This may seem a dumb enquiry,but I'm happy to sound like the slush box novice I am. I have a numbers matching 67 GS 400 with a sp 400 short tail , also 71 GS455 with BT ( heavy case I think) long tail from a 71 Rivera , I need to rebuild one of these tranny,s the 67 was last on the road in 1995 ,the 71 ,I've no history however the 455 has little wear, is it possible to build a tyranny which combines the switch pitch and the 3rd to 1st kickdown from the BB into the heavy case BT, I intend to rebuild the 455 to around 450hp for street use ,and maybe the odd pass when I revisit my childhood Ron
Short version: Yes. Long version, you need a transmission guy who knows what he's doing. It would be easier just to build the correct coded light duty short tail case 67 Trans, and use parts from the BT valve body for the 3rd-1st kickdown..Just because it hasnt been on the road for a while doesnt mean its in worse shape than the 71 trans.
Yes. Read this article by Mark DeConti. It explains all the characteristics of the switch pitch transmissions, http://www.buickperformanceclub.com/SPTrans.htm You'll need to use a later valve body. The SP transmissions had very different calibrations as the article explains. The latter part of the article deals with the 3-1 downshift.
Thank you BigPig455, im happy to hear that's possible ,as far as I can ascertain the BA has never been rebuilt but was OK in 1995, I was considering flushing the trans with the engine running to remove the red , then see how it responds, but 55 years and an added 90hp is I think expecting a bit much , I still have some contacts from the strip who would be able to do a rebuild ,much obliged
I would put the 71 Riviera valve body into your switch pitch 400. That should give you everything you want. I used a 71BC valve body in my 67BT Switch Pitch transmission. Mark Deconti swapped the valve body for me. Played with the governor weights, and it WOT shifted 1-2 at 5600, and 2-3 at 5400. It had a part throttle downshift, and it would go back into 1 below 25 MPH, although that just resulted in the car going sideways.
Your 67 should have the smaller od yoke, sometime in 68 they went to the larger od yoke. The internal splines are the same. Keep this in mind when you figure out your plans. The 67 should have the more desirable intermediate sprag set up....the smooth inner race making the 34 elements sprag upgrade possible. The later uses a roller sprag. Which was stronger then the factory 16 element smooth sprag....but not upgradable. The earlier trans should also have a 34 element low reverse sprag where the later has a roller there too.....at your power level none of these will be an issue.........but those parts do have value........the direct drum with smooth sprag is an easy 100-150 bucks and the lower gear set with that better sprag is worth a few hundred
You'll have to insect the output to determine if you have the large or small (thin wall) yoke. Myself and others have seen both on 67's. Mine in particular Cali built had the larger yoke.
Some '67's do use the big yoke. I have three '67 BA transmissions (GS400) and they all have the bog yoke and a tail housing with the "C" cast into it. The other 3 '67 transmissions I have here are from full-size '67 Buicks and they have the smaller tail housing and yoke.
