700R4 reliability questions...

[myclone]

I'll have to go back and check my info on when GM decided to start using the 30 spline input shaft but like I said Ive found 27 spline shafts in units up through late 87. The units could have been gone through before I got hold of them though so that may explain that in some or all the cases. FWIW/BTW, the GN/Turbo Buicks use the same small 27 spline input shaft on their 200R4 which has gone low tens fairly reliably so the small shaft isnt a huge issue as much as the early slush boxes not having a proper lube set up and/or pressure for hi po use as well as other fairly weak parts.

In general the later the unit the more updates or factory "fixes" will have already been done for you from the factory like one piece apply plates versus failure prone multi piece plates, lube mods for better reliability, etc. Try to get a vette unit or at least one out of a TPI car (IROC or GTA preferred) as it will already have stiffer servo springs and the big 2/4 servo which gives you nice crisp shifts but wont rattle your teeth at light throttle. One plus of the vette unit is that it will shift into OD at WOT where as some of the F body boxes will and some wont.



Pick up a "Beast" sun shell as the stock sun shell is a failure prone factory part and the beast part is cheaper than the updated GM 4L60E part if you shop around ebay.

If youre going to build the unit yourself then pick up an ATSG manual (ebay for ~$12) as well as a rebuild video of some type. Both those will help quite a bit if youre not familiar with building the unit.

If I can help just shoot me a PM or email as there are a few things you can do to help reliability that arent mentioned in the ATSG manual.