Size of front driveshaft slip yoke grease plug? (1 Viewer)

[Freewheel]

The grease plug that fills the end of the front drive shaft is missing from my truck and I'd like to replace it.
This is the plug that protects the driveshaft slip joint from water and dirt and also lets you grease the slip joint using the grease zerk. Without the plug, grease pumped into the joint just fills the bottom of the driveshaft without pushing grease through the slip joint.
It's really difficult to tell what size it is as the edge is tapered and its hard to get a set of calipers behind the U joint.

It's bigger than 32.5 mm - that was the size of generic frost plug that I bought and tried after I thought I had measured it correctly...

Anyone know how big the plug is?

 

[Output Shaft]

It will probably be easier just removing the driveshaft, cleaning everything up, then install a breathable plug of some sort. Once it's out it will be easier to deal with.

 

[stoshzack]

Hopefully, someone can answer this as it is also asked here:

Wanted: - late FJ60 front drive/propeller shaft

@65swb45 @cruisermatt

 

[cruisermatt]

I have a slip-yoke with the plug blown out... It's a spare and just like everything else, just need to get around to it.

 

[stoshzack]

@cruisermatt - just added you incase an answer was given - so you were aware of this thread as I know you wanted to know. Received my front driveshaft - thank you!

 

[cruisermatt]

I have some spare time tomorrow morning, I'll press out the u-joint and take a measurement.

 

[Freewheel]

Hey Matt, that would be amazing.
Thx!

Output shaft- what do you mean by breathable? If it breathes, the grease zerk won't work... the grease will come out the breathable plug instead of being forced into the slip joint.

 

[cruisermatt]

I got ~1-7/16", or 36mm, which I think is a common size automotive freeze plug.

 

[Output Shaft]

I don't know if the caps fully seal the yoke from the factory.
If (for example) the cap was sealed on the end, a newly greased yoke would cause the grease to hydro (grease) lock the slip yoke, preventing it from moving in and out. Playing hell on the the front pinion and front transfer output shaft bearing.

I think that pressed cap is there to allow a pressure release to the DS to prevent drivetrain mayhem.

 

[cruisermatt]

I don't know if the caps fully seal the yoke from the factory.
If (for example) the cap was sealed on the end, a newly greased yoke would cause the grease to hydro (grease) lock the slip yoke, preventing it from moving in and out. Playing hell on the the front pinion and front transfer output shaft bearing.

I think that pressed cap is there to allow a pressure release to the DS to prevent drivetrain mayhem.

Right, and that's why I DIDN'T just weld the hole up, but I did think about it for a few seconds.

Dorman 555-025 (1-3/8") fits decent, however a plug advertised as 1-7/16" or 36MM is probably the way to go, this is just what I found locally within five minutes down the road. It's a spare yoke so I don't mind.

 

[Freewheel]

Hey Matt thanks for the measurements. That's super helpful! Saves me from buying 8 different sizes to try to jam around the u joint and hammer in with my thinnest drift.

I think it's true that the end is frost plugged so that too much grease pressure will blow the cap instead of putting pressure on the diff or transfer case. This would be the case if the joint was over greased and the truck hit a speed bump or offroad obstacle at speed, sharply compressing the driveshaft.

But I think it should be fully sealed so that some pressure will force grease around the splines of the slip joint. When I put grease in my rear slip joint (which still has the plug) I fill it until the pressure of the grease visibly moves the slip joint a little bit. Over the next few days of driving, the up and down motion of the truck drives the grease through the joint and it gets forced out to the outer sliding surface through the felt seals. If the plug breathed, the grease won't move, and the only way to successfully grease the joint during regular maintenance would be disassembly and hand greasing the splines.

 

[liveoak]

I know this is an old thread but it's the only one that provided useful information on the subject as I just noticed my driveshaft yoke cap was missing. I didn't find a 36mm plug locally but I found a 35mm at autozone. dorman part# 555-093.1 for $3. I first tried installing it like the picture above but it seemed to block the grease hole so I flipped it around and used a prybar and it seemed to pop in nicely with a little effort pressing on both sides. I didn't even take the driveshaft off. If it comes loose and falls off, I'll buy another and maybe add a little epoxy or a couple tack welds but it seemed like it pressed in pretty good

 

[cruisermatt]

Wait, so you mean you needed to find some information, searched, and found it?! Can you teach everyone else this magic?

 

[Freewheel]

I like it when threads come back- means they were actually useful!

 

[SBAdam]

Continuing the resurrected thread... I have this same issue on my '85 FJ60. Curious if anyone can confirm the factory condition (plug or no plug)? Both parts of my slip joint are rusted pretty bad, pretty sure there hasn't been a plug for at least 20 years, and probably should have been.

 

[TexFJ]

Just found the plug missing as well on my front. It has to have a cap as the grease would just come out the front. As soon as yo fill it with grease, the hole gets plugged up and the hole i'm sure isn't big enough to let the grease out in time, it just escapes between teh cover and the yoke. I'm guessing the holei is there so you can pull the yoke out? Otherwise this is where the hydro lock would take place. this is just my theory.

OK, so does anyone know how big the weep hole is in the OEM cap?

 

[OSS]

OK, so does anyone know how big the weep hole is in the OEM cap?

The original grease cap didn’t have a hole in it. It had a flat spot on the edge that allowed grease to ooze and air to burp. 1/16” gap on the edge is plenty.
Could easily be done with a metal file.
But a tiny drill hole in the cap should work fine instead. Maybe 1/16” too.

 

[TexFJ]

hmmmm.... I'll clean up my back driveshaft to help me understand what a flat spot is. Assuming it's the same on front and back.

I bet you that more people have a missing cap in the front DS than is known.

 

[OSS]

The front yoke on the rear driveshaft doesn’t have a pressure release cap.
A flat spot on the edge of the cap is as if you took a coin and held it against a grinder disc for a moment. Doing that creates a flat spot in the circumference which creates a gap.