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Triumph TR3 FAQ page

Triumph frame fatigue Discussions


> I got a nice email from Henry Frye this morning. Henry, knowing that we are reworking our TR4, pointed to inspecting the shock towers and anchor points
> for the cross member. He is exactly right.
> Although most everyone understands this, it bears drawing attention to it. 
This is why we are totally dismantling the TR4. Sean and I detected something
> amiss with the front suspension as we discussed winter storage. That led to moving the chassis to Niehaus Restorations. Keith is a master welder/fabricator.

> We did some gusseting twenty years ago that helped for a long time, but finally the shock towers were exhibiting large cracks. The anchor points for
> the cross member is light gauge sheet metal and they were crushed and torn.   All of this was fixed and reinforced with better materials. The x-member was
> showing rust and fatigue so it was redone. Sean painted the frame in an industrial grey so that we can better see what is happening with frame.

There has been some on track frame failures with TRs in the past. We noticed something going on when #197 came off the track the last race in 2012.
> Ignoring it would have resulted in a serious failure in 2013. Perhaps a free ride to medical, as well.

Anyway, unless you are investing in a RATCO frame, this is a good time to do a close inspection.

> Joe Alexander


It's worth taking a look at the sort of modifications that we do to the TR4 chassis for rallying.

Clearly the sump guards and belly plates etc which are there to protect vital things from flying rocks and damage from heavy landings and two wheel adventure are not required, however the reinforcement work is all done to preserve the integrity of the frame and proven by my gentle driving.

In terms of the front suspension and towers; even the Works Rally TR4s which were nowhere as tough as say my TR4 Beastie had a number of filleted plates added on the joints and corners, all sides filled in on anything that looked like a box, the main cross member plated up with another 3mm of steel and the welded joints all reinforced using triangular fillets. You should all be doing this as the majority of cracking and failures are due to fatigue, not from impact loadings.

Bear in mind that with one exception you are adding very small segments of 2mm thick steel, so weight gain is a few months of not eating at macDonalds.



> Do TR6s (1974) have this weakness also?

The ladder frames under the TR2-TR4 seem to be much more rust resistant than the wishbone frames under the TR4A-TR6. I have come across numerous rusty project cars over the years, and have seen plenty of rusted out TR3's and 4's with what appear to be good frames, but I have never seen a rusty TR4A, 250 or 6 that did not need extensive frame work. I should add I have come across plenty of nice wishbone framed Triumphs sitting on frames in dire need of attention.

I know the spring towers and cross members are different between the ladder and wishbone frames, and I believe the newer wishbone frame design is more robust. However, because of their propensity for rust, I'd venture a guess that the wishbone framed cars share the probability of failure in the areas Joe mentioned.

Remember, the stess we put on these cars running them on track with today's racing tires is way beyond what the designers ever dreamed possible. You need to reinforce many key areas, keep the frame clean, paint it with something that will not hide cracks, and be very diligent with close inspections between race weekends.



It is also not uncommon to find the welds cracked on the brackets that the steering rack attaches to on the TR6.


In my spare time, I am building a TR4 daily driver. I got a street car frame from another FOT member. It looked good and is in very good shape. When I had it media blasted, I found cracks on the frame around lower wishbone mounting brackets, cross member, and near the motor mounts. Keep in mind that this is a stock TR4 frame not subjected to the stresses of racing. Had I not had it media blasted, I would never have seen these. Now it is primed and painted with Eastwood Chassis Black. The build begins.


I had to repair lower front suspension point cracks on my TR3 frame that were not evident until I had it media blasted and started grinding on it, read started grinding on it. The shock tower diagonals looked good too, until blasting revealed pin holes on the lower end. A center punch went through the rusty metal with ease. These frames rust from the inside out. Grinding particles from the cutting of the diagonal gathered around the cracks in the frame and only then did they became obvious. Had I not seen the pin holes, the frame would have been painted and reassembled. Instead, I went through an exhaustive process of strengthening and gusseting many areas of importance. I even welded extra tubing inside the body outriggers creating more substantial roll cage mounts. My car has been out of service since 1975, so that's a mere 15 years of use before this type of frame failure occurred and my car has only lived in California.

Dave H.

I don't think anyone mentioned that the IRS cars are notorious for weakness in the mounts for the differential and the brackets up front where the lower A arms mount. These usually fail without the added stresses of racing. I did a frame off restoration of my TR250 last year. It has resided in Oklahoma (a relatively dry state) and been garaged for all but its first 6 years. It body was relatively rust free as Triumphs go (solid floors, etc). After repairing and reinforcing the usual problem areas, I noticed a very small pinhole on the bottom near the center (called the T-shirt) area. The thin metal was only a few square inches and may have been partially because it had scraped bottom there at some point. Since these frames rust from the inside, I wonder how many are out there with thin metal, which has not yet rusted all the way through?


I have fixed a number of these IRS frames and reinforced and welded them back together. For the most part you can still get the cruciform plates and the outriggers pieces for the rear control arms. I always put a gusset top and bottom in that area. The biggest problem I have had of late has been cars with the tube shock conversions or "Break Me Here Brackets". They fracture and break off the shock/rear diff cross member. Replacement cross members are very hard to locate. I developed a brace to over come that and have installed it on many club members cars. My sonic test for a rusty frame is a good body shop pick hammer or similar. Midwest and Eastern frames disintegrate at the sight of one of those. Cut out the rusty area and replace with suitable thickness flat sheet ( I use .085" sheet as original).


I had exactly that happen to my TR6 on the way back from VTR2007 at Valley Forge. Ripped a piece right out of the cross member. Lucky to make it home. I welded the piece back and went back to my old lever arm Armstrongs rebuilt by Apple Hyd. to heavy duty. I think the mistake I made was not adjusting the bump stops so they would engage before the shock reached its limit. Once that happens it looks for the weak spot which seems to be that cross member. If I go back to the tube shocks I'll weld a 1 inch piece of square stock up in the cross member so that it becomes four sided instead of the stock three.

Bud Rolofson

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