My cousin has a 91 Z28 with a 350 TPI and a 700R.The transmission stop shifting into 3rd.His uncle put a rebuilt one in and did the same thing.The next trans came from a junkyard and out from a chevy asto and the trans is doing the exact thing.It seems that 3rd gear has burned up,but why?

 

Well, that's just something that happens with 700 R4's. THe 3-4 clutch pack is a weak design. there are several variations of upgrades for them on the market, some with more clutches, and some (like GM's) with thicker steels.

As for the one from the astro, it could have failed because it was designed to be put behind a v-6, not a 350. There are many things that are different in each application, and that can affect how long it will last, and how it will perform in another vehicle.



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Working on:
'84 Z28 LG4 305 with 200,000 original miles!
Added dual elec fans.
145 MPH IROC Speedo
Building 430 HP 350 (ZZ430)
using primarily GMPP parts.
Short block sitting on a stand. (Man, those Fast-Burn heads sitting on it look good!)

Starting to look like the Kicker poster child!

ASE Certified Master Tech

 

Two primary reasons. One, the TV Valve sticks, even for a second and you get low pressure=slip. Two, crossleaks that drag the cluthces when they shouldn't be on.