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M35A2 Rear Spring Bearing Block Wear / Repair

wolfmech

Member
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Location
Missouri
Hello,

The other day I noticed my rear axles "dog-track" or shift side to side during hard turns (see photos). At first I was worried my center spring trunion bearings were shot, but so far I don't think that's the source of the excess play. It looks like the spring perches have metal side-pads that have been worn down so badly that the axle is free to wander left and right between the springs.

1. I don't know what to call the part I'm referring to that appears worn. Is it a spring "bearing?" Perch? Block?
2. Once I know the name for it, are they replaceable or are they part of the upper spring perch casting? It almost looks like they are riveted in.
3. I thought about drilling out the holes or rivets and bolting in replacement blocks, which I can make if the old ones come out.
4. My last thought was to weld in additional material to take up the slop, but I'm curious if anyone here has attempted a similar repair and how you did it.


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Thanks!
-Wolf
 

HDN

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Finger Lakes Region, NY
The tandem axles pivot vertically on what's called a "spring seat". The spring seat bearings are under round caps on either end of the spring seat bracket, which holds the whole spring seat assembly together to the frame.

The spring seat bearings need to be adjusted every 6000 miles, I believe, as well as lubricated. The bearing setup is similar to the wheel bearings, and use the same lock nuts. If they aren't adjusted properly, there will be too much horizontal play on the spring seat and the lock nut threads on the bracket will strip. At that point the bracket needs to be removed from the truck for repair. So be sure to keep up on that maintenance item! However while I'm pretty sure many trucks have gone thousands of miles without that maintenance and have no problems, that doesn't mean they don't need the maintenance.

As for the tandem axles sliding back and forth, that's normal. It helps the truck turn better. Many commercial truck axles and even railroad rolling stock truck axles do the same thing. It's when they don't stay mostly aligned after driving in a straight line some distance where there might be a problem, perhaps with the torque rods (dog bones) or if one of the spring seats is sitting at a weird angle horizontally that might indicate a big problem!

Note that I don't write this from experience, but from researching this forum and TMs on the subject. I do need to grease my spring seat bearings, which is detailed in the truck's LO.

EDIT: I wanted to add: Spring seat facilitates vertical motion of the tandem axles, mostly allowing them to pivot around a center to get the back wheels over an obstacle. Torque rods facilitate horizontal motion of the tandem axles to help with driving turns.
 
Last edited:

gringeltaube

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At first I was worried my center spring trunion bearings were shot, but so far I don't think that's the source of the excess play.
Sorry to tell you... but yes, that is exactly the cause...!
Time to replace parts - or adjust properly, at least.



Those pads you see on the inside of the spring pockets are hardened kind of "inserts", plug welded to the casting to protect those from premature wear.
Yours still look OK to me; they appear barely worn at all. (I have seen much worse...) But even if they were completely missing, that's not the reason for that much side-to-side shifting of the axles.

See this thread.... (my post #15)

I would say that's all pretty normal. Here's mine after backing in on a hard turn.
"Normal" ...? Not really. Well, after 50 years maybe yes... sadly - but that's not as they came from factory!
Most of our trucks have been abused and neglected in their previous life, and prob. never seen any preventative maintenance in that specific area.
 

wolfmech

Member
8
27
13
Location
Missouri
Thanks for all the great replies.

Sorry to tell you... but yes, that is exactly the cause...!
Time to replace parts - or adjust properly, at least.

Those pads you see on the inside of the spring pockets are hardened kind of "inserts", plug welded to the casting to protect those from premature wear.
Sounds like I'll pull the spring trunnion bearing caps and inspect them. That should tell me more. Also good to know on the hardened inserts. Thanks for putting me back on the right track!
 

Barrman

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When I was rebuilding my Gasser M35 16 years ago I had just the cab bottom, a seat and a few other things assembled. I took it for a drive. Watching the rear axles move in every different direction caused me to worry as you did to start this thread. Do your inspection as suggested above. You might have an issue. But, the axles walk around a lot more than you realize on a mechanically perfect truck.
 

Jeepsinker

Well-known member
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Dry Creek, Louisiana
The dog bones have very little to do with side to side axle movement. Any excess movement you get comes from either your trunnion bearings/ bushings adjustment or wear, your spring pocket and insert wear ( as G mentioned) and wear on your leaf springs themselves where they contact the spring pocket inserts.
I rebuilt my trunnions with new bushings and races but I still have more movement than I want because my inserts and my springs themselves have some pretty decent wear. Not much I could do about it at the time.
 
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