Mechanical drive radiator fan free play

richard5933 · September 13, 2020, 07:56:33 AM

I happened to bump into the fan on our GM 4108 today while inspecting for leaks and noticed that there is a slight amount of rotational free play in the fan - maybe 1/16" or so.

Guys with the earlier GM buses have to be careful about their hubs breaking down, so my initial reaction was to worry. (Of course, that's my default setting anyway.) Then I looked at the manual and parts book to see how the thing is put together. Didn't help much, but for sure the hub itself is not the problem.

Looks like the mechanical drive runs at 1.0 to 1.59, which tells me that there is some type of gear reduction going on inside the drive between the crankshaft and fan. This is not a hydraulic drive - it's mechanical.

There is no side-to-side movement on the fan at all, so I do not think it's a bearing issue.

So, my question is how normal is this type of rotation free play in a mechanical drive setup like this? Just gear lash or is this something to actually be concerned about, like a loose mounting plate inside the drive?

Anyone happen to have photos of a mechanical drive like this opened up?

Utahclaimjumper · September 13, 2020, 08:26:24 AM

Don't look for a problem,,,,,,it will find you soon enough.!>>>Dan

luvrbus · September 13, 2020, 10:54:27 AM

They have backlash in the gears .about the only thing that goes bad is the rubber spacer and when it starts to fail you will know it,does your manual show a direct drive or a clutch pack drive ?

richard5933 · September 13, 2020, 11:28:41 AM

Definitely a mechanical direct drive with a 1:1.59 ratio on the gears.

Manual shows a PTO option, which we don't have. A/C runs from a belt off the main pulley.

luvrbus · September 13, 2020, 11:40:47 AM

[quote autho\,the r=richard5933 link=topic=35011.msg402827#msg402827 date=1600021721]
Definitely a mechanical direct drive with a 1:1.59 ratio on the gears.

Manual shows a PTO option, which we don't have. A/C runs from a belt off the main pulley.
[/quote]

That drive wouldn't be a problem the clutch pack drives can be a bitch

HoBoJo Busman · September 13, 2020, 12:51:26 PM

Richard,
I have the exact same fan hub/drive, as you do in my 1970 4108 Buffalo with the 318 Detroit.
Last September, we pulled the housing off and ran the seal out to install a new one
(as it was leaking) and I got to see the inside...unfortunately, I have not been able to find the pictures I had of that, as we put it all back together.
I have the same "rubber block" as I will call it and THAT is the point of concern I was told to keep an eye on for wear, as the rubber dries out and cracks, it CAN let go and the fan will eat that $3-4000 radiator for lunch !
Now you have me wondering about the slop (free play) in the gearing...I do not think we saw any at the time we had this all back together.
If you want to expand on this conversation, I would rather do by phone if you can find a way to PM me...I am afraid I do not have the computer intelligence to figure out how to suggest you do that though. John

richard5933 · September 13, 2020, 02:50:16 PM

Quote from: HoBoJo Busman on September 13, 2020, 12:51:26 PM
Richard,
I have the exact same fan hub/drive, as you do in my 1970 4108 Buffalo with the 318 Detroit.
Last September, we pulled the housing off and ran the seal out to install a new one
(as it was leaking) and I got to see the inside...unfortunately, I have not been able to find the pictures I had of that, as we put it all back together.
I have the same "rubber block" as I will call it and THAT is the point of concern I was told to keep an eye on for wear, as the rubber dries out and cracks, it CAN let go and the fan will eat that $3-4000 radiator for lunch !
Now you have me wondering about the slop (free play) in the gearing...I do not think we saw any at the time we had this all back together.
If you want to expand on this conversation, I would rather do by phone if you can find a way to PM me...I am afraid I do not have the computer intelligence to figure out how to suggest you do that though. John

I sent a PM to you with my phone number. You should be able to get the PM through the link above which reads "My Messages"

Look forward to talking with you to learn more about this mysterious rubber block.

chessie4905 · September 13, 2020, 03:57:49 PM

My spare coach has that same play in the fan. Not a concern to me.

luvrbus · September 13, 2020, 04:44:09 PM

Quote from: chessie4905 on September 13, 2020, 03:57:49 PM
My spare coach has that same play in the fan. Not a concern to me.

They are a square cut spline and only wear in 1 direction, very little wear will translate into back lash on the fan nothing to worry about,just keep a eye on the rubber isolator aka block or spacer those are not to be had even from Luke

richard5933 · September 13, 2020, 05:36:54 PM

Quote from: luvrbus on September 13, 2020, 04:44:09 PM

They are a square cut spline and only wear in 1 direction, very little wear will translate into back lash on the fan nothing to worry about,just keep a eye on the rubber isolator aka block or spacer those are not to be had even from Luke

Good to hear that the backlash is normal.

I'm confused about the rubber isolator? Where is this rubber isolator/block/spacer thing to be found?

I'm not seeing it in the parts book either, so perplexed.

The only place I can see something like this would be inside the hub of the fan itself where the fan connects to the next piece which connects to the hub. There is zero free play between the fan and the pulley, either rotationally or side-to-side, so if the rubber thing is in the fan's internal hub I'm probably go.

HoBoJo Busman · September 13, 2020, 08:12:21 PM

Richard,
Yes, Inside the hub...if you use a mirror, you can see somewhat.
If there is no wiggle when you give the blade a good shaking... you should be alright, for NOW. When it lets go,(I was told, can be any time)... even if it feels somewhat tight.
This is subjective I suppose. BTW, I do not see any PM to contact you.
What the heck am I to look at to find it ?
Seriously, I struggle with this computer business. I am of a different place I think.
John

richard5933 · September 14, 2020, 05:12:07 AM

The fan seems firmly mounted to the hub, so if that's the point of concern I suppose I'm good for now.

Funny thing is this is the first I've heard about a problem with the rubber on a fan being a problem on anything other than the earlier models like the 3751. Never heard of anyone with a Buffalo having their fan go ballistic (literally & figuratively.)

Would love to see photos of the end of the fan showing the rubber bit if anyone has one. (I'm a visual learner - what can I say?)

chessie4905 · September 14, 2020, 11:58:03 AM

Ahhh, go ahead and rip it apart. We're all curious.

chessie4905 · September 14, 2020, 04:25:06 PM

I pulled out the manuals. There are no rubber components there. There is a metal plate with damper springs though. If fan damper fails, it still won't come apart. He may be thinking about 4104 or 4106.

richard5933 · September 14, 2020, 04:50:17 PM

Checked with Luke today. He confirmed that the hub on these won't fail like the ones on the 3751, and that the free play is normal.