Rear Axle Centering

[JGHeller]

First let me start by saying what a great site this is.  I have learned so much information about working on my car by reading the archives of this forum.

I just replaced all of the rubber bushings and mounts in the rear axle and the shop manual says the rear axle centering needs to be 36mm +/- 2mm from the centerline of the car.  It calls for a special tool.  I have yet to find a shop that knows how to check this.  After searching this forum i found a picture of a homemade tool to check the centering of the rear axle.  I understand how the tool works, but I am not able to read the dimensions off of the picture to make the tool.  Can anybody here help me with this?


Thanks,
John

[jeffc280sl]

This should help.

Download Attachment: 113tool.jpg
17.64 KB

Jeff C.
1970 280SL 4-speed

[jeffc280sl]

John,

When I replaced the entire axle I reused the cross strut because the rubber was in good shape.  In fact I did not remove it from the original aligned position on the frame. I checked the axle by using the centering tool the alignment was dead on.  My point is that you should be in good shape if you did not remove the cross strut and replace the big rubber bushings.

Jeff C.
1970 280SL 4-speed

[JGHeller]

Thanks for the updated picture

I did replace all of the rubber bushings on the cross strut.  I did not change the adjustment on the strut.  I still would like to check the centering since this setting will affect the alignment of the front when checked.

John

[jeffc280sl]

John,

I understand.  I used the centering tool on the old axle as a check and on the new axle once installed.  It's a good tool and we can thank ADalton for it.

Jeff C.
1970 280SL 4-speed

[merrill]

so, I reviewed the photo to make the centering tool attached below and the one on the home page.

I am confused, both have different dimensions in each photo set.

for example the photo below has
424 and 453 to center line?
then the next slide has
460 and 417 for the centering tool?

just trying to verify before I make the tool

thanks
matt

Matt
Austin Tx
66 230 sl - "white"
78 300 D - Blue
98 C230

[waqas]

The centre of the chassis is located 424mm from the left trailing arm mount, and 453mm from the right one (424+453=877mm). However, the tool should be used to align the rear axle carrier (which is not at the chassis centre line). Hence the tool is designed to align a point 417mm from the right trailing arm mount, and 460mm from the left one (417+460=877mm).

When I replaced the lateral bushings on the rear axle (along with everything else vaguely rubberish!), I used Arthur Dalton's wonderful diagrams to take the measurements. I didn't make the tool (probably should), but used plumb lines to project onto the garage floor.

WAQAS in Austin, Texas

[waqas]

Forgot to make this absolutely clear:

Since the chassis centre line lies 453mm from the right trailing mount, and the differential carrier centre is positioned 417mm (+/- 2mm) from the same point, the carrier will end up exactly 453-417=36mm (+/- 2mm) from the chassis centre line!

WAQAS in Austin, Texas

[mal]

What happens if the Rear axel is NOT centered properly??
Thanks

Malek Mrowa - Beirut, Lebanon.
280SL 71-Light Blue/Blue
280SL 68- White-Gray/Black
250SE 66 Convertible-Silver/Red
190SL 61-Ivory/Red
220S  58 Cabriolet-Two Tone: Burgandy&Creme/Tan

[paults1]

I made the tool last year & it worked perfect. Some friends of mine saw it & had no idea what it was & asked me if was going to enter it in an art show.

[Vince Canepa]

If the rear axle is not centered correctly, or if the bushings are worn and not keeping the axle centered, the handling will feel very imprecise (scary even), especially at high speed.  When the chassis on these cars is dialed in correctly you should be able to remove your hands from the steering wheel at 100mph with confidence.

I used Arthur Dalton's information to lay out the dimensions on the garage floor.  I then checked the centering like wagas did.  It is an effective alternative to making the tool, especially if you don't think you will ever use the tool again.

Vince Canepa
1967 250SL
113.043-10-001543
568H Signal Red
116 Caviar MB-Tex

[merrill]

so, made the centering tool this weekend.  It worked out ok.

the only big difference is the drivers side of the centering tool was 453 - 454 in length not 460 mm.
I maintained the 417 mm on the passenger side length

After I cleaned the gunk off the diff pivot bolt I noticed there was a dot or small drilled out pit in the center.

when using the tool the pointer was to the right of the dot but close to the center.  probably +/- 2 mm from the center of the dot.

I have a friend that has a machine shop, I am going to have him verify the dimensions of the tool and double check the axle again.

thanks
matt

Matt
Austin Tx
66 230 sl - "white"
78 300 D - Blue
98 C230