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Posted by: bigkensteele Nov 24 2013, 10:20 PM

When I decided to backdate my bumpers, I wanted to have all of the answers before I started cutting stuff off and drilling holes. Using the fine search function, I was able to find all of those answers, but I had to wade through many, many threads to get them all.

With that in mind, I decided to write one up that will contain every last bit of information needed to do the job. I can’t take credit for much, if any, if any of the information below. I got most all of it from my searches, and I will try to give credit where credit is due. I apologize up front for the crappy phone pictures – while bad, they still tell the story.

While there are a few of us who like the looks of the late bumper (myself included, depending on the color of the car), there is one really good reason to go with early bumpers – weight. I have seen many figures thrown about, so I decided to weigh them both, including all mounting hardware, fog lights, grills, etc. I was quite surprised at just how much heavier the later bumpers are.

Front:
Early – 20 pounds, included pad, dog bones, lights, grills, and hardware
Late – 46 pounds, including the shocks, and hardware (non fog light bumper)

Rear:
Early – 18 pounds, including pad, dog bones and hardware
Late – 50 pounds, including the shocks, and hardware

38 pounds vs. 96 – 58 pounds, or roughly 3% of the entire weight of the car removed from the two places you would most want to lose it!

So, let’s get started.

Tools required:
- safety goggles (ask me how I know how much is sucks to have metal surgically removed from your eye)
-3/8 ratchet, extension and a set of metric sockets
- screwdrivers – both kinds
- pliers
- angle grinder, grinding disk and a metal cutting wheel
- mig welder if you are a hack like me
- left cutting (red) tin snips if you are right handed, right cutting (green) if you are left handed
- center punch
- step drill bit at least 5/8
- drill
- spot weld cutter
- hacksaw
- hammer and dolly

Hardware/misc. required or recommended:
- (8) 8M x 1.25 x50 bolts
- (8) 8M large flat washers
- (8) 8M lock washers
- (8) 8M nuts
- primer, body color paint, sandpaper, tape, paper, etc.
- early bumpers, tops, dog bones, etc.
- beer (optional)

I did the rear first, for no particular reason.

The first order of business is to remove the bumper. This is accomplished by first disengaging the bumper sides from the retaining rails on both sides of the car. Simply pull the bumper sides away, and they will peel right out. Next, unscrew the license plate lights and disconnect the wiring. Finally, remove the two 19mm bolts located in the holes on the underside of the bumper. The bumper should now slide right off, but remember – it weighs 50 pounds, so be prepared.

I removed my valence as well. Not sure if it was necessary, but it needed some dents removed and paint anyway, so what the heck, it was only a few screws.

Next, you will need to crawl under the car with a 17mm socket and remove the 3 bolts holding on each shock and work the shock out. I recommend putting the bolts back in place to keep water out.

Now for the fun part. You will need to remove those retaining rails from each side of the car. They are spot-welded on in 5 or 6 spots. There are a couple of ways to do this. You can use a grinder or cutting disc to grind through the welds, or you can buy yourself a spot weld cutter to drill them out. Or if you are an idiot like me, you can attempt to use a regular drill bit and drill them out, and then weld up the resulting holes. I bought a spot weld cutter before I did the front.

I forgot to take pictures of the rear, but here is one of the front – same procedure for both.


As far as the bodywork required to touch these areas up, I welded up the holes and ground it flat. I then taped off the area, primed it and used a rattle can of a fairly close blue that I found at Lowes. When the bumper is installed, these areas don’t show much, but they still needed to be painted.

Posted by: bigkensteele Nov 24 2013, 10:26 PM

Now the part that had me nervous – where do I drill the 4 holes for the early bumper? Right where I tell you, that’s where. On each side, you will see that the rear panel has rectangles formed into it. The holes will be roughly centered in that rectangle. Mark your top hole first by measuring 2 ¾ inches horizontally from the body seam shown in the picture. The vertical mark can be made 1 3/4 inches from the ledge underneath the taillight as shown. The bottom hole is also 2 ¾ from the seam and 4 ¾ from the ledge.

Posted by: bigkensteele Nov 24 2013, 10:27 PM

Using one of your dog bones (they are the same front and rear), verify that your marks are centered in the holes of the dog bone. If not, adjust the bottom mark accordingly.

The point of no return – drill your holes. I think that the factory holes are about 5/8, but I got by with ½ on the rear. Use a punch to dimple your mark, or drill a pilot hole – either method will keep your larger bit from walking. I used a regular bit on the rear, and it tended to bind up and make for an ugly hole. On the front, I wised up and used a step bit from Harbor Freight. They turned out much nicer.

Posted by: bigkensteele Nov 24 2013, 10:28 PM

This is where your top hole should be looking inside the trunk.

Posted by: bigkensteele Nov 24 2013, 10:30 PM

You may need to dig out some seam sealer to get a flat spot for your washers and nuts. Yes, I said nuts, not bolts, because I am about to impart more wisdom upon you (Craig at Camp914, not mine). It is much, much easier to hang the bumpers (especially if you are working alone) if you use studs and nuts, rather than bolts like the factory. I made my own by buying 8 M8 x 1.25 x 50 bolts and cutting the heads off. Screw those into the bumper, and it makes it a one person job!

I chose to prime the holes before installing the bumper.

Posted by: bigkensteele Nov 24 2013, 10:32 PM

Now it is time to mount the bumper. If you haven’t already installed the bumper top, now is the time to do it. You have already installed the studs into the bumper, so now slide the dog bones down over the studs and put the thing on. Have a couple of M8 x 1.25 nuts handy to thread onto the top studs and hold it in place while you check fit, positioning, etc. I had to use a file to make my ½” holes a little bigger to give me the wiggle room that I needed, but I was pretty jazzed about how nicely it fit, given the fact that I wasn’t 100% sure that I had drilled my holes in the right place. Now, I am, and I couldn’t be happier with the results!

Posted by: bigkensteele Nov 24 2013, 10:33 PM

My bumper didn’t have the plug when I got it, so another trip to Lowes, and I found this 1 inch plug that fits perfectly. Zinc rather than chrome or stainless, but it looks fine.


Remember those license plate lights? On my car the wiring was way long, and I had two too many wires (don’t recall why). So I pushed the two extra wires and all the excess back through the grommet into the trunk. Just to be safe, I put some heat shrink around the exposed spades on the extra wires. Hook up the wires, and done.

Posted by: Cap'n Krusty Nov 24 2013, 10:34 PM

Nice post. Ask the admins to put it in the classic forum. BTW, are you aware primer is NOT waterproof? Best put some real paint on there before the tinworm comes a knockin' ..............

Posted by: bigkensteele Nov 24 2013, 10:36 PM

On to the front, which provides a different challenge. On the rear, the location of the holes was my main worry. The holes are the easy part up here because they are already in place (sort of). More on that later. With the front, you get to deal with not just the side retaining rails, but also the upper support on the front that requires surgery.

Of course, the first order of business again is to get the bumper off. Not surprisingly, this is very much the same thing you did in back. Pull the bumper sides out of the retaining rails. Use a 19mm socket to remove the bolts from the holes on the bottom of the bumper. You should now be able to slide the bumper off.

Next we remove the shocks, but before they can be removed, the seal around the shock tube must be removed from the front panel. There are two 13mm bolts holding each one on. Remove the bolts and pry the rings and seals off. Here is one, along with the nifty block off plate and gasket that I made to seal the resulting holes where the shock tubes used to be.


Open the trunk, and you will see the three 17mm bolts holding on the bumper shocks. You can now remove the shocks. Again, I put the bolts back in just to fill the holes. I think installed the above sheet metal plates to seal up the big holes in the front panel. Some folks weld in patches here, but I chose to just leave them as I am better at cutting sheet metal and bolting it in than I am at welding.


Again, I removed the valence to spruce it up, and give me more room to work.

Posted by: bigkensteele Nov 24 2013, 10:39 PM

Hope you have bought that spot weld cutter by now. It is time for surgery.

Let’s start with the side rails, tabs, whatever you want to call them. Remove these in the same way you did them on the rear. I won’t go over all that again. Here is one in process.


Now for the part that has never been covered all that clearly in earlier threads. You will find that there is an S shaped strip that runs all the way across from the outside edge of each headlight eyebrow. This strip is there to support the top of the late bumper rubber and is not present on early cars. Unfortunately, this strip completely interferes with the early bumper top, so it must be partially removed and the part that remains must be trimmed. This really isn’t as bad as it sounds, so lets get started.

The sections underneath each headlight must be removed altogether. The section in front of the trunk must be retained so that the trunk seal will still have a channel to live in, but trimmed back so it won’t interfere with the early bumper pad. The first step is to use a hacksaw or cutting disk to cut the strip just on the outside of each corner of the trunk seal channel. Do not cut through the metal underneath. You are effectively cutting the strip that runs all the way across into three sections. The two outer sections under each eyebrow will be removed by cutting out the spot welds.

Posted by: Eric_Shea Nov 24 2013, 10:39 PM

Excellent.

Posted by: bigkensteele Nov 24 2013, 10:42 PM

For the center section, I used tin snips to cut off the outer lip, leaving just the vertical part that will hold the trunk seal in place.


When you are done, this is what you get. There are three drain “tubes” that I left in place. I will probably go back and cut them off because they hit the bumper top.

Posted by: bigkensteele Nov 24 2013, 10:43 PM

And here is the corner.


I used a hammer and dolly to straighten the channel strip and then ground it smooth. Depending on how anal you are, this may be optional. After all that, I taped everything up, primed it and painted it.

Posted by: bigkensteele Nov 24 2013, 10:45 PM

Remember how I said the holes were already there, sort of? Well they are, but you need to make them go all the way through. If you look inside the wheel well, you will see that there is a reinforcement plate with two holes that was welded in at the factory to support the early bumpers. Why they continued to put them in on late cars, I don’t know, but it works out in our favor. All we need to do is punch or drill the center of these holes and drill them out to 5/8.








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Posted by: bigkensteele Nov 24 2013, 10:46 PM

And from the outside...

Posted by: bigkensteele Nov 24 2013, 10:48 PM

You may have noticed that I am a little out of sequence since you see me painting it in the earlier picture and the holes are already there. So sue me. No wait, don’t sue me. You could probably shop around and find a lawyer and jury that would actually award damages for something that stupid.

Anyway, after all the rails were cut off, the front strip cut and modified, prime and paint it all so it won’t rust.

Now we are ready to hang the front bumper. Screw your studs in, slide the dog bones on and offer it up. It should slide on nicely. Put your washers and nuts on in the fender well loosely so you can position the bumper to where you want it, and then tighten everything down.


All done!

Except for the fog lights. Another mod is needed for those. I am currently running non-fog grills, so I haven’t tackled this yet.

The lights are mounted using a M10 x 1.50 allen bolt, but the receiver nut is not installed on the late cars, and clearly, they must be. One option is to use nutserts, which are pretty expensive because they require a special tool to install (which you will probably never use again). The option that I plan to go with is a flanged nut spot welded into place after the hole is located and drilled. I will update the thread when I have tackled this.

Posted by: Chris H. Nov 25 2013, 06:21 AM

Nice work Ken!

Did my Laguna Blue car a few years ago and was amazed at the difference. The chrome bumpers really set the paint off don't they? You'll be staring at it for days. Walk to the front...walk to the back...walk to the front...walk to the back...

Posted by: computers4kids Nov 25 2013, 09:35 AM

Nice write up! If you go to a Harley Davidson shop, you can find a "chrome" plug that fits instead of the zinc one. I had posted the part number when I had backdated mine.

PS you need to a one last step to your excellent write-up...how ti get rid of those monster bumpers. I tried selling, giving away...finally a dumpster stepped forward

Posted by: bigkensteele Nov 25 2013, 09:59 AM

Thanks!

Not sure what will happen to the BUBs. They may go up in my garage attic, or they may find their way into a dumpster too.

Posted by: boxstr Nov 25 2013, 11:43 AM

I have used the nutserts that you have pictured. Drilling a hole and then small pop rivets around the edge work great.
Not sure what special tool you are referring to?
Craig at CAMP

Posted by: bigkensteele Nov 25 2013, 01:23 PM

I was talking about these:


which requires this $80 - $120 tool to install:


Nice solution, but too rich for my blood.

Posted by: Eric_Shea Nov 25 2013, 04:05 PM

Already added to the "Classics"

Posted by: bigkensteele Nov 25 2013, 05:55 PM

I am honored. Thanks!

Posted by: johannes Nov 26 2013, 05:54 AM

Very well done tutorial. Thank you for sharing.

Posted by: dlee6204 Nov 26 2013, 06:40 AM

Nice write up!

Posted by: maf914 Nov 26 2013, 06:53 AM

Very good write up. Thank you. And thanks to all who have posted to similar threads, showing their ideas and tips for backdating bumper installations.

I have a small question: What size spot weld drill bit works best for the spot welds in this situation? Thanks.

Posted by: 69telecaster Nov 26 2013, 07:46 AM

"While there are a few of us who like the looks of the late bumper (myself included, depending on the color of the car), there is one really good reason to go with early bumpers – weight. I have seen many figures thrown about, so I decided to weigh them both, including all mounting hardware, fog lights, grills, etc. I was quite surprised at just how much heavier the later bumpers are."

I agree about the car color...our '76 is black.
I was wondering if there's any way to simply lighten them, rather than backdate.

cm

Posted by: Chris H. Nov 26 2013, 08:29 AM

Yes, you could remove some of the material from the metal piece that is underneath the black plastic. It's where a lot of the weight is. I believe someone on the board has done this before.

I think a company (HPH?) used to make a fiberglass copy that was superlight...that might be cool.

edit: as noted below the shocks weigh a lot as well....just moved the box with mine in it...ow my back!!!

Posted by: mepstein Nov 26 2013, 09:20 AM

Zack - Vacca rabbit - lightened his with a hole saw. I don't know what he did with the shock supports but I imagine you could make a lighter bracket to hold up the bumper.

Personally, I like the backdated look.

Posted by: ndfrigi Nov 26 2013, 09:23 AM

Great Documentation!

God Bless you for sharing a detailed procedure!

Posted by: Dave_Darling Nov 26 2013, 12:40 PM

IIRC, the late European cars used the black rubber covers, but had a simplified metal bracket holding them on rather than the shock absorbers. I think they were trapezoid-shaped? And would bend to absorb some impact. Probably somewhat lighter than the US version.

Someone replaced the metal support with a thinner aluminum one, which I'm sure saved some decent weight.

--DD

Posted by: andys Nov 26 2013, 01:14 PM

See this thread for bumper mounting studs:

http://www.914world.com/bbs2/index.php?showtopic=194622&hl=bumper

Andys

Posted by: bigkensteele Nov 26 2013, 04:20 PM

I ended up using a 3/8" cutter. It is more or less a flat faced bit with a pointed pilot in the center. I think it might be in one of the pictures above. I only paid $25 for this one (only ), but there are nice units that will not leave a hole. Jim Kelly has one pictured in his bumper thread. I couldn't find one locally and didn't want to wait for an online purchase.

http://www.914world.com/bbs2/index.php?s=&showtopic=194668&view=findpost&p=1741754

Posted by: bigkensteele Nov 26 2013, 04:23 PM

Nice, I might have to pick some of those up!

Posted by: 1970 Neun vierzehn Nov 26 2013, 08:26 PM

Nice work on the bumper backdate (upgrade?). As you noted, you lost some significant weight where it is the least wanted....and your car looks better for your efforts. BUT..........

.....now you have to update your avatar

Paul

Posted by: bigkensteele Nov 26 2013, 08:56 PM

Thanks for the Paul. I was thinking the same thing as I was posting it. Every time I added a new post to the thread, I would see the old look in the avatar, and I was thinking that I guess I should have unveiled a new pic along with the thread.

I will pick an interim until I get a good photo with valances.

Posted by: Vacca Rabite Nov 27 2013, 07:01 PM

Hole saw? Not enough setting-myself-on-fire potential.
I free handed it with a plasma cutter.
And yes, the sparks from the plasma cutter did set my pants on fire. That was interesting.

Doing this took a CONSIDERABLE amount of weight out of the front a rear bumpers. They weigh what the early stockers weight now. Just ditching the shocks saves about 25 pounds.



Zach

Posted by: Type 47 Nov 27 2013, 11:19 PM

OMG...had the body guy do all the cutting before painting....as you mentioned...not mentioned in the other thread was the top front cutting. DAMN i'm going to have to now cut off, per your instructions, my freshly painted chassis...

tremendous thanks for posting this...I was just slightly nervous about drilling the bolt/stud holes but now I know there is more work to be done.

you turned a potentially frustrating situation into a more logical process!!!

You also contributed something HUGE!! to this forum. When I 1st saw the post I said...oh yeah been there done that...but NO you had more complete info which showed that just doing a search might not always fully cover the subject.

Lesson learned...NEVER be concerned to post info about a subject that you might think has been covered before!

Again, for someone who is getting ready to hang back dated bumpers, your post to an "old" subject was GREATLY appreciated!

Posted by: colingreene Dec 5 2015, 05:36 PM

just so anyone knows, i marked the holes as indicated and they did not line up with my bumper at all.
So check before you drill people.

Posted by: bigkensteele Dec 5 2015, 07:44 PM

I believe that I got the measurements from post 8 of the following thread:

http://www.914world.com/bbs2/index.php?showtopic=63085&hl=backdate++bumpers#

Craig at Camp 914 (boxstr) is also the guy who suggested using studs, so props to him.

How far off are they? I had to enlarge my holes a bit for some wiggle room, but mine fit great using those measurements.

Posted by: colingreene Dec 5 2015, 10:08 PM

about half a inch. the up down was approx but they were too wide spaced.
The studs were a good shout, i used them.

Posted by: 914Sixer Dec 6 2015, 12:20 PM

You could use the dog bones for a hole pattern with the metal inserts removed.

Posted by: Porschef Dec 6 2015, 01:56 PM

Here's what I did, took all guesswork/ individual car variability out of play

http://www.914world.com/bbs2/index.php?showtopic=237899&hl=Bumper

Posted by: Steve Mar 17 2016, 09:51 AM

Great article. I just used it to swap out my fiberglass GT bumpers for Chrome bumpers. Looks much better. Curious...
1. What are people doing for the rear bumper top center bracket? I used an L bracket, but its too wimpy to hold the rubber up, so the center is sagging.
2. The BUB's had built in tow hook nuts. What are people doing for front and rear tow hooks? Otto's in Venice Beach installed a Tow hook nut in the front using the right shock bumper mount. PIA, but i had to cut a section out of the chrome bumper and drill a hole in it to clear the tow hook.

Posted by: flat4guy Apr 12 2020, 01:21 PM

Great article - are you able to run a front lower valance? Did not see a pic. Thanks

Posted by: DRPHIL914 Apr 12 2020, 07:11 PM

i maintained my stock ‘75 front valance following my update/backdate.



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Posted by: r_towle Apr 12 2020, 10:05 PM

TL;DR
I think we need another thread

Posted by: mcbrems Jan 21 2021, 12:27 AM

A perfect fit for those shock holes is an item sold by EV West, used as a cover plate for the hole remaining in the bell housing after removing the starter from a VW/Porsche. Link here:
https://www.evwest.com/catalog/product_info.php?cPath=41&products_id=302&osCsid=9v4vl1rhk89dug81o4j2u54ii2




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Posted by: mcbrems Jan 21 2021, 12:28 AM

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