So I'm just about finished up with butt sag repairs on my CMC  widebody. All that's left is undercoating and re-securing the oil cooler lines and remote oil filter. Before wrapping up these last minute details, I took a few photos and wanted to post them along with details of the repair, for the benefit of anyone else contemplating this task. 

Before I started, the rear bumper was rubbing the exhaust tips. I pulled the car onto my low-rise lift, supporting it with wooden blocks under the pan edge at the front and the rear beam. I removed the wheels and supported the rear of the body on each side with a pair of floor jacks an blocks.

I used a right-angle drill with a 1/4" bit to drill out the existing rivets securing the inner fender wells to the box frame. Whomever built my kit glassed the rear of the engine compartment to the rear crossmember of the box frame, so I had to cut that loose. I loosened the bolts securing the CMC roll bar to its brackets, since I wasn't sure whether or not it would move with the body. Then I jacked up both sides of the body until the door seam gaps improved. At this point the rear bumper cleared the exhaust tips by about 7/8".   

I bought three sections of 1-1/4" x 1/8" x 4' mild steel strap at Lowes. I cut one section in half, making two 2' lengths to be used as clamping bars to hold the inner fender wells against the box frame. I drilled 1/4" holes every 2" from one end to the other of both. I enlarged the last hole on one end of each to 3/8" to accommodate the bolt for the diagonal brace. The last two sections were cut to 47", with two 3/8" holes drilled at 45" apart, to be used as diagonal braces. 

I drilled a transverse 3/8" hole at the top of each of the short pillars in the front of the rear fender wells. These holes also extend through the CMC roll bar brackets.  I attached the front of the diagonal braces to the inside edge of the pillars and snugged the bolts. I drilled the box frame for the 3/8" bolts at the rear of the diagonal braces using the braces to guide the placement of the holes. I inserted bolts through each hole to guide placement of the clamping bars. 

Before installing each clamping bar, I applied a bead of Liquid Nails Fuze-It all-surface adhesive between the inner fender well and box frame, and another bead to the inside of the clamping bar. I used small bar clamps to draw out the excess glue  and hold everything in place while I drilled the holes.

Rather than through-bolts, I used 1/4" blind rivets, POP brand, P/N AD8375UG, to secure the clamping bars. These rivets are used to hold semi-trailers together, and have a grip range of 0.8" - 0.375", which is perfect for this application. I used an air-powered rivet gun, Astro model PR14, available on Amazon, to install the rivets. Take off the tailpiece to access the last couple of rivets in tight quarters.  

After the clamping bars were installed, I bolted in the rear of the diagonal braces and tightened the hardware. When I let off the jacks, the body settled about 5/8" above the exhaust tips. The door seams look much better, but not perfect, I was expecting a tad less settling. However the door latches now both function smoothly, and the rear end seems stiff, so I'm pleased. I've attached some photos.     

IMG_20190818_120826797_HDRIMG_20200405_175333372IMG_20200407_153854518IMG_20200407_161129624IMG_20200407_161139677IMG_20200407_161202804IMG_20200407_161211351IMG_20200407_161251723IMG_20200409_141707183_HDR

57 CMC widebody, 1776, Dell 40s, IRS, 4 wheel discs, 18" Boyds, 225/35/18

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Last edited by McGruff
Original Post

Had the same issue with my CMC widebody. I jacked the rear of the body up until I got nice gaps on the doors. I then drilled and tapped the subframe along the sides of engine bay and also along the back. I made up two fibreglass mounting tabs for the back portion of the subframe and bonded them to the body and then ran bolts along sides and on rear mounts into the predrilled and tapped holes. Next I welded brackets to the underside of the subframe and to the frame horns on the chassis and installed two 1" square tubing to tie the subframe and frame horns together. Maybe a little bit overkill but it eliminated body sag and also took the twisting out of frame horns that you can get under hard acceleration.DSC_1284DSC_1283DSC_1280DSC_1277

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Follow-up. Got the oil cooler lines and remote filter re-secured yesterday. When I took it off the lift and for a ride, I immediately noticed how much quieter and more solid the rear end of the body is. Almost all of the squeaks and bumps I attributed to the doors have disappeared. IMG_20200411_163335647IMG_20200411_163339826IMG_20200411_163348001IMG_20200411_163355697IMG_20200411_163434004 

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Agree - 50 year old frame horns (rusting from inside out) designed for a 50 hp engine and grocery getting.  Add a 90 hp engine and spirited driving with sticky tires and they are bound to twist.

WOLFGANG posted:

Agree - 50 year old frame horns (rusting from inside out) designed for a 50 hp engine and grocery getting.  Add a 90 hp engine and spirited driving with sticky tires and they are bound to twist.

Gene Berg once made the comment that he didn't think a stock Beetle needed any more bracing until after rather spiritedly driving his totally stock '67 for several months. He then noticed the rear apron over the exhaust was down and no longer lined up with the engine compartment seal. Gene pulled the engine and trans, bent the frame horns back up, installed everything back with a GB 645 engine support (traction) bar and drove merrily off into the sunset. New or old, every VW based car with Type 1 frame horns needs additional support if driven in a more energetic than stock manner.

Last edited by ALB

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