425 nailhead to switch pitch trans

[Dr. Frankenbuick]

I think that was a switch pitch ST300 trans in the F85. The converter will fit, but will have a higher stall in your ST400. The other issue is that you don't know how the condition of it or if it works . Your best bet for is to find a rebuilt 13" ST400 converter.


Sent from my iPhone using Tapatalk

[nailheadnut]

If it's the same part number as the converter that was in the 401 powered GS cars then it should fit. It's the same transmission within a different case. The smaller converter behind a big block will have a much higher stall than the larger diameter converter would. You should be able to go into a reputable transmission shop and purchase a rebuilt converter over the counter.

[Grhopperass]

We need to know if the transmission you have has the Nailhead bell housing or the BOP bell housing. The transmission will bolt right up to the 64 425 if it has the Nailhead bell housing.


Sent from my iPhone using Tapatalk

The tranny fits the engine block OK. I was wondering if the torque converter will fit the crank without a special bushing.

[James Angus Mccullen]

I'm planning on dropping a 63 401 in where the the 300 was in my 66 skylark.

I have a 401 motor and 400 tranny out of a 65 riviera ( complete and still bolted together) that I was going to take my time and rebuild. As fate would have it, I picked up a rebuilt and running complete 401 out of a 63 riviera, and would like to use the 400 tranny w the 63 motor. Do I have to take the motor to a machine shop for the bigger bushing? or is it something that I can do at home? and will the larger bushing and adapter plate be all I need to acquire to make the combo work?

[telriv]

The 12" converter will work on the 400 without mods. Would be best to send it to Jim Wiess at TSP for a PROPER rebuild. He is the ONLY ONE in the country who does them correctly. You will need to drill 3 holes in your flexplate to fit the 12" converter as it has the smaller diameter mountings.



The rear flange needs to be ground off the rear of the crank & the bushing inserted along with the CORRECT flexplate. Make sure to line up the pilot hole in the crank & flexplate or you will end up with an unbalance condition.


Tom T.