Powerglide to 350 Turbo swap question - Impala Tech
Transmission & Driveline Transmissions & Differentials

 
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post #1 of 18 (permalink) Old 01-25-2010, 06:09 PM Thread Starter
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Powerglide to 350 Turbo swap question

In my 65 the 350 turbo servo contacts the tunnel ( where floor starts to make the hump ) and will require some modification ( beating the hell out of it with a hammer ) , anybody else have this issue? The Powerglide servo is more forward.
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post #2 of 18 (permalink) Old 01-26-2010, 10:53 AM
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I'm shocked that it would be contacting!!! That must mean that the trans tunnel is different for the certain 65-70 B bodies.

BTW that's the 1-2 accumulator housing on the TH350.
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post #3 of 18 (permalink) Old 01-26-2010, 11:25 AM Thread Starter
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Quote:
Originally Posted by Jeff406cid View Post
I'm shocked that it would be contacting!!! That must mean that the trans tunnel is different for the certain 65-70 B bodies.

BTW that's the 1-2 accumulator housing on the TH350.
Hmmm , I dont get it. If all the crossmembers are the same ( big block and small ) , the trans mount is the same , WTF is it hitting for?

I just purchased a crossmember from a donor , mine was rotted out. It looked the same , fits right in.............unless the "perch" for the big block cars was higher ( why would it be ).

BTW , I'm a manual trans guy , knowing little about automatics LOL Can that screw in the circle be replaced with a threaded plug for more clearance?
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post #4 of 18 (permalink) Old 01-26-2010, 12:47 PM
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The TH350 and the PowerGlide are the same size. It was introduced in 1969 to replace the PowerGlide. It uses the same output yoke and drive shaft as the PowerGlide, and mounts in the same location as the PowerGlide. The TH400 is a physically larger transmission (longer, taller, and bigger around, but it still fits in your car's trans tunnel without hitting anything if it was a factory option), and because it is longer the transmission mounting point is pushed further back in the car (1965-'73 cars all had dual holes punched to mount either a TH350 or the bigger TH400). The TH400 has a larger output shaft yoke (more splines) and needs a shorter drive shaft.

All transmissions are designed to mount flush; that is no washers or anything else that affects the rear mounting height. It should bolt flat to the mount, and the mount should bolt flat to the cross-member. The cross-member must bolt flush with the frame. If you change anything at the back of the transmission then you have to break loose and reweld on all the mounting brackets on the rear axel to maintain the same pinion angle that was set by the factory. Failure to maintain the front angle results in vibration in the drive shaft and excessive U-joint wear.

If your car has issues with the TH350 hitting the trans tunnel that tells you your body is sagging and you have to address the issue of rotten body mounts (what separates your body from the frame).

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post #5 of 18 (permalink) Old 01-26-2010, 05:02 PM Thread Starter
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The body mounts have already been replaced prior to my purchasing the car. The only thing I can figure is that since the engine is ALSO out of the car , the location that the trans is angled at is HIGHER than what it will be once the engine is in. It is resting on the mount at the rear and supported by the floor jack in the front. I suppose it COULD be too high ( hell , it looked right ) so what I'm going to do is drop one off my spare blocks in there and bolt it up to see how it works out. The driver side fender well is also out so this whole deal will allow me to fabricate the shift linkage and/or mods as required. I sure as hell didnt want to dimple the floor for clearance.

I also didnt realize you were able to order one of these cars with a Turbo style trans , be it a 350 OR 400.
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post #6 of 18 (permalink) Old 01-26-2010, 06:50 PM
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Quote:
The only thing I can figure is that since the engine is ALSO out of the car , the location that the trans is angled at is HIGHER than what it will be once the engine is in. It is resting on the mount at the rear and supported by the floor jack in the front. I suppose it COULD be too high
I think we have figured out the problem...
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post #7 of 18 (permalink) Old 01-26-2010, 07:45 PM
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Trans swap:

Did the car originally have a powerglide or turbo 400. I am asking because the cross-member mounts for the turbo 400 are in a different location than the powerglide. The powerglide and turbo 350 use the same locations for the mounts.

Paul

Paul

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post #8 of 18 (permalink) Old 01-26-2010, 08:08 PM Thread Starter
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Quote:
Originally Posted by fsc66 View Post
Did the car originally have a powerglide or turbo 400. I am asking because the cross-member mounts for the turbo 400 are in a different location than the powerglide. The powerglide and turbo 350 use the same locations for the mounts.

Paul
It had a Powerglide originally.

Jay , maybe I didnt realize just how low it actually sits when its bolted to the block ( sure didn't look high )
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post #9 of 18 (permalink) Old 01-26-2010, 09:08 PM
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Yes, 65 was the first year for the TH400, so I have to think that TH350 would slide right in there. So many others are running them (along with TH200-4R and TH700R4s) with no reports of floor pan massaging that I thought something must be wrong. Glad it isn't the body mount issue!
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post #10 of 18 (permalink) Old 01-26-2010, 09:21 PM Thread Starter
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post #11 of 18 (permalink) Old 01-27-2010, 08:00 PM Thread Starter
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Here is a pic showing just how close it is now after block and trans mock up. Everything is at correct position with correct mounts. You can imagine they werent thinking about the Turbo trans when they designed these floors. Yes , it fits ,but you have maybe a quarter of an inch between the accumulator and the floor.

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post #12 of 18 (permalink) Old 01-27-2010, 08:37 PM
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If you replace that tap plug with a flush mount NPT plug you'll gain a little more clearence.
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post #13 of 18 (permalink) Old 01-27-2010, 08:53 PM
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The good news is that when you rev the engine, you will get more space instead of less.
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post #14 of 18 (permalink) Old 01-27-2010, 09:50 PM Thread Starter
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Quote:
Originally Posted by Jeff406cid View Post
If you replace that tap plug with a flush mount NPT plug you'll gain a little more clearence.
I dont know the function of that plug ( or adjustment )
I asked that question earlier and you're the first one to reply......if , in fact , it is just a plug I'll do that.
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post #15 of 18 (permalink) Old 01-28-2010, 06:27 AM Thread Starter
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One little small detail I forgot to mention.

I had already taken a mallet to the floor to achieve the clearance I have.
I anticipated that it wasnt going to clear in advance of installing the block based on what I stated at the start of the post.
Remember , all the body mounts have been replaced and appear to be correct.
So it may very well have touched the floor had I done nothing.
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post #16 of 18 (permalink) Old 01-28-2010, 12:22 PM
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Quote:
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I dont know the function of that plug ( or adjustment )
I asked that question earlier and you're the first one to reply......if , in fact , it is just a plug I'll do that.
Joe it's a pressure tap to see what the pressure is in second gear. Transmissions of old had taps for diagnostic purposes. That's why it needs to be an NPT plug. I do believe 1/8" NPT to be exact .
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post #17 of 18 (permalink) Old 01-28-2010, 01:36 PM Thread Starter
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Quote:
Originally Posted by Jeff406cid View Post
Joe it's a pressure tap to see what the pressure is in second gear. Transmissions of old had taps for diagnostic purposes. That's why it needs to be an NPT plug. I do believe 1/8" NPT to be exact .
OK , thanks , then I'll just change it .
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post #18 of 18 (permalink) Old 02-17-2010, 10:35 PM
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awesome post/thread ...good info...nice

MR.CHARLIE
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