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Early shorty rear bumper Conversion


doza59
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I was recently looking for a reference on the body clearance for early bumpers (about 1/4 to 1/2 inches).  Your setup looks like the bumper will probably chafe on the body when mounted--it might be missing the inner mounting brackets (what BMW calls a "base").  You need some sort of spacer to mount the bumper further out from the body.  But this might be irrelevant depending on how you attempt the conversion.

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It is certainly not a simple "bolt on". You have all the needed bits it seems, not sure what hardware is in your possession? You will need to remove the body filler the factory applied over the early style bumper bracket mounting holes which was previously mentioned, you can just pry the stuff off for the most part. You will need to drill some holes from the inside of the trunk to access the nuts that will secure the bumper brackets to the rear of the vehicle. I believe I even had to drill a hole on either side of the car (within the recessed depression where the shorty bumper sides will reside after installed). You need to get these holes in the perfect spot as the sides of the bumper will slide into and lock down and thus hold the alignment of the ends of the bumper in the perfect spot. I used rubber isolators between all painted body surfaces and the mounting hardware so the paint work isn't abraded over time, a pice of thin gasket material or rubber sheet material works well behind the bumper brackets themselves.

 

I recommend filling and painting over the huge and now useless holes left over from the big bumper you removed. You will see them behind the shorty bumper no matter how close you tuck it into the body. 

 

Let me look through my old 1974 M2 build thread, I think I included this modification there.

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Yes you can see the roundie bumper mounts on the outside. Good luck accessing from the inside, my 76 has interior bracing that blocks access to the mount holes. Could be done but I opted to fab new mounts that used the original 76 mounting holes. Either way you will be cussing in German by the time you are finished. It's worth it. ?

+1 on locating the holes to mount the side wings. You only get one chance to get it perfect. 

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I think all the square tails have the same access issues for the rear shorty bumper. After you uncover the early bumper holes circled in red in another post above, take a punch form the outside of the car and inserting into the newly uncovered holes mark the approx. location with a hammer blow. After you mark the 4 areas, pull the fuel tank and get the spare out of the trunk. You should be able to find the punch marks from inside the trunk now. I took a 1 inch hole saw bit and centered it up on the punch mark. Drill away! Removing these will allow you to get a magnetic socket and extension through to secure the brackets and bumper onto the car. It really isn't that bad of a job once you think it over and make some markings on the car. 

Edited by RCM3
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Blunt has all the correct bolts, rubber spacers and a couple of special metal v shaped spacers that go between the bumper bracket and the bumper.  You really want to look at the parts diagram and get all the parts there for the big brackets and the ends of the bumper.  A rectangular piece of inner tube or a piece of silicone rubber between the bumper bracket and the body is a good idea.  Also you will see the reflection of the big former bumper holes if you don’t fill them in as part of you bodywork.  I didn’t and I’m not about to do it now!  Woulda, shoulda, coulda

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10 hours ago, doza59 said:

See my car in pics with the bumper just acquired. Has the brackets.

When you mount your new chrome bumper in those existing four mounting holes (currently plugged), suggest that you (1) make a reinforcing plate (3/16 - 1/4" steel) to go between the body sheet metal and the bumper bracket.  That will spread the load around if someone bumps your car and prevent that very flimsy rear panel from being bent.  Also be sure and use sealer around the bolts and flat washers inside the body to make the joint watertight.  Otherwise water will leak into the trunk and cause rust.  

 

cheers

mike

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