The Stovebolt Site Forums The Shop Area Driveline Pilot Bushing & Throwout Bearing - Why Do They Need Replacing?

Kind of a 2 part question:

A: What is the role of the pilot bushing? What does it do?

B: Why the PB and TOB need replacing when switching transmission?

the pilot bushing keeps the trans input shaft properly lined up, otherwise it'd be flopping around, and it provides a "wear surface" that acts like a bearing, they can wear out and get loose - the primary reason to replace the 2 [and the clutch pak as well] is so you don't have to pull the trans again when any of them cause problems a short while down the line ... and throw out bearings can have a shorter life than the clutch disk depending on how the operator treats it ... if all have been recently renewed, then switching transmissions doesn't necessarily require the rest, although it's prudent

Bill

But the input shaft doesn't actually go into the pilot bushing, right? Does it push against it? I am assuming the PB being of brass allows the input shaft to smoothly rotate while in contact with it?

Yes the input shaft slides into the pilot shaft bushing. There is a stepped down area at the very beginning that fits in there. It supports that input shaft and takes a lot of the lateral load off the main bearing at the front of the transmission. Early pilot shaft bushings were made from "Oil-lite Bronze" A porous casting with lots of holes for oil to hide in. That bushing is made to be sacrificed, it wears much faster than the expensive main shaft. Just for an easy read:

http://en.wikipedia.org/wiki/Oilite

Glad I asked! So I need a PB to fit the T5 input shaft.

Yep

The pilot bushing should be a National # PB656HD

One way to remove the old pilot bushing is to pack it with grease and then use a dowel rod of the same diameter as the transmission input shaft and a hammer to force it out hydraulically. When it comes out, wipe off the grease (wheel bearing grease is good to use) and drive in the new one using a piece of wood of the same overall diameter and the hammer.
Jon

I've read that silicone caulk can be used and is less messy and less likely to splatter.

I agree that it makes sense to install a new pilot bushing and throw out bearing when the transmission is out for service. The clutch pack would depend on age and performance. Resurfacing the flywheel should be considered.

Wet tissue paper will work instead of grease. Or a tap for making threads. Get the right size tap and screw it into the bushing. When it hits the end of the crank it will start pushing the pilot bushing out.

Its not a big mess using the grease, find a dowel that fits tight into the bushing you are removing, pack it with grease, get a rag and wrap it around your dowel and hold it close the the flywheel. Take a good sized hammer and give the dowel a good quick wrap, the bushing usually comes out and the grease is contained by the rag.

The last time I removed one with a friend (from his truck) we used a piece of bread. Easy and easy cleanup.

A glass of wine, a little cheese and you got lunch covered also.

The tap is the best next to a set of dedicated bushing jaws
on a slide hammer.
DG