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Joined: Mar 2022
Posts: 53
Hello All,

I'm trying to figure out what additional covers I need at the bellhousing on my 1957 235 engine with a manual transmission and clutch. They didn't come with the truck I purchased.

Looking for what I need and where to purchase would be great.

Thanks for the help.

Joined: Sep 2009
Posts: 3,602
Gearhead, Moderator for The Swap Meet and General Truck Talk

According to this page Pg 148 of 1929-57 Master Parts Catalog [] the pieces you seek are as follows:

Underpan: GM# 3725088 (they often come up for sale on eBay, bit couldn't find any active listings tonight)

Extension: GM# 839180 (there is one currently listed on eBay - search using this part number to find it)

Bolt w/washer (4 each): GM#839301 (Online references show these as under new GM# 3817006 - 1/4"X20, 7/16" long - readily available from various sources)

Just a note that you can always post an ad in Truck Parts Wanted as there are often fellow Bolters that may have what your looking for too.

Good luck in your search! thumbs_up


1951 Chevy 3 window 3100 (My Grandpa's hunting truck)
1966 Chevelle (Wife's Hot Rod)
2013 Chevy Silverado (Current daily driver)
US Army MSG Retired (1977-1998)
Com Fac Maint Lead Tech Retired (1998-2021)

Finally time to get to work on my Grandpa's (now mine) truck!
Joined: Jan 2001
Posts: 5,322
Hope this helps

Attached Images

See the USA in your vintage Chevrolet!
My Blog []
Joined: Mar 2022
Posts: 53
Thanks guys for the information.

I'm surprised no one makes an aftermarket replacement but I guess its not something you need very often.

Have a nice new year.


Joined: Mar 2022
Posts: 53
One other question, can the extention piece be put on after installing the bell housing or is that somehow pinched or needs to be installed first before mounting the housing.

I saw one video of the 57 installing the bellhousing, flywheel, and clutch and it didn't mention the front cover/extension needing to go on first.

Thanks Again,

Joined: Mar 2010
Posts: 1,968
Pictures shamelessly stolen from various websites.
Thanks Denny.

Attached Images
Extension Cover.jpg (105.2 KB, 105 downloads)

"Adding CFM to a truck will only help at engine speeds you don't want to use."
"I found there was nothing to gain beyond 400 CFM."
Joined: Mar 2022
Posts: 53
Thanks Buoymaker

Looks like they can be installed after, which is great, this way I can move forward with engine installation while I get those parts.

Stay well,

Joined: Jan 2001
Posts: 5,322
Yes, easy to install any time.

See the USA in your vintage Chevrolet!
My Blog []
Joined: May 2022
Posts: 52
I noticed that the passenger car of the same era has a different underpan part number. Why wouldn’t a car or truck with a 235 mated to a standard transmission have the same underpan? Can anyone explain the pan’s physical differences between the car and the truck? We’re the bell housings different?
Can someone post a picture of the differences?


Last edited by Mike34; Tue Jan 03 2023 11:05 PM.

1955 Chevy 2nd Series 3100 Stepside, 235cid
Joined: Mar 2004
Posts: 6,200
It's easy to ID the late 50's car and truck bellhousing from each other, the car bell housing uses (2) small bolts to hold the motor mount on while the trucks had one large bolt.

I can't help with any differences in the sheet metal pans...

Mike B smile

Mike Boteler

1956 Chevy 3100 Resto Rod []
1956 8400 Wrecker w/Holmes 525 []
1956 9200 Tractor w/Allison Automatic []
1952 Willys M38 Army Jeep
1953 Willys M38A1 Fire Jeep
1978 CJ-5 Navy Jeep
Hughesville, MD

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