0%

  • TH400

    Votes: 0 0.0%

  • TH400 stage 2

    Votes: 1 16.7%

  • 700R4

    Votes: 2 33.3%

  • 700R4 stage 2

    Votes: 3 50.0%

  • Other

    Votes: 0 0.0%
  • Total voters
    6
Meir

Meir

Registered Member
Joined
Jul 17, 2015
Posts
16
Reaction score
5
Location
Corl springs FL
Hello guys and girls.
first post here, and i would have loved to introduced myself, only if i could find the "introduce yourself" section :pimp:.
so if someone can direct me to the introduction section, it will be appreciated.

to the thread subject.
i recently bought a 89 K1500 with a bad transmission.
the truck has a 5.7L SBC and the original 700r4 trans whs replaced with TH350 at some point.
behind the TH350, i have a NP241C.
i spent the last two weeks doing research online, and this is what i found (thanks to many posts on this forum).
1. i need to join the CK5 forum :D - Done.
2. i want a TH400 stage 2 transmission - still looking (and will get back to that later).
3. since the 400 is a 32 spline output shaft, and the NP241C is 27 spline input shaft, i will need to convert one of the two to match the other.
4. i will need an adapter that will bolt to the trans on one side and on the transfer on the other.

so far, so good.
i found a transfer input shaft online, that will do the job.
this one if i have the TC with the wide bearing:
http://www.ebay.com/itm/GM-Chevy-GM...-shaft-with-24mm-BD50-8-bearing-/262494239320
and this one if i will need the thin one.
http://www.ebay.com/itm/GM-Chevy-GM...ash=item3d2f77498c:g:7WQAAOSw2s1UwtCD&vxp=mtr
i guess i will figure out which one i need once i have the TC apart.
second step, is the spacer. i believe i will need that one (?)
http://www.ebay.com/itm/Adapter-to-Replace-a-4WD-700R4-Transmission-with-a-4WD-TH400/132311054940?ssPageName=STRK:MEBIDX:IT&_trksid=p2055119.m1438.l2649
so i'm looking at $200-$300 in parts, and i will have to spend a weekend on the transfer (i like to work slow ;)).
in this case, i will end up with a matching 32 spline tran to a 32 spline TC.
my biggest problem, and the main reason for this post, is that i do not have a trans at the moment, and when i try to get one online, the suppliers are asking me for the output shaft stick out i need.
i know that the TH400 4X4 came with 3 different shaft lengths.
shafts length..JPG

which one i need?
i thought it's going to be the easy part right?. just call the transmission company and they will know.
wrong.
i called monster transmissions today, and after talking and waiting on the line for 30 minutes, and going from one person to another, the guy on the phone explained to me that as far as he know, the TH400 never came with the NP241 transfer case, and the only way i could do it, is using this kit from advance adapters.
http://www.advanceadapters.com/prod...ansfer-case-adapter-kit-replacing-700r-trans/
he wants me to buy the kit and have it shipped directly to them. obviously, they will charge me an extra cost for labor, as they need to take a trans of the shelf, take it apart, and replace the output shaft.
another transmissions builder (geared up transmissions) also recommended i will buy the same kit, but said he will not charge me extra, as they are building their transmissions based on customer request anyway. i asked him about the option to convert the input shaft on the transfer, and he said no problem with that. i just need to let them know what stick out i want on the trans output shaft, and source the adapter myself.

yesterday i called advance adaptors, and the guy on the phone was honest enough to "admit" that the NP241 (with the 32 spline input shaft) will bolt with no issue to the TH400, but was unable to give me any information about the stickout i will need on the TH400 output shaft.
however, i was able to find a very useful document on their website that included a very detailed information about the TH400.

http://www.advanceadapters.com/tech-vault/2-gm-th400/

and then i read this line.

trans shaft stickout.JPG

so do i need a 2.4" stickout?

i apologize for the long first post, ands will appreciate if someone can confirm the information above.
also will be very thankful if one can direct me to a reliable source for buying the transmission i want.
based on google reviews i read, i'm not sure i want to go with one of the big name retailers that i found online or sell their products on ebay.

thanks in advance.

Meir.
 
Last edited:
welcome.

introduction thread: https://ck5.com/forums/threads/introductions-greetings.150262/

Intended use for the truck before you go down the rabbit hole?

might want to research monster transmission before you go that route. In all honesty a quality rebuilt th400 is pretty stout as is....again I'm not clear what your planning on doing with this rig.
 
skunked said:
welcome.

introduction thread: https://ck5.com/forums/threads/introductions-greetings.150262/

Intended use for the truck before you go down the rabbit hole?

might want to research monster transmission before you go that route. In all honesty a quality rebuilt th400 is pretty stout as is....again I'm not clear what your planning on doing with this rig.
Click to expand...

thank you Sir.
i also dropped a short introduction with few pics on the link you provided.
but to answer your question, the truck will be used as a fun hobby project. i intend to drive it occasionally, mostly when i'm working on my other car or need to move large stuff.
at the moment we have only sports car in the household.
now, since i live in south florida i cannot climb mountains or rocks, but we do have a lot of mud.
so if i need a new transmission, i might as well put in the best one i can get (within my logical budget) that will fit my plan to put large tires (35-37) and stronger power plant (383 stroker maybe)

i did researched monster transmissions, but after talking with them, and reading google reviews, i do not think it's the best option out there.

thanks for your reply.
Meir.
 
a th400 sounds to be overkill and a lot of extra work for what?

keep in mind the th400 with the taller 1st gear is a bit of a power killer. It's absolutely a stronger trans however I don't see the necessity in your situation.
 
I agree with @skunked here.
Not only does the ratio of 1st gear pull some of the power, the TH400 uses more power by itself.
But I won't use an automatic transmission without some sort of shift / pressure improvements.
I have a 700R4 behind the big block in my '70. (My avatar pic) It has 40K on it now.

Now as to your question, to do the 400 swap, I would find a factory adapter, swap the input shaft of the t-case, then measure things with the adapter housing on the t-case.
And if you are going to be running a 37" tire, I honestly think that you will want to ditch the 10 bolt rear axle and get lower gears at the same time.
(Rabbit hole!!!)
 
Hi skunked.
Thank you very much for the input. I agree that the 400 is probebly an overkill for what I will need to get out of the truck.
The extra work is purely for my enjoyment and interest. On the same note, I probably don't need a 450hp engine and 35 or 37 inch tires. But I'm going to do it anyway at some point.
Unfortunately (and only from that point of view ) I live in south Florida, so no rocks and mountains to climb. Just muddy trails.
I want a built proof transmission, mostly to compensate for the large tires and the high torqu/HP engine that will follow.
With that said, I whould like to consider myself as a smart man. And a smart man always listen to the smarter and more experience.
So what are my options?
Stick to the 350 Or go back to the 700r4 ?
Any other options I am not aware of?
Once again, thanks in advance.
Meir.
 
I love Th400's but in your case I think I'd just have the Th350 rebuilt and stuff it back in...they aren't as weak as people make them out to be,and the ones I've had in my plow trucks held up well for over 10 years and were not babied,nor did I change the fluid more than once in any of them--and I bet they had 100,000 on them before I bought the trucks..

Sticking with what you have is a lot easier and cheaper,and less likely to induce further issues than swapping to a TH400..as noted the 32 spline output requires the matching transfer case input,the flex plate you have might not bolt up to the converter,and the driveshafts may still work,or may not,the overall length may be different enough to be an issue there..you also need to rig up a downshift switch for passing gear if you want it to work by the gas pedal and not have to manually downshift..

The TH350 is a better transmission than a stock 700R4 is,but the overdrive and lower first gear of the 700R4 is desirable ,and they will fit in without any modifications (especially since your truck had one originally)--same output splines,etc..a rebuilt one of 1987 or newer vintage that has the upgrades and some heavy duty parts like the sun shell and others they are noted for having failures replaced will likely last as long as you own it...

I've read a lot of complaints about "Monster" transmissions and some other similar builders online..not sure I'd want to deal with a mail order company due to hassles with warranty and shipping costs if you had to return it..(and to R&R it twice will suck double too!)..
 
thank you guys that is really some good info there.
i guess i should have shared some background information about my project.
to keep this thread transmission related, i will open a separate thread, and will share some info there.
will also start looking at a rebuild 700r4's
anyone is familiar with these guys?
https://www.geareduptransmissions.c...issions/products/g-2-700r4?variant=6023605829
they are 4 Hours away from me, so if i have any issues i can drive the truck thru their window :weapon39:

just kidding. :D

the 350 on the truck is not a good candidate for a rebuild. i suspect it to have a cracked case.
i will put some info on my build thread.


thanks again.
meir.
 
keep in mind the 700 is a couple inches longer so you'll likely need to modify your drivelines.
 
Unless whoever swapped in the TH350 used the spacer on the tail,to make it equal to the 700R4's overall length..
 
yes. there is some sort of a spacer in there.
the cross member looks like it seats at it original location.
i will try to get some pics tonight, and share some more information about the current transmission condition.
 
So, this is the back ground.
when i bought the truck, the transmission was already bad. the seller told me that he "change the fluid and filter, put it back together and since then started having problems.
the symptom is, that when you put it in gear, it will not go in all the time. sometime it will, sometime it won't. sometime you have to warm it up, and all is good. once it's in gear, it will shift with no issue."
that was more or less the seller words.
so, when i bought the truck, i already took in mind that a new transmission will go in.
when i picked it up, i gave it a try (before calling a tow truck) and after 5 minutes of warmup, the trans went into gear.
i was able to drive it home (about 25 miles), the trans shifted from 1st to 2nd, but no 3rd and no kickdown.
as soon as i parked the truck the transmission fluid introduce itself to my driveway.
the next day i wend under the truck for a closer look.
the pan was still dripping fluid, and it was obvious that it was not installed properly. it looks like the bolts were over torqued, and also over use of a sealer (that if you ask me was not transmission sealer).


IMG_6567.JPG

the gasket is all squeezed out.
i looked around, and also the governor cover was sealed with RTV.
removed the cover, tested the governor, and the piston is stuck. ordered a new governor new transmission pan and gasket.
the mating surface of the governor was clearly pitted (i guess someone did a bad job removing the cover in the past) and the cover had no O-Ring.
i also found out that one of the thrads for the pan bolts was striped, and the kickdown cable was not properly seated in the transmission case.
i also found out that the whole cable bracket near the TBI was completely loose.
so i sort that out, adjusted the kickdown cable, installed a helicoil on the stripped thread, and waited for the parts.
when i received the new pan and governor (with new O-Ring and new cover) i installed them back on the transmission, and filled it up with 4 quarts of fluid.
not before i made sure to thoroughly clean the mating surfaces, and torque all the bolts in 2 stages to the correct spec (18ftlb).
started up the engine, run it thru the gears, and nothing.
most disturbing part, is that the dipstick shows overfill both on cold and hot. like if the transmission is not pumping the fluid.
i will not be surprised if some of the RTV he used was sucked into the transmission blocking passages, or just the pump went out.
on top of that, the pan is still leaking from one of the bolts (not the one i helicoild), not as bad as before, but still a leak.
don't know. maybe the case has a fine crack in it that i didn't see.
anyway, even if i decide to stick with the 350, i'm better off not using this one as a core.
 
Yeah,it sounds like it might have internal issues,or the RTV got in a place it shouldn't have maybe..could be a hairline crack causing the slow leak too,and if it is indeed cracked where the valve body passages are in the case,it could well be the cause of all your problems,the pressure will cross leak into other passages, instead of applying the clutches,or maybe the converter is getting air bound..

I've had vacuum modulators go sour on TH350's and they will act like you said as far as not upshifting into third until you get it going like 50 mph,and it will "free wheel" if you let off the gas in second before it finally goes into third..but a modulator most likely wont cause that delay going into gear until it warms up,or the govenor ,those just control the shift points..

I had a Th350 in a '72 K5 that did that for years,the "delay"--it refused to go into forward gears until the engine warmed up some--colder it was out,the longer it took...every morning it made me wait!.

-I almost got fired over it,finally got disgusted enough to buy a SM465 and transfer case and convert it to a manual transmission..

I never did an autopsy on the Th350 to see what caused that,it was probably a clutch piston seal ,said many transmission repair guys I asked...weird thing was I could drive it cross country once it went in gear with no slipping or shifting issues..and reverse worked instantly,regardless of the temprature too...
 
Ye. the symptoms sound very much the same.
After I’ll get the new transmission (we still need to decide what I’m getting guys :whistle:) I plan on taking the 350 apart. Just out of curiosity.
Since I will not have to put it back, I don’t have a problem to end up with a bunch of cool paperweights, and a base for a coffee table. :haha:

coffe table.JPG

or a sink.:yikes:


sink.JPG
 
Meir said:
Ye. the symptoms sound very much the same.
After I’ll get the new transmission (we still need to decide what I’m getting guys :whistle:) I plan on taking the 350 apart. Just out of curiosity.
Since I will not have to put it back, I don’t have a problem to end up with a bunch of cool paperweights, and a base for a coffee table. :haha:

View attachment 245977

or a sink.:yikes:


View attachment 245978
Click to expand...


Turn that around and it would make an awesome urinal!
 
That makes it the same length as a 700R4. No driveshaft work when they did the swap.

So with the power that you are wanting to shoot for, and the possible tire size, are you still leaning towards the 400?


And then solid axle swap with better gears to go with 37" tires?

I think that you should!!!
 
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