I've developed a better subframe bushing replacement tool than the typical design using a central threaded rod. I'm hoping a few people will replicate this tool and report back with a confirmation that it works well for them, along with any suggestions for improvements.
The tool design pulls on the bottom flange/lip on the stock bushing, pushing against the subframe tube through the notches in that lip. It works entirely from the bottom of the bushing, takes just a few seconds to set up without getting under the car, and applies on-axis tension directly to where the bushing grips the subframe.
Another advantage of this tool design is that allows extracting the bushing from the subframe without removing the center bolt or lowering the subframe beam. That's a plus on the convertible, where the top of the bolt is difficult to reach, and on the Z3, with its fixed stud. (Replacing the Z3 bushing usually requires removing many parts to lower the subframe.)
This design is simple to reproduce at home. It uses a U-shaped bridge in compression against the subframe tube. A two/three jaw puller grips the bushing flange, and the screw from the puller pushes against the bridge to pull the bushing down into the bridge.
The compression bridge is the only special part. It is fabricated starting with a Pitman arm puller ($6 on sale at H-F, about $10 list/elsewhere.) The Pitman arm puller needs to have the legs and claw ends cut or ground down to fit the profile of the bushing notches. The only critical clearance is at the feet, where tool presses against the subframe tube. If that part is cut too wide the bridge could slip to the outside of the tube. Widening the opening further up the legs doesn't need to be as precise, but if it is close to the bushing notch profile the legs will act as a rail to hold the puller in line.
The other modification is filling in the hole for the drive screw. The plug is made with the tip of the Pitman puller drive screw. Turn the drive screw into the hole until it has full thread engagement -- it will just barely comes out the bottom. Mark there and cut it off flush. Punch or drill a center divot so that the centering pin on the two jaw puller won't wander. Or take a short cut and just cut two shallow grooves in an X.
My first tool took about an hour and a few Dremel disks / grinding stones just to partially shape the jaws. The ductile iron of the Pitman arm tool is very tough, and a Dremel is too small and weak for this work. I subsequently used an air cut-off tool which is far faster.
If you don't already have a suitable tool you can pick up a 4" angle grinder at Harbor Freight for about $20. The $20-on-sale Chicago Electric grinder has a great reputation, while the $10 Drill Master will barely last through this easy job.
The other half of the tool is the puller. I'm using a medium sized two jaw Craftsman puller that I already had. It's rated at 5 tons, which is more than powerful enough, but is only long enough for pulling. If you need to buy one a better choice would be a longer puller that could also press new stock bushings in place. The outside shell of the bushing is about 75mm tall, so a 6"+ reach is needed to grab the upper end of the subframe tube.
________________
Why this design?
This design started as an effort to build a better subframe bushing tool
for club use. The major problem with loaner subframe tools, both
commercial and home-made, is the screw drive. The screw quickly wears
out. Worse, the threads sometime fail, leaving a partially removed
bushing and a useless tool. The home-made tools fail faster, but at
least they have locally available replacement parts.
The wear can be reduced by keeping the threads greased, heating the
bushing with a hot air gun, and turning slowly. But this is actually a
negative for a club tool -- more blame ends up on the unlucky person
holding the tool when it fails.
I wanted to replace the failure-prone, rapidly wearing, high friction
screw with a common bottle jack. This would eliminate the wear on the
tool and take much less effort to operate. The special-purpose section
of the tool could be small and light for shipping and storage, while the
bottle jack would be easy to buy locally and useful elsewhere.
I played around with many different designs. They were all complicated
by the need to keep the force aligned with the center of the bushing.
That put the jack where a pulling rod would come through the center of
the bushing. Using two jacks with a central rod solves most of the problems,
but would be awkward to use.
Changing to a design that gripped the bushing lip avoids the need for a central
rod, but required that the compression support have open sides.
That necessitated using the notches cut in the bushing to push against
the subframe tube instead of indirectly against the arm.
Even with those problems solved, a major problem remained: any design
that used a bottle jack was tall. Even the most compact -- using a pair of
jacks with a central rod -- was tall enough to be a problem working on jack stands.
I re-thought the original problem. The screw designs failed because of
high loads on a small screw. The screw was limited in size because of
the bushing hole. I could use a better thread profile or a longer nut.
I could join a bigger screw with a tension rod. This lead to a few more
ideas, and few rounds of buying tools just for their Acme threads. But every
design seemed to require welding or bending thick plates -- which made the
tool hard to reproduce.
My current design is the result of all of those awkward and complicated prototypes. It's
simpler and easier to replicate than any of them. It starts with only two
inexpensive off-the-shelf tools, and only one of them is modified.
Last edited by djb2; 01-31-2010 at 05:53 PM. Reason: Wording changes for clarity.
Interesting. Do you have any pictures? Also, can this design be used on other BMW models?
I only have a picture of a test fitting right now. This picture was taken just after we figured out this approach was a winner. The tool in this picture isn't complete -- only the bottom inch of the legs have been cut to the correct profile. We hadn't even cut off the drive screw of the Pitman arm puller, we just inserted it the wrong way to plug the hole. But you can see the that the bushing has come out about 1/2", even with the core pushing against the screw.
This also fits the Z3, where it's even more of a win. The Z3 uses a fixed-in-place stud rather than a removable bolt. To use a pipe-and-plate tool the subframe has to be dropped to clear the stud, which requires removing many parts.
I'm uncertain what other models it might also work with.
Last edited by djb2; 01-30-2010 at 01:41 PM. Reason: Reworded for clarity. Added pictures.
Damn, that's quite a process!
It looks (and sounds) really good though.
More pictures please, as I want to do this on the vert sometime....possibly before the new engine goes in.
Politics is the art of looking for trouble, finding it everywhere, diagnosing it incorrectly and applying the wrong remedies.
-Groucho Marx
I added two views of older pictures, which will have to do for now.
I'm currently on the west coast, but should be home in about two weeks. We already have a car day planned for the 13th. I'll add better pictures then, and perhaps even do a video. I think that we can do a single take, pulling the bushing in under five minutes. (Remove bracket screws w/ 6mm hex driver in air ratchet, jack up car at diff, place jack stands under body AND subframe, release jack pressure, remove 22mm (7/8") nut with impact driver, place tool, use air ratchet to turn drive screw, done.)
Of course I'll do the video on a car where I know that the bushing isn't solidly corroded into place on the body. That can add a few hours to the job.
Last edited by djb2; 01-30-2010 at 02:38 PM.
I'd love to see the tool in action. I live pretty close. Mind if I stop by if I'm available that day? I have some experience with the regular subframe bushing tool and you're right that the threaded rod takes a lot of abuse in a club setting. I have another e30 and would be interested in trying your method in comparison.
Thanks for the ingenuity. Used the concept to make a device and it worked like a charm.
Last edited by JRW21; 02-01-2010 at 06:44 PM.
GENIOUS! thanks...you just made life easier for me and pretty much anyone else doing subframe bushings.
Molon Labe.
Thanks for adding more pictures.
Did you have that subframe sitting around, or did you drop it just for the photo?
For anyone else planning on building one, Harbor Freight has the Pitman arm puller on sale for $5.99 through tomorrow, Tuesday Feb 2 2010. If they follow their usual pricing pattern it won't be on sale for another month or two.
http://www.harborfreight.com/cpi/cta...temnumber=1752
You can use the coupon page below to get almost everything else you need. A 20% off coupon for the puller, a $7 air cutter or $17 angle grinder, a $10 digital caliper (I love them!), and get free flashlight to sweeten the trip.
http://www.harborfreightusa.com/usa/...e=magurl1.html
Last edited by djb2; 02-01-2010 at 08:40 PM.
I had it laying around, a spare. I will be replacing my subframe in the spring when the weather warms up. I saw this thread and decided to try it out! Thanks again!
excellent! doing all the bushings on the new race car, was going to order the akg tool but this looks far more effective!
'91 SpecE30 #523
'12 F30 328i Sport Line
'00 F-350 Dually
BMWCCA #360858 NASA # 128290
https://www.facebook.com/COTABBR
does that go for e36 also ?? Great idea anyway man thanks for R/D
Last edited by rpob5t; 02-01-2010 at 09:15 PM. Reason: I can't spell!
Greg - 2006 Chevy Silverado 2500HD - tow mule / 1987 325is - weekend track rat
'91 SpecE30 #523
'12 F30 328i Sport Line
'00 F-350 Dually
BMWCCA #360858 NASA # 128290
https://www.facebook.com/COTABBR
I believe that this design is both faster and easier to use than the AKG tool. You don't have to remove the central bolt, nor get on top of the bushing to place the drive plate and nut.
It should even be strong enough pull out a bushing stuck in the body, although the approach of threading in a 5/8" bolt and using a long punch from inside the car is a better way to break free a really stubborn bushing.
Because of a snowed-in driveway and garage we couldn't get any pictures of the subframe bushing tool in action today.
Hopefully we will be able to tomorrow or Monday.
I love harbor freight!!!
now what about a tool that allows re-installation without removing the subframe?
Molon Labe.
A long two jaw puller works best.
Or you can block the subframe away from the body with a chunk of wood and use a bottle jack to press the new bushing into place. You'll need to lube the rubber with water and liquid detergent. Pre-heating the subframe tube with a hot air gun significantly reduces the pressure needed.
For either method you'll need a plate to put the force on the bushing outer shell. Using the bottom bracket works, although it risks distorting it.
Here is a video showing a subframe bushing being removed.
It can be done in well under five minutes, including jacking the car up, if the tools are ready and the bushing isn't corroded into the body.
[ame=http://s878.photobucket.com/albums/ab344/LongevitySolutions/e30/?action=view¤t=dscf0318.flv][/ame]
[ame=http://s878.photobucket.com/albums/ab344/LongevitySolutions/e30/?action=view¤t=DSCF0320.flv][/ame]
Here are tools laid out before I started. It would have gone better if I had opened the air valve and set the turning direction.
And it would have taken much less pressure to remove if the subframe tube had been heated up instead of below freezing.
Last edited by djb2; 02-19-2010 at 07:34 PM.
Nicely done! Yeah, I would agree that the two jaw puller is the way to go. The three jaw puller I used didn't quite fit right and tried to slide off the bushing, but it did do the job.
This is pretty awesome. Search the entire internets for help on subframe bushings and either you have to spend $600 on a special tool, which still involves you taking a lot of stuff apart, or you have to remove the entire rear subframe.
And there comes this thread with an explaination of how to do it in less than 5 minutes.
Yo djb2. I need to pull off my subframe in the next couple of months. How much to make me one of your tools?
Could you explain in a little more detail on how to put the bushing back in? This is a very awesome tool you've made here.
Last edited by grimm862; 03-19-2010 at 09:04 PM.
The sleazy way is to block the subframe beam with a chunk of wood between the beam and body (which may put a little dent in the metal under the seat). Then just use a jack under the bushing to push it into the beam.
A better approach is to use a long two jaw puller. Hook the jaws over the top of the subframe and use the screw against a plate (or pipe cap, or similar) to push the bushing in.
BTW, this tool works on the Z3 as well. It saves a bunch of time if you install stock-style bushings, although you still have to loosen a bunch of parts to install urethane bushings.
Bookmarks