Replacing Tailwheel Leafsprings

[Lee]

I have a '54 C-170B and in the process of refurbishing/upgrading the airplane, decided to replace the leaf springs and clean up the tail wheel assembly. Removing the leaf
springs was difficult ... but got them removed and then tried to install new leaf springs. The first issue was re-installing the bushing (tail wheel attachment) ... I had painted the leaf springs and the bushing did not slide in. I made sure the bushing was clean and then removed any trace of paint in the hole that the bushing rides in. It went in but is a little tight that bothers me. I got the leaf springs in the channel and the bolt through the bushing relatively easy. The main point though is that the channel that sits on top of the leaf springs can not be seated such that the 8 bolts that attach the channel to the bracket can not be positioned to reinsert the bolts except for the two most forward bolts. we did put a "C" clamp on the spring stack before attempting to install. Any ideas on this? If the problem has apparently always been with the main spring, would it be safe and acceptable to only replace the main spring? I decided to replace the springs because it appeared to me that the tail wheel geometry was wrong based on Association pictures I have seen. Does the arc (geometry) principally come from the main leaf? The airplane has not flown in 15 years and has been hangared most if not all of its life and the entire time I have been working on it ... there is light at the end of the refurbishment tunnel!
Thoughts/ideas?
Thanks
R/Lee (N1967C)

[GAHorn]

The MAin (lowest leaf) spring is the Only one usually necessary to replace. It is the most important and the only one which actually holds the tailwheel.

[DillanMcL]

Hi I’m N2636V’s(1948 C170) caretaker. The tailwheel geometry on this bird was iffy so after I bought her 5 years ago my IA installed a clamp block on the springs to stiffen them, which allowed for slightly better steering and unlocking etc. Now she’s starting to shimmy fairly violently after any sort of serious crosswind landing. It doesn’t matter if I wheel land and slow it down, if the wheel comes down while I’m pushing the rudder it shimmies.

What’s the best option for fixing this? I’d love to be able to just install a new spring stack but I hear the this can be a pain with the 1948 model bracket. My original bracket is in pretty good shape minus a single missing rivet head. The springs currently have some “non-standard” clamps holding them together, which worries me as someone may have thought this was easier than replacing the spring.

I believe these are the springs I need, tho I may just need to replace the single main spring: https://www.aircraftspruce.com/pages/lg ... 0twspr.php

[DillanMcL]

Here’s one more view showing the geometry:

[Bruce Fenstermacher]

The main spring is usually the only one needing to be replaced. A 170 with the first original steel bracket used 5 springs in the pack. 170s that came with or were upgraded to the later "fish" mount mount only use 4 off the same 5 springs leaving out the top small short spring.

Yep you have some home brew stuff on that spring pack and your main spring should have been replace long ago. That geometry is terrible.

[Bruce Fenstermacher]

Look here: download/file.php?id=3148 on the first page which is the Scott 3200 Installation Instructions showing just how a Scott 3200 should be installed on a 170. Note how the front of the swivel of the tailwheel is slightly higher than the back. This is how yours should be. This angle should not be any flatter then level when the aircraft is fully loaded.

[DillanMcL]

Thanks Bruce. In the interest of not disturbing what isn’t otherwise broken I guess I’ll just try to swap in a new Spruce main spring and hope it works with the custom clamp work and the other old springs.

[Bruce Fenstermacher]

Screen Shot 2024-11-20 at 6.13.33 AM.jpg

Looking closely at the IPC drawings, which are fairly accurate as to what parts look like, you can see that the two clamps at the top of the spring at the fuselage bracket are manufactured repair parts. The double clamp looks to be two clamps with a tab welded on holding them apart. You already know you should only have one clamp here. Also the clamp that is now doubled should have a bottom half which is found missing on many 170s. I only count 4 springs, your setup should have 5. Sometimes it's hard to see the small 5th spring but I don't think it is there. If it is not, it may have been removed to make space for a thicker main spring. These are all the things I see repaired/modified from the way it left the factory.

You definitely need a main spring. I would not hesitate to replace this. If you would see the $$$$ worth of damage which happens when that main spring snaps, you would know why. Personally I would not fly that plane until the new spring is install cause I personally know the price if it should fail.

As for leaving the other stuff as is. My opinion is so long as you feel the material and wear is equal to what it replaced, ie the clamps at the top, I don't see how a second clamp in the middle as it is could hurt.

[dstates]

I also had to replace my entire tailwheel spring stack on my 170A. See here for a picture of what mine looked like.
viewtopic.php?p=145475#p145475

I also had the older style of tailwheel bracket. I don't believe spring stack thickness is as important with this design.
viewtopic.php?p=140374#p140374

Be careful about what parts catalog you look at. You say you have a 54 B model. Those would only have 4 leaf springs. Bruce seems to mis-remember the older tailwheel bracket can have 4 if it is not a straight 170. The leaf spring kit I purchased had all 5 springs for a straight 170 and I still have the top short one on a shelf somewhere. It is not used. Take a look at this thread where you can see the 170 vs. 170A (red label in pictures) and then here is the image from the 170B parts catalog.
viewtopic.php?p=140339#p140339

170b_tailwheel_bracket.jpg

Also, the rubber pads (item #3 in above image) is not available anywhere. I ended up purchasing some rubber and a hole punch to make my own.
https://www.amazon.com/gp/product/B002J ... =UTF8&th=1
viewtopic.php?p=138107#p138107

The strip assembly (#7 in above image) is available. I think I got my replacement from Air Repair (https://airrepairinc.com/).

If you get it all taken apart and find that there is damage to the tailwheel bracket, then you start to investigate the fishmouth version and I would start here.
viewtopic.php?f=40&t=9442&p=84173

I hope this helps. When you are done you will really like the results.

[n2582d]

Welcome to the forum! There’s been numerous threads on this subject written here over the years as tailwheel shimmy is a common problem. The search function is your friend. However, I think the best synopsis on the subject is not found here but in a tech article written by the late Neal Wright on the Cessna 120/140 Association’s website. The 170, being an outgrowth of the 140, shares many part numbers with it. These models also share the tailwheel assembly’s idiosyncrasies/problems. Neal’s article is found here.

Information on free IPC’s (Illustrated Parts Catalogs) can be found here. For what it’s worth, there are a couple of errors in Fig. 20 of the C-170 IPC. 20-91 is actually stiffener p/n 0442115 and 20-92 is actually p/n 0442127. The tailwheel spring abrasion strip assembly is identified correctly as 0442124 but incorrectly as fig. 20-92. It is not depicted in the illustration.

Several members here have converted their early style steel tailwheel bracket (C-170, C-170A, and C-170B through s/n 20805) to the later aluminum fish mouth style. You might try advertising in the Trademart for the parts you’re missing for your early style tailwheel mount as it’s possible these members have the parts you need gathering dust in their hangars. I have a stiffener assembly, p/n 0442127, which can be yours for a fraction of what Univair charges for p/n 0442115. As you can see in the photos below, 0442115 appears to be 1/2 of p/n 0442127.

IMG_1152.jpeg

IMG_1155.jpeg

If you’re looking for the correct parts, in addition to Univair and Aircraft Spruce, take a look at Preferred Air Parts. It looks like they have most, if not all, of the leaf springs you need.

[DillanMcL]

Thanks Gary and Bruce.. This all confirms what I suspected about restoring the original ‘48 tailspring equip being an archeological adventure. Gary I may take you up on your offer depending on what my IA says about just swapping in a new main spring.

[n2582d]

I just saw that Univair's p/n U0442115 is $48.72. Compare that to the same part without the "U" -- 10X as much at $482.04.

Your photos don't show how the leaf springs are attached to the mount at the front. As you work to correct the hardware further back it might be worth checking the forward attach as well. The C-170 IPC does a poor job of illustrating how this all goes together. Although, in the listing for fig. 30-82 it lists three retainers, the illustration only shows one retainer. Compare the C-170 fig. 20-82 to fig. 28-4 in the C-170B IPC:

C-170 IPC.png

C-170B IPC.png

Note too the position of the rubber pads in the two illustrations are different. Both the rubber pad and the retainer add a "-1" to their respective part numbers in the C-170B IPC. I'd be tempted to make the pads out of polyurethane sheet material.

In looking at my spare parts stash I came across these three tailwheel attachment retainers -- basically square washers with two turned up legs. ... not sure if they are p/n 0442116 or 0442116-1. They're for sale to whoever needs them. Here's a picture of how they are stacked in the C-170B IPC.

Forward Attach Retainers.jpg

[counsellj]

Just save yourself the hassles and install a T-3 Tailwheel. Eliminate the many issues with worn out, ill-fitting, prone to brake tailwheel springs.

[n2582d]

STC SA11841BO for the T3 tailwheel suspension system isn’t up on the FAA’s website yet. Does the AML for it include 170’s without the aluminum fish mouth style mount?

[sflynn30362]

STC SA11841BO for the T3 tailwheel suspension system isn’t up on the FAA’s website yet. Does the AML for it include 170’s without the aluminum fish mouth style mount?

The T3 Tailwheel STC has officially been approved. I've been seeing posts from the owner on various FB groups. According the website they will be available through Alaska Gear Company.