Restoring Rubber Bumpers

By Brynmor

After the crash, inspection of the front bumper revealed that it was beyond practical repair. A sizable peace of rubber had been severed from below the indicator so time for a replacement. That's where Martin came to my rescue with a more than reasonable offer for a set of rubber bumpers and a ride in a couple of now famous BGTs.

Once removed the true extent of corrosion in the rear bumper could be seen. The two halves of the box section were parting company and a huge section of the centre skin was gone. In short the inside at least was scrap.

I decided to strip the bumpers to make a decent job of them. Since the rest of the car was going to look basically new, I thought it would be a shame to bolt the rubber bumpers back on without making them look at least like I tried to sort them out.

I found out quickly that drilling out the rivets wasn't an option. They were far too hard and long for that and I'd have ended up melting the rubber skin. I drilled the heads off the rivets and prised the clamping plates off. (Where they hadn't completely corroded). I then used a brick chisel and very large screw driver to lift the rubber over the rivets an inch at a time. Once separated it was time to start the cleanup.

Removing the remainder of the rivets was easy. I just knocked them out with a hammer. Well, in, actually. I then spent 20 minutes tipping the box section from end to end trying to get them out again. Once I'd engaged my brain again a realised that four of the rivets, two at each end were trapped in the little blanked off areas. I used a small grinding head on a Dremel to open up a gap between the skin of the box section and the blanking plate to get them out.

I used a sanding wheel on an angle grinder to tidy up the box sections and clamps then removed about 5mm of material from the bottom edge of the front bumper lip. I have found that the distance between the bottom edge of the front bumper and the top edge of the ST spoiler is usually zero on the centre line of the car. I also rounded off the back of the bottom edge of the bumper to make sure. I'm hoping this will give me enough clearance between the bumper and the spoiler to fit the bumper without excessive spacers or having to fit it slightly high instead of flush with the bonnet line.

Luckily between the four bumpers I had, the components that were reusable, worked out. On the front I ended up with the metal box section, rubber skin and top clamp plate from Martin's bumper and the lower clamp plate from my own. On the rear I used the rubber skin and top clamp from my bumper with the box section and bottom clamp from Martin's.

Everything metal was rust killed with Dynatrol, then primed and given three coats of chassis black enamel. The rust that had grown into the rubber skins, where they press against the box sections and clamps, was also treated with rust killer. Then I gave the same areas a coating of red rubber grease. Wonderful stuff, I'm sure without it I'd still be trying to get them back together.

When it comes to refitting the rubber skins start with the two rivets in the middle. Then move to the ends of the bumpers. I used two thin screw drivers; pushed one through the clamp plate, rubber skin and into the box section through the third whole from the end. Then missing out one hole did the same again through the outer hole. This aligned the hole in-between, in the three components, enough to get a rivet through. Hence the red rubber grease. I repeated the process back towards the centre until I had every rivet in place before using the rivet pliers. On both bumpers I found it was only necessary to stretch the skins on the top side to align the holes.

Martin also made another brilliant suggestion. Drill holes in the box section of the bumpers to loose some weight! Blinded by the sole purpose of restoring the bumpers to make them last and look a little better, this had not even crossed my mind. I drilled (I think) 21, one inch holes into the front face of the box section of the front bumper removing 2kgs of weight. I weighed it before and after. Yes, I'm that sad. I believe it's as every bit as strong as it was when I started as its impact strength comes from the box sections depth on the horizontal plane and those two skins remain intact.

I only drilled three holes in the rear bumper mainly to allow access for rust killing and painting of the inner faces. I'm working on the principle that a bit of extra weight at the back will push the tyres to the road a little more, helping the parabolic springs to keep them in contact with the tarmac more often.

To clean up the rubber skins you can actually sand them with a very fine grain, wet and dry to get rid of any scuffs before giving them a good clean. Once they are refitted to the car, I will give them repeated applications of Autoglym's bumper care to get a nice satin sheen and keep the rubbers supple.