Pontiac GTO Forum banner

1 - 20 of 49 Posts

·
Registered
Joined
·
180 Posts
Discussion Starter #1
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.
 

·
Registered
Joined
·
1,611 Posts
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.
 

·
Registered
Joined
·
180 Posts
Discussion Starter #3
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?
 

·
Registered
Joined
·
180 Posts
Discussion Starter #4
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.
 

·
Premium Member
Joined
·
790 Posts
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.
 

·
Registered
Joined
·
180 Posts
Discussion Starter #6
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.
 

·
Registered
Joined
·
651 Posts
"...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.
 

·
Registered
Joined
·
180 Posts
Discussion Starter #8
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.
 

·
Premium Member
Joined
·
790 Posts
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.
 

·
Registered
Joined
·
180 Posts
Discussion Starter #10
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.
 

·
Registered
Joined
·
1,611 Posts
The holes in the 2 door A body frame were not to slide the trans crossmember back & bolt a longtail T400 in. Have owned several '68-71 Pontiac Abodys that had B series Pontiac engines/long tail T400's transplanted in them. The inclination of the eng/trans changes slightly & put the 19 1/2" fan into the bottom of the fabshroud. This slight change in angle also changes the pinion angle of the driveshaft. Engineers chose the short tail T400 for a reason.
 

·
Registered
Joined
·
180 Posts
Discussion Starter #12
PH that's kinda what I thought about the long tail with angles changing too. Glad someone else said it. Well there is one machine shop in town I can always take the trans to them and see if they can get that damn thing out...guess I'll see how the weekend goes. Finally pulling the engine and trans out this weekend, so I can start getting it ready for the new pair...if I ever get the trans figured out!
 

·
Premium Member
Joined
·
790 Posts
When I needed a driveshaft shortened I contacted a local rod shop that was very well known. They recommended a local shop that did their driveshafts, the guy was very nice and knowledgeable, shortened my driveshaft and re-balanced it. If you need to have this done, local rod shops know the best guys.
 

·
64-67 Expert
Joined
·
8,569 Posts
Be advised that using a long tail trans will throw your driveline angles off and could result in nasty vibration that you will be stuck with. Use a short tail TH400 and save yourself future headaches. BTDT.............
 

·
Registered
Joined
·
180 Posts
Discussion Starter #16
Yea that is definitely what I do not want to get into(pinion angles and driveline vibration). Over the weekend I was able to get that stupid bung to start coming up, but lost steam/time. I'm hoping I can get it out tonight though and put this misery behind me. Thanks
 

·
Registered
Joined
·
180 Posts
Discussion Starter #17
Well the transmission won. I cannot get that stupid bung out from the modulator! I twisted it too many times and too hard that what I had to grasp onto finally snapped off. I called around junkyards and found a guy that has a th400 case from a 71 laying around that he said for $350 he'd swap all my inners and short shaft into that trans and replace worn parts, as well as put firmer springs in for better shifting. He loves doing this stuff on the side and is a Pontiac owner as well. So tomorrow I bring mine to him, defeated, but optimistic and I'll have a "rebuilt" TH400 to boot.
Pic attached is how bad this modulator bung has beaten me and how bad I've beaten the case trying to get it out! Grrr
 

Attachments

·
Registered
Joined
·
180 Posts
Discussion Starter #18
I took it to a salvage yard guy that rebuilds transmissions in his spare time. He said he had a 71 TH400 case laying around and he'd just gut mine and swap it all over(including short shaft) to that one while using a rebuild kit and mess with the springs and stuff to get better shift patterns and put all new seals and whatever parts I already had for $350. I thought that was a pretty good deal so I went with it. I'll get it back in a week or two.
 

·
Registered
Joined
·
1,611 Posts
Guys quick one, will my dipstick/tube work on my TH400 from my TH350 or no?
No, the TUBE is bent differently & the Indicator Rod is a different length. There are actually several different T400 Tubes & Indicator Rods used by Pontiac over the years, 70 & 71's, for example are different than '72's. For your swap, probably the easiest to source in a boneyard would be a T400 Tube & indicator Rod out of a mid to late 70's big Pontiac or Caddy.
 
1 - 20 of 49 Posts
Top