'73 Front bumper mount alignment to frame?

[Crash513]

I'm finally re-mounting my nicely re-chromed front bumper (thank you Dave Varco) to my resprayed 1973 tii.  These are the original "triangle" shaped '73 style bumper mounts, using the original bolts that were on the car when it was disassembled.  Both front fenders are NOS stock BMW replacements were installed when the body work was done.  So I'm now trying to get the bumper lined up perfectly to mark and drill the fender mount bolts that slide into the bumper ends. 

 

 Everything has gone together fine, and I was able to get the bumper to where it seems like it's aligned perfectly.  It's sitting parallel to the the ground, and the bumper ends are equidistant to the fenders on both sides (~3/8").  The part that seems strange is the angle I had to shift the bumper mounts to (high in the front, low in the back) to get the bumper to line up correctly.  I'm just trying to figure out if this is normal or if maybe I missed something in the reassembly.      

 

Any advice is much appreciated!

 

Thanks,

 

Crash 

[esty]

with these cars, you have to do what you have to do to get it right...i've had to "rock"  the brackets with every bumper that's been installed

 

it's not a perfect world and certainly wasn't in 1973 on the o2 assy line

 

[Crash513]

 

18 minutes ago, esty said:

with these cars, you have to do what you have to do to get it right...i've had to "rock"  the brackets with every bumper that's been installed

 

it's not a perfect world and certainly wasn't in 1973 on the o2 assy line

 

 

Well they we're cranking a lot of them them out at the time right?   

 

Thanks for the advice.  This helps put my mind at ease!

 

 

[Billsmith]

Crash,

 

I think you are on the right track.  I hope to be in the process of doing the bumper reinstall on my ‘73 Tii.  Note in attached photo.  The left bracket, unique to the 1973 model, has holes not on the same axis which would cause the bracket and bumper to be slightly pitched upward.  The right bracket is pre ‘73 and those holes are centered along the same axis.  I tried to fit my ‘73 brackets on with the holes in the bracket closer to the bottom edge but would have had to force it and strip the threads on the bolts so I am pretty sure the proper mounting for the brackets is as shown in your photo with the holes closest to the top edge of the bracket resulting in the bumper “tilting” up rather than down.  Still not sure about my corner support bolts.  They just seem too short and not at the perfect angle to perfectly engage with the “U” plate on the back of the bumper at the corner.  My bumpers are still in the rechroming process.  I know you are happy to have yours back.  Kind of like Christmas Day I’ll bet.  Best of luck.

 

Bill 

[Henning]

Yes, don't worry. When I reinstalled my bumper after nose paint I chose a pair of brackets that were symmetric, even and straight. For me, the line-up to the grills and the rest is not the baddest:

(We're not talking about headrests here.)

But this has absolutely nothing to do with the positions of the brackets. They sit pretty different in height, length and inclining- and invisible.

These are no computer cars. Drive and have fun.

 

hen

[Mike Self]

US spec '73 front bumpers are mounted entirely differently from the 72 and earlier ones.  Those use carriage bolts that are inserted into keyhole-shaped slots in the frame rails, and those are located aft of the '73 mounts.  They are holes that are drilled all the way through the frame rails and use (IIRC) long 10mm bolts and nuts to hole the brackets in place.  This (slightly) sturdier mount was part of BMW's effort to meet the 2.5 mph bumper requirement in 1973--a precursor to the extensive bumper redesign for the 1974 5 mph requirement.  

 

There should be enough wiggle room between the bumper bracket mounting bolt holes and the bolts that hold the bumper to the brackets' outer ends to get everything leveled up.  I've always mounted the bumper so that it's parallel with the bottom edge of the grille, not equidistant from the ground at both ends.  Most cars sit a little bit skewed side-to-side, so a bumper that's parallel with the ground may be high or low when compared with the grille's lower edge.  

 

Also--you're gonna need two rubber spacers on the bumper ends to cover the gap between bumper and fender when using those '73 brackets.  That's what the factory did.  And finally, just barely tighten those end carriage bolts--only enough to keep 'em from falling out.  That way when someone who parks by ear bumps into your bumper, the carriage bolt will pop out of its U-shaped socket on the bumper end, instead of deforming your fender.

 

mike

[Crash513]

On 3/6/2021 at 5:46 PM, Billsmith said:

Crash,

 

I think you are on the right track.  I hope to be in the process of doing the bumper reinstall on my ‘73 Tii.  Note in attached photo.  The left bracket, unique to the 1973 model, has holes not on the same axis which would cause the bracket and bumper to be slightly pitched upward.  The right bracket is pre ‘73 and those holes are centered along the same axis.  I tried to fit my ‘73 brackets on with the holes in the bracket closer to the bottom edge but would have had to force it and strip the threads on the bolts so I am pretty sure the proper mounting for the brackets is as shown in your photo with the holes closest to the top edge of the bracket resulting in the bumper “tilting” up rather than down.  Still not sure about my corner support bolts.  They just seem too short and not at the perfect angle to perfectly engage with the “U” plate on the back of the bumper at the corner.  My bumpers are still in the rechroming process.  I know you are happy to have yours back.  Kind of like Christmas Day I’ll bet.  Best of luck.

 

Bill 

 

Thank you, Bill.  The side by side picture really helps.  As it turns out, there is a '72 in the shop where I'm reassembling my car and I got a chance to look at it over the weekend and see that the mounting design is COMPLETELY different.  

 

I had purchased the fastener full fastener kits for both my front and rear bumpers.   When I reassembled them, I found the end bolts for the fenders were long enough, but surprisingly the long bolts for the (supposed to be M8x100) were too short.   I had to source those locally.  Everything else in the kit seemed to work just fine.  I took a few pics when I was putting things back together, so when you get your bumpers back, PM me if you need any help.

 

Thanks again.

 

Crash

[Crash513]

On 3/7/2021 at 11:46 AM, Mike Self said:

There should be enough wiggle room between the bumper bracket mounting bolt holes and the bolts that hold the bumper to the brackets' outer ends to get everything leveled up.  I've always mounted the bumper so that it's parallel with the bottom edge of the grille, not equidistant from the ground at both ends.  Most cars sit a little bit skewed side-to-side, so a bumper that's parallel with the ground may be high or low when compared with the grille's lower edge.  

 

Also--you're gonna need two rubber spacers on the bumper ends to cover the gap between bumper and fender when using those '73 brackets.  That's what the factory did.  And finally, just barely tighten those end carriage bolts--only enough to keep 'em from falling out.  That way when someone who parks by ear bumps into your bumper, the carriage bolt will pop out of its U-shaped socket on the bumper end, instead of deforming your fender.

 

Thank you, Mike.  Once I finally got the bracket to frame bolts aligned and tightened down, I did end up dinking around with the bolts that hold the bumper to the brackets to get the alignment fine tuned.   It is all pretty much parallel to the ground, but miraculously also level under the grill.  I think that was sheer luck because I wasn't really looking at that alignment.

 

I did buy the fastener kit that came with the necessary rubber spacers.  But I opted for nylon locking nuts to hold them in place.  So I should be able to leave a little slack at the carriage bolt to safeguard against damage to the fender as you suggested.  Interestingly, the original passenger front fender on my car had exactly that damage and the bumper end had been bent from what must have been a very similar accident that the PO had.  Anyway, great tip... thank you!

 

Cheers,

 

Crash.