Land Rover Discovery Fuel Pump Swap and Rebuild Issues 1
My '94
Disco has 170k miles on it. Some web sources suggested the fuel pump may give
out at 100k+, so I thought I'd better check mine out. I read data on a few links
such as these:
http://www.rangerovers.net/repairdetails/fuelpump.htm
http://www.autohausaz.com/html/fuelpumps.html
My options
seemed to be to get a new complete pump assembly (around $170 if I shopped
around, over $300 for LR brand), get a
salvage pump, rebuild my pump unit by putting in a new motor in the
assembly ($60+ at NAPA etc?), and rebuilding the pump motor by replacing the
brushes in it (a couple of bucks at hobby shops?).
Since I
drive the Disco every day, I didn't want it laid up while I had the pump out.
The discount new unit price didn't sound too bad, but it wouldn't be an LR
brand, and some sites suggest the LR is better, in that it is designed to
withstand partial gas tank collapse--eg hitting a rock etc.
So, I found a pump from a salvage '96 Disco online for $100. I figured I'd get that, check it out, maybe rebuild it, put that in my Disco, then rebuild mine for a spare. In any case, I liked the idea of digging into the innards, as I like to understand how things work, which gives a good picture of their strengths and weaknesses.
The pump
arrived...
I disassembled it, starting with popping the tub off the bottom--by pushing in the tabs in the holes around the rim. This was fairly easy to do with a screwdriver, working one tab in at a time. I was then able to work the tub off of the pump (the silver cylinder below), but in retrospect, I should have taken the bracket screws out first (a Phillips screwdriver is shown pointing to one of the screws below). This would have allowed the pump to move up by flexing the output tube, and the tub would have come off much more easily.
I guess one of the innovations for adapting to a squashed fuel tank is the ribbed flexible intake and output tubes. A spring can barely be seen in the picture above, at left, on a silver shaft behind the upper flex tube (better seen in the first picture). This spring allows the entire assembly to collapse a few inches by sliding along that shaft, and the one below. The tubes flex when this happens, but everything else remains the same, so I guess that movement would accommodate at least a few inches of gas tank collapse.
Once the bracket screws were removed, and the two wires pulled off their tabs (one is marked +, with the red wire), the pump could be pulled downward by flexing the intake, or stuffed up through the hole in the plastic platform above it. The normal thing to do would be to pull the pump off the output tube to free it, but it wouldn't come off, no matter how hard I tried. I wanted to look at the brushes, so I did the next step with the pump still attached to the tube, and the assembly, being careful not to bend the fuel level float bar. What I should have done is to pull off the output tube at the upper end, where it slips over a metal tube. I'd have to trash the compression clamp and later replace it with a stainless hose clamp, but I went ahead with the gymnastic method.
This step involves getting the top cap off the pump. This is the piece with the wire tab connectors on it, plus two metal nubs, which are the attachment points for the brushes themselves. In the picture below, one wire tab is easily seen in the foreground, and one of the brush nubs, the tan cylindrical cap-like thingy, is just above it. The whole cap assembly is basically flat, with some tab-like parts that mate with the rest of the pump unit--this can be seen below. There's a squarish section just below the wire tab, which is part of the cap, and fits into a recess in the rest of the pump. To get at the brushes, it is necessary to CAREFULLY pry the cap away from the rest of the pump. I used several different sized small screwdrivers. It's a friction fit, but the friction is where the brush holder nubs fit into the brush bore tubes (invisible here). Thus, the main prying pressure should be applied as far in to the center of the cap as possible, as the cap is eased away from the pump.
Pry around at various points, to distribute the pressure evenly. After maybe 3 or 4 mm, the friction point will be passed, and the cap will come free, complete with the brushes and their springs. See below. Here you can see the brass brush holders that were causing the friction fit in the bores. The brushes on this unit, from the '96 salvage Disco, had about 8 or 9 mm of carbon left. I didn't know how long the originals were, but from measuring the depth of the bores, and the length of the assembly at maximum compression of the springs, I estimated that they could have been as long as 18mm or so. That would mean these brushes were about half worn down, although I suspect the originals weren't actually that long.
The inset closeup in the upper right shows the worn end of a brush. This shows the angled shape described in another web page rebuild (one of the links above). Square hobby brushes would have to be shaped to fit. Rather than file them, my experience has been that it works well to rub brushes on a piece of fine sandpaper on a flat surface.
To replace the brushes with hobby store brushes, I'd probably have to unsolder the brush feed wires on the top end of the brass nubs. Then, I'd solder the new ones in place, hoping that the heat of the soldering iron doesn't compromise the plastic cap. Since I was eager to see what my Disco's brushes looked like, I decided to simply put this pump back together, and swap it into my truck, figuring that these brushes at least looked like they had a fair amount of life left in them.
The first step was to take up the carpet and rubber pad in the load space. This was pretty easy after removing the screws on the rear hold down strip. However, with the jump seats, I had to run a wide wedge chisel under the edges to free it from the floor, where it had settled in.
One thing this exposed was a rusty seam on the floor.
This seam is fairly easily accessible from underneath too, so I plan to clean it up, use some rust neutralizer, and cover it from underneath with roofing tar, and on the top with Rustoleum paint.
Another problem that showed up was that the steel tubes going into the pump top were quite rusty. I don't have a picture of it, but I'd strongly suggest that anyone with a high miles Disco, or one that's often in water, should pull the mat and cover plate, and check out the pipes. Mine weren't quite rusted enough to be unusable, but they were on the way. Cleaned up and painted or greased, they'll be fine, but without attention, it wouldn't be too long before those fittings would have to be replaced--and the fuel pump assembly itself would be unusable, even if the pump motor was fine.
There's a plastic ring around the top of the pump that needs to be unscrewed to get the pump out (no picture of that). I used a hammer and a big screwdriver to knock against the protrusions around the ring, to get it loose. When pulling the pump out, care is needed to work the float free without bending the float rod. Also be careful to not let dirt fall into the gas tank. And, NO SMOKING :-)
When I pulled the pump assembly out and took it apart, I found brushes that looked like this:
The longer one here is about 5mm, or maybe 3mm less than my salvage pump ones. The other one has been worn on an angle. I presume it has gotten short enough that the brush could not be held straight by the bore channels. There must be a space between the bottom of the bores, and the commutator. The brush was able to turn sideways into that space. This could indicate that the commutators are worn too, or more likely, just that there's a design space in there. Anyway, I'm glad I pulled the pump when I did. It probably wouldn't have been too long before the brush got short enough to be pulled into the space entirely, although I imagine I'd have been good still for 10k miles or more.
I'd guess that by comparison, the salvage pump brushes might be good for another 30k or 40k or so. So, the next step is to decide whether to put in hobby brushes, or to substitute a non-OEM pump unit. At least I've got some time to decide now. And, I know it's not much of a job to swap the pumps. This biggest problem might be, if I put in another pump motor unit, it's still going to be a bitch to get the ribbed tube off the old one. I tried a heat gun, and that didn't help. I can replace the tube with some gas line, I guess, but I'd like to keep the original. Oh well.
Any questions, email John at jixix@aol.com
Well, I took another step. The fuel pump on my '92 Suburban had gone bad a couple of years back, and I replaced it. So, I opened up the old pump on that one to see what the story was. This step is documented here.