Cabrio arches and rear plastic bumper... Help

[bradnic]

trial fit on a friend's 7/89 DB vert

- NO mods to the bumper shock holes
- NO mods to the brackets on the sides of the bumper (for now)

[bradnic]

on a DB / pre-facelift E30 the lower area that sits below the bumper is not as long and tucks inwards more than on a late model E30. The shorter valance issue is well known but the difference in shape is hard to see unless you compare cars side by side.

We were fortunate to have both my 318is and my friends DB vert available for comparison. They're both alpine white too which is kinda cool :-) By comparing the two cars closely we were able to figure out how to install the rear bumper to the sides of the car WITHOUT any mods to the car body.



Details of a late model rear bumper area. Note the bumper sits recessed in the quarter panel. That's not possible on a DB vert. It also means the side mounting hardware from a late model car can't be used. Finally note the length and curve below the bumper. It's much longer and flatter than a DB vert.






Here's the rear bumper area on a DB vert.


The late model car rear bumper area is about 9mm deeper than on a DB car. For this reason there's no room to use any of the side bracket mounting hardware from a late model when doing a plastic bumper conversion.

you need to grind away those guides on the bumper otherwise they'll interfere and give you the problems you're experiencing.

Like this:

I DID NOT have to do this at all. Quite the opposite - you can use the standoffs that are molded into the plastic rear bumper carrier to space the sides of the bumper out. It leaves a perfect gap, but does require the plastic bumper carrier to directly touch the quarter panel. If you're ok with that then the only remaining issue is fastening the sides to the body. That's easily handled with the following hardware (x2 for both sides):
- a long M6 bolt (about 40mm or so)
- an M6 nut
- 2 fender washers. You'll want to notch one of them so it sits flat in the bumper carrier (see pics)
- a rubber washer (important! goes inside the car in the trunk area, keeps water out)
- an M6 flange nut or regular nut + washer
- some loctite so the nut on the bumper carrier doesn't back out.

Drill a hole in the bumper carrier under the bumper trim that's larger than what is needed for an M6 bolt (I used a 1/4" drill bit - about 12.6 mm). Location can be seen in the pics, but it's purpose is so you can attach a bolt and nut to the bumper that is long enough to go through the existing hole in the side of the DB car - about 17.3cm from the edge of the quarter panel. We very carefully trial fitted the bumper to the car and from the inside of the trunk marked where the bumper covered the existing holes in the quarter panel. You can see the measurements marked in the panel in the pictures.

The bolt goes under the bumper trim, through a notched fender washer. Throw another washer on the other side, apply some loctite and a nut. You now have side mounting studs on your bumper that fit an existing hole in your db vert.

When attaching the bumper don't over torque the nuts in the trunk area - they can cause fit problems if too tight.






This is a great picture to see what's going on. Note the bumper gap on the top is just about perfect, all the way to the edge. Also note the metal valance pulls inward away from the bumper. Nothing you can do about that other than get a plastic valance or weld in a replacement.


Mount inside the trunk. Note rubber washer and flange nut.


One more thing - DON'T forget to seal the upper bumper trim holes all along the back of the car! use rubber washers with short m6 bolts, nuts and washers. Or seal them from the inside with whatever you want.

Here's the result. Yes there's a bit of a curve mismatch below the bumper but it's mostly obscured when looking from eye level. If it really bothers you then just do the jand3rson facelift mod - requires a late model valance+bumper section though. Full details on his thread.




Before


After


one more pic: this is a converted rear WITH late model lower valance conversion as well


UPDATE: we added an ACS rear apron to complete the package. We'll post more pics as we have them

[phenryiv1]

Thank you for the awesome tutorial!

[bradnic]

Delighted to do it! there's so much partial info out there for the folks that have done this before. I just hadn't see one writeup with everything on it specifically for verts. The end result is really quite good looking!

[phenryiv1]

Since the rest of this thread is solid "WIN" I decided to add the info about slotting the mounting location for future users. I also added my take on the placement of the hole for the M6x40 bolts.

Based on info in bradnic's post, I started taking measurements and trying to determine the proper place to drill the hole. After a few minutes of monkeying with the measurements I looked at the pictures and looked at the bumper and decided to center the pilot hole horizontally in the center of those horizontal slots and vertically I centered the hole on that triangular tab. Fast foward to the results- it was dead-on.

Here is the locationof the hole:



3/32" pilot hole and 5/16" final hole (using a pilot-tip bit).

To provide some insulation to avoid direct trim-to-body contact I used some sound deadening insulation (used in car stereo applications). I wish that I had had black but I can change it later. I cleaned the tabs with alcohol, let it dry, and applied the deadner.



Next up is the part where I forgot to slot the bracket location and installed the bumper at this point only to discover that it was too low and looked like crap.

So it was time for some creative efforts to get the bumper up about 1/4-3/8" across the back. First step was to remove the brackets and determine how far up the brackets could go without major work. I determined that I was going to be able to get about 1/4" of vertical movement at best. This was due to the fact that while the 2 studs could move up a bit more, at the 1/4" mark the cylinder for the bumper shock would contact the top of the channel in which it rests. To get that movement I was going to have to drill new holes (or slot the existing holes) where the studs go and to sand/file/grind away a lip at the top of the opening to the cavity where the cylinder goes.

Next up I needed to drill some pilot holes.



Enlarge the holes:



Use a round file to slot the holes and a rounded (flat on one side, rounded on the other) file to remove as much material from the top of the opening to the channel so that the channel and the (former) lip are now flush:





At that point I taped/masked it and sprayed the raw metal edges to prevent rust, then re-installed the bumper.



I then used the M6x40 tactic and secured the sides.





And installed:



I then took a stab at re-installing the fiberglass no-name rear apron/valance:

[bradnic]

We added an ACS rear apron to the white vert. Thought I'd add it to my DIY post. Will post more pics when we get them.

[bradnic]

BTW

NICE JOB Patrick.

[Das Delfin]

...bookmarked

[bradnic]

more ACS rear apron pics

[TimeMachinE30]

AW ACS Vert. Stealing my thunder :-) looks great. Sub'd as I need to do this work too... after I remove front subframe and tear out this wiper assembly without taking a plasma cutter to the front to cowl :(

[bradnic]

I picked up an ACS rear spoiler for my friend too but he wants to stick with the stock spoiler and late model IS front. I'll probably end up selling at some point.

note how he painted his rockers white too. we tried talking him out of it but it does look good..

wiper assy is def the worst job on the car - scars to prove it. and no you don't have to cut the cowl, but a little flexing on the driver side opening helps

[TimeMachinE30]

LMK about the rear spoiler. I may still spring for one.