what is an acceptable play for a W108 4.5 rear axle? - PeachParts Mercedes-Benz Forum

GGR · #1 03-09-2009, 08:53 PM

Hi all,

tomorrow, I'm going to see a W108 4.5 rear axle in view of replacing my 3.92 rear ratio axle with it. this link poster on an earlier thread shows clearly the play that these axle can have when worn out: http://video.google.com/videoplay?do...74313884505435

The axle I'm seeing tomorrow is still on the car and I am planning to do the same test. What is an acceptable play? Half an inch at the perimeter of the wheel? One inch? What else should I look at?

Thanks in advance

cth350 · #2 03-09-2009, 10:07 PM

Can't see the video (google suggests that it's too new). But in general all the rubber bits that hold the rear together should be replaced after a while. Certainly 40 years is about time.

-CTH

GGR · #3 03-09-2009, 10:40 PM

I repost the link, hope it works:

http://video.google.com/videoplay?docid=6365474313884505435

Tomguy · #4 03-09-2009, 11:32 PM

Honestly you'd probably be hard-pressed to find one with no play at all. I think the play he is showing is acceptable. I dont know how much my 4.5 has but I fear it is far more than that and it still runs fine

The 6-cyl doesnt put out enough torque to keep tearing it down like that honestly, it'd last another 15 years EASY.

GGR · #5 03-10-2009, 12:27 AM

Thanks!

Let's see how it goes tomorrow.

Arthur Dalton · #6 03-10-2009, 08:20 PM

The play in that video is way too much and has a worn spyder pin casing..but it is typical of a 3:27 b/c most 4.5 rears have that problem..[ which was the point of the warning]

A test you may want to make is to jack your 3:92 and try the l/r wheel...that will give you an appropriate measure and feel for it as it is most likely that your 3:92 does not have the pin casing wear b/c they did not have the higher torque to contend with. Then try the 3:27 in the same manner.
Just make sure you watch the pinion flange for no movement when doing the rotation of the wheel/hub.
You can drive with a worn casing, but everytime you gas it or let off , you will feel the clunk in the rear b/c of the torque moving the pin foward in the worn case with gas , and the clunk when letting off b/c of the kenetic force of the moving car w/no gas...[ down-shift]
I had one in a stick years ago and it was not bad until you used downshift driving when coming into corners or a stop, and I finally tore it down cuz it drove me nuts... those little thing's bug my driving experience.

ja17 · #7 03-10-2009, 08:59 PM

Hello Arthur,

There is a spec in a Technical Data Manual which lists the backlash at 0.08 to 0.14mm. I will need to re-visit this spec to see where it is measured. Normally I get concerned when the backlash at the rear wheel rim is greater than 1/8". Stay away from anything over 3/16" unless you plan on doing repairs.

I have been successful in welding the worn pin holes and pins as one solid unit. Pin removal is out of the question in any case since repairing damaged spider gears does not make sense economically. Solid welded pin and casting does not wear. The best choice is to find a unit not worn, but this is something to think about.

Arthur Dalton · #8 03-10-2009, 09:56 PM

Hello JA..

Yes, I agree... and not only does the excess back lash cause further wear of the casing, but it also puts undue impact forces on the right side cross universal and sliding joint at every trans engagement.... both Foward and Reverse..........something no one wants to be getting into.

I like the way you jack up the chassis on that one.......

wbain5280 · #9 03-11-2009, 12:29 AM

I like the method of jacking up the car too but the load on the bearings is quite large.

Is it possible to insert a sleave of some kind, brass or stainless steel, to reduce the backlash?

Arthur Dalton · #10 03-11-2009, 10:59 AM

>Is it possible to insert a sleave of some kind, brass or stainless steel, to reduce the backlash? >>

Way too much machining. It's an easy weld job.

When I was a kid, I remember the Stock Car drvers used to weld the spyder assembly to get a soilid straight axle.....now, that's Positraction..!!

GGR · #11 03-11-2009, 11:05 AM

Would an LSD "hide" that play when doing the test shown on the video? How do we know if an axle is equipped with the LSD option?

Arthur Dalton · #12 03-11-2009, 11:10 AM

It should still show up..LS will have a tag for the LS lube warning. If it is a LSD and not big bucks , buy it anyway.

Tomguy · #13 03-11-2009, 11:15 AM

Quote:

Originally Posted by ja17

I have been successful in welding the worn pin holes and pins as one solid unit. Pin removal is out of the question in any case since repairing damaged spider gears does not make sense economically. Solid welded pin and casting does not wear. The best choice is to find a unit not worn, but this is something to think about.

That sounds like a good idea. If it's worn (and unless you want to pay shipping, with more and more 4.5's being crushed at least around me and the rarity of the 3.27), get it, and if the play is too much and you don't like the clunking, have it welded.

GGR · #14 03-11-2009, 11:16 AM

Thanks. Is the tag at the back bottom? If the tag has gone, is there any other way to know? Foe example, both rear wheels up, if I turn one should the other one turn in the same dircection?

Tomguy · #15 03-11-2009, 06:01 PM

Aside from taking the diff apart the "Test" for a LSD rear is to move 1 wheel with the transmission in park. The other wheel will rotate opposite on a normal diff and in the same direction if it's a limited slip.

The PROBLEM with the test though is that after 40 years or so, the clutch for the LSD is usually worn and needs adjustment or replacement, so it's not a good way to really tell. If there was a tag on one of the bolts though you should be able to see the "leftover" of it. Even if you need to loosen them all to make sure there's no leftover tag.