Identify your transmission bell

bob k. mando

Team Member
Moderator
Both the Chevy and BOPC ( Buick, Olds, Pontiac, Caddy ) transmissions were 6 bolt housings for most of their production life. The original Chevy housing was 7 bolt and thats why their trans housings have a peak. In fact, most Chevy blocks were manufactured with the top center bolt hole drilled and tapped long after Chevy had changed to a 6 bolt housing.

So how do you tell the difference between the common as dirt Chevy pattern and the far more desirable ( to us :D ) BOPC housing?
1. Well, the first and most commonly stated visual reference is the Chevy peak versus the BOPC saddle at the top of the bell housing.

Here's a picture of the Chevy ( L ) and BOPC ( R ) pattern bells:
ChevyandBuickBells.jpg
Notice the engines in the background? We'll be taking a closer look at them in a second.

2. Also, only the two bolts below the alignment dowels share the same position between the two patterns. This is why a dual-pattern housing has 10 bolts, all the holes above the dowels must be duplicated. A Chevy bell has two bolts on each side aligned vertically with the respective alignment dowel. A BOPC bell only has the bottom bolts aligned vertically with the dowel and the higher bolts are moved inboard.

Here is the closeup of the blocks. A Chevy 350 and 1970 Buick 350:
ChevyandBuickpattern.jpg

Then we have the differences between the most common GM automatics, the TH-400 BOPC short-tail ( L ), BOPC long-tail ( C ) and Chevy TH-350 ( R ):
ChevyandBuickpattern.jpg

Here's a Super Turbine 400 ( early name for what is basically a Turbo-Hydromatic 400 ) for a 1965 401 Nailhead. Notice that even though it's still a 6 bolt pattern ( the second hole up from the bottom on both sides is for a guide pin, not a bolt ) it's wildly different from the later 'standardized' patterns. I have no idea if this pattern is found on anything besides Nailheads.
65401Nailheadbell.jpg




back of 215 / Land Rover engine
Roverbell-backofengine_zps7a351c10.jpg
 

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Here's a picture of a BOPC TH350 connected to an Olds engine and a Dual pattern trans:
TH350.jpg

Interestingly, I've seen a factory dual pattern Manual housing within the last month.

Manual transmission bells:
Buick bell (cutout for starter on passenger side only) with a GM manual trans pattern on the back
BuickManbellwithGMtrans.jpg

BOPC bell (has cutouts for a starter on both sides of the bell) with both a GM and Ford manual trans pattern on the back. The GM pattern has the 4 bolts in it.
ManBOPCBellw_GMandFord.jpg


Buick 215 / Rover Bell
RoverLT77bellhousing_zps6770580e-1.jpg
 

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Thanks for posting this important information with photos
this will help many owners with their projects.
:beers: :beers:
 
trans_pan_id.jpg

1 - Aluminum Powerglide 14 bolts
2 - TH200 Metric 11 bolts
3 - TH350 13 bolts
4 - TH400 13 bolts
5 - TH200-4R 16 bolts
6 - TH700-R4, 4L60, 4L60E 16 bolts
7 - 4L80E 17 bolts

trans_pan_shape.jpg


BOPC bell pattern, begins in 1964 for Buick small blocks
BOPCbell_zpsf379ea0a.jpg


pre-1965 Pontiac transmission bellhousing bolt pattern and dimensions, THIS IS NOT A BOPC PATTERN:
attachment.php


Chevrolet transmission bellhousing bolt pattern and dimensions, note that while Chevy retained the center peak, they have not actually used the top hole since the 1960s. This means that most Chevy transmissions that you find will only have 6 holes in the transmission bell. You must compare the holes above the dowels to truly determine whether you're dealing with a Chevy, BOPC or early Pontiac bell:
attachment.php
 

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heh, we took an extra TH-400 over to the guy with that dual pattern manual bell (he needed one for his 500 Caddy powered 1 ton pickup) and he just handed us the bell + saginaw trans. bonus!
 
400 nailhead trans bellhousing picture

This is off a 1965 401 nailhead .It is a turbo 400. out of a 65 riv:shifter:the second holes from the bottom on each side are guide pin holes.I have more pic ,but no more room .If you would like to have pics ofthe back of the bell or engine block.Just contact me thru this site

Rocky
 
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can you post a pic from the rear of the trans also? i've already copied this one if you need to delete for space reasons.

edit: full size pic added to OP.
 
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Here's a picture of the back of the bell housing. Will put a full lenght picture on as soon as I take it.This trans look like any other GM 400 except for the bell housing
 

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Message to Bob

Hey Bob did you get the picture of the back of the nail head bell housing?
 
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adapter question

Hey Bob ,I bought a sleeve that is made to be use to adapted a 400 flex plate for a nailhead.You grind off the larger centering ring (or have it turned in a lathe)then either have it pressed in or drive it in . Have you heard of this type of sleeve? It also keeps the converter centered.
 
a lot of Jeeps used Buick v6 and v8 engines in the late 60's and early 70's. check with those guys about what they are using.

also, you can buy adapter plates to bolt up a standard Chevy/GM corp 6 bolt trans to the BOP bell so any GM/Chevy trans could be made to work.
 
Jeep used the old round bell housing transmission (nailhead) in some of their wagoneers for a while after Buick discontinued it in '66 . It wasn't a s/p though. It was mounted to the back of the Jeeps V8 (AMC and/or 350 Buick??) with an adapter. So, there is a source for more of the nailhead type trannies out there than were originally produced up through '66.

Take a look at this link and see what you think of the bell housing.
http://64.233.167.104/search?q=cach...ransmission+adapter"&hl=en&ct=clnk&cd=5&gl=us

Ed
 
It was mounted to the back of the Jeeps V8 (AMC and/or 350 Buick??)

yes, Jeep used Buick 350 v8s and 225 oddfire v6s ( Dauntless ) from the late 60s to 71(?). obviously this raises the possibility of a viable 4 wheel drive for a Buick car but i think i'd be leery of trying to adapt a rock crawler trans to a strip or road track car.


Take a look at this link and see what you think of the bell housing.

yeah, that has that round Nail look to it. weird that AMC would contract for a defunct bell housing and then use adapter plates for every application they put it in.


Ed, you've posted several good, oddball pieces of information. keep it coming man, it's great to see. :bana:
 
It was mounted to the back of the Jeeps V8 (AMC and/or 350 Buick??)

yes, Jeep used Buick 350 v8s and 225 oddfire v6s ( Dauntless ) from the late 60s to 71(?). obviously this raises the possibility of a viable 4 wheel drive for a Buick car but i think i'd be leery of trying to adapt a rock crawler trans to a strip or road track car.


Take a look at this link and see what you think of the bell housing.

yeah, that has that round Nail look to it. weird that AMC would contract for a defunct bell housing and then use adapter plates for every application they put it in.


Ed, you've posted several good, oddball pieces of information. keep it coming man, it's great to see. :bana:

My daughters refer to me as a fount of trivial information.:bgrin:
 
jeep trans

I had a 79 Cherokee at the time I didn't know ,but I now recognize the bell housing pattern as a nail head bolt pattern.They also used Chrysler transmission too. This was bolt to a AMC 360 CID engine
 
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