Subject: Re: [TR] TR4 - TR6 front suspension

From: Tony Drews <[email-masked]> mail.com>
Date: Tue, 05 Aug 2014 12:11:57 -0500

Lower A-Arms changed between the TR-4 (with 3 degrees of castor) and 
the TR-6 (with 3 degrees of castor), possibly when they went to the 
TR-4A IRS with the adjustable lower A-arm brackets.  Vertical link 
changed between the TR-4 and TR-250 / TR-6 - went from studs sticking 
out of the lower trunnion to one with a bolt through the lower 
trunnion.  The lower trunnion width changed with that, the "screw" 
that goes into the trunnion is larger diameter and shorter in the 
TR-6, and the location of the bolt / pivot changed in a way that 
lowers the car.

Spring pans are the same.

http://www.tonydrews.com/Front_Suspension/tr4_front_suspension_upgrade.htm

But, the springs will fit, but will be a bit shorter than the 
original if I'm doing my math right:
9.75 + 1.25 = 11"
vs
10.1"

Tony

At 09:21 AM 8/5/2014, Brad Kahler wrote:
>I'm trying to do an analysis of the front suspension dimensional
>differences between the early TR4 cars and the TR4A and later cars.
>
>Below are some assumptions that I've made:
>
>The lower a-arms are the same from tr4 thru tr6. The upper a-arms are the
>same from later tr4 thru tr6. The vertical links are dimensionally the same
>except for camber/castor angle changes. I'm pretty sure the lower spring
>pans are the same with probably only slight differences but I believe the
>basic dimensions are the same. The upper fulcrums are the same just the
>orientation changes between tr4 and later tr4 thru tr6.
>
>Since the vertical links are the same overall length that should mean the
>distance between the upper fulcrum pivot point and the lower a-arm pivot
>point (on the frame) should be the same for all models. With all of that
>being said that tells me the installed spring height from the lower spring
>pan seat to the upper spring seat should be the same for all models.
>
>I'm betting the overall front end weight is pretty close between the 4 and
>6 cylinder cars as I've read that the stock spring rate between 4s and 250s
>is only about 2 pounds (310 vs 312)
>
>So my unless I'm missing something then springs that are 10.1 inches tall
>from a tr250 should fit in a tr4 that originally had 9-3/4" springs and a
>1-1/4" packing piece. In other words the 10.1" springs (and no packing
>piece) should be a direct swap for the 9-3/4" spring it its associated
>1-1/4" packing piece.
>
>Anyone see any holes in my logic?
>
>Thanks!
>
>Brad
>
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---

From: Brad Kahler <[email-masked]>
Date: Tue, 5 Aug 2014 16:30:14 -0400

Tony, thanks for the info!

The key would appear to be the location of the old style trunnion studs
compared to the trunnion bolt on the later cars.  I have both style of
trunnions on hand so I'll give them a closer look this evening to see just
how much difference there really is.  From what documentation that I have
found it seems that the installed spring height is supposed to be the same
on all models, i.e. 6-3/4" (or was it 6-1/2"!)  Either way from bottom
spring pan to upper spring seat the distance is hopefully the same.

Should be interesting once I install the springs this weekend.

Thanks!

Brad

On Tue, Aug 5, 2014 at 1:11 PM, Tony Drews <[email-masked]> wrote:

> Lower A-Arms changed between the TR-4 (with 3 degrees of castor) and the
> TR-6 (with 3 degrees of castor), possibly when they went to the TR-4A IRS
> with the adjustable lower A-arm brackets.  Vertical link changed between
> the TR-4 and TR-250 / TR-6 - went from studs sticking out of the lower
> trunnion to one with a bolt through the lower trunnion.  The lower trunnion
> width changed with that, the "screw" that goes into the trunnion is larger
> diameter and shorter in the TR-6, and the location of the bolt / pivot
> changed in a way that lowers the car.
>
> But, the springs will fit, but will be a bit shorter than the original if
> I'm doing my math right:
> 9.75 + 1.25 = 11"
> vs
> 10.1"
>
> Tony
>
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