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Discussion Starter · #1 ·
View attachment 614773


Need some help guys, trying to install a Locar shifter to this tranny that looks like a turbo 400 (13 bolt pan) but linkage shifting doesn't line up with shifter detents. A friend of mine tells me it is a Turbo 375. I can't find a serial cross reference so thought I would check with the experts.
Thanks for all any any help.
Capt'n Jim
 

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Old(s) Fart
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The TH375 is externally identical to the TH400. It uses the same pan. The difference is internal - the TH375 uses lighter duty internals and a TH350-sized output shaft. That won't have any effect on the shifter attachment. They both have pans that look like this. There is no difference in the manual shaft or in the angle position of the shaft for each gear. I'd say the problem is with Lokar.

 

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Discussion Starter · #4 ·
Thanks for this info. So, if I can't (or don't) have the 400 turbo for it's durability I think I would rather have the advantage of an overdrive gear. Which should I be looking for a 700R4 or a 4L60 ? I would rather not have the "E" version as it is going in a '39 P/U and I am trying to keep electronics to a minimum.
Hopefully I can get some knowledgeable comparisons.
 

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Old(s) Fart
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Thanks for this info. So, if I can't (or don't) have the 400 turbo for it's durability I think I would rather have the advantage of an overdrive gear. Which should I be looking for a 700R4 or a 4L60 ? I would rather not have the "E" version as it is going in a '39 P/U and I am trying to keep electronics to a minimum.
Hopefully I can get some knowledgeable comparisons.
I would first confirm that the trans is a TH375 and not a TH400. The TH375 only came in the longtail version - it was only used in heavy, long wheelbase cars with small blocks. They are not that common. What's the size of the output shaft? Got a photo of the ID tag on the side of the trans?

TH400 uses a 32 spline output shaft. TH375 uses a 27 spline output shaft.

 

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Discussion Starter · #6 ·
Thanks again Joe, for the info but after looking at the underside of the tail shaft it is stamped as a 375 and has a 27 tooth shaft. It was sold to me as a 400 but my lack of education and his dishonesty... hopefully karma will win out eventually.

614775
 

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Old(s) Fart
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Thanks again Joe, for the info but after looking at the underside of the tail shaft it is stamped as a 375 and has a 27 tooth shaft. It was sold to me as a 400 but my lack of education and his dishonesty... hopefully karma will win out eventually.

View attachment 614775
Yup, unfortunately that's a 375. Out of curiosity, is this a BOP case? I don't think I've ever seen one that's a Chevy case.
 

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All the TH 375 trans I’ve seen were Chevy cases.Never seen BOP.Only difference inside as I recall was clutch count.1 less friction in the forward and direct drums and the output shaft.A few changes and you can call it a TH400.
 

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Old(s) Fart
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All the TH 375 trans I’ve seen were Chevy cases.Never seen BOP.Only difference inside as I recall was clutch count.1 less friction in the forward and direct drums and the output shaft.A few changes and you can call it a TH400.
That's pretty much the difference, but you need to change both the output shaft and the tailhousing due to the diameter of the bushing that the driveshaft yoke rides in. Oldsmobile used them in Delta 88s and Vista Cruisers with 350 motors.
 

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More for Less Racer
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OK, that would make sense. I haven't done anything with vans. I know Buick used them in the same applications as Olds.
Wasn't the BOP TH-375 actually the TH-375B...basically just a heavy duty Th-350 with long tail shaft(13" IIRC). That's how my 1976 version of Chiltons Manual has it.

Regular TH-375 is TH-400 light duty as has been noted. All I touched were trucks or vans in the early 1980's....in fact, the first year 1990 454 SS truck was TH-375.....they called it the 3L80, iirc

Captn_Jim
As far as the Lokar shifter, in the picture you posted, what gear is the trans lever in right now??

Looking at it in the Lokar intructions on their site, it should be oriented with the link attachment hole at approximately 1 o'clock position when in Park....right now it appears it is is pointed at about 10 o'clock???
 

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Old(s) Fart
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Wasn't the BOP TH-375 actually the TH-375B...basically just a heavy duty Th-350 with long tail shaft(13" IIRC). That's how my 1976 version of Chiltons Manual has it.
This is the confusing part. GM called the light duty TH400 the TH375, and the HD TH350 the TH375B. Olds actually used both of them in different years. Prior to the release of the TH350 in mid-1969, the BOP cars used the TH400-based TH375. I had a 68 Vista Cruiser with 350 2bbl that had that trans. And yes, despite being an A-body, the extended wheelbase Vista used a long tail TH375. The Olds Chassis Service Manuals and assembly manuals document this. Olds typically used the "OA" trans code on these TH375s. In the early 70s, I've seen both installations, the TH375 and the TH375B. In most cases, Olds still used the TH400-based version.
 

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I’m in Canada so transmissions and engines used may be different than in theUSA models.
The 375B or long shaft 350 was only used a few years ending I think in 1976? GM started using the famous TH200 in most of the full size cars.The TH375 started being used in the 80’s.The long shaft TH400 used in the 70’s had a 32 spline output shaft.This is how I remember this stuff,but I’m old so I may be wrong.
To the OP,that lever looks like it’s in low gear.Grap a pair of channel locks and try and turn the output shaft.
 

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Old(s) Fart
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I’m in Canada so transmissions and engines used may be different than in theUSA models.
The 375B or long shaft 350 was only used a few years ending I think in 1976? GM started using the famous TH200 in most of the full size cars.The TH375 started being used in the 80’s.The long shaft TH400 used in the 70’s had a 32 spline output shaft.This is how I remember this stuff,but I’m old so I may be wrong.
To the OP,that lever looks like it’s in low gear.Grap a pair of channel locks and try and turn the output shaft.
The TH375B is a different trans than the long tail TH350. They use the same TH350 case, but the TH375B internals are stronger. All TH375Bs were long tail, but so were some TH350s.
 
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