Rear bumper brackets and bolts puzzle
 

I was hoping someone could help me work my way through installing the multiple brackets and bolts for a 1970 GTO rear bumper.

I have included pictures of the brackets and bolts that I have. I also have the "blue" Assembly manual everyone recommends but it isnt helping me much to decipher the correct washers to use ect.

One thing to mention is I went to NPD website and they listed 3 different bolt kits for 70-72 GTO rear bumper brackets. I purchased all 3 to make sure i wasn't going to be missing any. I dont know if I needed all 3 so I may have extra hardware I dont need.

Its pretty obvious I start with the 2 brackets on the top Left and each bracket gets 2 bolts to hold it to the frame. I am unsure which washers are correct. I have 4 big washers that I presume would be used either in front or behind the brackets to start.

It's not really clear what you are asking... do you want fastener descriptions for the parts on the assembly drawing so you can match yours or are you having a hard time interpreting the drawing?

Unfortunately, as you see, the assembly drawing will reference part numbers but you will not find a complete description. For example, I circled a bolt and washer (#19 and #3) along with their PNs. It's hard to read, but I think the bolt is PN 9428480...best guess. The washer is PN 9798965, again a best guess.

https://forums.maxperformanceinc.com...1&d=1760586884

What I have done in the past is pull the part numbers off the drawing, then search for them on the AMK web site. They do a fair job referencing original part numbers but between the poor assembly drawing and AMK not covering everything, it's a crap shoot at best. When AMK doesn't cross-reference, check their Pontiac kits. They often substitute with the same size and you can guess based on their description.

And just to illustrate how difficult this can be, AMK doesn't recognize those two PNs... which turns this into a real scavenger hunt.

I think others on PY have old GM Parts catalogs that would describe those two (an all other) parts sufficient for you to figure out which of your bolts matches.

If there are specific questions, maybe post them to narrow the scope a little?

Mike

I did do what you recommended before posting my question. I looked at diagram #s and then got the part #s from the side bar and searched them up. Unfortunately they didnt come up with much when I did that to help.


My specific question was written in the last two sentences of my original post. There are 4 big washers included in my hardware that I am unsure about. I know im supposed to start with the brackets on the top of my picture and attach them directly to the rear body. I assume the 4 big washers get installed with them? And if they do......do they go between the bracket and body OR do the get installed between the bolt and bracket.

Sorry for the confusion.

No apology needed and I feel your pain, just not sure how to help as I don't have the experience others on here definitely do.

The two brackets that bolt to the body appear to use "optional" washers. In the assembly drawing, they are labeled "AS REQ'D".

Others need to chime in but I assume the "inner washers" between bracket and body are used as shims but there is no guideline nor measurement shown on the drawing to determine if you need them.

The washers under the bolts are "3", with a PN neither you nor I could find with an online search.

The washers between the bolts and the body (shims?) are "20" with what I read as PN 3760886.

In this case, AMK DOES have a listing: https://www.amkproducts.com/search-result/?ser=3760886, which shows them as 1.88 diameter with a 0.47" ID. This tells me the bolts should be 7/16". Are your bolts 7/16"?

You can guess better than I can, but it seems your brackets were shimmed with these large washers.

Do you see "witness marks" on the brackets or body from these washers?

As to the bolts and washers, AMK sells a kit, G-7466 for the bracket to body:

https://forums.maxperformanceinc.com...1&d=1760627632

If you click on the "PIC" contents, I find bolts with their PN B-10182 that are 7/16-14 x 1.5 with pointed tips. They don't have the same PN as the Pontiac assembly drawing but they are likely equivalent and will hopefully confirm the size of the bolts you have.

Similarly, the washers under the bolt heads are in the AMK kit as their B-11286. Again, not the same Pontiac PN but should help confirm what you have.

Good luck and I hope someone with experience chimes in on how to adjust the rear bumper. I have a rear bumper waiting to install and have seen a few that look wonky. I'd love to see a procedure for aligning these.

Mike

No witness marks on my brackets because the previous owner installed everything using Lowe's general Hardware and washers. The car was even missing the 2 lower brackets that I had to buy off Ebay after noticing they were never on the car.

Yes my bolts are 7/16-14x1.5 pointed. I am pretty sure as you stated the big washers go in between the brackets and body. lm going to wait to see if I get any other replies before proceeding. Appreciate your help

How did this go for you?

I pulled my bumper today and yes, the big washers are the spacers between brackets and body.

I was surprised to find the washers were held in place with some spring clip/pal nut things. This made it easy to keep it all together.