CRG Research Report
1967 Camaro Radius Rods
© 1998-2011, Camaro Research Group
Primary Author -
, updated by Kurt Sonen
Reviewed by the CRG
Last Edit: 13-Oct-2011
Previous Edits: 23-Jan-2010, 21-May-2004, 08-Aug-2000, 18-Aug-1999, 23-Dec-1998
Original Release: 24-Sep-1998
In mid-1967 model year, high-performance 1967 Camaros received a
passenger-side traction bar, known as a "radius rod."
There were two factory designs - the first
design used a round rod while the rod in the second design
was rectangular with increased stiffness. Additionally,
later in the year, a rectangular rod service retrofit kit
was made available to dealers to address wheel-hop
complaints. The service kit could be applied either early
vehicles with no rod at all or to vehicles with
the round rod.
First Design - Round Radius Rod
The question of which rod was applied to what model, and
when, has often been a subject of much confusion. This
report defines, as clearly as possible given the known
data, the applications of each rod, and also discusses
specific areas where data and information is lacking or
weak. We encourage all 1967 Camaro owners with installed
radius rods or rod brackets to please see the
CRG Forum research post
to contribute information about their vehicle, that we might
continue to improve this report.
Second Design - Rectangular Radius Rod
The overly-simplified summary of radius rod application is
that starting mid-December 1966, cars with a 12-bolt axle
received the round rod. After February 1967, cars with automatic
transmissions and 12-bolt axles (L48/M35 and L35/M40) continued to
receive a round rod, while cars with manual transmissions and 12-bolt
axles received a rectangular rod. This is overly simple because there
are two caveats:
Table 1 illustrates, in a different format, these findings to
date, model by model.
- The rectangular rod was not introduced to all
manual transmission models at the same time, therefore some
manual transmission cars continued to receive the round rod
after other models had changed to the second design. The
start date of the rectangular rod for each model is discussed
- The L48/M35 car, while fitted with round
rod brackets, did not always have the rod itself actually
installed at the factory. Data to date indicates that only
about one-third of this model have installed rods. No
specific patterns of installation have emerged.
Table 1: 1967 Camaro Radius Rod Conclusions To-Date
mid-Dec to Mar-Apr
Mar-Apr to End-of-Model
|L30 4-speed 1, 2
|L48 4-speed 2
|L48 Powerglide 3
|Z28 4-speed 4
- Introduction of the radius rod into the L30/M20 apparently
lagged behind the L48 by about a month, not appearing until
January/February, when the 12-bolt axle was introduced
to the L30/M20 (see the
L30/M20 CRG Research Report). Note that it appears that
both the 10- and 12-bolt axles were used in L30/M20's in
- The L30/M20 and L48/M20 transition to the rectangular
rod appears to vary by plant. Norwood transtioned to the
rectangular rods about 04A. There isn't enough data on
Los Angeles cars to be certain, but it appears that the transition
occurred later in April.
- About one-third of L48/M35 cars have been noted with the round
radius rod installed, while the remainder have the rod brackets
but are absent the rod. No definite installation pattern has emerged.
- Z28s used the rectangular bar starting in early March.
High-performance 1967 Camaros under heavy initial
acceleration experienced a rear suspension problem called
"wheel-hop" (or "wind-up"). This problem was accentuated by
a combination of insufficient suspension stiffness about the
axle centerline and insufficient suspension damping in the
monoleaf spring/vertical shock system. High engine torque
applied to the differential rotated the entire differential
assembly about the axle transverse centerline toward the
front of the vehicle and twisted the monoleaf springs into
an "S" shape, until the torque broke the tires loose. With
the tires off the ground the engine torque no longer applied
a load to the deformed springs - with the result that the
springs violently rebounded and forced the tires back on the
ground, starting the cycle over again. This shuddering,
traction-losing, U-joint-breaking, behavior repeated at high
frequency until the driver backed-off the accelerator.
The temporary fix implemented by Chevrolet engineering
during the middle of the 1967 model year (until the 1968 model
year suspension changes were implemented) was a form of
traction bar, known as a "radius rod." The radius rod was a single,
end-hinged, rigid link between the passenger side of the rear axle and
Floor mount, under the rear seat
The theory was that such a rod would allow an acceptable
amount of vertical translation in the rear suspension, but
resist rotation of the suspension about the axle centerline
such as occurs when a large torque is applied to the
driveshaft during a hard start. In practice the Chevrolet
factory rod reduced, but did not eliminate, wheel hop, and
therefore neither of the two Camaro versions of the radius
rod were fully successful.
Both of the Camaro radius rod designs used a rigid steel rod
with one end thru-bolted (hinged) to an axle bracket
and the other end attached to a bracket bolted to the body
(under the passenger-side rear seat). The first design was a round
steel rod with a bushing at each end, part number 3914808.
The second design improved upon the first and was a stiffer
1-inch by 1.25-inch rectangular rod, part number 3920234,
with a modified axle bracket interface.
In the 1967 Camaro Assembly Manual, sheet B3 for RPO L48, dated
08-Nov-66, describes the first design version used with the round rod.
The 07-Apr-67 revised sheet A8 for RPO L78 describes the second
design version. The bracket welded to the rear axle was slightly
modified for the 2nd design - it was wider with an extra hole added and
the foward edge of the bracket was stepped. It is believed that all
axle brackets were changed to the second design about the time the
rectangular rod was introduced.
A supplemental "stop" bracket that included a new rubber bumper was
bolted to the bottom of the ears in the second design. For both
designs, the body bracket was identical: part number 3914806. The body
bracket was bolted to the rear
frame rail and to the two studs that protuded through the floor.
In contrast, the 1967 Pontiac Firebird included radius rods
for both left and right sides of the axle on their higher
performance models. The Firebird rod had an I-beam cross-section
design (compare to the round or rectangular bars used on the Camaro).
See Firebird rod - view 1
and Firebird rod - view 2
for pictures of the Pontiac-designed radius rod.
Radius Rod Applications
The first rod design was applied in mid-December 1966 to all models
with a 12-bolt axle. This was expanded to the L30 275HP/4-speed model,
when the 12-bolt axle was included in the L30/M20 in January / February.
The second design rectangular rod was introduced in early February for
the L35 big-block manual transmission applications, and was also applied
to the L78/M21 from the start of that model in late March.
The replacement of the round rod with the rectangular rod on the Z28
appears to have occurred in March. The L48/M20 and L30/M20 cars
transtioned to the rectangular rods about 04A at Norwood and later
in April at Los Angeles (though the data on the Los Angeles cars is not
definitive). Despite an assembly manual cancellation notice, the
round rod remained in use for the rest of the year on
L35/M40, as well as (sporadically) on L48/M35.
GM documentation was used to derive these applications and actual
vehicle data supports that information.
The one area of ambiguity is the L48/M35 model, which has
sporadic radius rod application.
There is no indication in the assembly manual that the
traction bar was not applied to all SS-350 models, but other
Chevrolet documentation indicate that it was not applied to
the L48/M35 SS350/Powerglide combination. The CRG vehicle
database provides insight in the actual usages. Of the
approximately 100 L48/M35 cars built 012A or later for which we
have rod-related data, 35% are reported with the round rod, and
5% with a rectangular (presumably) service retrofit. The remainder (60%)
do not have a rod, but have one or more of the mounting
brackets There is no obvious pattern of application. Even cars with
optional performance axle ratios do not have the rod.
The rectangular rod documentation in the 1967 Assembly
Manual was revised after initial release; CRG has only the
revised version of this sheet and does not know what the
initial release looked like. The 1967 Assembly Manual UPC
L78 Sheet A2 table of contents lists the radius rod sheet in
the initial release as for "RADIUS RODS" (note the plural).
CRG speculation is that the initial release of this sheet
included both round and rectangular rod configurations, and
that the April revision to the sheet was for the purpose of
eliminating the round rod configuration from this sheet.
Chevrolet Dealer Service Technical Bulletin
67-T-30, dated 12-May-67 (pdf file), indicates the round radius rod was actually
implemented in production on 15-Dec-66.
This same bulletin indicates that the second design went
into production on 27-Mar-67. However, use in the L35/M20 pre-dates the
production introduction date in the bulletin, since we have
several L35/M20 datapoints from 02A to 03A, all of which
have the rectangular rod.
It would appear that the 27-Mar-67 introduction date only applies
to the L30 and L48 vehicles, which does match with vehicle data.
The scope of Bulletin 67-T-30 is to specify retrofit
instructions for the rectangular radius rod for L30 and L48
4-speed complaint vehicles, and therefore it makes sense
that the information in the bulletin literally applies only
to these vehicles.
Note also that Bulletin 67-T-30 includes a reference to "...
vehicles built after December 15, 1966, with provisions for
a radius rod." Note that this quote doesn't say "with a
radius rod," but says with "provisions" for one - indicating
that some vehicles had the brackets installed at the factory
(the provisions) but without the rod in place.
A significant complication to the analysis of the radius
rod applications is the rectangular radius rod service retrofit kit.
This makes it a bit more difficult for us to be sure if a rectangular
bar was factory installed or dealer installed. However, by
comparison of the service replacement instructions with the
original factory assembly instructions, it appears that
there are three clues that should distinguish a service
replacement rectangular bar from its factory brother:
- When the service kit was applied to a car with no
previous bar, the body bracket was welded to the body,
rather than bolted-on as was done at the factory.
- If the axle bracket didn't have holes to mount the stop bracket,
the service kit required the
bumper stop bracket to be welded to the axle bracket, rather
than bolted-on as was done at the factory.
- When the service kit was applied to a car with a
pre-existing round bar, the round bar axle brackets were not
replaced with the new brackets but remained on the axle and
were used as-is. The two bracket types have distincly
In chronological order, here is what is recorded in the 1967
Camaro Assembly Manual, 3891775, combined with information
from Bulletin 67-T-30, and key datapoints from the CRG
Table 2: Chronological Documentation of Radius Rods
RPO Reference Status Date Notes
--- ---------- ------- ------- -----------------------------------
M40 67 AIM new dwg 26Aug66 M40 docs released include drawing with
M40 all radius rod ears on the axle indicating
that this change was contemplated even
at the beginning of production.
L48 67 AIM new dwg 08Nov66 L48 docs released for round rod
L48 B3 (1st design).
Z28 67 AIM new dwg 09Nov66 Z28 docs released referring to L48 for
Z28 A2 round radius rod.
L35 67 AIM new dwg 30Nov66 L35 docs released referring to L48 for
L35 A2 round radius rod.
--- Bulletin start 15Dec66 Round rod (1st design) usage started in
67-T-30 prod production.
L30 67 AIM rev dwg 16Dec66 L30 docs revised to add radius rod
L30 A2 reference to L48. This was never revised
to delete the reference.
--- CRG database December Several mid-December-built L48 cars have a
round radius rod. Usage is not consistent.
--- CRG database 01B 01B Z28 car with round radius rod.
L35 67 AIM rev dwg 08Feb67 Reference to L78 radius rod added to
L35 A2 existing reference of L48 rod.
Z28 67 AIM rev dwg 08Feb67 Reference to L48 radius rod changed to
Z28 A2 L78.
--- CRG database 02A Several 02A L35/M20s exist with
L78 67 AIM new dwg 17Feb67 L78 docs released with reference to
L78 all "RADIUS RODS"- plural. Only sheets
A1-A6 released on this date. Remainder
L78 67 AIM new dwg 23Feb67 Remainder of L78 sheets released, incl.
L78 A8 sheet A8 with initial L78 radius rod(s).
Note that L35 and Z28 have already
released docs referencing this.
M40 67 AIM rev dwg 17Feb67 M40 docs revised to change M40 axle part
M40 A3 number from 3910882 to 3920569. If this
was for the purpose of using the rect-
angular rod axle brackets, it didn't
materialize in actual cars. Done same day
as initial release of rectangular rod.
--- CRG database 03B 03B Z28 with rectangular radius rod.
--- Bulletin start 27Mar67 Rectangular rod introduced on assembly
67-T-30 prod line. Scope of this bulletin may be
limited to L30 and L48.
L34 67 AIM new dwg 30Mar67 L34 docs released referring to L48 or L78
L34 A2 for radius rods. The L34 was not released
in 1967 despite this documentation.
L35 67 AIM rev dwg 06Apr67 L35 docs reference to L48 radius rod
L35 A2 removed, leaving only the L78 reference.
Despite this, all L35/M40 used the
L48 67 AIM cancel 06Apr67 L48 docs cancel round rod design sheet
L48 B3 dwg for L48 (and, implicitly, for L30).
However the round rod continues in
L78 67 AIM rev dwg 07Apr67 L78 docs for sheet A8 on radius rod
L78 A8 "revised and redrawn". New release
shows only a rectangular rod.
Parts Manual Data
Supporting data from Master Parts Catalogue 721A, Dec 1971, Section
- L35, L78, and Z28 M/T cars initially had the round rod of PN
- L35, L78, and Z28 M/T cars later had the rectangular rod of PN
3920234 (but superseded by another rectangular rod service part
- L30 and L48 4-speed, and L34 M/T engine used a 3920234
rectangular rod (but superseded by another rectangular rod service
Note that the L34 was never released in 1967. L34 is not the only
unreleased RPO to be mentioned in a GM manual.
- All engines with TH400 transmission used the round rod.
Despite assembly manual cancellation of the round rod, the
parts manual appears correct on this point - M40 cars did use
the round bar.
- Upgrade kits were part numbers 3929559 to update from round to
rectangular rod, and part numbers 3929559 and 3929299 to add the
brackets and the rectangular rod.
Note the absence of an upgrade kit to add the brackets and
the round rod.
- No mention is made of the round rod on L30 and L48
CRG believes that Bulletin
67-T-30, forced the issue and
caused all of these to be changed to rectangular rods in the
event of a need for service.
- Small-block 3-speed standard transmission references
are conspicuous by their absence.
- Powerglide transmission references are conspicuous by