I'm in a position where I have my '91 568 apart to fix a small issue with the case and while I have it apart I was considering swapping over to the 3.50 FD. I see that it is recommended to use a main shaft out of a '91 523. I was wondering what is different about the '90 main shaft that prevents us from using it. I know the input shaft is different but can't find any difference on the main shaft.
I'm sure it's probably been posted somewhere but I can't find it.
Thanks
There is no difference. Just keep in mind if you want to swap things around that the ring gear must match the pinion shaft/main shaft if that is what your referring to? Its not just swapping the differential but the shaft has to be changed as well.
Ok, thanks. That was my understanding but Cliff seemed pretty specific about using a 91 only donor trans for the main shaft and ring in the knowledge center post. Just didn't know if I was missing something.
I am not sure of the thought behind that. For the parts you need a 90 or 91 523 with the 3.50 final drive would be fine.IMPORTANT 91+ 568's need to use a 91 ONLY 523. After 91 the 523 got a slightly revised gearset that included a more coarse tooth pitch and a 3.77 F/D. The F/D ratio makes this trans useless for this purpose.
The clutch disc spline is different which doesn't matter because your still using the 568 input shaft. The 1990 transmissions did use a different 3-4 shift fork with a odd one year only fork pad insert but again that is of no consequence here. The main shaft/pinion shaft and ring gear/differential are the same.
That's what I'm thinking. I can't see a reason why you would need a 91 only 523 main shaft.Originally Posted by 135sohc
Great. I'm going to try to track down a 3.50 523 ring and "pinion". If i do end up with a 90 I'll follow up with what I find. Thanks
If you already have a clutch for the '91, then you are going to want a '91-up main shaft (aka input shaft). The intermediate shaft shouldn't matter.
Was planning on using the input shaft from my 568 along with the gearset. I may be mistaken on the terminology. I was calling the shaft that holds all the gears the main shaft.
I'm pretty sure there was a bearing change in the front of the case with the larger shaft too right?
That's what most of us call the main shaft. That's interchangeable with intermediate shaft, but that gets confusing as some will think of the shaft coming off of the pass side of the trans for the equal length axles.
The 523 input shaft does not get used.. It and the speed gears can fall into the nearest trash can for purposes of this conversion. Of course if there not trashed then I would never throw away good parts but thats just me.
Yes. The straight roller bearing that supports the bell housing end of the pinion/intermediate/main/counter shaft is larger on a 523/568/543 than the predecessors. Year to year that bearing is the same on all 523/568/543
I would definitely keep the 3.77 gears off of a 92+ 523. The 3.50 gears would go in the bin for emergencies.
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