TR5/TR250 Trailing Arm Question

[arbs_53]

I'm reaching out to anyone who might know the answer to a question I have concerning trailing arms: Did the geometry of the trailing arms on late TR6's change from the trailing arms on TR250's and early TR6's?
The reason I'm asking is I am trying to figure out why my TR250 sags to the left. Before everyone chimes in with suggestions of checking for worn springs, bushings, cracked spring tower, loose shocks, improperly mounted trailing arm brackets or rusted frame, know that I have new Goodparts springs all around, adjustable Goodparts brackets, fairly new shocks and links, new polyurethane bushings, no cracks in springs tower and a solid frame that is square- I personally checked out the frame this past weekend with the car up on jacks and using a plumb bob in order to check for squareness and all is good, except, except that one point (point D, left side, for those of you who are familiar with the frame diagram in the blue Bentley manual) is 5/16" higher than the right side.
My reason for zeroing in on the trailing arms is that the T/A's on my car are from a late TR6, Stanpart # 308224 & 308225. I have read in Roger Williams book "How to Restore Triumph TR5/250 & TR6" 2003 (page 134, 1st column) that "...it's not generally appreciated that at the same time as the mounting bracket 'notches' were changed, a change occurred to the trailing arms, and the angles varied from earlier castings. This can be another reason why some home restorers have difficulty re-establishing rear suspension geometry."
I have spoken to some very knowledgeable people who are very sure no change in geometry took place, but because of these two sentences in a book written by an widely accepted expert, I'm wondering who is right. Can anyone out there say with certainty that the geometry changed, or did not change, in the years between 1968 and 1976?

Dave Arbour
Augusta, Maine

 

[malbaby]

IMHO....assuming you mean left rear sag....and that the trailing arms adjustment is set correctly for camber...and that the car has been rolling... and that the front and rear coil springs are correctly matched for length and compression lb/ft....and that the frame is not slightly twisted...the sag can only be from the coil spring height...I would try fitting a coil spring spacer of appropriate thickness to the left rear.

 

[Foura]

The original parts manuals (see Revington's site) lists 307481/2 as the numbers for the TR4A trailing arms. These have the bump rubber mounted on the body. TR5/250 through to late TR6 have the part numbers 308267/8 for the trailing arms. These have the bump rubber mounted on the trailing arm. Both Moss and Rimmer use these numbers, with Rimmer recommending that the TR6 arms be used as a replacement for the TR4A ones. Where did you get your parts numbers from?

My 4A sagged on the right rear with Goodparts springs and poly bushes. I put the Goodparts 1/2" spacer under the right rear spring and it levelled the car up perfectly front and rear. I suggest you put a spacer in and enjoy the drive!

 

[arbs_53]

Rocky, believe it or not, I got the numbers from the trailing arms themselves. I found a few internet references to them belonging to late TR6's doing a Google search for those part numbers.

 

[pdplot]

If you have a tube shock conversion, be careful about adding a spacer. My Goodparts spacer leveled the car fine but caused the shock piston rod to bend and make a clunk as you drove along. Took out the spacer, added a new shock and problem solved. Car still leans slightly to the left but who cares.

 

[Tybalt]

I..... My reason for zeroing in on the trailing arms is that the T/A's on my car are from a late TR6, Stanpart # 308224 & 308225. I have read in Roger Williams book "How to Restore Triumph TR5/250 & TR6" 2003 (page 134, 1st column) that "...it's not generally appreciated that at the same time as the mounting bracket 'notches' were changed, a change occurred to the trailing arms, and the angles varied from earlier castings. This can be another reason why some home restorers have difficulty re-establishing rear suspension geometry."
I have spoken to some very knowledgeable people who are very sure no change in geometry took place, but because of these two sentences in a book written by an widely accepted expert, I'm wondering who is right. Can anyone out there say with certainty that the geometry changed, or did not change, in the years between 1968 and 1976? ........

...... TR5/250 through to late TR6 have the part numbers 308267/8 for the trailing arms. These have the bump rubber mounted on the trailing arm. Both Moss and Rimmer use these numbers, with Rimmer recommending that the TR6 arms be used as a replacement for the TR4A ones. Where did you get your parts numbers from? .......

Rocky, believe it or not, I got the numbers from the trailing arms themselves. I found a few internet references to them belonging to late TR6's doing a Google search for those part numbers.

I cannot say with certainty that there was no change to the trailing arms during the TR250/TR5/TR6 production run, but may have an explanation for the numbers you are seeing on the trailing arm vs what is shown in the parts catalogs. I don't know why I did not think to mention it earlier, but it is probably tied to their configuration management method. It is fairly common for parts that are cast or forged to carry one part number for the as cast or as forged item and a different part number for the ready use to use item. What you saw is probably the casting number. If you are looking to try and nail down a date, the trailing arms typically would have the casting date scratched in the greensand mold, you can see the date on the trailing arm in this picture, its casting date was 7 June, 1970. Have you noticed a casting date on the ones that you have? That help let you know when they were made relative to the production date of your TR250.

Another example on these cars would be the dash support. If I'm recalling the cast in number correctly, everyone I've seen has the number 908895 cast into the dash support, but there were different final configurations for the dash support made from that casting and therefore multiple part numbers listed for the ready use dash support assembly.

 

[Tybalt]

D'oh! Operator error, deleted accidental double post.

 

[glemon]

Are you sure the problem is in the back? Raised right front will cause left rear to sag, etc. Also, are you sure the Goodparts brackets are adjusted the same? This will affect ride height too.

 

[Tybalt]

..... example on these cars would be the dash support. If I'm recalling the cast in number correctly, everyone I've seen has the number 908895 cast into the dash support, but there were different final configurations for the dash support made from that casting and therefore multiple part numbers listed for the ready use dash support assembly.

Correction, the cast in number is 903985. That's what I get for relying solely on memory for something like this.

 

[arbs_53]

Tybalt,

I'm certain the numbers like the ones on yours are nowhere on mine and I've had them in my hands a few times over the years. The numbers I gave were stamped into the casting.

glemon,

I can't be 100% certain it's not due to a misalignment in the front frame section, but when I took measurements a couple of weeks ago, the front end showed no discrepancy between left and right sides either in height or with diagonal measurements.

I am coming to the realization that I may not find an answer to this until I take the car off the road and strip it down to the bare frame-something I plan on doing anyways as it needs body work and paint-all part of my unofficial 5-year plan. I can then take some better measurements than I could get while crawling under a car on a hot summer day. I was just curious if anyone out there had an answer. To be honest, I'm a little surprised no one, with the broad appeal of this website among British car enthusiasts, has been able to confirm or deny what Roger Williams wrote in his book. But my sincerest thanks to all who replied.