Rear A-arm geometry...
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Post by: Brock » Fri Jul 07, 2023 6:38 am
Hi All,
Are there geometry specs for the rear A-arms? I am guessing that the two axes (inner and outer) should be exactly parallel. I have been checking mine.
If I place the A-arm on my lathe's bedways, I can precisely measure the relative level of the outer end compared to the inner end. The bedways are very close to level -- more importantly, I know exactly how far they are from level (right now .005" per foot) (I'm making new lathe feet, so I haven't chased it beyond eliminating bedway twist -- and it's not necessary for lathe accuracy).
The passenger side A-arm from my car is out from parallel by .095" or 2.41mm (at the inner mounts). So, toed in... That's a .095" gage pin in the photo (not a guage pin here, weirdy). This A-arm has a little bit of jack damage to the inner longitudinal. That toe-in sounds about right doesn't it? Obviously it needs to be checked once assembled, but I'm trying to save time by identifying bad A-arms.
My spare is dead nuts perfect -- and is damage-free.
Are the inner mounting points on the chassis parallel to the centre line?
Am I barking up the right tree?
Thanks.
Are there geometry specs for the rear A-arms? I am guessing that the two axes (inner and outer) should be exactly parallel. I have been checking mine.
If I place the A-arm on my lathe's bedways, I can precisely measure the relative level of the outer end compared to the inner end. The bedways are very close to level -- more importantly, I know exactly how far they are from level (right now .005" per foot) (I'm making new lathe feet, so I haven't chased it beyond eliminating bedway twist -- and it's not necessary for lathe accuracy).
The passenger side A-arm from my car is out from parallel by .095" or 2.41mm (at the inner mounts). So, toed in... That's a .095" gage pin in the photo (not a guage pin here, weirdy). This A-arm has a little bit of jack damage to the inner longitudinal. That toe-in sounds about right doesn't it? Obviously it needs to be checked once assembled, but I'm trying to save time by identifying bad A-arms.
My spare is dead nuts perfect -- and is damage-free.
Are the inner mounting points on the chassis parallel to the centre line?
Am I barking up the right tree?
Thanks.
Last edited by Brock on Fri Jul 07, 2023 7:06 am, edited 2 times in total.
1964 Elan 1600 #3370
- Brock
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Post by: Brock » Fri Jul 07, 2023 7:03 am
Yeah... Good question. I'm taking back my guess. It makes more sense that it comes from the A-arms... but I'm not guessing.
* It just dawned on me that there no such thing as a passenger or driver's side A-arm... They're the same... just flipped.
* It just dawned on me that there no such thing as a passenger or driver's side A-arm... They're the same... just flipped.
1964 Elan 1600 #3370
- Brock
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- Posts: 75
- Joined: 11 Sep 2013
Post by: Brock » Sat Jul 08, 2023 4:20 am
The other side came in at .120" or 3.05mm
If the chassis is straight (and I think it is), that should make for .069" / 1.75mm toe in on one side -- and .092" / 2.34mm on the other. We'll see.
If the chassis is straight (and I think it is), that should make for .069" / 1.75mm toe in on one side -- and .092" / 2.34mm on the other. We'll see.
1964 Elan 1600 #3370
- Brock
- Second Gear
- Posts: 75
- Joined: 11 Sep 2013
Post by: ill_will » Wed Aug 02, 2023 11:47 am
It's a tenuous data source, but TTR do fixed geometry rear wishbones with 'extra' toe in, implying the standard item has some toe in. That doesn't exclude there being some in the casting or the inboard pickup points though!
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