It looks like I will be getting the TH400 in my 70GS455 rebuilt soon. The car is pretty much bone stock. Can you guys give me any tips on what rebuild kit to get/not get? Replace the torque converter? Thanks for any info. Bert Roll Tide!
I just got done building my first one. If the car is stock I don't see any reason to do more than a stock rebuild. The direct clutch dual feed is something you may want to do along with a roller thrust bearing but are not required. They are not too hard to rebuild yourself, get Ron Sessions TH400 rebuild book and it'll tell you everything you need to know. The only pain is replacing the bushings without the bushing drivers. For the big bushings I used a cam bearing tool and improvised on the small bushings. Use good clutches and stock steels (not Kolene steels). There are five/six seals that were cast iron from the factory that should be replaced with teflon or graphite. I've been working with CK transmissions and Jakes Performance for parts. Both have been very good. Transgo shift kit is supposed to be a good one. I used a TCI shift kit last fall and was not impressed. Good luck.
70 and back direct drums can be upgraded to a 34 element sprag. 71 and up direct drums cannot be upgraded and need to be replaced to use a 34 element sprag. Sprag is about $75, drum/sprag assembly is about $300. If you have a 70 and back drum I would upgrade the sprag. If you have a 71 and up sprag and have to buy a drum to upgrade the sprag then it may not be worth the money if the car is bone stock as you said.
I would not leave a 9 element sprag behind a respectable big block. If the direct clutch has 6 frictions, I REALLY would not want a 9. I used to collect the older drum assembly for later trans conversions when scrapping stuff long ago, wonder how many I have left? Bruce Roe
Bert.. the car just a cruiser? Not beating on it? If that's the case, then the biggest thing that it needs is the soft parts. The seals dry up with time. Since you have a 70 BA trans (assuming it's the original, and no one got in there and stole the sprag type direct drum), then upgrading to the 34 element sprag is a good idea. While not absolutely required for light duty driving, in 71 GM went with the spacer ring behind the center support, to ease a lug damage issue they were seeing. Never a bad idea to use a 71 or later center support, and installing the spacer ring. No machineing required here, with the right parts it's a drop in upgrade. Absolutely required for HD use. Get a good rebuilt converter, they are inexpensive. I also recommend a fully welded lug HD intermediate band, the standard duty rear band will be just fine, and it's very possible that you can re-use your original one, they often have very little to no wear on them. Other than that, get a top quality kit with waffle type Borg Warner clutches, you can typically tumble or sand the steels, as long as they aren't burned up. If you don't want to fool around with the steels, then just get a master kit with new steels. Buick's GS valve body calibrations were pretty good for a stocker, and if just light duty cruising is all your doing, then just clean it all up and put it back together, and it should give you many more years of reliable service. Having build dozens of TH-400's, I can tell you that as long as you don't have electrolysis damage (from a missing engine to firewall ground) then the only two bushings you will need to replace are the front pump and extension housing ones. TH 400's are very easy on the internal bushings. Replace all the torrington bearings in the rear gear unit, there is a kit available that has them all. Your trans may or may not have the hi-roller count HD bearings, the kit has all new HD bearings. A thrust washer kit will also get you all new metal thrust washers, there may or may not be several plastic ones in that trans. If your really driving it hard, or contemplating engine upgrades in the future, then the weak point of the 400 is the direct clutch hydraulic application. A Trans go 400 1-2 kit is a good upgrade for the trans, the dual path separator plate addresses the direct clutch issue nicely. It's also a very good shift kit. Cleanliness is the most important thing on a rebuild, it's just as important as in engine building, if not more so. Close fitting spool valves to bores don't like dirt. Finish if off with a nice brass filter, and you should be all set to go. JW
Thanks to everyone for all the great info. Its the original BA transmission and has not been out of the car since I got it which was 1978. The car is just a cruiser, I use it to run errands on the weekend and loaf around in. Sometimes I drive it kinda hard but usually just a few seconds at a time because of the fear of getting arrested. I dont plan on doing the rebuild myself so I have to find a shop that hopefully wont play "Ferris Buellers Day Off" with my car. Thanks again. Bert Roll Tide!
Update I located a fellow through one of my old team mates from the dirt track days. I carried him the car Tuesday and had it back 48 hours later. He even cleaned all the gunk & grease off the case. Upgraded the sprag. It seems to be working just like it did when I got the car so no complaints as of yet, thanks again folks for your help. Oh yeah, its not leaking a drop either and it used to leak from several locations Bert Roll Tide!
Good start ibmoses. Can I see your car together with its new kits? And keep us more on updated. Good luck!
Good work! Probably will serve well for another 20 years or 250,000 miles, which ever comes first. Any trans that old needs the rubber seals replaced, regardless of miles (before anything bad can happen!). Some of the rubber piston clutch seals I take out break in half when bent. Bruce Roe
