Just wanted to know if TH 400 is an option on 455 Centurion's or it came as a standard fitting ? If not, what can make me easily recognise a TH400 from a TH350 ? (easily, I mean without opening the box, but I still can crawl under the car :grin: ) Thanks.
I pretty sure the 455 was never mated with a TH350 from the factory, though it does bolt right up, with slightly different tranny mount position.
OK, now I'm confused (again) I'm pretty sure my '72 Chassis Manual and another book I've got list the THM 375 as a THM350 beefed up with extra 2nd gear clutches to handle extra torque, and indicates that it was installed in LeSabre 2-doors and some Skylark wagons (I guess "middleweight" cars) behind 455's. When I had my THM350 rebuilt, the trans guy said it already had the extra clutches of the THM375 in it. But in the above Tranny id chart, it shows the 375 to be same as THM400. Any transmission builders out there to clarify exactly what a THM375 is/was? o No:
AHA!!! :TU: THM375B = heavy-duty THM350, THM375 = light-duty THM400. Via http://www.s10blazers.com/transmission.htm; So my books and tranny guy aren't wrong...oh the difference a "B" makes! :laugh:
The THM 350-375B had a longer extension than the regular 350 transmission. But they are not all the same. In Centurys, the 350-375B has less clutch plates than in LeSabres. The 400-375 was also used in LeSabres with the 350V8 but the LeSabres with 455 engines had regular 400 transmissions. The 350 and 400 transmissions required different crossmembers. The 350 had a kickown cable while the 400 had an electric kickdown. The 400-375 also had less clutch plates than the regular 400 and a different output shaft. When I bought my 74 LeSabre, it needed a transmission. I thought I'd use a 67 switch pitch 400 (too short) or a 76 400 (too long) to replace the 350-375B as I had the accelerator linkage and the crossmember from a 76 Electra. I changed my mind after I noticed that the driveshaft would have required modifications and a different yoke. Instead, I had it rebuilt for 400$ and I didn't have to mess with the driveshaft and accelerator linkage.
I wasn't aware of that. 455's weren't mated to 350-375B or 400-375 transmissions in the 74-76 period.
Jean-Luc, you don't even have to look under the car. Find if it has a kickdown cable or a switch. If you open the hood there's a kickdown cable next to the accelerator cable on the firewall, the car has a 350 transmission. If it has a kickdown switch near the accelerator linkage under the dash, it has a 400 transmission.
According to the information I have and the trans' I have worked on, the TH375B was only used in the 71-75 (maybe even 76) LeSabre. The major difference is that the direct (3rd) clutch had 5 instead of 4 plates. A special piston was used in it to fit the extra plates. The reason it was called "B" was because Buick used the HD TH350 while chevy Pontiac and Olds used a "detuned" TH400 called the TH375. The TH375 had one less clutch in forward and direct than the TH400. I don't think Buick ever put a 455 with a TH350 or TH375B. However, I do know that Pontiac put their 400 (maybe 455 too) in the Trans Am with a TH350 sometime between 1974-76 as I worked at Pontiac then and saw it. :shock: There is a good possibility that the TH350B and TH400 used different driveshaft lengths during that time. Another wrinkle is that chevy used a unique output shaft and tail housing on their TH375 that used the same yoke and driveshaft as a TH350. I once converted a TH375B LeSabre to a TH400 that I rebuilt with those parts and it fit perfectly with the original driveshaft/yoke. uzzled: The easiest way to tell a TH350/350B from a TH375/400 is that the modulator sticks out the passenger side on the TH400. It is on the passenger side back on a TH350. Mark
If you're looking at a '71, don't even need to open the hood. The THM350 kickdown cable will connect to the gas pedal link right by the throttle cable, under the dash. If there's only one cable, but an electric switch, you've got a THM400. :Smarty: I'd bet lotsa money that Buick only put THM400's into '71-'72 Centurions... I'm gonna have to dig out some books and try and confirm/correct my impressions about the THM375B w/ 455 applications. o No: Heck, I'm just happy to clear up the fog about that "B" thing... :laugh:
In 71, the TH400 was an option. The 3 speed manual column shift was the standard transmission. You don't see too many of those, do ya? There was ONE 1971 Centurion convertible built with the 3-on-the-tree column shift. I don't have any information for the coupes or the sedans. It is not listed in my spreadsheet as far as how many cars had it. For all I know, all coupes and sedans had the TH400 in 1971....which might be why I don't see it on my list.
I swear, I've seen Buick literature that listed the 250-inch inline 6 and the 3-on-the-tree as standard for '71 LeSabres... :shock: I'm gonna have to go digging through some boxes... I did see a big late-'70's Ch*vy with a straight six and an automatic at the boneyard, thought about taking a picture for evidence. :laugh: Talk about GUTLESS!!! Then again, my bro-in-law used to have a '69 Charger with a slant-six and 3-speed. Quite a pig to get moving, but it did get pretty good mileage, and the body was incredibly tight and squeek-free...just like new, and never been abused or especially raced! :Brow:
Mark, I had you till the last sentence when you lost me. The easiest way to tell a TH350/350B from a TH375/400 is that the modulator sticks out the passenger side on the TH400. It is on the passenger side back on a TH350. What do you mean passenger side back on a TH350. My buddy just bought a 72 GS clone. It has a 455 and what I saw last night to be a THM-375. The THM-375 has a connector on the driver's side for a kickdown switch, but noticed there's no switch mounted on the gas pedal. No surprise there, being a clone. I guess what I'm wondering is it should be no big deal to put the correct bracket and switch needed and just rin the switch to the tranny right? o No:
Phil, if 455's weren't mated to 350-375B or 400-375 transmissions in the 74-76 period, what else was left to mate them to? o No:
