MTFCA Forum

I missed the $300 high speed gear set in the classifieds the other day, but it got me to thinking. How big of a job, time wise and special tool wise it it to change out the gear set?

After owning a TT firetruck for a while, and seeing that humungous rear axle, all I can say is, it will be a BIG job. Super heavy.
The rest of your question, can be answered by those actually "in the know"!! Good luck in your endeavor. Too bad you missed the gear, I hear they're hard to find, and expensive when you do find them.

I did it once, yes everything is much heavier but with the right tools and jacks you should be able to do it.

The biggest challenge for me was to get the truck up high enough to separate the axle from the spring perches. Safely supporting the truck frame so that you won't get crushed in the process.

Get some help to move things around, easier than doing it by yourself.

Have some extra floor jacks , you will need them.

The TT rear axle actually rebuilds quicker and easier than the car axles once you know what you’re doing. There’s no setup work for mesh or lash. The only inconvenience is bigger heavier parts. You need a TT wheel puller & sleeve puller.

Used gears are fairly subjective regarding wear. An excellent used gear may have almost zero lash, while a gear that is so thin it might be dangerous will seem to work just fine... Until it fails...

There's no doubt about the fact that it's a lot of work. The unit is heavy and it takes some wrestling with. However, it's not really that complicated. The only special tool you'd need (as far as I can remember) is a bearing sleeve puller for the outer axle bearing sleeves at the hubs, and that's not actually necessary. You can disassemble the unit, replace the gears, and reassemble it without removing the bearing sleeves. The rest can be taken apart with a socket set, combination wrenches and something to remove then replace cotter pins.

It you take it apart be sure to get all new seals. There are 6, two outer felts and two inner seals (new neoprene seals are available for this one) for the outer roller bearing and 2 felts for the inner ball bearing. Also check all four bearings (2 roller and 2 ball), 2 bearing sleeves and both axles at the contact surface for excess wear.

As I recall, the hardest part of the whole job is putting the new inner felt in its cup, installing that in the housing, then sliding the differential/axle assembly through the felt. It is a force fit and difficult to get into place. Once you do get it in place you then must do the other side.

If you're at all mechanical it's not a job that takes a lot of brain power. Take a couple of photos as you go so you have a reference as you put it back together. There are no adjustments or settings. It simply bolts together.

I just did mine, and it was not hard, but mine was a two speed Hall Scott (Ruckstell) rear end. It is a lot heavier than a standard TT rear end. Just follow the MTFCA book on rear ends, and it will be just fine. Like what was said before, everything is heavier and use plenty of blocks and jack stands to support the truck and rear end. I made rolling platforms, for both sides of my rear end, to sent my rear end on. When I split it, I just rolled both sides apart. To put it back together, I just rolled both sides together. Just need to support the internals on blocks when rolling both sides together. That way there was no lifting, and saved my back.

Forgot to say, if your rear end is already rebuilt, then the change over to the high gear set is not hard. If you are rebuilding your rear end then there will be more time, and the trouble of finding good parts. Mine was a rebuild, and I though it was not hard to do. Just finding parts and time in preparation of all the internal parts. To pull the drive gears from the axel, you will need a big three jaw puller.

A trip to Harbor Freight produced some roll-around floor skates. I added some
custom "saddles" to hold the rear end off the floor enough to move it around.
This saved a lot of grunt work. I have ceiling and engine cranes. Can't remember
which I used, but getting it onto a work bench was the second grunt task. With
these two obstacles resolved, the rest was just nuts and bolts, like any project.

Re;
As I recall, the hardest part of the whole job is putting the new inner felt in its cup, installing that in the housing, then sliding the differential/axle assembly through the felt. It is a force fit and difficult to get into place. Once you do get it in place you then must do the other side.
Biggest problem replacing the seals for example above, the felt seals were made wrong. The hole in the center is way too small. I would use the felt seal at the outer bearing inner seal and get the cap kit for the outside. I am pretty sure the carrier bearings are the same as the car Ruckstell thrust bearing.
Heavy is correct also cumbersome. Easy to do but cumbersome.
Update re felts;
I talked to Tom the guy that make the correct sized felts, he has not gotten them to Snyder's or Lang's yet, but can be bought from him.

There is a modern seal that fits in place of the can for the inner felt that works way better. Machining a carrier for a modern seal that replaces the washer inside the outer sleeve is also the way to go if you have a lathe.