1970 Rear bumper assembly cushion or gaskets ?

[Bill Balkie 24172]

Hello ,
    When I disassembled my rear bumper on my 1970 Cadillac I noticed there was a gaskets or cushions separating the center section and the two end units right  and left .
It makes sense to me because you would not want to bolts two Crome plated parts together for fear of cracking the chrome . My question is what  kind of material or fabric should I use to cushion or insulate the three piece assembly .

Thank you ,
         Bill

[76eldo]

I don’t remember seeing that on my rear bumper but I guess you can just buy some gasket paper which is pretty inexpensive and make your own.

You could also try a thin sheet of rubber but if you just bolt the ends to the center metal to metal I really don’t think you will have any issues with it.

If you have an illustrated parts book it would show an “insulator” in GM lingo of one was originally installed by the factory.

Jerry Parnes would know as he has done a lot of work on and parted out many 70 Cadillacs.

[35-709]

Rubber the Right Way sells masticated rubber by the square foot, that should serve your purpose well.  Or, Google masticated rubber, it is available from many sources.

[Scot Minesinger]

I have taken apart rear bumpers on 1970 Cadillacs too, even low mileage originals, and never saw the rubber between center and end sections.  Like the other posters wrote the material is readily available today in sheet form to be cut as needed.  Buy a gasket punch, that is best way to make holes, and if you don't need it now you will eventually.

[Bill Balkie 24172]

Thany you ,
   Thank you all 3 of you guys .  I value all of your opinions . I think i will order the 12 X12 sheet of Masticated Rubber form Rubber the Right Way . It goes against the grain to clamp  2 surfaces that are not 100% flat and are chrome plated.  Something has to give . Chrome is very hard  material and can crack, especially when two chrome parts are bolted together . When  I disassembled the bumper assembly there was some sort of gasket that deteriorated . looked to be a faberic of some kind . Anyway for now that is my plan . I am counting on thin material to be maybe .062  1/16 think . If thicker  i might just go with a standard rubber sheet like a  bicycyle inner tube .  I will let you know how i make out in a few weeks .
Again thank you Brian , Scott and G. Newsome for your input .

     Bill
     

[Roger Zimmermann]

If you are using a thin rubber or masticated sheet, by tightening the bolts you will deform the attaching points and the chrome will crack. I restored 3 cars; the various element doing the bumpers were installes as it was originally and had no issue except some tiny noises (cracks) when tightening the bolts. Years after, still no issue.
If you want to use a gasket, please consider something which is not soft.

[The Tassie Devil(le)]

I wouldn't have thought that the makers would install any "gasket" between the Bumper Bar pieces, as it has been mentioned before that a flexible chrome surface will run the risk of cracking when deformed.

Bruce.

[Bill Balkie 24172]

Hello ,
   My thoughts were that the masticated ruber would take up any imperfectiion in the two mating surfaces . These two surfaces are not machined parts . The are bent pieces of metal with a hard chrome plated surfaces  . All the rubber is doing it compinsating  for the imperfection of the metal itself and the chrome .  That is my opinion right or wrong .

     Bill

[Roger Zimmermann]

Do first a test with scrap metal, unchromed: 2 bolts and in between your rubber. It will be difficult to have the proper torque at the bolts because the rubber is getting squeezed. If you have sufficient torque, the rubber will get so thin around the holes that the scrap metal will be deformed between the holes. Just do a try!

[76eldo]

To find out what the factory did you would need to consult the master parts book.
I’m pretty sure I have one but can’t seem to find it right now.
The fit between the parts should not have any gap. Any irregularities if they exist can be adjusted before you get the bumper parts chromed. I agree with the others that any material in between the parts will only open a gap and make the areas with the holes distort slightly and possible crack the chrome.

My bumper did not have anything there to isolate the parts from touching.
Anything you put on there will be very compressed anyway when you tighten the parts together.

Be prepared for spending several hours when you go to put it back on the car to get the alignment correct. The gap between the decklod and the bumper should be very tight and even all the way across. The gaps on the ends where they wrap around and meet the quarter panel need to be straight up and down and tight.

You also get adjustment from the stud, rubber block, but amd washer inside of the trunk.  Be prepared with a patient helper and also a heavy ratchet strap that you can use to pull on the brackets as you tighten the bracket to frame bolts.

If you think installing a straight bumper right back on the car it came off of will be simple and easy, it’s not. At least it wasn’t for me.

[chrisntam]

Be prepared for spending several hours when you go to put it back on the car to get the alignment correct. The gap between the decklod and the bumper should be very tight and even all the way across. The gaps on the ends where they wrap around and meet the quarter panel need to be straight up and down and tight.

You also get adjustment from the stud, rubber block, but amd washer inside of the trunk.  Be prepared with a patient helper and also a heavy ratchet strap that you can use to pull on the brackets as you tighten the bracket to frame bolts.

If you think installing a straight bumper right back on the car it came off of will be simple and easy, it’s not. At least it wasn’t for me.

In the end, you'll say, "That's good enough, I'm done."



My bumper had no insulators, but I think mine had been apart prior to my ownership.

[76eldo]

Good enough didn’t cut it for me.
Joe Caristo and I spent about 4 hours on aligning the bumper.
Looks perfect.  I was obsessing over it and then after we got it done I looked at pictures of the car from before and it didn’t fit as well as it does now.
It’s a 30,000 original (except for the rear bumper rechrome) so I wanted it right.

[The Tassie Devil(le)]

Do first a test with scrap metal, unchromed: 2 bolts and in between your rubber. It will be difficult to have the proper torque at the bolts because the rubber is getting squeezed. If you have sufficient torque, the rubber will get so thin around the holes that the scrap metal will be deformed between the holes. Just do a try!

I agree with Roger.

If a Bumper Bar was to be assembled with a gasket between the two chrome plated surfaces, then the attaching bolts would be machined with registers so that when tightened, one side of the bolt would be up tight against the inner face of the end piece, and the register end would be hard up against the opposite washer/nut, so there was no distorted compression of the two bumper mating surfaces.

The only "Special" items  have seen with Bumpers and Mounting Bolts is with my Ranchero, and this had bolts going through the bumper bar face, and into the mounting arms/brackets.   These has special washers to stop the deformation of the bumper face as it was tightened up.   Can't show the pictures here as it is not a Cadillac.

Bruce.

[hornetball]

then the attaching bolts would be machined with registers

Translating Australian into American . . . "would be machined with shoulders"

[Cadman-iac]

Are you sure you're not seeing the bumper to body seal instead? I know that GM and others used a seal to keep dust,dirt, and mud from splashing up between the body and bumper.
It could be that someone in the past might have had an end off the bumper and in the course of reinstalling it had gotten a piece of the seal caught between them.
I've had several of the '69 to '72's and Ive not seen any such thing in between the bumper pieces either.
I have seen pieces of that splash seal, (and it's made of masticated rubber by the way), just hanging off of the body after its fallen apart due to age.
I have to agree with the others here about not putting the rubber between the pieces of the bumper.  As I think about this,  I haven't seen that on any bumper regardless of make.
Just good for thought.
Rick

[wrefakis]

no insulators as per master parts book and many untouched original cars

[Scot Minesinger]

This car could have been in a mild rear end accident back in the early 1970's and it was repaired, re-chromed back in the 1970's, or etc.  My Dad had his 1970 Olds 442 Cutlas rear bumper re-chromed in the 1970's because for some reason it rusted - the front was perfect - ??  The shop that did the job (including removal and reattachment) may have done some additional work beyond factory original.  Take a look at the gasket between end and center section again - does it look factory?  That would be perfectly cut holes, perfectly spaced, perfect curve on each side, both ends the exact same, no hand made look to it, and etc.