Two Speed TH350
 

Took my '76 on the highway the other day and I just couldn't get it to stay at highway speed. The trans kept slipping. I thought it was low fluid, so I checked and it was OK. Back on the highway again and it accelerated well, but it was revving really high. The next time I accelerated I paid more attention to the shifts and sure enough, I lost 3rd gear. So what is my plan? Is there any point in trying to fix this thing or is it off to the wrecker?

:gmc:

again, try the correct forum.

You've got a great tranny and they are not expensive to rebuild. I'd keep it and rebuild it. TH-350's can be made very tough and a shift kit will get you some thrills along with the return of third gear...:D:D:D

yup definately get it rebuilt, TH350's are bulletproof, and when they do go, rebuild is *relatively* cheap.

TH350s are weak with any kind of hint of power especially in stock form. TH350Cs are even weaker. That said you can build up a th350 to handle some power but in stock form there isn't to much to be said for them in a heavy truck. This one probably has failed due to age and wear though. If you pull it out and have it rebuilt you should be able to save some money. Rebuild with new convertor should run about 500-700.00 depending on the area.

As a trans builder by trade,I completely disagree.A stock TH350(in good working order)will live a long,healthy life behind a mild bigblock.I can actually beef a 350 much more so than a 400,for much cheaper,billet aftermarket goods aside.I ran a Th350 with a hardened sprag gear,redline race clutches and steels,and a slightly modified pump in my mudracer,powered by a nasty 496 BB,with a 500hp shot of spray,and never hurt one tranny.This was in a 4800 pound truck.Please,don't be misinformed.Dollar for dollar,unless your truck already has a 400,the 350 is where it's at.
For the record,350Cs have very few differences outside of the pump and convertor,and will accept all internals of a non lockup 350,so still worth building if you have a competent trans builder.

how close did you pay attention?

our truck has a 400, and i listen all i can and it only shifts twice and also revvs high. The truck has no tach, but it runs at 60 fine, so i think it's just common nature of the 400 and 350 that the 1-2 shift is inaudible and lack of overdrive just makes the engine seem abnormally loud (our truck mathematically runs at 2500 RPM at 60 with 4.10's and no OD).

There isn't to much you can say about what I have experienced in the th350s Ive had. Mudracing with a built transmission isn't like taking it to the track with slicks and seeing how long it holds up. There will be a lot more stress on the th350 then it will ever see in the mud.

Believe me,NOTHING is harder on any part than mudracing.I've built trannys for about anything you can imagine,and nothing produces the heat and abuse that a good ol' fashioned pit does.Yes,it takes a stout trans to live at the strip,but a TH350 is more than up tp the task,as long as it's properly prepped to live behind the powerplant in front of it.
I'm sorry you've had bad experiances with this trans,sounds like your builder wasn't on his game.

bloertcher , would you agree that bluec10 should check his governor?

Yes, you are right about there not being a transmission guy worth anything around here or that I have ever found. Its almost made me seriously look at rebuilding one myself to get the feel for it. There again I don't have all the tools or parts washers and things like that to do a good job nor the money to blow just to experiment. I haven't found anyone I've even thought would be willing to help out with me rebuilding one. Everyone is in it for the money, I know nothing comes free. But its like 1200.00 for 3 month warranty on a stock th350 rebuild with convertor non lockup. In six months I had it two weeks tops, the rest of the time in was in the shop with something wrong. Driving down the road and the governor cover with the clip installed fly's out dumps all the transmission fluid on the ground. They didn't rebuild it or even look at in just installed the governor and cover with the clip put trans fluid in it and said its done. Slipping, bad convertors, warped valve bodies, front pumps. The said rebuild at 1200.00 didn't included "hard parts" other than pump and convertor just the standard "soft" parts.

Getting back on topic, I would drop the transmission pan and inspect it. Look to see how much stuff and shavings are in the pan. More likely than not it is just in need of a rebuild. Possibly look at the governor but I don't see why that would make it slip.

$1200 fpr a 350 rebuild? You sure that's not for a 200/700 series? That's double what a firm shifting tranny rebuild costs here (for a 350). I mistakenly had a four speed rebuilt [2004r in an MCSS] once and it cost me $1600...never again!!

This was a TH350 that didn't have a lockup torque convertor just a basic old style TH350 with a 9in tailshaft. Nothing about it new or warent the 1200.00 dollar for a stock rebuild or only to drive it two 2 weeks out of six months. But that is all combined in the two weeks that was spread out in the six months. Shop look like a good one, had a lot of city vehicals and taxi there. Made sence to me that they would be good place to have do it.

Can you not buy one for less thatn 1200.00 I dont have my summit but I swear they wee like 700-800 for a nice one from them.

Whats the question? I could have bought a transmission from Summit. I didnt know it was going to be that much going into this, it started at 800.00. I dont think I would care to much if I had to ship the transmission back to the factory if anything should go wrong plus the shipment fees. Me being out a vehical to drive, down time, me having to remove and install it, fluid and all that stuff.

Man,$1200.I was born in the wrong place!Unfortunately,this world is made up of a lot of money hungry people who just want the check.I have had trannys come back to me before,(being human and all,I screw up once in a while:()But if there's anything I doubt,I go back through it.On a stock 350,though,there's not really much to go wrong,it's usually your manual valvebodies and trick stuff that make you scratch your head.And luckily,the shop I work for has a dyno,so we rarely have a screw up go out the door.As for building one yourself,if you've got some mechanical skill,I wouldn't really be afraid to try a 350 or 400.They are both pretty simple trannies.Get a good building manual,(I like the transgo manuals)as far as tools,about the only thing out of the ordinary you'd need is a small "press" to push the clutch packs down while your removing the snaprings.All of the snaprings in a 350 or 400 can be removed with a pick tool.While your overdrives and FWD transmissions are pretty tricky,your basic trannies can be done by anyone with competent skills.Just don't tell my customers that!;)Seriously,there's no reason to give over $700 for a TH350,unless it's got some really trick parts in it.And in my opinion,that $700 should live a long,healthy life in a healthy car or truck,as long as it's maintained.Another tip when looking for a good tranny shop,they are rare,but look for one that rebuilds their converters in house.I've ate several trannies over what mylilbowtie mentioned,bad converters,There are some quality rebuilds out there,but there is some junk,too.The shop I work for has a converter shop,and we can build anything from a stock converter up to a 5500 stall with a billet cover and balloon plates,and we rarely ever have a converter failure.

P.S.Yes,he should look at the governer,but this would most likely be a band-aid fix.Sounds to me like it's time for a rebuild.

just wanted to add this...... basic garage built th350 with hardened sprag,good clutches,steels,manual valave body. This has lived behind my 355 solid roller motor + 150 nitrous works kit for the last 3 seasons. This is in a 3600 pound street driven 78 camaro that runs a pretty consistant 10.60-70@128.

I say the th350 is pretty dang stout.

There's nothing weak about a 350 unless a moron built it. I've had one behind my 355 in the Elky for the last five years...it was rebuilt in 1997 (before I bought the truck). I've had several 350's over the years and the only tranny that's stronger is a 400.

I think the 80's 4-speed trannies are the junkers of the lot (200's and 700's)...you couldn't pay me to take either one and install it (I'd sell it on ebay though!). I have owned [1] 200 and [2] 700's so I speak from experience. The 80's were the decade of the least quality from GM as well as many a stop-gap emissions fix on the motors. I tend to stay very far away from any motors/tranny built from 1980-1987.

We have A-1 Transmission in Antiock Ca, here in THE GOLDEN STATE (people think everything is gold) that does a built 350 with shift kit, converter and FULL 1 year warrantee for $650 (you install) He tells me it will hold up to my mild 454 with no problem. The 454 just went in last week so we'll see but I have faith. They’ve built transmissions for me before and never had a problem. Hope you can fine a good reliable shop to help you out.

I would rebuild yer TH350. I had one with a 203 TC behin my BBC 427 for a year, an I wailed on that tranny. No problems. they hold up quite nicely if they are built right. and they should be in expensive to build and rebuild. just my .02$

Have no worries.Should live a very long,happy life behind a mild 454.Honestly,don't tell my boss,but knowing what the cost is on parts,there's a ton of profit in these trannies,even at the $600-$700 range.Anyone who has ever bought a stall convertor would be sick if they knew the markup.
By the way,don't you just hate the tourque of that 454? :burnout:

hi all ,

I got the same slipping problem on my 1977 Impala ( straight six 250ci / TH350 ).

I just did a good oil & filter swap on the tranny and I drove it further 10 000 miles without any problem.

try something : while you drive at least at 30 MPH in "D" mode , try to put your tranny in "N" , while you're driving , and put it back to "D"

this is what I did , and the third speed shifted without problem , for about a 30 miles driving , before it did it again... :banghead:

just my 02 cents , before you throw it all open :D

the Baron