I've been asking around for a while and can't seem to get a solid answer from anybody. How is the caster angle set when using Laurel style front lowering brackets? I've got a set of undrilled castings that I picked up a few years ago and I need to know how I should drill them. These are for the early style wishbone. I'd assume that the holes for the wishbone and shackles should be parallel to one another, but I should tilt the axle holes back about 8 degrees in relation to them. Is this how others are doing it? The drawing on p.168 of Model T ford in Speed and Sport looks almost as if it's straight up, with no caster at all. That just doesn't seem right.
My understanding is that the angle shouldnt change with the Laurel style fitted. Im not sure though if you are going to drill them yourself.
Maybe my wording is confusing. The stock perches have the caster angle built into them. On the early style perches, the shackle and wishbone holes are parallel to one another and the stud that goes through the axle is angled to tilt the axle back giving it the proper caster angle. The Laurel brackets replace the perches. If I drill the shackle and wishbone holes parallel to each other and drill the bolt holes for the axle at 90 deg. to them, as the Speed and Sport (p.168) and Speed Secrets (p.110) books imply, it doesn't appear that I would have any caster angle, making a very skittish car.
The caster can be adjusted, by twisting the axle ends. Thats what that big axle bending wrench is made for.
On the stock perches the caster is built into the perch where the shackle mounts. I would think you would need to drill the shackle holes to produce this angle, or drill the axle holes to come up with it if the shackle holes are allready drilled. I would think 82* between the holes would give you the 8* caster you want. If drilled at 90* you would have to twist the spring to get your caster, and rely on the wishbone to hold it there. Jim
For what it's worth, our local chapter learned, by experience, that a 280lb. man jumping on on 6' pipe slipped over an axle bending wrench still isn't enough to put a permanent twist in an axle. It was kind of fun jumping up and down on that springboard.
I think that you and I are on the same page. Just as the caster is built into the perches, it seems that I should build it into the machining of the castings. I wonder how much caster is too much. I'd like for the car to be stable at speed, but still steerable.
If my answer sounded sarcastic, that wasnt my inetent. I think James has the correct fix for your situation.
From a previous time this was discussed at: http://www.mtfca.com/discus/messages/80257/91559.html?1242263469 it appears the answer was all the holes were parallel in the reproduction version that Bill produces (where I have read, his products received good reviews on the forum -- note his reproduction brackets are probably the same general style as the orignals except for what they are made from.) (http://cgi.ebay.com/ebaymotors/ws/eBayISAPI.dll?ViewItem&item=380180179495&ih=025&category=34200&_trksid=p4506.m7&_trkparms=algo%3DLVI%26itu%3DUCI%26otn%3D3%26ps%3D6 shown below:
and that the castor in the front axle would have to be produced by applying torque on the axle. Bill provides a kit with a split wishbone and adjustable ends so you can ste the castor within a reasonable range. http://cgi.ebay.com/ebaymotors/ws/eBayISAPI.dll?ViewItem&item=380187390134&ih=025&category=34200&_trksid=p4506.m7&_trkparms=algo%3DLVI%26itu%3DUCI%26otn%3D3%26ps%3D6 Model T Ford adjustable spit wishbone
That same method has been used by at least one restorer on his Model N Ford – his Dad just bent the wishbone to add the right amount of positive castor (about 5 1/2 degrees for a stock axle). I don’t know if I would want to do that on a speedster. And of course in the MTFCA posting referenced above Stan Howe posted that after reviewing that he elected to build his own brackets rather than put the stress on the spring and spring shackles.
Below is the picture from page 168 of the Model T Ford in Speed and Sport.
If the drawing is accurate – then the original Laurel front bracket holes were 90 degrees to each other also.
That would allow you the two options already mentioned – either using the wishbone to force the front axle to have the proper caster or bending the axle so it has the correct castor at the kingpin. Note the axle could be bent at several different locations to obtain the same correct caster. On a stock axle it is 5 1/2 degrees positive. As long as you do not go negative it should work – but it will get really sensitive the closer to zero castor and it will go full hard left or hard right on its own if you go negative castor.
Note: Any good truck alignment shop can bend your axle very easily and precisely. Since you only have one set of brackets to drill – if you make a small mistake they can adjust the castor by bending if you need it done.
One suggestion on help on finding out about how parallel or nonparallel the hole were is to locate the paten drawings. There are a couple of folks on the forum that seem to be really knowledgeable on how to find the patent drawings. I want to learn how to do that. But I currently don’t have much success with it.
My own thought (free and maybe worth a little less) I would have the bracket drilled so the provided the amount of castor you wanted. For me – I’m older and would want the caster around 5 1/2 degrees positive. But with good reflexes you should be able to run it around an oval dirt track with 1/2 degree of positive castor and it would be very light and quick on the steering. But very tiring to drive for a long period of time.
Recommend you contact the Northwest Vintage Speedster group and ask concerning the caster for a speedster. They should be able to help you out on that.
Hap Tucker l9l5 Model T Ford touring cut off and made into a pickup truck and l907 Model S Runabout. Sumter SC.
I think James would be right about drilling the shackle holes to produce the proper caster. It looks to me like the brackets should have been made with the caster taken care of in the area between where the shackle/wishbone bolts on and the big C for the axle. That way, the holes could have been drilled square for a much better fit.
Did you notice the brackets on the photo that Robb Wolf posted in another Forum question about lowering the chassis or radius rods (don't remember which one it was)? It looks like they are made out of a channel. It would be easy to bend the legs on it to get the caster. I guess those kind of interest me because they are a use for the many spring perches that have bad threads in the nut area. The perch can be saved by cutting off the bad threads and installing new threads! I'm kind of leaning towards that style. Does anyone have comment about that method over the Laurel style?
Looks like I missed the image...Verne
Maybe this time...
I have found that when you lower the front with that type of bracket,the axle swings up closer to the frame pivoting on the wishbone ball and it provides the back angle the axle needs.I drilled my holes all at 90 degrees. Les
90 degrees provides comfortable safe steering even at 75 mph.
Les and Fred,
Thank you. Your respected, real-world advice will have me drilling them at 90 deg., despite my trying to over think it on my own.