From TH350 to TH400 - Pontiac GTO Forum
User Tag List

 1Likes
Reply
 
LinkBack Thread Tools Display Modes
post #1 of 13 (permalink) Old 04-13-2017, 10:17 AM Thread Starter
 
KowalskiCW's Avatar
 
Join Date: Jul 2016
Posts: 106
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 23 Post(s)
Garage
From TH350 to TH400

So I had a TH350 in my Lemans and I bought a used TH400 and am trying to refresh it on my own which is turning out to be a HUGE nightmare.
First I broke off two pan bolts out of 13...the two that are exposed in the bell housing area. They were so rusted in I drilled them almost completely out and still cant get the threads to release!
Second the modulator is also so rusted in I cannot pry it out. I've tried everything. Hammer, pry bars, rust release spray for days upon days. Nothing. I finally sawzalled the fat part off and got a vice grips around the base and got it to turn every so slightly. I'm beyong going back now but need help! How can I get that thing off? Do I have to take it to a shop after all? Oh I tried heating up the trans case around it too. Nothin.
Third there is a plastic electrical connector which I believe powers a downshift solenoid. I'm not sure my TH350 had that? Do I HAVE to use it? Can I just downshift manually which I like to do anyways since I really wish the car was stick anyways?
That's all...for now.

69 Lemans
KowalskiCW is offline  
Sponsored Links
Advertisement
 
post #2 of 13 (permalink) Old 04-13-2017, 07:49 PM
 
Join Date: Jan 2015
Location: Injun Territory, 'Merica!
Posts: 1,069
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 62 Post(s)
What a fubar disaster. what's the year & two letter ID code on the alum tag that is attached to the side of the T400 case??? if it's nothing special, it's time to make a trip to the "nice fellow that made you such a good deal" on the T400 & driveshaft.

Kick down switch mounts off a stamped steel bracket that mounts off the gas pedal rod. There are several different '68-72 A-body gas pedal rods, I believe the '69 rod is the same as T400, do know the rod is an oddball on a '72 with T350. Should have, in stock, the kick down setup if you ever get squared away with a decent T400 to have rebuilt.

Last edited by Pinion head; 04-13-2017 at 07:59 PM.
Pinion head is online now  
post #3 of 13 (permalink) Old 04-14-2017, 08:10 AM Thread Starter
 
KowalskiCW's Avatar
 
Join Date: Jul 2016
Posts: 106
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 23 Post(s)
Garage
Yea PH he had 3 or 4 trans sitting around and the one I chose was from a 69 Lemans/GTO. It looked dirty but it turned nice and free. I didn't want it rebuilt by anyone. I just wanted to drain the fluids, replace the output seals, filter, modulator and anything that looked worn. I had no idea nor did he that the bolts were seized and the modulator was seized. I don't want to make enemies with this guy he has been a tremendous help and has every GTO part any of us could ever ask for just sitting in his storage and home shop.
I believe FJ - 69 are the digits from a picture I took but if that doesn't sound right I'll have to check tonight. Thanks for the kickdown offer. I'll keep that in mind. Is it easy to add as an after thought if I end up getting annoyed with manually shifting?

69 Lemans
KowalskiCW is offline  
 
post #4 of 13 (permalink) Old 04-20-2017, 01:38 PM Thread Starter
 
KowalskiCW's Avatar
 
Join Date: Jul 2016
Posts: 106
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 23 Post(s)
Garage
So please someone give me an idea of how to get a really rusted modulator out! It should just pop out with some force right? I mean it's not screwed in or anything on a 69 TH400? My last resort is a slide hammer which I plan on trying this weekend. I've soaked and soaked and bashed with a hammer and tried heat. I finally cut the main body off and used vise grips and was able to move it in one direction BARELY but hurt my shoulder in the process like I mentioned in my initial post.

69 Lemans
KowalskiCW is offline  
post #5 of 13 (permalink) Old 04-21-2017, 10:15 AM
 
1968gto421's Avatar
 
Join Date: Mar 2014
Location: Travelers Rest, South Carolina
Posts: 402
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 22 Post(s)
The TH400 housing is aluminum and the bolts are steel as is the modulator. I could be very wrong, but its possible some form of electrolysis has corroded the metals together a this sometime happens with aluminum intakes. If this happens its kind of like an electric weld. I think PinionHead said it all, time for a trip back to your "guru" to see if he'll swap trannys with you. Getting these parts separated is possible but I do not know the exact procedure.

Best of luck!! Hopefully someone here will have a good answer for this. Another possibility is to post it on the PY forum ( Pontiac - Street - PY Online Forums ) which has way more members and I'm pretty sure someone will have a procedure for you to use.
1968gto421 is online now  
post #6 of 13 (permalink) Old 04-21-2017, 12:52 PM Thread Starter
 
KowalskiCW's Avatar
 
Join Date: Jul 2016
Posts: 106
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 23 Post(s)
Garage
Well that's definitely not a good answer! haha. The guy I got it from said to try to drill it out and if it still wont come out to bring it back and he'll swap it....but he only has a long shaft left and I don't want that, especially since he sold me a gto driveshaft from a short shaft th400. I'm going to try the slide hammer tonight and last resort drilling. I was able to drill out and re-thread the two broken off bolts! First time I've ever done that and it turned out pretty well.

69 Lemans
KowalskiCW is offline  
post #7 of 13 (permalink) Old 04-21-2017, 04:21 PM
 
Join Date: Jul 2016
Posts: 131
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 8 Post(s)
"...but he only has a long shaft left and I don't want that..."


Nothin wrong with a GOOD long-tail. We won lots of races with a long tail TH400, in a '68 Bird. I also bought a '74 Ventura bracket car, which had a long-tail in it. It ran great. You just have to move the crossmember back, and shorten the driveshaft.

The last TH400 I had rebuilt was a long-tail. My tranny guy just replaced the long-tail parts with short-tail parts. Most tranny guys who build for local racers & hot rodders, have a stash of TH400 parts they've accumulated over the years. Because of bad & broken cases, there are lots of good short-tail parts left. So, my short-tail parts may have come from a Chevy TH400, or any other brand.
1968gto421 likes this.
bigD is offline  
post #8 of 13 (permalink) Old Today, 09:26 AM Thread Starter
 
KowalskiCW's Avatar
 
Join Date: Jul 2016
Posts: 106
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 23 Post(s)
Garage
Well if I don't get that modulator stub out this weekend I'm giving up and going to take that guy up on his long tail th400 offer. I'm out of patience. It's holding my entire project up.

69 Lemans
KowalskiCW is offline  
post #9 of 13 (permalink) Old Today, 09:38 AM
 
1968gto421's Avatar
 
Join Date: Mar 2014
Location: Travelers Rest, South Carolina
Posts: 402
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 22 Post(s)
Quote:
Originally Posted by KowalskiCW View Post
Well if I don't get that modulator stub out this weekend I'm giving up and going to take that guy up on his long tail th400 offer. I'm out of patience. It's holding my entire project up.
If you do have to swap it out, see if the guy has a short tail assembly to swap onto the long tail. This would make driveshaft/crossmember issues easier but as previously said, nothing wrong with a long tail.
1968gto421 is online now  
post #10 of 13 (permalink) Old Today, 01:18 PM Thread Starter
 
KowalskiCW's Avatar
 
Join Date: Jul 2016
Posts: 106
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 23 Post(s)
Garage
Man transmissions scare me and I would never feel confident taking apart the trans to swap those. My frame has multiple holes for moving the cross member so I'd assume that part would be easy. Getting the drive shaft cut and welded is the only part that annoys me but it can get done.
KowalskiCW is offline  
Sponsored Links
Advertisement
 
Reply

  Pontiac GTO Forum > The 1964-1974 Pontiac Tempest, Lemans & GTO > 1964-1974 Tempest, Lemans & GTO Undercarriage, Frame, Transmission and Differential Discussions.

Quick Reply
Message:
Options

Register Now



In order to be able to post messages on the Pontiac GTO Forum forums, you must first register.
Please enter your desired user name, your email address and other required details in the form below.

User Name:
Password
Please enter a password for your user account. Note that passwords are case-sensitive.

Password:


Confirm Password:
Email Address
Please enter a valid email address for yourself.

Email Address:
OR

Log-in









Human Verification

In order to verify that you are a human and not a spam bot, please enter the answer into the following box below based on the instructions contained in the graphic.




Currently Active Users Viewing This Thread: 4 (0 members and 4 guests)
 
Thread Tools
Show Printable Version Show Printable Version
Email this Page Email this Page
Display Modes
Linear Mode Linear Mode



Similar Threads
Thread Thread Starter Forum Replies Last Post
th350 to 2004r conversion ucaddoc 1964-1974 Tempest, Lemans & GTO General Discussion 1 12-31-2016 10:44 AM
st300 to th350 swap Thurber73 1964-1974 Tempest, Lemans & GTO Exhaust, Suspension, Alignment, Fuel Tank and Brakes. 1 04-21-2015 05:50 PM
th350 tranny swap 66tempest 1964-1974 Tempest, LeMans & GTO Technical and Electrical Wiring 6 09-17-2012 02:22 AM
TH350 to TH400 conversion nygtofl 1964-1974 Tempest, LeMans & GTO Technical and Electrical Wiring 0 07-24-2012 12:51 PM
Rebuilt TH350 DFW, Tx Area Hot_Rod 1964-1974 GTO parts for sale (Price & Pictures Required) 0 04-06-2012 11:15 AM

Posting Rules  
You may post new threads
You may post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are On
Pingbacks are On
Refbacks are On

 
For the best viewing experience please update your browser to Google Chrome