68-72 removable front X member ???

[Geoff C.]

I have a question regarding the attachment of the removable front cross member to the large U-shaped brace that supports the center of the front bumper. There are 4 bolts that mount this U-shaped brace to the cross member. The rear most 2 bolts screw upwards through a hole in the cross member and into a weld nut affixed to the U-shaped brace. The orientation is opposite for the front 2 bolts. These pass through a hole in the U-shaped brace and then into the weld nuts affixed to the removable cross member.

In other words, the front most bolts screw in downward, while the rearmost bolts screw in upwards. A fellow with a 69 told me that all 4 should screw upwards – hence no weld nuts should be present on the front lip of this cross member. I examined both of my 68’s and my 69 and they mount as stated in the first paragraph. Who is right?

Check out section 14 sheet A2 in a 68-72 AIM. I know the cross members and U-shaped braces did change slightly from 68 to 69 however, however I believe the method of attachment and orientation of the mounting hardware is the same for all 68, 69, 70, 71, 72

The only visual difference between my 68 and 69 are the addition of two large (approx. 3” dia.) drain holes added in 69 to the lower surface.

Geoffrey

[Joe L.]

Re: 68-72 removable front X member ???

Geoffrey------

The forward bolts go "down" and the rear bolts go "up", as you described your observations of your 68s and 69.

Several different u-braces and several different cross members were used over the 68-69 period. However, I don't think that the orientation of the bolts changed with any of the parts.

My original owner, September, 1969-built convertible is configured as above.

[Geoff C.]

Joe and I must have the only 68 & 69's here

Joe,
Thanks for confirming my belief.
Geoffrey

[John A.]

Re: Joe and I must have the only 68 & 69's here

Geoffrey & Joe,

My 69 also has a four-up bolt configuration. I have always wondered if this config was original to the car. The NOS replacement and the repo replacement cross member I checked out have the two-up / two-down configuration. This makes replacing any bent components difficult because a pair match is needed. Don't know if it makes any difference, but this car has a Jan 69 build date.

[Joe L.]

Re: Joe and I must have the only 68 & 69's here

John-----

If you can, check the configuration of the u-shaped bumper bracket on your car. For your 4 bolt "up" configuration to be original, there should be 4 weld nuts on the bracket flange. Also, there should be NO weld nuts on the crossmember if there are 4 weld nuts on the bracket.

Although it was a 1969+ PRODUCTION part, crossmember GM #3954506, was the GM-catalogued SERVICE part for all 68-72 Corvettes. If the crossmember had 2 weld nuts attached to the center bolt holes (for the u-bracket) and if the 68 and/or early 69 applications used 4 "up" attaching bolts, then the 3954506 crossmember could not have serviced the 68 and/or early 69 application without removal of the weld nuts from either the crossmember or the u-bracket. Chevrolet specified no such modifications required for installation of the 3954506 cross member for 68 and/or early 69 applications.

[John A.]

Re: Joe and I must have the only 68 & 69's here

Joe,

All four nuts are welded to the center bumper bracket. Is this the 68 configuration as well? Also, there is a 2" L shaped (extends to the rear) bracket welded between the two bumper-bolt mounting holes. Not sure what this is for - serves no application. The cross member also has some additional mounting holes/nuts. Viewed from the top, there are 2 1/4" or 3/8" bolt holes about two inches apart centered on the leading edge of the cross member - a set on each side of the center bracket. There are also two other holes about the same size just below… on the forward side of the cross member. Does this further indicate a 68 application?

More importantly - how do you straiten these brackets once there slightly bent ;-)

[Mike Baker]

Re: Joe and I must have the only 68 & 69's here

My 68 also has the bolts in a "four up" configuration. However, I do know that the nose was damaged at some time in it's life, so I cannot vouch for the originality of the bracket or crossmember.

All four of the nuts are welded to the bracket, and John I do not see the other holes in the crossmember that you described in you post.

I doubt that my post really helps much but I thought I would contribute my observation.

[Geoff C.]

Humble Pie and 68-72 Cross Members

As they say in football, “After further review” ... I am more confused than ever. I believe all three of the following models have original GM cross members and bumper braces, however realistically they may or may not be the ones that St Louis actually installed on that particular VIN. Both of my 1968 models are lacking two large drain holes (about 2” in diameter) that my 1969 does exhibit. All bear a large “W” as seen on many other original parts including bumper braces and brackets. I have not seen a repro with the “W”.

My 1968 L89 (which currently is dead) is under my 56, which is on top of one of my car lifts. This makes it difficult to examine with ease. However, I managed to prostrate myself and looked more carefully. This 68 has a VIN # 7,366 and both the front and rear cross member to bumper brace bolts screw in upwards. Therefore there are no weld nuts on the cross member and 4 weld nuts on the brace.

My 1968 435 is on top of one of my car lifts and easier to examine. This 68 has a VIN # 15,886. The rear 2 bolts screw upwards and front 2 bolts screw downwards. Therefore there are 2 weld nuts on the cross member and 2 weld nuts on the bumper brace.

My 1969 is also on the top of a car lift it matches the arrangement on the 1968 435 directly above. The rear 2 bolts screw upwards and front 2 bolts screw downwards. Therefore there are 2 weld nuts on the cross member and 2 weld nuts on the bumper brace.

I have summarized this info as follows from the AIM UPC 14, sheet A2. All the model year specific AIM’s show 2 bolts up and 2 bolts down, however a generic 1968-1972 illustration in a part book shows all 4 bolts up.

The AIM shows that this cross member was bolted to this brace.
1968 shows # 3935593 was bolted to # 3938080 sheet dated Jan 3, 1968
1969 shows # 3954506 was bolted to # 3938080 sheet dated July 31, 1968
1970 shows # 3954506 was bolted to # 3963129 sheet dated Sept 17, 1969
1971 shows # 3954506 was bolted to # 3963129 sheet dated May 22, 1970
1972 shows # 3954506 was bolted to # 3963129 sheet dated Nov 26, 1971

The AIM shows that either removable cross member (3965593 or 3954506) could be used with either center bumper brace (3938080 or 3963129). There needs to be two additional part numbers – one each for a third style cross member and third style brace if all 4 bolts screw upwards.

The Chevy dealer part books of the 1968 to 1972 era, only show one cross member (3954506) being used with one brace (3980824) for all 68-72 models without mention of restrictions or modifications required. The cross member is the same part number as production, however that brace is a service replacement that accepts either 68-69 or 70-72 center grill mount brackets.

Summary: both my 68’s have removable cross members without the large drain holes – however the earliest one has no weld nuts and the later has 2 weld nuts to mount the center brace. These differences should require 2 different part numbers. My 69 cross member has 2 large drain holes and 2 weld nuts for the center brace. Therefore it should have another different distinct part number. Soooooooooo there must be at least 3 different removable cross members.

If Mr. Andre’s 1969 has 4 bolts pointed upward (and now I do not doubt him) then that VIN is of interest to see where it lies in relation to the 3 models in my possession. It his has no weld nuts and 2 large drain holes – that would necessitate a fourth distinct different cross member. If it has no drain holes then it matches my early 1968, but not the later 1968.

Fill in the blanks
1968 VIN 7,366 no drain holes; 4 bolts go up, no weld nuts on x-member
1968 VIN 15,886 no drain holes; 2 bolts go up, 2 weld nuts on x-member
1969 VIN 34,096 2 drain holes, 2 bolts go up, 2 weld nuts on x-member

Confused in Connecticut
Geoffrey Coenen

PS Mr. Andre please accept my apology for doubting your arrangement and my braggadocio about my “outstanding” knowledge. Please disregard the snotty letter that I just mailed you today. I currently have a case of foot in mouth disease.

[Joe L.]

Re: Humble Pie and 68-72 Cross Members

Geoffrey-----

OK, I THINK that I might have it figured out now. But, I've got to admit, this thing was a REAL challenge.

As it turns out, there WERE 4 different u-brackets and there WERE 3 different crossmembers. Here's what I found:

1) the original u-bracket used for 1968 Corvettes was GM #3914260. This, apparently, is the bracket with 4 weld nuts for the "4-up" configuration. This bracket may or may not have been used for all of 1968 PRODUCTION and/or it may or may not have been used for early 1969 PRODUCTION. I figure the model year changeover "syndrome" may apply here. The GM #3914260 bracket was discontinued from SERVICE in October, 1969 and replaced by the GM #3980824 bracket

2) the original cross member used for 1968 Corvettes was GM #3915769. This is likely the crossmember with NO weld nuts and is used with the 3914260 bracket. It's period of use in PRODUCTION is not known to me. It was discontinued from SERVICE and replaced by the GM #3935593 in October, 1968. It may have been used in PRODUCTION throughout the 1968 model year or it may have been replaced by the GM #3935593 sometime during the the later part of the model year. The GM #3935593 was discontinued from SERVICE in May, 1969 and replaced by the GM #3954506. I expect that both the 3915769 crossmember and the 3935593 crossmember are configured alike with respect to the absence of weld nuts for the bracket attachment;

3) I question whether the GM #3938080 u-bracket was ever actually used during the 1968 model year, regardless of what the AIM says. I think that this bracket is the one with 2 weld nuts and 2 holes for the "2-up, 2-down" bolt configuration and was used for the 1969 model year. The GM #3938080 bracket was NEVER available in SERVICE. This bracket was likely the one set up only for the 68-68 style grilles/bumperettes;

4) I think that the GM #3963129 bracket used in PRODUCTION for the 70-72 model years has the same weld nut configuration as the 3938080. However, I expect the difference is the accomodation for the 70-72 style grilles/bumperettes. The GM #3963129 bracket was NEVER available in SERVICE, either. Only the SERVICE-only GM #3980824 bracket was available for all 69-72 SERVICE requirements.

The only thing that all of the above does not answer is how the GM #3980824 bracket could have replaced the GM #3914260 for SERRVICE of 1968 models OR how the GM #3954506 crossmember could have replaced the GM #3935593 for SERVICE of 1968 models. However, here are some possibilities:

a) The 3980824 bracket could have been used to replace the 3914260 if the 3980824 had used 2 weld nuts AND the user added two conventional nuts to secure the other 2 bolts used in the 68 configuration; in the 69-72 configuration, the bracket would be used as-is. Or, the 3980824 might have had NO weld nuts and conventional nuts were to be used by the customer for all 4 positions. The weld nuts are a convenience in PRODUCTION that GM might not have felt was so necessary in SERVICE;

b) I cannot come up with any way that the 3954506 cross member with 2 holes and 2 weld nuts could have been used to SERVICE the 68 application IF the u-brace was not changed at the same time. But, I KNOW that GM DID specify the 3954506 to replace the 39355593 for SERVICE of 1968 models.

I can also report that I have checked a friend's original owner, early build 1969 which I KNOW to be original. His car was built in October, 1968 and he has the "2-up, 2-down" bolt configuration. As I stated previouly, my original owner late-build 1969 has the "2-up, 2-down" configuration, too.

Incredibly enough, I do not have a known example (with GM parts tag) of either the GM #3980824 bracket or the GM #3954506 crossmember. This is a deficiency that I hope to remedy when I get a chance. However, might you have examples of either of these in your inventory to refer to?

[John A.]

Re: Humble Pie and 68-72 Cross Members

Geoffery,

This has turned out to be a novel of a tale... But following through with regard to your question...

The VIN of my 69 is 12027... Also, the drain holes you referred to... I believe are actually access holes for the two bolts that attach to the radiator support.

As I mentioned, my car has had front end repairs, but doubt that these two pieces were ever replaced - they both show signs of minor stress at the bolt holes and are not perfectly straight. When Buba was making repairs back in the 80's I'm sure that service replacements would have been easy to find. It was easier to just straighten the original as best as possible to save money.

From your information and Joe's explanation - it appears that almost anything is possible!

...Also... did you say you sent me a nasty letter?

[Geoff C.]

Yes, it is confusing and I apolgize

The 68 radiator supports are different and mount differently than 69-72 and did not have those access holes. They also assisted greatly in the slowing the rust out of this x-member. The solid ones on 68 were a problem. My friend George and I went to look at a 69 390 convertible with factory side pipes. That x-member even with these 2 large holes, it was swiss cheese. (The car was pretty complete and original – but shot. Even though it ran, and 10-11K could have bought it - it was a turd requiring $25+K work. He was disappointed, but grateful he did not buy it.

I’m still dazed and confused.
Early 68 has 4 up bolts; Late 68 has 2up+2down bolts,
Early 69 had 4 up bolts: Late 69 has 2up+2down bolts
All?? 70-72 have 2up+2down bolts.

Doesn’t make sense. Do it one way, then abandon it; then do it the first way again and abandon it again.

We need more VIN’s

Yes it was a snotty letter; my shorts were in a knot and, I apologize for doubting your word. Last week I strained my back doing yard work and did not examine one of my own cars close enough – because it was stored under a lift and I just could not get prone enough to see it as clearly as my other 2 examples that were up on lifts. I looked at it but, but not close enough. Later after checking every AIM & relevant part book I was still convinced all 68-72 were 2 up+2down. After my back felt better, I took a much better look last night. I really couldn’t get down last week.

My apologies
Geoffrey Coenen

[Jim T.]

Re: 68-72 removable front X member ???

On my original owner Feb built 68 the two bolts in front are placed down in a caged nut on the crossmember and rear come from under the crossmember into the u-shaped brace. This crossmember does not have the additional holes that were mentioned. My 70's U-shaped brace attaches the same way but the crossmember does have the two additional holes which two bolts are used to secure the radiator support at the bottom.

[Geoff C.]

Re: Humble Pie and 68-72 Cross Members

Joe,
I has some NEW GM big U braces up until about 2 years ago and cannot recall the weld nut configuration. It has been a very long time since I have has a New GM x-member.
Geoffrey

PS I'm still confused if you look at the VIN's on my 3 cars, yours, yor buddys and John Andre's - the succession of arrangements or evolution is redundant at best.

[Geoff C.]

Above HAS should be HAD; I can't type well *NM*

[Shannon Burgess]

Re: Joe and I must have the only 68 & 69's here

I'm chiming in late here, but my April '69 build date car has the 2 up / 2 down setup. Seems strange that they would have switched back and forth during production.

Shannon