Gm Part Number 3789665

[Mike M.]

I have in the boxes of parts for this 63 frame I'm restoring, 2 rings that would be used to change the height of the front springs. They would either go on top or under the spring and are some sort of hard rubber. I have never seen these on a original car or heard of them being used by GM. The other thing is that one of them has 9/16 on it and is thicker then the other which has 3/8 on it. They must have been used by someone to level the body or frame.
I just Googled the part number and this is what I got.

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1959-1961: Service Bulletin: Front and Rear Coil Spring Heights
Subject: Front and Rear Coil Spring Heights
Model and Year: 1959-1961 Passenger Cars
Source: Chevrolet Technical Service Bulletin
Bulletin Number: DR #437, Section III
Date: June 30, 1961

In the event a side-to-side or front-to-rear out-of-trim condition is noted on 1959-61, Passenger Cars, Spring Spacers are now available from Service Parts Stock to correct this problem. These spacers eliminate the necessity of replacing springs to correct an out-of-trim condition.

PARTS DATA
Part No. Description
3789664 Spacer-Special (3/8" Thick)
3789665 Spacer-Special (9/16" Thick)

Spacers may be used where trim heights vary more than 1/2" from side to side measured from the front of each body rocker panel to a level floor. When checking front-to-rear trim heights, the measurements are made from the front and rear ends of each rocker panel to the floor. The dimension at the rear should not exceed that at the front by more than 1-1/2".

These parts are of a polyethylene and rubber compound and may be inserted at either top or bottom of the spring.

NOTE: These spacers may be of particular help on units with Accessory Installed Air Conditioning.

Could these have been installed at the factory or maybe by the dealer or a owner later on?

[Joe L.]

Re: Gm Part Number 3789665

Mike-----

I don't think that these spacers were ever factory-installed on Corvettes. At least, I've never seen or heard of a known case of it. They may have been factory installed on some passenger cars of the period. I know little of passenger car spring installations.

[Clem Z.]

sometimes these were used in A/C cars

to compensate for the extra weight on the front springs.

[Joe L.]

Addendum

Mike-----

The early editions of the Chevrolet P&A Catalogs specify the 3789664 and 3789665 as applicable to 59-62 Chevrolet passenger cars with A/C or Cool Pack.

Under part description it states..."SPACER, to correct trim front and rear, right hand side (plastic)". The 3789664 is further described as 3/8" thick and the 3789665 as 9/16" thick.

The term "to correct" used in the item description further supports the notion that these were SERVICE-only items, not used in PRODUCTION. Regardless, according to this reference, they have no applicability to Corvettes. Of course, that does not mean that they are absolutely not usable on Corvettes.