TH400 issues

[Mrturner1]

Ok so I have a 1970 c10, mild build small block with a th400. So with the gear selector in D (drive) when I'm in wide-open throttle from a dead stop it shifts from 1st to 3rd when it should be hitting 2nd. But if I put the gear selector in second from a dead stop and floor it, it shifts into second just fine and barks the tires, and holds 2nd til I shift into 3rd.

Any ideas?

I was about to bring the truck to a tranny shop to get my much needed stall converter (which I'm so excited about, thanks you guys for steering me that direction) and told the guy over the phone exactly what the tranny is doing as explained above, and he says I'm lacking vacuum because of the big cam, and need a vacuum boost canister. I know he's not just trying to sell one because he doesn't even carry them or install them.

He quoted me 525$ for a 10" race converter built local with billet parts and is comparable to high end Coan converters. And another 500 to remove my tranny, inspect, and re-install with new converter.

I'm not a tranny guy, but I do know th400 is an awesome tranny and strong as heck. Can anybody offer some insight and ideas for what to do next? For anyone reading my head and cam combo thread, I decided to take your word for it and leave the motor alone and focus on these obvious issues, so this is where I'm at

[davischevy]

Why not just put a temp. vacuum canister on it and see what happens?

[Mrturner1]

Originally Posted by davischevy

Why not just put a temp. vacuum canister on it and see what happens?

I posted a thread about which ones guys on the site are using and how hard the install is.

[Mrturner1]

Any transmission gurus have ideas?

[hugger6933]

A 10 inch converter is gonna be mighty loose for the street. I had one in my Chevelle and it would flash about 4500 RPM, but that was behind a big block motor. You had better make double sure you put on a good trans cooler cause that converter could cause the trans to get hot.

[60case]

Do you have the electric kick down hooked up and is it working. The connector on left side of the trans should have power when at full throttle

[Grumpy old man]

adjust the modulator valve ,Pull the vacuum hose there should be a small flat head screw adjust 2 rotations to the right and check ,It's not the best correct way to change shift points but it works ,also you would be better served by using a B&M governor kit to change shift points and /or a shift kit . You may want to rethink the whole "race" converter change for street use your just not pulling anywhere near the HORSE POWER to warrant a 10 inch higher stall converter .

http://www.ebay.com/itm/TURBO-HYDRAM...-/320226822325

Just a note WIDE OPEN THROTTLE from a dead stop only lasts so long before you get LOTS of little metal pieces and an oil slick under your truck .


I just read thru some of your threads and I understand it's tough to build a truck with 2 young kids and living in an apt . Maybe buy a nice house with a 2 car garage for your family to enjoy and then you'll have the space to buy all the tools you'll need build your truck and go as fast as you want ? farming out performance work gets real expensive real fast !

[Mrturner1]

Originally Posted by Grumpy old man

adjust the modulator valve ,Pull the vacuum hose there should be a small flat head screw adjust 2 rotations to the right and check ,It's not the best correct way to change shift points but it works ,also you would be better served by using a B&M governor kit to change shift points and /or a shift kit . You may want to rethink the whole "race" converter change for street use your just not pulling anywhere near the HORSE POWER to warrant a 10 inch higher stall converter .

http://www.ebay.com/itm/TURBO-HYDRAM...-/320226822325

Just a note WIDE OPEN THROTTLE from a dead stop only lasts so long before you get LOTS of little metal pieces and an oil slick under your truck .


I just read thru some of your threads and I understand it's tough to build a truck with 2 young kids and living in an apt . Maybe buy a nice house with a 2 car garage for your family to enjoy and then you'll have the space to buy all the tools you'll need build your truck and go as fast as you want ? farming out performance work gets real expensive real fast !

Do I need one of those adjustable vacuum modulators, or is that already on the transmission and is what I should be looking for to adjust as you suggested?

It is a bummer about the apartment. I think waiting on the motor work is a wise decision and I'm glad I asked because id be spending 3400 bucks on a head and cam install right now had I not. But, I do want the truck to at least run good so I can enjoy it now, and my Fiance and daughter really miss going for rides in it too. As it sits, the truck needs a new gasket on the trans pan because its leaking, and with the cam being the way it is, I think a stall converter would make it much more drivable (its a bear at stop lights) and Id make good use of the power I already have. As far as what kind of converter, I asked of couple guys on the site and a 2500-2800 rpm stall is the general consensus for street/weekend driven truck. I don't know the difference between a 10" and 12" converter, I just know that I need a tranny cooler for sure, and would like to get ABOUT 2800rpm stall and have a nice converter that I don't have to replace later with a better one.

[Grumpy old man]

Just my opinion but buy your young family a nice safe home before wasting money on trying to make a long bed 45 year old truck go fast, their only young once and time flies by so fast you'll wish you spent more time and money on them than an old truck . you have plenty of time to invest in a cool truck later after buying a home you don't have plenty of time to invest in your young families future .rent is gone forever ,Mortgage payments mean you're buying something and will get it back in the long run .Take it from a grumpy old man you can't get back the time you spent playing with guy toys instead of kids and their toys ...Go out and buy them some nice Christmas presents and forget about building a go fast truck . Sounds like the money you want to dump into the truck would be better spent as a down payment on a house ? And NEVER NEVER NEVER BUY PERFORMANCE PARTS FOR YOUR TOY WITH CREDIT CARDS.

[Mrturner1]

Originally Posted by Grumpy old man

adjust the modulator valve ,Pull the vacuum hose there should be a small flat head screw adjust 2 rotations to the right and check ,It's not the best correct way to change shift points but it works ,also you would be better served by using a B&M governor kit to change shift points and /or a shift kit . You may want to rethink the whole "race" converter change for street use your just not pulling anywhere near the HORSE POWER to warrant a 10 inch higher stall converter .

http://www.ebay.com/itm/TURBO-HYDRAM...-/320226822325

Just a note WIDE OPEN THROTTLE from a dead stop only lasts so long before you get LOTS of little metal pieces and an oil slick under your truck .


I just read thru some of your threads and I understand it's tough to build a truck with 2 young kids and living in an apt . Maybe buy a nice house with a 2 car garage for your family to enjoy and then you'll have the space to buy all the tools you'll need build your truck and go as fast as you want ? farming out performance work gets real expensive real fast !

I am getting what you are saying though, and thank you for the words of wisdom. its a bumber but most of this stuff is just gonna have to wait. it'd be funner to do it on my own anyway for the learning experience and since it is my truck, and i plan on keeping it forever. I'm only 30 now, so theres time

[Mrturner1]

VA home loan is in process and we got approved yesterday so were shopping for a house now. The down payment is secure, this truck money is just what I set aside after all the important stuff has been taken care of. Theres just not much in the truck budget is all haha

[68c10owner]

Originally Posted by hugger6933

A 10 inch converter is gonna be mighty loose for the street. I had one in my Chevelle and it would flash about 4500 RPM, but that was behind a big block motor. You had better make double sure you put on a good trans cooler cause that converter could cause the trans to get hot.

Only a cheap 10" converter is going to be loose on the street. A high end converter from ATI or Coan will drive like a stocker until you nail it. Foot brake and flash stall are 2 different things and engine torque has to do with it. your converter behind a 350hp sbc would never see 4500. Torque multiplication is a hole other story too. The OP`s cam is unknown but from the video he posted in another thread it is far from stock and needs a converter. Needs gears too.