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Alpine caster

Discussion in 'Modified Alpine' started by Charles Johns, May 18, 2018.

  1. Charles Johns

    Charles Johns Donation Time

    I have not removed the suspension yet but looking at the shop manual and the car, it appears the spacer between the frame and front cross-member could be a place to increase/decrease caster. A plate cut at an angle allowing the front to be higher than the rear would seem to add positive caster. The manual says caster is FIXED. Am I misunderstanding what I see? Reason: I am building for long runs on the highway and a degree or two of extra + caster keeps things going straight.
     
  2. Ken Ellis

    Ken Ellis Donation Time

    That would be the place to adjust it. "Fixed" means not casually adjustable, the way toe-in is. I've seen new wedges from time to time, and they're not really rocket science to produce. Best is to find a milling machine and a sine bar, though there are cheaper and more expensive ways to make them.

    While a simple spacer/washer could be used to test-run a different alignment, using it long-term would have some point-load considerations to address. Probably best to make new wedges with the new angle for the long run.
     
  3. 260Alpine

    260Alpine Silver Level Sponsor

    Stock caster was 3 degrees, 5 would be better.
     
  4. Barry

    Barry Platinum Level Sponsor


    According to the WSM's, stock caster was just under 4 degrees (3 degrees, 50 minutes = 3.83 degrees). That is OK for bias ply tires, but radial tires need a couple of degrees of extra caster to develop the same side force at low steering angles.

    Most Alpines do not have enough "shim" adjustment to get to 5-6 degrees, so more sharply tapered wedges is probably the only feasible solution.

    The original wedges on my S-V are about 8" long and taper from about 3/8" to about 1/8" which works out to be about 1.8 degrees. Stacking two stock wedges (thick to thick) would give a total of about 3.6 degrees (an increase of 1.8 degrees) which should be in the ballpark (3.83 + 1.8 = 5.63 degrees). A "custom" wedge that tapers from 5/8" to 1/8" would also be about 3.6 degrees.
     
    Last edited: May 18, 2018
  5. Charles Johns

    Charles Johns Donation Time

    THANKS guys. I thought I was looking at things correctly. Most likely I will make a couple of aluminum tapered spacers while I am rebuilding the suspension for about 4 degrees positive caster.
     
  6. Bill Blue

    Bill Blue Platinum Level Sponsor

    I added about 3/8" to the rear of the stock shim. Improved road manners a lot, increased steering wheel effort some, but I'd never go back to 3 degrees. I'm close to a practical maximum, any more and crossmember to bolt angle becomes problematic.

    Bill
     
    Barry likes this.
  7. Barry

    Barry Platinum Level Sponsor


    Bill,

    Nice solution and good info. Noted that the additional 3/8" shims at the back crossmember bolts is pushing the limit on crossmember to bolt angularity.

    What are your actual alignment numbers with the 3/8" shims at the back crossmember bolts?

    FWIW, adding 3/8" shims at the back crossmember bolts should increase the backward tilt of the crossmember and the caster by about 3.6 degrees. Using 1/4" shims at the back crossmember bolts should increase the backward tilt of the crossmember and the caster by about 2.4 degrees.

    Also FWIW, I remeasured the factory wedges and think they are about 2 degrees rather than about 1.8 degrees as I previously stated.

    The factory caster spec. is 3.8 degrees.

    Adding 2.4 degrees with 1/4" shims on the rear crossmember bolts should give about 6.2 total degrees of caster.

    Adding 3.6 degrees with 3/8" shims on the rear crossmember bolts should give about 7.4 total degrees of caster.

    Stacking 2 factory wedges (thick to thick) should give about 5.8 total degrees of caster.​

    Most sources suggest that modern radial tires need at least 5 degrees of (positive) camber to improve straight line stability. A short wheelbase car is inherently "twitchy" at highway speeds and the Alpine has a very short wheelbase. Getting the camber up to 5+ degrees should make a big difference in stability (and cornering because increased caster also increases negative camber as the front wheels are turned).
     
    Last edited: May 22, 2018
  8. Bill Blue

    Bill Blue Platinum Level Sponsor

    I thought I had answered this, but don't see it. Short answer, I don't know. The guy that did the last alignment did not record the numbers and the wiz-bang alignment computer does not record final numbers. Camber had been +30 and toe was +1/8".

    Bill
     
  9. Charles Johns

    Charles Johns Donation Time

    Question, are the stock shims available? If so, I may just buy 4 and put 2 on each side after reading Airborne Barry.
     
  10. Charles Johns

    Charles Johns Donation Time

    Okay suspension specialists, if I make two shims that are 3/4" thick in the back and 1/8" in front, out of hard aluminum, using the OEM spacers as a pattern for length, width, and hole location, what will my +caster be? I also hope to lower the car about 2" front and 1" to 1 1/2" in back, which can change caster. I would put on my thinking-cap and do all this math myself, but somewhere around age 70 I lost it. Those 2 hour jobs now take all day, and if thinking is required, I usually lose interest. But, I can follow simple instructions.
     
  11. Barry

    Barry Platinum Level Sponsor


    The important factor is the change in total shim thickness at the attachment bolts.

    Every additional 1/8" of shim thickness at the rear attachment bolt will add about 1.2 degrees of tilt to the front suspension crossmember.

    Take note of Bill Blue's comment that 3/8" of additional shim thickness at the rear attachment bolt is about the maximum before crossmember to bolt alignment becomes an issue.

    HTH
     
  12. mikephillips

    mikephillips Donation Time

    If you do work on adjusting them be aware that once you loosen the bolts and separate the crossmember from the body the original shims will probably crumble. They were alloy pieces and water and dissimilar metals pretty much eats them up. You could be an exception but be sure you have something to replace them with before. Just a "be aware" type thing.
     
  13. Toyanvil

    Toyanvil Gold Level Sponsor

    If I were you, I would lower your car and drive it. My car is lowered with wide tires and drives great on the highway at any speed, our speed limit is 70 mph and am at 80 mph most of the time. The steering is the only thing I have not changed on my car, if it's not broke, don't fit it :) If your front end is old, rebuild it first. My series 2 is on the original front end and I am now just rebuilding an extra one I have to replace it one day, I will install the rebuilt one when my car starts driving odd. This sounds like a lot of work and math, and I don't see any gain.
     
  14. seriesIIIgt

    seriesIIIgt Platinum Level Sponsor

    Charles
    The shims on my front cross member where riveted on You will not be able to remove them without dropping the front end The holes in the shims are quite large so lam thinking that you must just move it back and forth to adjust the camber
     
  15. Charles Johns

    Charles Johns Donation Time

    I appreciate the help! I built cars frame-up for decades and caster, camber, toe-in/out, and Akerman (scribing different archs when turning) are not new to me. The problem is, a street rod is not a sportscar and straight-line racing is far different from left-right-left road-racing. I can't remember how many cars I have built or helped build but it is considerable...maybe 50. With bigger rear tires lifting the back, the caster + number drops, and I do not want too much + caster or too little. You guys know the Sunbeam and I don't...that is why I am asking. On a different subject. Are the Beam discs up to regular traffic city and highway running if rebuilt? Are rebuild kits available? Any parts places recommended? Any swapping brakes worth the effort? Are door latches good on the Beam? I got rid of the twin tanks last year and now have a 16 gallon fuel cell from Summit...but a lot less trunk space. May opt for a luggage rack. For luggage, has anyone used carpet in the back so-called seat area? With luggage purchased for that space and tie-downs fabricated, one could save trunk room. After driving Bill's I can tell wind noise may be a problem when flying at altitude (70+ MPH). The hard top looks like a MUST! That is enough for now. THANKS ahead gentlemen.
     
  16. Charles Johns

    Charles Johns Donation Time

    Thanks for the heads-up. I will install an angle finder at the axle to see if things change as the cross member is moved. I don't think it would be any measurable amount...but I have been wrong many times.
     
  17. Bill Blue

    Bill Blue Platinum Level Sponsor

    The Sunbeam brakes are fine for general highway work. That includes the rear drums. It is very easy to overdo rear brakes when "upgrading". My brakes are real old time hot rod. Rotors from Pontiac Grand Prix, calipers S10, rears are second gen Miata calipers with Nissan Maxima rotors, with a 13/16th master cylinder and a modified 6:1 brake pedal. Would I do it all again? Probably not. It was a product of the products available, my mindset and input from Barry. Not really necessary. And although I shudder at the thought of all that cast iron flying around, I do got brakes!

    Door latches on the Alpine are good, somewhat difficult (impossible?) to operate the same each and every time the door is opened or closed. But when latched, stay closed.

    Don't worry about caster. It is easily and cheaply changed and does not change other settings. After you build the car the way you want it and don't like the way it goes down the road, start messing with caster. That's how I got to where I am. Cost was virtually nothing. I will tell anyone that cares to listen, my car was terrible when caster just south of 3 degrees. If your car is terrible and has to be herded down the road, change the caster.

    Bill
     
  18. Barry

    Barry Platinum Level Sponsor


    What matters is the shim angle. Moving the shims back and forth (forward & backward) does not change the angle of the shims and will not change the camber.
     
    Last edited: Jun 16, 2018
  19. Barry

    Barry Platinum Level Sponsor


    The crossmember location is fixed by the 4 attachment bolts; don't see how it can be moved other than up / down.
     
  20. Alpine66

    Alpine66 Donation Time

    I ditched my tanks and that transfer pipe and went with a tank from summit too.

    Using the mercury capri calipers up front, manual brakes, no complaints.

    I change my caster to 4 degrees which helped but will probably bump to 5.
     

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