Tightening bearing cap bolts decreases backlash? (1 Viewer)

[theamigo]

Just when you think you’re done...

I had it all set up right then torqued the bearing cap bolts down and it made the backlash virtually disappear... makes sense I guess given that they’re essentially pushing the bearing cups and assembly down more.

The FSM doesn’t address how to correct for this neat occurrence.

I asked and Zuk helpfully responded(thanks) to a question and says that he torques the bolts down before adjusting for backlash, so he hasn’t seen this. I just can’t imagine the force necessary to move the adjusting nuts with the cups fully torqued down.

Any ideas?

 

[Pin_Head]

The adjusters turn fine after the caps are torqued down. If they don’t, the adjusters may be cross threaded.

 

[theamigo]

The adjusters turn fine after the caps are torqued down. If they don’t, the adjusters may be cross threaded.

Thanks for the response.

The cup bases are fully and flatly joined, and they seem perfectly aligned. I can hand turn the adjusters until they get well loaded.

I’ve tried this several times now. When the bearings are fully preloaded and the cap bolts are torqued they are very, very firm. I thought that was supposed to happen.

 

[coonassjohn]

Sounds like the pinion depth is off.

 

[theamigo]

Sounds like the pinion depth is off.

Hmmm. The pattern looks great, I thought. I’ll have to consider that.

 

[coonassjohn]

Hmmm. The pattern looks great, I thought. I’ll have to consider that.

Did you check the pattern with everything torqued down? May sound stupid, but I've seen it not done.

 

[theamigo]

Did you check the pattern with everything torqued down? May sound stupid, but I've seen it not done.

The backlash essentially goes to zero(there’s no more room) when I torque them down. No real way to pattern. I wonder if that’s the cause (the depth shim size needs to change) or if the backlash disappearance issue is a symptom of something else.

My main question is, I guess: should torquing down those bolts to spec change it that much?

So many fun variables.

It’s not listed as a variable in our FSM, but I’ve found other makes/models that do seem to use bearing cap bolt torque as a variable to check and redo if backlash is affected.

 

[RustyNailJustin]

Yes it totally affects the backlash! Think about the bearing caps closing that small gap if they are loose(which is miles in gear talk). I appreciate the FSMs trust me but they also are taking to people that are also trained.
I have set up hundreds of gears and I always just snug up and assume a few thousands movement. Then check when the caps are tight. Very straight forward.

 

[theamigo]

Yes it totally affects the backlash! Think about the bearing caps closing that small gap if they are loose(which is miles in gear talk). I appreciate the FSMs trust me but they also are taking to people that are also trained.
I have set up hundreds of gears and I always just snug up and assume a few thousands movement. Then check when the caps are tight. Very straight forward.

So, go with a slightly higher backlash that get’s lessened by torquing the cap bolts? I know something is getting changed by the torque; just trying to settle on which way to go when I start again in the morning. Backlash or pinion depth. Given that backlash is what’s disappearing, backlash seems the best place to restart.

 

[RustyNailJustin]

Yes, it's kinda like knowing torque by feel. I try to get closer to. 012 snug then when torque you are around .008.

 

[coonassjohn]

I would recheck everything.

 

[theamigo]

I would recheck everything.

Definitely. I have and will again. Just trying to understand what I’m seeing here.

 

[RustyNailJustin]

Hmmm. The pattern looks great, I thought. I’ll have to consider that.

Don't check pattern until you have proper backlash.

 

[shawnfj40]

I am just curious how you know that you have a good pattern and you haven't got the backlash set yet?

 

[theamigo]

I am just curious how you know that you have a good pattern and you haven't got the backlash set yet?

I understand that in the FSM pattern checking comes after the final torque of the bolts. I agree that my pattern, in the end, is no longer correct since my backlash is wrong after torquing the bolts. That said, I did a cursory pattern check between setting the starting backlash of .008 and setting the preload just to see if I was in the ballpark because I did have to make several initial depth shim changes.

 

[coonassjohn]

Just curious, how did you set your pinion depth? Do you have any special tools required to measure the depth? If the pinion is too high it will cause problems like this.

 

[coonassjohn]

I understand that in the FSM pattern checking comes after the final torque of the bolts. I agree that my pattern, in the end, is no longer correct since my backlash is wrong after torquing the bolts. That said, I did a cursory pattern check between setting the starting backlash of .008 and setting the preload just to see if I was in the ballpark because I did have to make several initial depth shim changes.

This post makes me think you put the horse before the cart, so to speak. The first thing done is to set the CORRECT pinion depth using a dial indicator and pinion depth gauge. Then you go from there with the rest. If you try to do it any other way you will be chasing your tail forever, or at least until your gears wear out from improper set-up.

 

[theamigo]

Just curious, how did you set your pinion depth? Do you have any special tools required to measure the depth? If the pinion is too high it will cause problems like this.

No special tools, just a continual change and recheck of everything as per the FSM.

To summarize, we seem to have two schools of thought:

1. The loss of backlash is due to the pinion being too high. Starting over with a thinner shim would be the logical step according to the FSM.
2. The loss of a little backlash is normal when torquing the bolts, therefore you should not set it to the exact specification listed in the manual before you torque the bolts. Instead, you should expect a loss of some backlash when you torque them down, so you should set it a bit loose prior to torquing.

Both may technically work if all you're after is all of the ranges within spec. If you go with 2 AND your ending backlash and pattern are good enough then you're set. It's also quicker. If you go with 1 you're changing the pinion depth with a new shim and could end up with a slightly different pattern that may also be within spec.

I think I'm going to restart with a smaller pinion depth shim. This path is the stated recommendation on pages 7-23(flow chart) and 7-28.



-Nathan

 

[theamigo]

This post makes me think you put the horse before the cart, so to speak. The first thing done is to set the CORRECT pinion depth using a dial indicator and pinion depth gauge. Then you go from there with the rest. If you try to do it any other way you will be chasing your tail forever, or at least until your gears wear out from improper set-up.

The FSM doesn't specify the use of a depth gauge. It walks you through the steps of trying and retrying shims, setting and checking preload, and then finally checking the pattern.

I should also add that this is not my first attempt on this differential. I've followed the FSM to the letter including the final pattern check on the previous run throughs. On prior attempts, after torquing the bolts, the pattern wasn't quite where I thought it should be so I started over. On this last attempt I've experienced the issue I wrote about in the first post above - I lost my backlash. This is also why I think the depth shim is the fix.

 

[coonassjohn]

Good luck because if you are not going to build it as it should be then you are just asking for trouble. The FSM doesn't specify a gauge but the rest of the world uses them. Not trying to sound mean but I think your hit and miss approach is not the way to go. As the man said "FSM's are made for technicians who know what they are doing". Sorry you are going to learn a lesson the hard way.