Monday, July 17, 2017

How to replace a series Land Rover rear cross member

After the fairly long-term success of my post on repairing outriggers (5,700 page views over four years and quite a few comments), here's another on the rear crossmember replacement job.

First, the preparatory work: This is a 1971 Series 2a 88 inch, LHD with the wheels removed. It's now on jackstands (placed forward of the rear springs). The floor, seats, seat box, and tub have all been removed. the rear spring shackles have been undone or cut off, and the differential gearbox and spring assembly rests on the floor jack (AKA "trolley jack" in the UK) or on blocks. The frame has been pressure-washed and brushed lightly with a wire wheel on a hand grinder to remove the worst of the dirt and any loose old finish.

Here we are measuring to record the distance between the front and rear outer tub brackets. We'll keep this measurement the same when we put on the new crossmember. Lots of people advise using the tub as a jig to set this measurement, but to my mind that runs the risk of shortening or lengthening the distance between the front spring mount and the rear upper shackle anchor, which helps set the rear wheel alignment. The tub is flexible, and could be squeezed into a different shape, throwing these measurements off.

As it stands, the passenger side is actually 1/4 inch longer than the other due to a slight driver-side fender-bender. We'll fix this when we fit the new crossmember. The final target measurement to square up the truck is is 48 and 3/8 inches.

We also measured the difference in height between the cross member and the flat top of the frame using a level as a straight edge. We'll keep this measurement the same too, at 1 and 3/8 of an inch.

Then it's time to cut your Rover up! Not for the faint of heart. I started with my 7 inch grinder. My new crossmember has 16 inch frame extensions with four inch welding tabs, so I cut the frame just shy of 12 inches from the old crossmember.

The heavy duty grinder proved too clumsy and in fact broke a cutting disc off, so we finished with the 4.5 inch hand grinder.

Once through about three quarters of the way, we position jack stands under the old crossmember to catch the weight. Leave these about a notch lower than the crossmember. After a while the old crossmember will bend down, or can be pushed down, to rest safely on the jack stands. This allows you to finish the cut with a hacksaw from the top, which is easier and safer than using a hand grinder from below.

Once  the old junky cross member is removed, it's easier to burn out any old shackle bushings. Use a gas torch to burn out the old rubber, and the inner bushing can then be pushed or pried out.

You then cut through the outer bushing metal with a hacksaw, being careful not to cut into the spring itself. The new crossmember comes with shackle bushings installed, so unless you plan to remove and/or service the spring or diff too, you only need to buy two new ones, but you may need some new bolts and nuts too, and perhaps new shackle irons. (Remember, only the inner shackle iron is threaded.)

You now have a once-in-a-Landy-lifetime opportunity to rust-proof the inside of the frame easily. Here I'm using Fluid Film, popular here in New England where we use a lot of winter salt on the roads, a proprietary Fluid Film air-powered product dispenser, and a long piece of hose which reaches forward all the way past the dumb irons, but you could use Waxoyl or similar.

First, test where you can see to make sure product is coming out in a suitable spray pattern. Start spraying with the hose fully inserted, then withdraw the hose an inch or two at a time. Repeat to be sure of getting enough product in there.

Now turn your attention to the new cross member. Bend the welding tabs out gently with a mallet and test fit it to the old frame. Using trial and error, get the best fit. Reproduce the old measurements above and clamp it in place, then tack weld it.

This is the bit where the old-timers say to fit the tub, and use the tub as the final jig to get the measurements right, but that ignores my objection above, and it requires that you put the tub on and take it off again to weld the top of the new frame extension. This is too much trouble for me, and indeed, my tub isn't square anyway.

Instead I relied on careful measurement. I then welded all around each side, and up and down the tab slots. You can easily tighten any gaps between the tabs and the old frame with a hammer once you start welding and get everything nice and hot.

Now, if you're brave, measure again! Mine was within a sixteenth of my target 48 and 3/8 inches, so I was pretty happy with that.

Having reconnected the shackles, my plan now is to spray everything I see except the transmission with POR 15 rust proof paint, and Fluid Film on top of that.

That should last a while. Enjoy.

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