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How To: Fix Pump Rub

44644 Views 26 Replies 18 Participants Last post by  Duramaxed02
Just did the pump rub fix on my truck using Merchant Automotive's pump plate. This is a 175 dollar kit which is a bit pricy for a piece of aluminum, however, it's a nicely machined pump-casing that should keep the pump from ever rubbing through your transfer case.
There's an online instruction pdf that you can download, and i followed this for my work. However, as there's not currently a "how-to" on this forum, i thought i'd post one since i'm anal about my work and like to document everything.

The contents of merchant's kit:

To start, make sure your parking brake is on and/or your wheels are chocked, as you'll be dropping the driveline. Remove the U-joints from the driveshafts (tape the caps on so they don't fall apart) and slide the shafts out of the transfer case housing.

There are 2 electrical connectors on the t-case: the speed sensor and the selector/solenoid wiring (not sure about that terminology/id). Disconnect these two, and un-clip the vent tube to allow it to drop free with the transfer case. There are also a few clips to hold wiring and maybe fuel lines (i can't remember, just make sure you d/c everything attached to it).

You can drain the t-case before you drop it, or you can just place a drainpain on the floor to catch the fluid as you brake the casing loose. There are 6 15mm fasteners mating the t-case to the trans. Remove the bolts from the transfercase, not the transmission casing (like i started to do). The transfercase isn't that heavy, probably 50 lbs and you should be able to manhandle it out without a problem. After removing the 6 fasteners, slide it backwards to free it from the tranny, then slide it down and forward to get it out. I think i had to rotate the front twds the passenger side to get it out, you'll see when you're wrestling it out.

Now that the tcase is out, you can go to work. Start by removing the speed sensor and the rubber plug that hides the c-clip on the mainshaft bearing.

The speed sensor is all-plastic construction (so be careful putting it back in), 3/4 inch hex. The rubber plug simply pulls out with your fingers.

Remove the 17 x 15 mm bolts that hold the tcase halves together. They line the perimeter of the case, be sure to note where the brackets mount. I etched little drawings of the respective brackets infront of each bolt on my case.

In the hole where the speed sensor was, slide a flathead screwdriver or mini prybar in front of the gear (as you're looking at it) and apply a little pressure. Using duckbills, spread the c-clip that is visible where the rubber plug was. Pry the gear (try not to damage the threads in the speed sensor hole) towards you as you're spreading the c-clip. I didn't have any duckbills handy, so i used a pair of circlip plyers. I also put electrical tape around the ends to help keep the c-clip from sliding off my circlip plyers. The reluctor gear should slide away from you and free itself from the c-clip.

There are 2 prypoints on opposing sides of the casing, they're easy to find. The case halves should split without any problem.

With the case halves apart, you can start removing the pump. This is a gerotor style pump (the same style that harley davidson uses for their oil pumps), it's very simple. Start by removing the large c-clip on the splined shaft. Using my circlip plyers didn't work that great (sure wish i could have got some duckbills), so i had to use a flatblade to pry up on the clip while spreading it open. This pretty much requires a third hand.

After sliding the c-clip off the shaft, you can pull the bearing off by hand. Then slide the gear off and you will have access to the pump.
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After removing the gear, you have access to the pump. On the side of the pump, there is an oil feed line. Pull this out of the pump, being sure to note the o-ring that is in the female portion, where the line inserts. This will need to be seated in the bore during reinstallation.

The pump can now be slid off the shaft. There are 6 t-15 screws that hold the pump together. Remove these from the stock pump plate and remove both portions of the gerotor. It's a good idea to keep the same orientation, meaning keep the gears facing the same way when you reinstall them. I'm a stickler for cleaning everything before i put it back together, and i recommend using some brake parts cleaner to clean everything and dry it up nice at this point.

here's the inside of the pump, with the top plate flipped upside down.

After cleaning the threads of the 6 torx screws, apply the supplied blue loctite. Lube the gerotor gears with some fresh ATF and drop them into the new pump plate. Mate the top plate and bottom plates of the pump together, orienting the triangular and rectangular cut-outs so they align. these cutouts can be seen in the above image, it's simple.

Install the torx screws. Once the bevelled shoulder begin to make contact with the top plate, tighten them incrementally to align the plates. Merchant's instructions say that the screws can be torqued to 80 in-lbs, but i think you will strip the aluminum if you go that tight! I think 30ish sounds more realistic, but i just tightened them by hand with a quarter-drive ratchet. If you've worked on a few things in your day, you can get a feel for how tight things ought to be. that's called a calibrated elbow.

Now it's time to put it all back together. Slide the pump onto the shaft, pop the oil line back into the pump, again ensuring that the o-ring is seated in the bore.

Slide the gear back onto the shaft. The tapered edge of the gear goes on bottom and the smooth lip goes on top, as shown here.

Slide the bearing back onto the shaft, then reinstall the c-clip. Ensure that the c-clip is fully seated in its notch. i like to tap on them with a screwdriver just to be sure.

Before you put the case halves back together, clean the mating surface well with a rag and brake parts cleaner. They don't require a gasket and come from the factory with a silicone sealant. So make sure the surfaces are good and clean and oil free, then apply a bead of RTV along the edge. Don't put too much as it will bead into the case, and could get sucked up into the oil line, obstructing it. Merchant's says to apply a 3/16" bead; i personally just rub it on with my finger, then go back around the inside of the mating surface with my finger and clean away all the rtv to about 1/3 the distance from the inside of the mating surface. this should keep most of the silicone from getting squished in when you torque the bolts back down.

Now it's time to put the case halves back together. Slide the shaft in the bore carefully, put the bolts back in and be sure you get the brackets back where they go. Torque to 40 ft-lbs in a cross-pattern.

Now you'll want to reinstall the c-clip on the reluctor gear. This is done reverse of the disassembly instruction. Spread the clip with snapring plyers and gently pry the gear back. As you do this, note the notch where the c-clip rests in the case to help with alignment.

Now reinstall the speed sensor (don't overtorque it!) and the rubber plug. The tcase is now ready to be reinstalled into your truck, the reverse of how you took it out.
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Here's a few pictures of why you may need this kit. This is a common problem with earlier duramax's and i'm glad i did mine, as it was in need of this correction. The pump hadn't worn through the casing yet, but it would have in time.
Allisons are great machines, it's a mystery why they left such a weak retainer to do the job. When i opened my t-case, the retainer fell out. It was broken and as you'll see, the casing had started to wear. Thank God it wasn't too far gone.

here's the retainer sitting where it fell in my oil pan

and here you can see where the pump was rubbing on the inside of the case

So, it's either a 175 dollar pump plate, or who knows how much for a new transfer case. I'll take the pump plate fix.
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nice writeup good info how many mile on truck when ya did this
nice write up man ! :drink
nice writeup good info how many mile on truck when ya did this
thanks man. My truck's got about 184,000 miles on it. I was dropping the trans to do some other work, and a guy here on the forum recommended i do the pumprub fix while i had it out. i'd never heard of it before that, so thanks to Siewell Dmax for bringing it to my attention!!
did you take the front shaft off the t-case or just leve it on? if off how did you get it off? i have to do this but i think i way need a rear case hafe but im hoppiong to have it welded.
I took the front shaft off also. It just pulls right off. It may be a little hard but it will come off
Great write up! I am gonna do this soon and have a few questions. What's the torque on the 15mm bolts that hold the case together? How much ATF does the T case hold? And can amsoil torque drive be used?
yeah, the front shaft should slide right out, just like the rear. It's wierd (to me), there's no slip-yoke, it just slides out of the tcase.

not sure what the 15 mil bolts are torqued to, i just did them 'about that tight' working in as much of a "star" pattern as i could. I left the instructions at my friends house, i'll see if i can dig them up next time i'm there.

The tcase should hold about 2 qts if i remember right, i just used one of those big 4-qt bottles and filled it until it started draining back out the filler plug. Just buy a few qts and fill it until it's full.
ok thanks i wasnt sure after i saw the rubber bout on it.i just hope i didnt kill it and got to it in time to fix it
Very Nice writeup man......reminds me I need to do this in the spring when I change fluids.
Those 15 mil bolts are @ 40 ft-lbs.
do the 2006 lbzs have this pump rub problem too? or is it corrected by then
do the 2006 lbzs have this pump rub problem too? or is it corrected by then
do the 2006 lbzs have this pump rub problem too? or is it corrected by then
Yes...New process corrected it in 2007 AFAIK
do you use your 4wd alot wintermetal?
We pay enough for these trucks so you have to wonder why do they go cheep in these critical areas? I have an 02 should I be thinking of doing this? Also what are the signs if any that this needs to be done? Thanks!
Just found this this morning Only 95 Buck-a-rooos!!
GM Transfer Case Pump Upgrade Kit Merchant Automotive

We pay enough for these trucks so you have to wonder why do they go cheep in these critical areas? I have an 02 should I be thinking of doing this? Also what are the signs if any that this needs to be done? Thanks!
Yes you should be thinking of doing this before its to late. As to the signs of this happening I noticed a grinding in my t-case while in 4wd, along with the fact it would never stay in 4wd or sometimes go into 4wd at all. I also happened to notice transmission fluid sprayed all over the bottom of my truck from it leaking as i was driving.
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