BB vs SB 4-speeds

[Greg B]

I'm trying to confirm that a 1971 GS is a true Stage 1 or at least a GS 455 - not getting very far with the Stage 1 issue but would the manual transmission be different for a big block vs a small block? If so I could at least confirm the car is a GS 455 but not a Stage 1.
Thanks
Greg
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[flynbuick]

For a 70 just as an example I see no differences in either the assembly manual or the parts books.


Post a pic od the steering shaft at the flange around the rag joint and let us take a look.

[ts-gs]

Is it an original Stage 1 or clone? If original, the engine code should be TS located on the deck of the block between the #5 & #7 spark plugs.

Check out this (http://www.stage1registry.com/stage1info.html#E1) web page for more info.

[Greg B]

The original engine is long gone replaced with a 72 GS 455 block so without documentation all I see is potentially a cloned GS 350.
Thanks
Greg
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[flynbuick]

If the steering shaft has not been changed it will reveal whether it was a small block or a 455.

[IDOXLR8]

If the steering shaft has not been changed it will reveal whether it was a small block or a 455.
?????????? :Do No: AL.

[hemikillerstg1]

The z-bar and linkage should be different for a BB car, unless that's been changed too. Otherwise I thought there was a number stamped in the Frame somewhere on the rear drivers side of the frame that would tell you if it was a 350 or 455 car. The other tell tale sign is the sterring shaft coupler.

[flynbuick]

?????????? :Do No: AL.


The flange at the rag joint is unique between small and big blocks.

[TXGS]

Second What Jim is saying! :TU: Unless column and shaft were switched at some point.

[Greg B]

Thanks, the column looks to be blue so on a cinnamon car I would imagine its been changed. Where would I look relative to the z-bar?
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[TXGS]

To determine if it is a BB car would the first few numbers of the Vin denote it is a GS 455. I know 70 does, but not sure of 71.

[Adam C]

Hey Greg,
The big block car has a shift fork that uses a heim joint push rod, ie" the push rod has a bushing in it and it is held to the fork using a pin.
I believe that on the small block fork, the push rod sits in a depression in the fork and is held in by preload on the linkage. ala Chevrolet.
I seem to remember seeing pics somewhere on the site awhile ago.
Hope this helps
Adam

[buick64203]

If its a small block 4 speed, the input shaft will be coarse spline (1 1/8x10). The big block cars used a fine spline (1 1/8x26). Also, small blocks use a 10 1/2" disc while big blocks use an 11"

[bignastyGS]

If its a small block 4 speed, the input shaft will be coarse spline (1 1/8x10). The big block cars used a fine spline (1 1/8x26). Also, small blocks use a 10 1/2" disc while big blocks use an 11"


Not so in 73 though...My 73 GS has a M21 fine spline(26) in it an if I were a betting man...I bet some came that way in the 70-72 cars.I also have a matching number trany(M20) out of my 68 GS400 (coarse spline)I would say that finding the frame numbers will be your only chance to prove authenticity.

[buick64203]

Thats interesting Pat. The trans from my 73 Stage 1 was also fine spline. And the small block 73 I had was coarse spline. I had found a definite pattern over the years with it. But, if its like everything else on these cars, its whatever they had available got put in them. Another mystery to solve...

[flynbuick]

To determine if it is a BB car would the first few numbers of the Vin denote it is a GS 455. I know 70 does, but not sure of 71.


Phil

On a 71 the same convention is not used and the GS 350 and GS455 used the same 2 digit code. So you cannot tell from a 71 VIN.

[TXGS]

Thanks Jim. I thought that was the case. :TU:

[IDOXLR8]

The flange at the rag joint is unique between small and big blocks.
What does the rag joint got to do with the transmission? :Do No: AL.

[buick64203]

The lower steering shaft flange where it attaches to the steering box is different between big block cars and small block cars. On a big block car, the flange is cast. There is a 12 point bolt that tightens the cast pice to the splined steering shaft. On a small block, the flange is stamped steel.
Its just one thing to look at when your trying to determine if a 71 GS was a BB or SB originally. Another way is the gas pedal if its an automatic. On a BB, the gas pedal will have the T-400 kickdown switch. Big blocks also used different tranny crossmembers. All little pieces to the puzzle

[buick64203]

Here (http://cgi.ebay.com/ebaymotors/RARE-68-69-70-CHEVELLE-SS-396-454-2PC-STEERING-SHAFT_W0QQcmdZViewItemQQcategoryZ34200QQitemZ46062 41816QQrdZ1QQsspagenameZWDVW) is a BB shaft. Note the 12 point bolt. Next time I sell one of these, im going to say it fits a BB Chevelle instead. Looks like advertising it that way is worth another 100 bucks :error:

[David Hemker]

71 GS's are the hardest to verify due to no special vin code for engine size.

On Buick 4 speeds, there is no difference between a bb & sb 4 speed muncie.

There is:
the M-20 wide ratio with 2.52 1st gear,
the M-21 close ratio with 2.22 1st gear,
the M-22 heavy duty with 2.22 1st gear AKA rock crusher. These had straighter cut gears (noisy) & different steel alloys for strength.

Buick used exclusively the M-21.

70 & older Muncies were the 10 spline input.
In 71 there was a design change on the Muncies.
71 & newer Muncies were the 27 spline input.
All M-22's were 27 spline input regardless of year.

If there is a 10 spline Muncie in a 71 & newer car it was swapped in.

For more info, parts etc go to www.4speeds.com.

[buick64203]

Buick used exclusively the M-21

They used M-20s as well. It depended on the final drive ratio.


If there is a 10 spline Muncie in a 71 & newer car it was swapped in.

What information are you baseing that from?

[David Hemker]

Chassis manual and experience.

[buick64203]

The only reason I question you is that I owned a 22,000 mile original 73 GS 350 that had a 10 spline M-20. I would just need some additional confirmation on those statements. maybe Duane "the thread ender" Heckman can chime in on this one

[David Hemker]

All the information I have come across over the past 28 years from manuals, articles, people with more 4 speed experience, parts suppliers etc have verified my earlier post.

I do know from past experience that for street manners even my 455 likes the wide ratio M-20. I have driven a few 350's as well. I can see where the 73 with lower compression and more weight would greatly benefit from the
M-20. My guess is the original owner had one sitting around or found one had it changed over. But stranger things have happened.

[ts-gs]

If the M-20 was original to the car, shouldn't there be a matching VIN stamped in it where the tail meets the housing?

[Greg B]

If the M-20 was original to the car, shouldn't there be a matching VIN stamped in it where the tail meets the housing?

I didn't look for a matching tranny yet but was hoping that there was a unique 4 spd like the BB TH400 for the Stage 1 or at least the big block cars.
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[David Hemker]

The build date and VIN should be stamped on the passenger side of the main case towards the top just in front of where the center support and tail shaft housing bolt on. I have seen the last 6 digits of the VIN and I have seen the last 8 digits of the VIN stamped here.

[Qship]

David my original 1970 GS 350 had 3.23 gears and was original with a M20 and yes I checked the serial number and it matched the VIN. So Buicks did use the M20.

[IDOXLR8]

1972 was easy, I think power disc brakes and the 3:42 posi was a standard issue in that year, AL.

[David Hemker]

That's interesting. All information in the Buick manuals I have list the M-21 only and make no mention of the M-21. I had a 70 350 car with 3.23 gears that had the m-21.

[buick64203]

The type of manual trans GM used was dictated by the rear axle ratio. Muncie M-21 & M-22 trannies (and their 2.20:1 1st gear) work best with a numerically high rear axle ratio (3.70 and up). Mating an M-21 with highway gears causes excessive wear on clutches and weak acceleration. Which is why GM used the M-20 in these situations

[70GREENROCKETS]

Just fyi my 70 stage 1 ac 3.42 rear built 09\03\69. On the body shop inspection paper i found in the dash it has M20 typed in @@@@@@s!! so at least its on the FLINT paperwork. Gregg

[Marco]

Just fyi my 70 stage 1 ac 3.42 rear built 09\03\69. On the body shop inspection paper i found in the dash it has M20 typed in @@@@@@s!! so at least its on the FLINT paperwork. Gregg

Hi Gregg -

M20 is the Buick UPC code for a manual 4-speed transmission, just as M40 is the UPC code for the TH400. It does not represent a Muncie 'M20' transmission. If you have your original trans, look at the verticle stamping on the passenger side and you'll see the stamping ends in a 'B', which represents an M21.

Notice how Buick has only one UPC code for a 4-speed transmission? :Brow:

UPC codes can be found on the 1970 new car order form found HERE (http://www.stage1registry.com/BuickGS/1970_order_form.jpg).

:beer

:3gears: