My TH350 and alternatives (TH400?)

[GoGoGirl]

Tomorrow I will probably know if it's time to pull my tranny and bring it to a professional. I'm mentally preparing for the possibility that it needs to be rebuilt or replaced.

Looking for anyone's advice, input, comments, wiseassery, etc

I would love the pride of solving this problem myself and before anyone rolls their eyes about a relatively clueless chick crawling around under a truck to try to remedy anything, rest assured that I have the willingness to learn and get dirty and hurt in the process. I've even decided not to put on nail polish for work tomorrow in case I spend the morning crawling around the Blazer

Vehicle is a M1009 CUCV converted to 12VDC, 350ci gas engine, NP205, and TH350.

I've had the vehicle for a year, she has a TH350, which was working fine. I don't drive it often, usually commuting to work once a week and maybe to move things on my days off. I have barely begun to do all of the work that I plan to do (mainly cosmetic and body work). I noticed the truck occasionally wouldn't move forward when I shifted to Drive and gave it gas. It hesitated and I heard a sound like a belt squealing, but only for a few seconds. That seemed to be getting worse lately, to the point where I would need to rev pretty high (going by ear since no tach) for 10 seconds or so, and hear something squeal like a hurt pig before moving. Once warmed up, it seemed to shift fine and if I stopped and re-started, the squeal noise wasn't there.

The truck sat for 2 weeks at a friend's house as they were doing some work on the interior and upholstery for me. I went Friday to pick it up. It started fine and then I went to drive away. It squealed and would not move. I tried all the forward gears, same thing. Put it in reverse and it was perfect. So at that point I had reverse but nothing more. I reversed out to the street so I had more room to try to pick up speed if it decided to work. I tried to go forward again and nothing happened, though the squealing eventually stopped (which could be a bad sign from what I read). I pulled the dipstick, and I was shocked-- for the first and only time since I bought it, the dipstick was bone dry. I wasn't sure how many quarts of fluid I needed (of course I searched online, but could not find a definite answer), so I started adding until it showed up in the zone on the dipstick...roughly 8 quarts. It took forever as the fluid trickling down the dipstick tube kept me from getting a good reading. Please understand I have zero prior experience with transmissions and the people I was visiting don't know much about them either. My friend's dad was a regular basic shop mechanic and crawled under as I shifted through the gears and he said mechanically it looked like everything was working and moving properly. He doesn't know transmissions well but said that everything looked normal. I tried again and same thing happened, so now with all the fluid in it, we have the tranny still not wanting to go forward, only reverse. I left her parked in my friend's driveway until tomorrow morning.

Best case scenario: I just need to let the fluid trickle down the dipstick into the tranny, and it will work fine tomorrow.

Worse case scenario: New tranny and transfer case, and who knows what else.

Now, with all that being said, is there anything else my not-very-knowledgeable mind can check? Maybe loose vacuum hoses, etc? Try my best to avoid paying anyone to do anything, even to look at it.

If I bring this to an expert and they say it needs a rebuild or replace, is the TH400 a better choice? I do use this vehicle for plowing sometimes (easy residential driveway) and intend to keep doing so. Some forums I read seem to say the TH350 is fine for that, others say the 400 is better. If I went to a 400, do I need to replace the transfer case or anything else?

Thank you all.

 

[sweetk30]

have you chatted with @Greg Ducato on here yet ? he is the trans guy here .

th350 is 27 spline output shaft and 4 bolt pattern .
th400 is 32 spline output shaft and 6 bolt pattern .

th400 is longer also = drive shaft work front and rear . and th400 has bigger parts to spin so it eats 20hp or more to do the same work . so unless you need a th400 then a th350 is just fine.

if needs reman job a good quality reman with transtar rebuild kit and noyoyo shift improver kit with a fresh remaned converter will get you a good reliable th350 .

 

[skunked]

Reman the th350 if it needs it. Don't see the point of going th400 for your use. Maybe a 700R if you want overdrive......

 

[diesel4me]

I plowed my 110 x 30 foot Y shaped driveway for 15 years with a '77 GMC K2500 that had a 454 & Th350 when I bought it,after a few years I put a 400 small block in it because the 454 developed a weird wrist pin knock --the Th350 lasted a lot longer than it should have,I had many 2+ foot storms with deeper drifts and it was the "wet cement" snow we often get here,and the truck was not able to be used until the storm ended...

It finally lost reverse one summer day without much warning..it may have been a simple problem but I decided to part the truck out instead of getting another tranny (and I regret that now,I could have got a few more years out of it)...

I also had for my first plow truck,a 1971 GMC K1500 with a 305 and TH350,I plowed with that truck nearly 10 years too,both my own driveway and the parking lot at the place I was working at..
The 305 ended up dying,it had a burnt valve and I yanked the head off that side and replaced the burnt one,and lapped the rest in,then it smoked like a tire fire afterwards..so I bought a 350 for it..
I did not baby that truck either..

My '72 K5 had a TH350 in it too,that one would refuse to go forward after a cold start for up to 5 minutes,reverse worked fine though..after waiting with it in drive or low ,it would start "bumping" into gear--once it fully engaged,I could drive it anywhere,any distance,and it worked perfectly..shut it off and let it cool off several hours,or overnight--no forward gears until it warmed up again..
I "fixed" it by installing a SM465 4 speed setup from another truck..

I was told the TH350 probably had bad lip seals on the forward clutch drum,but I never did take it apart to see--my ability to repair an automatic is limited to fluid and filter changes,and replacing the modulator valve..anything beyond that I either get another good used one or take it to a pro..

The Th350 is a bit weaker than a Th400,but in my experience they hold up pretty good..better than a 700R4 by far..

 

[GoGoGirl]

Thanks for all the replies! Fingers crossed for the morning!!! Ugh I hope the damn thing just needed fluid and is fine!!!

 

[diesel4me]

The squeal and it being 8 quarts low is not good--the TH350 only holds around 10 quarts if I remember right,and the pump can starve for fluid even if its only a few quarts low..when it drops too low the clutches cant apply firmly enough to propel the vehicle and the pump cant make everything work with the fluid level too low..

The squeal was probably the pump or the clutches slipping..

You may have a leak at one of the tranny cooler lines ,that much fluid just doesn't drip out overnight..

I've had automatics with a clogged filter make a siren type noise,similar to a power steering pump thats low on fluid..but a clogged screen would likely affect all gears,not just forward..

Like I said before,I haven't tried doing any repairs beyond what I listed,Greg Ducato here is the man who would know what can cause that squeal and advise you if it might be a simple fix..

I have pulled and replaced a few automatics lying on my back in the driveway..its not a fun job,or easy,but you can do it with a good floor jack on a hard surface..the hardest part for me was getting it out from under the truck once it was out..I used two floor jacks--one to lower the transmission and the other to jack the truck up high enough to drag it out from under it..holding the torque converter still while loosening the bolts to the flywheel was difficult,I used a piece of wood jammed against the teeth on it..


If I had to do another one I'd cut the steel cooler lines about 6" from the transmission and use compression fittings or the right kind of rubber hose and clamps to splice them together--its a sucky place to get at if you want to remove them with a wrench at the transmission..

It took me about a half hour just to get one line fitting to thread into my TH400 on my truck a few weeks ago,the front drive shaft rubbed on the line and almost wore a hole in it..luckily I spotted it just before it started leaking..

 

[GoGoGirl]

Thank you, I sent a message to Greg.

The Blazer didn't want to move again this morning. I will be away for the rest of the week and so she sits.

 

[Greg Ducato]

With that much fluid loss my guess is that you have seriously damaged the forward clutch pack. With your described use I would have a qualified builder go through your trans and converter and apply upgrades such as the late 700R4 low sprag ( extra helpful under load especially with a plow) and a good shift improvement kit that addresses increased line/lube pressure not necessarily hard shifts. A small box kit from Superior or TransGo will do the trick. I would request a TH-400 torque converter while it is out and apart. This will give you greater fluid capacity and a bit less stall speed so the trans will run cooler under load and reduce converter slip at highway speeds. No need to mess with the transfer case unless it needs a few seals. Be sure and flush the cooler and lines and consider adding a cooler to the system at this time in series with the radiator. A good stacked plate design doesn't take up much room but will make a good bit of difference in fluid and trans life.

 

[RubberFloorMat]

Trans is toasty. Shouldn't be that much to get a basic rebuild. I did a complete rebuild last year on a th350 that died exactly like that and I just got the best kit I could find, a transgo shift kit and new converter. Maybe 450 in parts and 400 in labor.

 

[GoGoGirl]

For all of those who have contributed above, for all who are interested in what an M1009 can or can't be modified to do...I present to you an update!!

I followed advice above as well as from friends. First I sought out an old man who has been rebuilding transmissions for decades. I was assured that's the kind of person I needed rather than a corporate place with a bunch of kids rushing the jobs for maximum profit. This was surprisingly easy through word of mouth. I found a guy named Fred with a shop in the absolute middle of nowhere (and wow do I mean that...look up 228 Cross Rd, Ferrisburgh, VT) and almost all he does are transmission rebuilds.

I explained to Fred the alleged history of my vehicle and that it was used to plow snow in the past and I intended to continue. He assured me that with proper maintenance and careful selection of gears, I could continue to use the NP205/TH350 combo.

I printed this thread and gave it to Fred and told him to take his time and do the best job he possibly could with the best components (it's been about a month now). I don't have the invoice in front of me as I have yet to go pick up the truck, but he called today and it's ready.

The first piece of good news is that I do indeed have a 205/350 in there. At least the previous owner was honest about that.

What about how the PO said it was rebuilt just 1000 miles ago? Fred said the previous "rebuild" looks like it was done by someone who had never worked on a transmission before and only a couple things appeared to be replaced. The gaskets were even re-used! Even I know not to do that!

So now I'm totally psyched and can't wait to get the truck back!! Total he's charging me is $650, with no markup on some parts that he already had on hand. I think that's fair. I know it needed a torque converter, and when I go get it Fred will review everything else with me.

Yay!!!

 

[Capt Ron]

Fred Where Abouts? Ummm yep that is the boonies! $650.00 is reasonable provided all has been done that was discussed. It would be double that here.

 

[GoGoGirl]

Fred Where Abouts? Ummm yep that is the boonies! $650.00 is reasonable provided all has been that was discussed. It would be double that here.

That's him!

I never looked it up on Google Earth til now...the orange vehicle with the white roof you can see, to the southeast of his shop, is a 73 K5, and the white vehicle just south of that is a 76...he loves squarebodies!!!

Shop itself is very impressive in person, two bays with rollup overhead doors, each tall enough to get a semi with stacks in there. Long enough building to fit vehicles two deep plus having a fabricating shop in the back and a little "office"/den on the side (northernmost portion of the building as soon on GE).