Curt 13070 receiver install - the right way

[Bread]

This weekend I installed a Curt receiver on our ’02 4.6is and found some things I’d like to share. Yes, it’s not a hitch. It’s a receiver J The included instructions were essentially crap (wrong wrench sizes, wrong hardware quantities, and just very vague in general), and I was shocked how they propose it should be installed. I’ve emailed the company regarding their poor, and in my opinion unsafe installation method. For some background on me, I’ve been a Millwright and industrial maintenance technician for the last 10 years. I troubleshoot and repair failed equipment for a living. Not to mention being a motor-head and wrenching on vehicles before I could even drive.

The Curt receiver itself is a well made fabrication. The welds look good, and the mounting plate is a heavy ¼”. Despite having a couple chips from shipping, the finish is nice as well. It is my second choice over the factory receiver, but my g/f’s first choice since she paid for it J The DrawTite hitch with the drop bar is garbage. It does not bolt to the reinforced unibody rails, but rather the weaker center brace. I would never touch one. The Curt receiver bolts directly to the reinforced rails and brackets on the unibody, and is only second to the factory hitch because it does not also incorporate the center brace like the factory receiver does. This is likely the reason the tow rating is reduced from the vehicle max of 6000lbs to 5000lbs. The rating makes no difference to me as we only purchased this receiver to mount a Softride bike/ski rack. And we also won’t need any wiring. When I want to tow I use my F350, and save the X5 for haulin’ ass up to the slopes. However, that doesn’t mean that a future owner won’t try to hook a trailer up, so I want it to be right!

Oh, and it makes no difference if you tow at 80 or 90mph as I’ve seen some testimonials report. That’s so annoying because speed is irrelevant. The major stresses placed on the receiver are during braking and accelerating. And the 4.6is can brake and accelerate pretty damn hard!

Just some basic disassembly notes before getting to the important stuff. We have the optional slide out cargo tray on our ‘02, so the pictures are specific to our model. I say that because from what I’ve read that there are also some differences in the bumper bracket mounting hardware from year to year. YMMV.

Step1: Prop up the cargo tray, and remove the carpeted floor trim panels, one on each side secured with three Phillips screws. Slide the trim towards the center to release the two catches underneath and remove. Also remove the cover panels on each sidewall which conceal the DVD/NAV system and speakers.


Step 2: Remove the plastic trays on each side with a 10mm socket driver. Also remove the wheel chock holder held in with the same plastic nuts.


Step 3: Unplug the PDC harness at the passenger side rear corner. Rotate the cam lever to release, and push the grommet and plug through the hole in the body.


Step 4: At the lower rear of each fender liner there are a couple small screws. On each side remove the bottom screw only with an 8mm socket.

Step 5: Release the 4 tabs at the bottom of the rear bumper skirt, where it attaches to the spare tire pan. It takes some finagling to get them loose. (NOTE: In this pic I have already removed the plastic cover that resides just behind the tabs).


To remove the bumper, you now just need to remove the two T55 bolts above the exhaust tips. If you have a 3.0 you can probably get to those bolts at this point and skip to step 8. If you have a 4.4 or 4.6is with the wide exhaust tips you’ll need to remove some more stuff . Continue to the next step.

Step 6: Underneath the bumper again, remove the plastic cover in the center of the bumper. Remove the three Phillips screws, and then pry/push the plastic tabs on the sides inwards (towards the center) to remove the piece. Here it is removed so you can see what those tabs look like. The arrows show which direction to push.


Step 7: Loosen the (2ea) nuts per side on the REAR muffler hangers with a 13mm socket and extension (pictured with the bumper off for clarity. Yours is not off yet). You don’t need to remove the hangers forward of the muffler. You also don’t need the jack stands at this point as you want the exhaust tips to drop all the way down in the opening in the body to access the bolts above. They will be put back under when the bumper is removed and installed.


Step 8: Now you should be able to remove the two T55 bolts securing the rear bumper brace. I still had to use a u-joint to reach up there. These were really damn tight, and my T55 socket is a 3/8” drive. So I put a longer 3/8” drive breaker on it to get them loose. I also put a rag, and a piece of cardboard on the exhaust tip to protect it from my wrench.


Step 9: Support the exhaust tips back into place either with jack stands, or by simply bolting them back up. Pull the bumper straight back and off. The fender liner tends to hang up on the bumper trim on the 4.6is, so it takes a good tug to break them free. Be prepared, it’s heavy! I cleared my work area first so I had a clear path to walk outside and set the bumper down on the grass. Also make sure the PDC wire doesn’t get caught as the bumper comes off.


Step 10: Remove the bumper mounts/shock absorbers via the three nuts located inside. Then remove the rear brace secured with (8ea) T50 bolts on the face, and (2ea) bolts underneath with a 13mm socket.


Now the fun stuff. Curt provides (2ea) ½-13 bolts with nice serrated flange nuts to be installed in the top two holes of the hitch. They also provide (2ea) 7/16-14 bolts and flange nuts to install in the bottom two holes. These really just locate the receiver and serve no structural purpose due to the thin sheet metal they are bolted too. For the other two main structural mounting holes per side Curt instructs to re-use the tiny 8mm studs that were used to hold up the rear bumper. This is lacking in a major way! Those 8mm studs are designed to hold up the plastic bumper, not pull 5000lbs (as Curt rates their receiver). The only bolts which are rated to carry load are the two they have you install at the very top of the receiver. Their setup is actually fine for braking, when the receiver is pressed against the body and the top two bolts stop the rotational force which is pushing in on the bottom. But during acceleration all of the stress is pulling on those tiny bottom studs which are not rated for any kind of heavy load. So after shaking my head in disgust for a few minutes in my garage, I threw the instructions in the trash, bolted the mufflers back up and headed off to the hardware store. I hate driving this thing as it is with the winter wheels/tires on it, but with the bumper missing people look at me like I’ve carelessly destroyed this thing with my lack of driving skill J


So this is what I did. Instead of only punching out the stop stud, I punched out all three of them, and drilled out all three holes to accept ½-13 bolts (9/16” holes). Enlarging the holes was easy using a step bit with some cutting fluid. Keep the rpms relatively low. Drilling these bumper brackets is the only modification required. The holes in the chassis and the receiver are already large enough to clear larger bolts. I have no idea why Curt wouldn’t have just instructed to replace all of them. Makes absolutely no sense to me whatsoever.


I picked up some grade-8 bolts, grade-8 fender washers (larger diameter than standard washers), and grade-8 stover/pinched flange nuts which are self-locking and therefore don’t need to be serrated under the flange. They will never loosen up. I chose grade-8 bolts because they don’t stretch like the grade-5, but in retrospect grade-5 would be just fine. I was angry and went overboard Pictured below from R to L is the factory stud, the bolt Curt includes, and the grade 8 bolts I used.


This hardware upgrade cost me $20, and only a few extra minutes to install. After putting the receiver in place and loosely installing all of the bolts, I snugged all of them, then fully tightened the lower 7/16” bolts to align everything. Then I hit the rest of them with my impact gun. The large washers are installed INSIDE the chassis, directly against the sheet metal to help distribute the load over a wider surface area.

The large fender washers I purchased were too big to use in the uppermost two holes. They ran into the radius in the body and would not sit flat. I could have ground down the side of one of the washers to create clearance. But instead I decided to use the flange nut that came with the Curt hardware kit, which just clears.


Here the receiver is fully installed with the 1/2-13 hardware.


I’m 100% confident with this modified installation. I wouldn’t hesitate to tow up to the 6000lb vehicle chassis rating if I needed to. The receiver looks clean, and required no modifications to the structure or bumper of the vehicle. We purchased it for $140 off Amazon, and I would recommend it to anyone when installed with the proper ½-13 hardware in all 6 mounting holes.


Extra/upgrade hardware list:
(6ea) ½-13 x 1.75” long bolts
(4ea) ½-13 stover/pinched flange nuts (self-locking)
(4ea) ½” fender washers

Tools Required:
T55 socket
T50 socket
13mm socket
10mm socket or nut driver
8mm socket
9/16” socket
9/16” open ended wrench
#2 Phillips screw driver
Needle nose pliers (for getting those plastic nuts back in their holes)
3/8” ratchet
3/8” drive extension
3/8” drive U-joint
¾” sockets (2ea) (one impact, one steel)
¾” ratchet
½” drive breaker bar
½” drive impact gun if you have one

[Papa13]

Nice DIY! Thanks! How much was this unit?

[Bread]

Originally Posted by Papa13

Nice DIY! Thanks! How much was this unit?

$160.56 including shipping from Amazon. And then another $20 for the hardware I added. Can't beat that!

[Ghost-Flame]

The Curt receiver itself is a well made fabrication. The welds look good, and the mounting plate is a heavy ¼”. Despite having a couple chips from shipping, the finish is nice as well. It is my second choice over the factory receiver, but my g/f’s first choice since she paid for it J The DrawTite hitch with the drop bar is garbage. It does not bolt to the reinforced unibody rails, but rather the weaker center brace. I would never touch one. The Curt receiver bolts directly to the reinforced rails and brackets on the unibody, and is only second to the factory hitch because it does not also incorporate the center brace like the factory receiver does. This is likely the reason the tow rating is reduced from the vehicle max of 6000lbs to 5000lbs. The rating makes no difference to me as we only purchased this receiver to mount a Softride bike/ski rack. And we also won’t need any wiring. When I want to tow I use my F350, and save the X5 for haulin’ ass up to the slopes. However, that doesn’t mean that a future owner won’t try to hook a trailer up, so I want it to be right!

I love it, Guy comes on here and makes a pretty good write up. In the process he trashes the Drawtite 3 pt hitch as garbage. Basically questions the sense of anyone who would choose one as not knowing as much as his life as a failed design expert. tells us he is doing it the right way.... Then tells us he is going to tow a bicycle and a ski rack. sounds like the tallest horse in the mini horse Rodeo.

I have a drawtite 3 pt hitch. I saw the Curt when I bought mine and I wouldn't touch the curt, looked flimsy to me. Mine is rated to tow 6000 lbs out of the box. Yours is 5000 pounds. Granted you modified with bigger bolts. I've been towing heavy loads for the last 3 years with this hitch and truck, probably about 9000 miles of towing MC, ATVs, Gear. My drawtite 3 pt hitch/reciever looks like the day I bought it. I'm not saying the Curt is a bad receiver for what it is even with the bigger harder bolts.

Who died and left you the king of hitch knowledge. Oh I just noticed you have 2 posts. You may think you know everything about steel fabricated add ons but, you don't know a thing about easing into the community.

I'm the first one to admit the BMW reciever is a better set up than the Drawtite. But the Drwatite is no slouch

[JCL]

Bread:

Excellent write up. I like your approach to improving the Curt hitch, it is what I would have done if I had to use that hitch as you had to.
I don't quite agree with the following:

The Curt receiver bolts directly to the reinforced rails and brackets on the unibody, and is only second to the factory hitch because it does not also incorporate the center brace like the factory receiver does. This is likely the reason the tow rating is reduced from the vehicle max of 6000lbs to 5000lbs.

The difference isn't the center brace, as the factory hitch doesn't use one. The difference is the reinforcement of the pentagon-shaped mounting surfaces located behind the collapsible bumper support struts. You have identified the attachment weakness, and rectified that. However, you are still relying on the stability of the rear mounting surface not to flex. The OE hitch removes the collapsible struts and replaces them with solid struts that are very beefy at the pentagon-shaped mounting surface, and which are cross bolted to the reinforced rails in the unibody some distance forward, in multiple planes. No comparison in terms of strength. Is it required? Well, it is keeping with the design approach of the vehicle, so in that sense it is very appropriate. I like it because it is classic German engineering.

I share your opinion of the Drawtite. Ghost, I am not questioning your manhood. Just your hitch receiver.

Jeff

[PropellerHead]

Originally Posted by JCL

However, you are still relying on the stability of the rear mounting surface not to flex. The OE hitch removes the collapsible struts and replaces them with solid struts that are very beefy at the pentagon-shaped mounting surface, and which are cross bolted to the reinforced rails in the unibody some distance forward, in multiple planes. No comparison in terms of strength.

+1

My factory hitch was ~$400 with the wiring harness and the factory brake module. Install will reveal that it is the best option as described by the OP:

The Curt receiver bolts directly to the reinforced rails and brackets on the unibody, and is only second to the factory hitch

I have seen pics and discussions of non-OEM hitches inducing flex on the rear of an E53, then twisting the frame. Of course this is extreme, and may even be possible given an accident while towing, but I am absolutely not willing to risk it for a couple hundred $.

But as they say, mine is mine and yours is yours. We'll both do as we please!

[civdiv99]

Tough crowd.

[DallasGV]

Nice write up! And, I have a lot of respect for the blue collar re-engineering (I mean this in a good way) No need to ease into the community, if you have another way of doing something or experience and share, that's what it's about.

[swissfrank]

thank you for taking the time to post this =)

this has given us a great way to see the differences between oem and aftermarket

[Bread]

Originally Posted by Ghost-Flame

I love it, Guy comes on here and makes a pretty good write up. In the process he trashes the Drawtite 3 pt hitch as garbage. Basically questions the sense of anyone who would choose one as not knowing as much as his life as a failed design expert. tells us he is doing it the right way.... Then tells us he is going to tow a bicycle and a ski rack. sounds like the tallest horse in the mini horse Rodeo.

I have a drawtite 3 pt hitch. I saw the Curt when I bought mine and I wouldn't touch the curt, looked flimsy to me. Mine is rated to tow 6000 lbs out of the box. Yours is 5000 pounds. Granted you modified with bigger bolts. I've been towing heavy loads for the last 3 years with this hitch and truck, probably about 9000 miles of towing MC, ATVs, Gear. My drawtite 3 pt hitch/reciever looks like the day I bought it. I'm not saying the Curt is a bad receiver for what it is even with the bigger harder bolts.

I'm sure the DrawTite itself is equally well-built. The issue is not the receiver itself, but the attachment points it utilizes. That chassis cross brace is not designed to carry a load. It's in fact so weak that the factory installed the removeable cross member there to beef it up. Which is also why DrawTite has the drop down bar to reach under and grab ahold of something stronger. The weak attachment location, combined with the required modifications you need to make to the vehicle in order to install it are negative points the other two receivers don't have. There really isn't any debating that it's the least desireable design of the three.

Originally Posted by Ghost-Flame

Who died and left you the king of hitch knowledge. Oh I just noticed you have 2 posts. You may think you know everything about steel fabricated add ons but, you don't know a thing about easing into the community.

It's a receiver.

But seriously, this isn't my first barbeque. I have made thousands of posts on dozens of boards over the past 10 years. Cars, trucks, boats, motorcycles, and so on. The fact that I have less than a handful of posts on THIS board is quite irrelivant. I see no correlation between post count and knowledge, ability, or credibility. I understand that my username is new here though, and I understand that to many a 'new user' is viewed as a newb to anything automotive.

I'm sorry I didn't use enough lube when I "eased" into this community, and as a result your butthurt. But the reality is this post was soley put here to shine light on a product needing improvement, which other people may own or are interested in owning. BMW folks can be far more particular than owners of other brands, so I hope this information can be found useful.

Originally Posted by JCL

The difference isn't the center brace, as the factory hitch doesn't use one. The difference is the reinforcement of the pentagon-shaped mounting surfaces located behind the collapsible bumper support struts. You have identified the attachment weakness, and rectified that. However, you are still relying on the stability of the rear mounting surface not to flex. The OE hitch removes the collapsible struts and replaces them with solid struts that are very beefy at the pentagon-shaped mounting surface, and which are cross bolted to the reinforced rails in the unibody some distance forward, in multiple planes. No comparison in terms of strength. Is it required? Well, it is keeping with the design approach of the vehicle, so in that sense it is very appropriate. I like it because it is classic German engineering.

Ah, noted. I don't know why I was thinking the factory receiver uses the center brace. Although the bottom bolts on those brackets are mounted in shear, the bars themselves do help distribute the rotational forces further into the chassis rails. I dig it!

And again, if it were MY car I would have bought the factory receiver just because I like to have all factory componets and wiring. The extra cost is nothing for that piece of mind, even if we never tow with it. But the reality is that even though I do most of the drivng, it's not mine. It was more than enough to suit our needs with the included hardware, and the price is a steal. I've installed three other hitches in my life, and this was by far the easiest. The other three all required laying on my back, drilling 9/16" holes in truck frame rails with a hand drill. Nothing like hot chips falling on your face!

I have full confidence in the strength of the Curt as I have it installed and still would not hesitate to pull the full 6000lb chassis rating. Although I wouldn't overdo any towing with an X5 regardless as it's much more costly to replace worn drivetrain componets than on my F350.