correct angle or measurement for front axle caster

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FrankHarris
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correct angle or measurement for front axle caster

Post by FrankHarris » Mon Feb 18, 2019 2:08 pm

Toady  with the top up.jpg
Toady with the top up.jpg (28.92 KiB) Viewed 1828 times
We are replacing the wishbone with a set of front radius rods with Laurel lowering blocks with the spring mounting system. The front axle is perfectly aligned with the front of the frame and now we need to know the correct angle or measurement so can move the axle forward in order to get the proper caster and install the rear of the front radius rods to the frame. The rods are adjustable but are a pain to do so, so we want to get it as close as possible without having to play "trial and error"a We don't want to guess this one because the record holding "King of the Hill" Chris Egsgaard Hill Climb engine is being used in this build and we think we have about 85 horsepower or so, so it's not just a Model T any more and must be safe to drive at speed. We have a Layne Warford and a rear end with safety modern bearings in the drive train and safety hubs with Rocky Mountain brakes. Every thing is strong and done correctly and we seriously need either the correct angle and where to measure it, or the the measurement of the space between the angle at the top of the axle when using a framing square to measure the space. Thank you for any assistance on this matter. I have not been well and can finally get back to progressing with this build.

We are attempting to build a copy of Terry Horlick's "Toady" who graciously sent us a copy of a set of his own one off plans for the build. As suggested by Terry, we are using a TT frame in order to balance the rear end passenger load better at speed. Because of the fact that the Laurel blocks lower the front end, we have Zee'd the rear of the frame to conform with the desired body stance. We are looking forward to helpful information on this matter.
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Center Pistons up very small copy - Copy.jpg
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frame modification for Laurel  equipment.jpg


jab35
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Re: correct angle or measurement for front axle caster

Post by jab35 » Mon Feb 18, 2019 2:59 pm

Frank: The Ford service bulletin July, 1921 (From Ford Service Bulletin Essentials pg 202) states that the spring perch is built with 5-1/2 degrees of castor, meaning the axis of the king bolts make an angle of 5.5 Degrees to the ground, top hole is rearward of bottom hole for kingbolt. Here is an earlier discussion showing Ford specs for Castor. Using a square from a flat floor up against the king bolt bushing bosses on the front side of the axle, the top boss should be 1/4 to 3/16" to the rear of the bottom boss. IIRC, the Ford measurements recommended when using a square gave less than the 5.5 degrees Ford claimed they built into the perches, but most people adjust with the square method and things seem ok. http://www.mtfca.com/cgi-bin/discus/sho ... post=78296 Best, jb


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FrankHarris
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Re: correct angle or measurement for front axle caster

Post by FrankHarris » Mon Feb 18, 2019 4:31 pm

Thank you Jim and I understand that the faster you go the more caster you need. So I will set up originally at 1/4" remembering that there is about an inch and a half of threads and that I have the jam nut set at half way. I think I will screw it in a little more because the thread count is so close together that I can adjust the length by a very small few thousands of an inch at each turn of the castellated hex nut with a cotter pin.

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GrandpaFord
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Re: correct angle or measurement for front axle caster

Post by GrandpaFord » Mon Feb 18, 2019 8:09 pm

Don't forget to check the tow in after any change in caster. Because of the camber, changes in caster will change the tow in.

Here is a good tread on caster math: http://www.mtfca.com/discus/messages/822076/847393.html


Erik Barrett
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Re: correct angle or measurement for front axle caster

Post by Erik Barrett » Tue Feb 19, 2019 12:22 pm

When I built first speedster I set it up with specified caster. Didn't work on this light car with Corvair steering box. I had to double it and now it tracks fine. For your car I would suggest a little more than stock caster as it will clearly by faster than a stock car.

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Thorlick
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Re: correct angle or measurement for front axle caster

Post by Thorlick » Sun Feb 02, 2020 10:45 pm

Frank,

That's a photo of "Toady". I sure wish I still had that car. After I sold it Terrie told me that was the only car I had that she liked!

You may be interested in the car I have sitting in the garage awaiting restoration. I wanted one which can carry Terrie's friends or lots of kids. I hope she will like it too!

1912 Omnibus
1912 Omnibus
Rear entrance seats 6-8 in the rear and 2 -3 in front
Rear entrance seats 6-8 in the rear and 2 -3 in front
Terry[/color][/size]
Terry Horlick, Penn Valley, (Northern) CA
1927 Mountain Patrol Vehicle from the Los Angeles City Fire Department (L.A.F.D.)
1912 Omnibus project


YellowTRacer
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Re: correct angle or measurement for front axle caster

Post by YellowTRacer » Wed Feb 05, 2020 5:39 pm

Hey Frank, using the straight edge (big carpenters square) resting on the floor and against the bottom of the yoke casting, the distance between the straight edge and the top of the yoke casting is 5/8-11/16 inch. on old #4 and I could not be more comfortable at 80 MPH. Same at speeds above 80 MPH just a lot more vibration. Hope this helps a little.

Ed aka #4


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Re: correct angle or measurement for front axle caster

Post by Allan » Wed Feb 05, 2020 10:48 pm

Ed's suggestion makes sense. It allows for any fall in the floor. Rather than measure at the castings, would it not be more accurate to measure to the top and bottom king pin bush flanges. Can anyone tell me what the difference should be if the caster is set at 5 degrees? It's been a long while since I did any trigonometry.

Allan from down under.

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Re: correct angle or measurement for front axle caster

Post by TRDxB2 » Wed Feb 05, 2020 11:19 pm

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Luke
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Re: correct angle or measurement for front axle caster

Post by Luke » Wed Feb 05, 2020 11:58 pm

Allan,

First of all my apologies, I grabbed my metric verniers when I went out to my car...

I get 117mm between the centre of the bottom and top flanges. At 5 degrees the difference from vertical would be 10.2mm, at 5.5degrees it's 11.2mm.

Also, when I did my alignment recently I used a cross-laser level for this task. It made it very easy, and accurate.

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TRDxB2
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Re: correct angle or measurement for front axle caster

Post by TRDxB2 » Thu Feb 06, 2020 12:12 am

117mm = 4.606inches 10.2mm = 0.4018 inches 11.2mm = 0.4410 inches
https://www.google.com/search?client=fi ... +to+inches


Allan
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Re: correct angle or measurement for front axle caster

Post by Allan » Thu Feb 06, 2020 4:39 am

Thanks Luke and Frank. I am looking to make a fixed tool to use to check this. I had thought of screwing fixed metalthreads into a 6" spirit level body, but that would only be usable if the car is parked on a level floor. Ed's use of a large square takes the level floor out of the equation an make my tool more practical to use. With the square in position, all that needs to be done is match the back of the level to the square.

Allan from down under.


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Re: correct angle or measurement for front axle caster

Post by Luke » Thu Feb 06, 2020 4:58 am

Allan,

If you have a perfectly flat floor then that should work fine (flat not being the same as level!).

Out of interest; over the years I've tended to look for simple but accurate methods to do my alignments. The first one I did was nearly 40 years ago now (using a Dunlop optical gauge that I still have) and it fairly quickly became obvious how much a small anomaly in rim or base surface could affect the results.

Subsequently I've improved what I do, and some time ago I obtained an alignment hoist. However I found the most effective and simplest method for cars such as the T was to use the self-levelling cross-laser on the garage floor.

With this any anomalies in the floor, sagging springs and the like are able to be compensated for and, simply using my verniers from the laser line against the rim or kingpin bush, I can easily check camber as well as castor.

I mention this because these laser levels are relatively inexpensive now, and some people might be surprised just how much their floors are uneven or their springs sagging...


YellowTRacer
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Re: correct angle or measurement for front axle caster

Post by YellowTRacer » Thu Feb 06, 2020 5:57 pm

I'm probably going to get a lot of flack for this, but guy's.....it's a model T! Not a Bugatti or Rolls Royce. I'm not a finess mechanic. Even on the race car. I don't put a level on the floor. If it looks level to my eye, it's good. Close is good. Make sure everything is tight (not necessarily bushings and bearings), cotter pins or lock washers in place, you're good!


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Re: correct angle or measurement for front axle caster

Post by Erik Barrett » Fri Feb 07, 2020 1:54 am

I am going to agree with my friend yellow T racer on this one. The specification he gave is about twice the positive caster Ford called for on the model T. We have found this is perfect for light cars and especially for fast cars. And he’s right, model T’s don’t need laser alignment. A carpenter’s square on the floor is all you need.


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Re: correct angle or measurement for front axle caster

Post by Luke » Sat Feb 08, 2020 5:46 pm

Ed, Erik,

You won't get a lot of disagreement from me, however in my case after a series of earthquakes the garage floor just isn't what it was so finding a reasonable spot to use a square isn't that easy.

As I use the laser for other cars it wasn't hard to use it on the T, and since I see no reason not to do as good a job as possible (and it makes it simple to do camber as well) it works well for me ;)

Also in my case I needed to prove the alignment before being able to register my T for use on the road here so I felt it would help to do it 'accurately'. Trying to prove alignment using a square and string to youngsters with clipboards and tickboxes may not have worked very well, although in the end I struck some decent people who understood old cars so all was well :)

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