Hi guys, as the header states, I've got my hands on a '67 Buick Switch Pitch trans. It looks to be in decent shape, but I don't have X-ray vision and can't tell what shape the internals are in. Selector moves through its range nicely, but that doesn't tell me much. I've never rebuilt an automatic transmission before, but have had a couple manual transmissions apart... It can't be THAT much more complex, right? I can have my drivetrain and chassis professor guide me along during the rebuild. All I need to know is, what rebuild kit do I need to purchase? Will a standard TH400 kit do the job, or is there a special kit only available through so-and-so? Thanks everybody!
Standard kit should cover it, you won't get the factory tube style filter with a standard kit, but that can be purchased separately or you can get a filter tube and switch to the flat filter the later 400 use. All the drums, lip seals, clutches, etc are the same size
I believe you will need one extra 1 inch iron seal to be replaced. If you change the brass one inch input shaft bearings, note that the one closest to the trans is a little shorter, this is necessary to clear a lube passage. The center support section rests directly on the case, by 70 this was made 40 mills thinner so a steel case protection ring could be inserted. Changing to the later filter/pan is cool, its possible to drill/tap the original valve body for the support bolt. Bruce Roe
While you are in there, might as well just change to a later valve body. You can use the later filter, and you gain shift point and kick down advantages with the later valve body. Read this, http://www.buickperformanceclub.com/SPTrans.htm
Do any of you have a recommended rebuild kit? This is a street trans, might see the strip a time or two, and will definitely see a handful of burnouts. Really great article, thanks for the link! What all does changing out the valve body entail? Is it just a bolt-in deal? I know it's kind of blasphemy, but this trans will be going behind a 472 Cadillac engine in my rat rod project. Would you recommend changing out the valve body especially for that application? Thanks for the info. Do you happen to have a link to a place that sells that extra seal?
I think all those seals were the same sized used throughout the trans. If you dual feed the direct drum you will have 1 extra seal anyways. To dual feed is very simple it's leave the second ring on the center from the top down off and or the inner seal out of piston drum.....I do both.....then install an 11 plug cup in the case to into the reserve passage next to the center support bolt......depending which way you have you case oriented when assembling will effect which side.....but a quick search will get you a picture, I have one in my shop I will dig out and post. This really increases the holding capacity of 3rd gear, plus adda a little cushion to that shift. I don't like the iron sealing rings, they can cut into parts espeacially if you increase the pump pressure. It's worth the money to get the softer ones on, even if you need a trans shop to put them on which if you do the none cut ones is smart. As far as clutches.....it sounds like there is no reason to go all out race stuff here, just get some high energy clutches used in the 4l80e......you should be able to get a kit with them for 150
Bolt in replacement as far as I know. If you read that article in it's entirety, you'll see that the later valve body gives you a part throttle kick down. It also negates the tendency of the SP valve body to short shift 3rd gear. Buick intended the switch pitch to accelerate the car using the high stall of the converter. When I first took my car down the track, I had set up the governor to shift 1-2 at 5500 RPM. Never checked the 2-3 assuming it would be close. During my first pass, it shifted 1-2 at 5500, the RPM dropped back to around 4500, and it immediately shifted into 3rd gear. No matter what I did to the governor, it would short shift 3rd gear. It also would not kick down at less than full throttle. I then replaced the valve body with one out of a 1971 big car transmission (71BC). I immediately noticed I could get a kick down at 40 MPH with about 1/2 throttle. I was also able to extend my 2-3 WOT shift point to 5400 RPM. Seems to me you would want the later valve body for any street performance car.
Cool, thanks for the information! I'd appreciate it if you could take a picture of that plug so I can see what you're talking about.
Pic 1 is the whole to plug......use a 7/16 or 11 freeze plug........just tap it in flush. Just make sure you look at all the passages to make sure your case is oriented the same same direction.......if you put it in the wrong whole you will gave no reverse and no 3rd. Pic 2 This is the sealing ring to leave off the center support. Some ppl grind this land completely off.......but its not required. Those 2 mod alone will dual feed your direct clutch, but I also like to do pic 3. Pic 3 Remove the inner sealing ring in the diet drum. To put this piston back in will require a couple special tool, if doin a full rebuild this piston would be out anyways to replace the lip seals. If your doing the dual feed mod to a good performing transfer you do have to pull the drums out, to do the center support, buy nothing has to come apart in the drums. Tech tip.....lining the drums up through all the clutches can sometimes fight and it's hard to know when you are through all the clutches..........if not through them all when you put the pump on it will not turn correctly. I like to mark the case with a small scribe or screw driver. B4 pulling the forward and direct drums just set the scribe/driver on the edge of the drum and scratch the case, now when you think you all in you will have a reference point. You can also lightly bounce the drums.....if all lined up when you pull up and push down you will hear good metal thud......if not you hitting a clutch plate. Do this by pulling apart so you know the sound
The sealing ring Bruce mentioned is for a VP trans only.. it's located on the input shaft, in front of the forward drum. Here is where you can buy it, it does not come in the standard TH 400 sealing ring kit. http://www.transmissionpartsusa.com...ne_Shaft_Sealing_Ring_Var_p/460-000046453.htm I strongly beleive in what Gil Younger said "The perfect shift is when the vehicle speeds up and the engine slows down, there really is nothing else to talk about".. I would add that it should happen so quick, and smoothly, you should not notice it at part throttle. It's not harsh, folks think that is a "good shift" but that is a matter of opinion, and most pro tranny builders will dispute that. Trans Go, the company Gil Younger founded, has a dual feed plate that feeds the direct clutches, and allows you to retain, and work with the hydraulic controls of the trans. Having built a TH 400 in just about any way you can, I prefer the use a these parts, even if it is a bit more expensive, it's money well spent. I have built many copies of the exact trans your working on, and agree that the part throttle downshift is a nice thing to have, if you don''t have, or are not going to use, the original throttle switch for the VP. There is no 3-2 downshift valves in the early transmissions because at 2/3 throttle, the converter went to high stall, which is in effect like a downshift. Beyond that, it did have the electric detent solenoid, that was activated at WOT. The VP went away in '68, it was two model years before the need was seen, and the parts were developed and implimented for that part throttle 3-2 downshift.. my favorite vintage trans to steel the valve body from is the 71-74 "BC" big car transmission, they usually have the correctly sized valves in them to allow the 3-1 downshift. And to make your VP trans more fun, find a 12" converter from a 65-7 ST 300 trans, to replace the big 13" unit. While only an inch smaller the ST 300 converter is very different inside, and will allow right around a 3200 stall speed in high, when properly modified, and we still do that here at TSP.. The converters were standard in 65-7 Buick and Olds mid size cars, with a small V-8 or V-6.. The ST 300 is a two speed trans, known as the "BOP powerglide". JW
