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carcrazyken

manual trans to auto trans swap

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I am swapping my manual trans to auto trans in my 1976 280z.  I think I have all the parts but I did not pull the auto trans from the donor car so I am not sure of the parts or orientation . My problem is that after installing the trans ,the flex plate and the 2 spacers the torque converter is too far back for the flex plate bolts to reach the torque converter. I put the big spacer to the motor side of the flex plate and the washer looking spacer to the rear side of the flexplate. the flexplate teeth are set back about 1/2" into the bell housing which looks right for starter engagement but the torque converter has a about a 3/4" gap to the flexplate which is too long for the bolts to reach. do I have the spacers in wrong or am I missing something. Thanks in advance for any help Ken

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Posted (edited)

Pic's would help..  You have the auto trans flex plate?  (because thats a different one.)

One seldom hears of this, most of the time it's the other way around.. going to a 5 speed and throwing the auto in the trash..

As the auto from a 240/260/280 Z is a slugish p.o.s.  (sorry)  i would research if a modern 350/370z auto could work behind a 240/260/280z engine?  I believe it has been done already?

Edited by dutchzcarguy

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Hey Ken, I am pretty sure the thin spacer is installed between the flex plate and crankshaft. 

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Doesn't the torque converter slide on the transmission input shaft?  3/4" seems like a lot but maybe it's right.  You should be able to slide it forward to get it bolted on.  What does the FSM say about it?

Here's a drawing of parts.

http://www.carpartsmanual.com/datsun/Z-1969-1978/engine-280z/piston-crankshaft

image.png

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Well, I guess the converter is meant to slide all the way on to the shaft.  But here's a way to tell if the problem is with the transmission/converter or the engine.

image.png

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In my manual it says:

"Line up notch in the torque converter with that in oil pump" 

"Be extremely careful not to cause undue stresses in parts in installing torque converter"

There was also a recommendation for scribing an alignment line on the flex plate and the converter. For balance I assume. 

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I just realized that "more than 21.5 mm" means that there must be room beyond that.  So you could pull it forward to 21.5 mm and it might be fine.  There's play in it, just not clear how much.  The 21.5 mm number is probably the "it's wrong, there's not enough room" limit.

Haven't messed with an automatic for years and never got very deep in to them.

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I appreciate the help, Zed Head the "A" distance on my transmission is 15/16 which is just a little more than the FSM says . I have had the trans out 4 times now and I still have 1/2 ' between the flex plate and the torque converter. The converter bolts are about 5/16 long . The guy who built my transmission said not to pull the converter more than 1/4" forward so longer bolts are not the answer. The only other thing that seem odd to me is when I turn the crank bolt to align the converter and flex plate holes is that they spin together. I had to remove trans line up holes and then replace trans to align holes. there is not a lot of binding though as I could put a lin up tool and move converter after I got it close. Thanks again Ken

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Just thinking about things to remember when doing this swap. I’m about to do the same on a 510. Don’t ask...

Did you remove the pilot bushing from the crank? The auto doesn’t use it.  I’m thinking you did, as I doubt you could get the trans on far enough to bolt it up, but there is a chance....

 

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3 hours ago, carcrazyken said:

The only other thing that seem odd to me is when I turn the crank bolt to align the converter and flex plate holes is that they spin together. I had to remove trans line up holes and then replace trans to align holes.

That doesn't sound right at all. Can you remove the converter from the transmission and test fit it to the flex plate. I think there might be something going on there. It should slide onto the bolts.

Make sure when you refit the converter to the transmission to turn slowly while gently pressing it into the pump. The two prongs wil click into the notchss and you will feel the converter slide in.

Btw: In Australia you could buy a performance upgrade kit for the 4N71B transmission, which is basically the 3N71B with a lockable sprag clutch. They used the RB30 engine with the 4N71B in the Holden VL commodores in 1985.

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Do you have the flex plate mounted backward?  

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I just pulled the transmission again. I pulled the converter from the bell housing and put it directly on the flex plate. there is still a gap of about  1/8" between the converter mounting pads and the flex plate after the converter is bottomed out. That cannot be right . Anyone have any other suggestions? The only thing I can think of is to shim the converter

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1/8" of an inch is ok. Normally they just touch or have a couple of mm.

You mentioned the transmissions turns with the engine. You should be able to turn the converter by hand using fingers or a screwdriver to line up the bolt hole to the flex plate.

If you can't get the converter to turn without turning the engine then the center section on the convertor is probably not lined up with the back of the crankshaft and not entering the crankshaft.

How did you fit the transmission. Did you use the bellhousing bolts to pull it in or did it push up by hand?

It's been a long time since I seen one of these in pieces, and that was in a VL commodore. Memory is fading.

Can you post some photos of the convertor.

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I pushed the transmission in by hand it bottomed out on the block pretty easy. My new question is how sure are you about the 1/8" gap between converter and flywheel? i would think that they would touch when the converter was bottomed out on the flywheel so as not to bow the flexplate to the converter  

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You've measured everything but the flex plate.  It seems like you either have the wrong flex plate or it's installed incorrectly. 

Position of the starter gear is not confirmation that it's the right one and installed correctly.

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I have two flex plates If you would like to compare measurements. 

1/8 inch is about the distance of the spacer / washer.

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I would be happy to post some measurements of the flexplate . i will do it tomorrow as I am at home and the car is at my shop. I have the big washer towards the engine and the smaller washer like spacer towards the converter. If I flip the flex plate over the teeth rub the block

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5 hours ago, carcrazyken said:

I pushed the transmission in by hand it bottomed out on the block pretty easy. My new question is how sure are you about the 1/8" gap between converter and flywheel? i would think that they would touch when the converter was bottomed out on the flywheel so as not to bow the flexplate to the converter  

As I said, digging up memories from 33 years ago working in an automatic transmission shop. We use to do an "upgrade" in the commodores. It was a simple heavier spring set in the valve body. You could get these transmissions to churp the tyres going to second gear with a bit of tweaking in the valve body.

Normally the converter will just touch the flex plate or maybe a couple of mm off. 1/8" is getting close to maximum, but it should pull together.

I don't think the 3mm is a problem. The 23mm covertor to flexplate when the transmission is fitted is a problem.

The convertoer has two prongs to drive the oil pump. Can you measure them they should be about 20mm if my memory serves me correctly? 23mm will mean if you get it to bolt up to the flexplate, the pump will disengage.

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Some thoughts for your puzzle...

Did the flex plate and spacer/adapters come with the transmission, or did you get them separately?

Did the bolts come with the flex plate and spacer/adapters?  How much thread engagement is there for the bolts?  If the flex plate is too toward the engine the bolts should be too long.

I can't find a distinct break point or how the various parts go together or what the difference is but Rockauto seems to indicate that there was a different flex plate before 1975, and after 1982/1983.

image.png

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Hey Zed,  Ken’s transmission conversion came from my 78 280. I am doing the manual conversion on mine. I provided everything for his conversion directly off of my car. The trans package was a complete set. 

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