View Full Version : MB Custom Sprinter in PDX can fix caster issue due to front crossmember

05-04-2018, 11:48 PM
My caster has been off for a while. After changing the steering rack, control arms, 4 struts, and front sway bars, it still doesn't drive straight and true, but it's a lot better. I have squinted and squinted at this tool and just don't see a way to accurately reproduce it to get it to measure accurately. Also don't understand why you can't just knock the front crossmember back onto the locating pins and check caster with a digital alignment machine, rather than devising this strange contraption (Pic below) from this thread: https://sprinter-source.com/forum/showthread.php?t=18665

Along with this repair, the last part to replace that should make it drive like it's new, is the steering column U joint that I got on ebay: Reference OE number: 9014601909

And then I suppose I should check the locating pins on the rear leaf springs due to loose U-joints in the past, then everything will be perfect. There's about 1.5" of play in the steering wheel and it requires minor corrections constantly, so I'm really looking forward to getting this fixed. Anyhow I was very happy to hear that https://www.custommbsprinter.com/ is familiar with this issue and can take care of it. For $75 an hour (Amazing rate) I'd rather have them do it correctly and try to learn what I can. I thought I was going to have to drive to another state or try to ghetto-rig this tool to get this fixed.:cheers:

05-05-2018, 12:19 AM
Eric made a similar tool using the hole in the frame in front of the subframe. The tool measured to the front A arm bolt head on the subframe. Loosening the frame bolts, and a bit of sledgehammer love does the trick. Most important is that the caster is equal left/right. You don't even need to measure the actual caster to get improvement by making each side equal.

A digital angle finder on the strut body can also be used to roughly balance caster left/right.

05-05-2018, 02:31 AM
Ah so the measurement is from these two spots? One could do that with a digital caliper with an elongated jaw on one side (Duct tape + straight rod?), no?

Also I don't see the locating pin. If it's the upper left green circle, I don't see a measurement spec for the distance. Maybe I'm not looking hard enough.:thinking:

05-05-2018, 03:24 AM
The "frame" rail has a ~1" hole in front of the subframe. They have a taper/flare "entrance". From what I have been told, these are used by the factory jigs which lift the subframe and engine into place. They should be exactly the same on each van with regards to the subframe locating pins.

The tool/jig you posted a photo of uses a ball which fits into this hole, and also has a turnbuckle which pulls against the recovery point. That turnbuckle could exert enough force to deform the frame around the locating pins if desired. Ideally you would just figure out which side was bent, and pull that forward, but the effect is the same. I was confused at first, but the measuring portion of this tool is essentially the same function as the one I saw

The locating pin for the subframe is not visible, as it is mid-way on the length of the frame/subframe contact surface.

05-05-2018, 07:06 AM
Oops I forgot to attach this pic:
Am I understanding it correctly now?

05-05-2018, 07:20 AM
Yep. I would measure parallel to the frame rail, but a direct distance would work, but given the size of the hole, it would be difficult to accurately measure without the jig.

That setup seems to pull on the A arm. So it may be able to correct bent mounts on the subframe.

Another often neglected cause of vague steering is worn wheel bearings.

Eric Experience
05-05-2018, 08:06 AM
That tool in the picture is mine. It is used to accurately measure the distance from the jig hole to the wishbone. I would never use a sledge hammer to move the cross member. The turnbuckle moves the cross member in a controlled way so you can "feel the dowel tough the front of the hole" when turning the turnbuckle gets a little tighter. People who use big hammers have no idea what they are doing. Eric.

05-05-2018, 10:02 PM
Ok, thank you very much Midwestdrifter.

Eric, I admire the tool you made, just have had a hard time understanding it all. I appreciate your help. Now I just don't see/understand where the dowel/locating pin for the front cross member is. "mid-way on the length of the frame/subframe contact surface", mwd said. So the front subframe connects to the frame, and in the middle of this connection is a bump(/pin?) that you can feel it sink into when you pull with the turnbuckle? Seems kind of hard to know which side is messed up, if you can't see it. Or is there a measurement spec?

05-05-2018, 10:36 PM
Here is a photo from the vancompass lift instructions (see attached).


There isn't a measurement spec anywhere. However, if one side has a caster difference from factory, you can generally use that to determine which side has drifted.

Eric Experience
05-06-2018, 02:23 AM
That's the point of measuring with the tool to find out which side is back. The dowel is still in the hole it has just bruised the back of the hole. we are talking about 1 or 2 MM movement so you need to be very good at fine measurement. Eric

05-06-2018, 03:40 AM
Damage to the A arm mounting brackets, or worn out A arm bushings could also cause a caster imbalance. All said and done, a small difference in caster angle generally does not cause major handling issues. I believe the factory service manual lists the allowable deviation between the sides.

I have not done the geometry, but 2-4mm of left/right offset on the subframe would probably be enough to put the wheels out of the factory castor limit. As this results in a net rotation of the subframe, which is multiplied at the wheels which are farther from the centerline.