Broken Jag rear - WARNING!

[rdorman]

I debated over if that was a weld at all when I first looked at the pictures. If that is a weld, it is one a very, very poor one. Looks like rust pitting as well. Xray any one?
Rick

[Bob Putnam]

The original tube is sweated into the outside forging. It works pretty well in a 4200 lb XJ.

Judging from the bend of the tube where it meets the end forging, I'd say that the stresses were pretty high. This wasn't a failure of the weld. Perhaps the car was bottoming out?

Was this arm shortened? Is there a trailing or leading arm?

[Tom Wells]

Hi Steve,

I use Simpson 4-point belts. The crotch belt and lap belts bolt thru the floor using large flatwashers. The floor on the E-M is, as my father in law would have said, "hell for stout".

The shoulder belts join ("Y") behind the neck and pass through "letter slot" shaped openings positioned about 1-1/2" below the seat tops. At the far end they are anchored to the rollbar support structure, continuing their downward slope.

All attachments are made using Simpson-supplied hardware.

I use the cam-lock release, although I don't think the release type is a factor.

Hi Bob,

The lower suspension arms are from a 3.8s or 420 Jag, unmodified as far as I know. There are leading arms as supplied by E-M that attach in the stock Jag leading arm position.

When the car was initially assembled, the rear shocks were too short, so the shocks reached the end of their travel indeed! But of course this would be the opposite of what we would think of as bottoming. After longer shocks were installed, this problem went away. I'm not aware of any bottoming in the usual sense.

I do use bronze bushings from Classic Jaguar in place of the needle bearings. We'll have a close look at those as we disassemble.

BTW, I notice from your web site that you triangulate the inboard ends of the wishbones. Could the outers be strengthened this way? Do you have a set I could buy?

According to Mike at CWI, he knows of no stronger wishbones, indeed he told me today he knew of no third party lowers that were as strong as the stock Jag units. Mike recommended triangulating and strapping the outer welds. The strapping would extend from the shock mount to the hub pivot bolt. Your thoughts?

Tom

PS: Remember that this car has 412RWHP and over 500 RWft-lb from about 2500-6000 rpm. The car weighs 3,000 lbs and uses 315-35/17 tires, so the stress is probably more than what most folks put onto their rears! You gotta hear it and try to pass it to see what I mean

[Tom T.]

Karl,

I agree. But the lower control arm in the picture doesn't look to me like the heavy duty ones CWI does. Anyway, thank God nobody got killed.

TT

[Bob Putnam]

Tom,

We only reinforce the inner end, mostly to take the load off the joint where we shorten the tube. Our control arms are a couple of inches shorter than the 3.8S or 420 - they actually duplicate Series I XKE dimensions. That way we can use standard ('60s vintage) offset wheels to get the correct track.

We typically use a short "tie-bar" between the rear shock mounting pin and the outside wishbone, but its primary purpose is for tying the car down on the trailer. It doesn't do much for strength.

At 3000 lbs, and using very stiff springs for racing, it couldn't hurt to reinforce the outside ends of the wishbone. If you could run a channel from the inside wishbone to the outside, and tie-in the shock mounting pin, that would be ideal.

[RICK LAKE]

Tom Wells Sorry about the rear on your car Gald your OK The ERA rear has gussets and supports on both ends of the lower arms I have poly bushing in my rear instead of the bushings. Fatigue look to be the problem with the arm. A watts rear kit would have helped with stopping the rear tire from coming forward and hitting you in the back. I have CWI housing for the rear and added a front bar to the upper part of the housing, to the frame. I use this for drag racing only. Autocross and roadcourse it's unhooked. I would go to a good welder and have him add plates and gussets to prevent the twisting the lower arm is under. CWI sells chrome poly arms, stub shafts, and other stronger parts for the Jag rearend. Currie Enterprises sells rear coversupport for the dana 44's It puts adjuster on the rearend caps to keep the carrier from moving in the housing 140.00$ You can do it your self in 1/2 hour need gasket and fluid. torque wrench to set the bolts. CWI sells chromepoly stub shafts that are good for 600 hp the come with harden spider gears. Chromepoly output hubs also. You can buy a 9 inch ford rear if you get the large bearing and "N" housing for 3500.00- 3800.00 It is no stronger than the dana if set set with improved parts. Dave S puts over 700 hp through a dana 44 with the same parts I listed. It is still cheaper and looks correct. The 2 cars that broke at R&G the red cobra 3 years ago was the car kit the the kids built for Carlisle kit car show the welds where weak and had not penitration and the arm came apart, the weld was holding on only 1/2 the tube. I have pictures. I didn't see the other car. A viper uses the same dana 44 for stick or 41 case for auto and they have the same tire as you 335-35 17's in the rear 500 hp 550 tork so it's a strong carrier. The lighter wieght of your car should make it easier on the rear unless you have bad wheel hop. Hopping does more damage than anything else. These rear where not ment to drag race. got to go. Rick Lake

[Tom Wells]

Hello Bob,

As usual, incisive and cogent observations.

I have surgery #2 tomorrow so when I get to where I can converse again, I may call - if you shortened an XJ6/12 pair, but left them somewhere around 2" longer than the E-type (the manual has the horizontal center to center distance as 17.635" between the pivot bores for the 3.8S) then I could do the suggested angle or similar for the outer ends, that might work!

Hello Rick,

The center section seems fine so far. Mike at CWI seemed to think that the only change I need to make is to beef the next set of arms. He built the diff so it should be OK

Tom the one-handed typist

[wicked fast]

Bob,

The 'tiebar' looks like a Jag oem part.

Did Jag have a problem and maybe this
is a retro fit to help relieve the problem ??

I have seen this part in a Jag
repair manual.

Seems like it would keep everything
in line.

Thinking about adding to my Mid-States
after this deal.

Thanks,
Bill Cook

[Mike Bontoft]

Hi Tom
The lower arm on your car looks like it has been modified or at least the weld has been ground off. I have a photo of what the stock arm should look like. I have never seen one break in that location with the factory weld. I have seen them bent like pretzels but never brocken on a factory weld. Glad to hear you are OK, could of been bad!

Mike

[KobraKarl]

welcome , mike Bontoft,

thanks for the photo, that is axactly the weld bead I was trying to describe, I have never seen hand work that clean.

KK

[A Snake]

I played with Jags for years with nary a problem. Simple fact is Jags don't make enough hp to break parts.

When I got my Contemporary, I got it with the watts linkage kit. My S/O made similar hp numbers to what you describe. I drove the car hard on and off the track and my only problem was the piddly little allen bolts used to secure the center pivot for the watts linkage. I'm not sure of the correct name for them, but they had a 1/2" shank which shouldered and became 3/8" thread. If the linkage wasn't adjusted to pivot freely throughout it's entire range, those lovely little bolts would shear off. Finally got it set right and the bolts quit shearing. Later I learned that some folks were drilling out the hub carrier to 1/2" thread and getting on very nicely with no more broken parts.

I did a lot of things that should or could have broken rear suspension, but I never had a failure like yours.

What I haven't seen mentioned is the amount of "fresh" metal showing in the break. To me, it does look more like fatigue, than the torn look one would get from a weld letting go.

Just a few thoughts.

Al

[Bob Putnam]

WickedFast,

As I said, the tie-bar was used to hold the car down when it was (literally) shipped across the pond. It adds little to strength.

----------------------------------------------------

Tom,

Sorry, but our jig is not adjustable.

[Tom Wells]

Hi Mike,

Thanks for the photo & info. We'll definitely check the weld area both sides for signs of "cosmetic grinding!"

It'll most likely take a couple of weeks to get this apart & viewed up close; I'll try to post more info at that time.

Tom

[427 S/O]

A few years back, I heard some folks with Big Blocks were bending their wishbones under hard acceleration. I built this to add strength and halt any movement.

[Tom Wells]

Hi Bob,

Sorry your jig won't flex We'll use plan b

Hi Perry,

That looks interesting. It would appear to prevent the outer yoke from pivoting about a vertical axis. Was that where the bending occurred in prior wishbone failures? Did it work

Tom

[KobraKarl]

Tom,

Something is buggin me a little about the fhoto's you posted , there is a significant upward bend apparent on the tube end of the control arm right at the end of the shaft. there also appears to be a bend on the yoke side.........but the direstion of the bend looks to be ......down??? or is that a taper ??? cant tell from the photo. It really does look like it was broken from bottoming or impact.

Hows the wrist? Karl

[Tom Wells]

Hi Karl,

Man, you got sharp eyes!

I believe both curves you are seeing are part of the taper of the yoke forging. I have added this observation to my list of things to check once the parts are out of the car.

Mike B. has reinforced your original observation about the lack of ridge in the factory weld area. If someone ground this weld ridge down for appearance, before or after I bought the arms, it may have been enough to cause the failure. Another thing to thoroughly check after the parts are out.

Surgery #2 was not as bad as #1, but the pain & swelling have returned full force today

[427 S/O]

Tom, this has no adverse effect on the vertical axis, the suspension pivots as normal. I made four new shafts, two inches longer to accommodate the rod ends.

[RICK LAKE]

Tom Wells Back again Tom that support for the rearend can be gotten with the added hole for the rods you see in Mikes car. You didn't say which jag rear you have in your car. An easy thing to do is add strapping on the 3 sides of the end and tube. and weld them to both parts. This will help strenghen the joint and stop the twist. You should add a Watt's linkage also if you are going to drive hard. 1 more thing I like CWI and have gotten parts there. Quality is good BUT. I found out that the stub shafts that are good for 600 hp twist. The earlier ones came from downunder and they twisted the splines. The latter ones come from Mark Williams and the steel is better and no twisting. The rear support cover is for added strength for the caps in the carrier housing. How much stress do you think that those carrier caps are under. You hit the gas and light up the tires, that carrier is trying to get out the back of the housing. A good rebuilt jag rear will take 450 hp with no problem as long as you stay with normal tires like BFG's. There traction is OK for street but poor for racing. I have 15" BFG's on the street and 17" Pilot's for autocross and roadracing. You allready broke a lower arm and are going to better parts, you will find as time and drive of your car what other things will break and you add stronger parts down the road. It's a work in process thing. Add the straps for safety. Rick Lake

[chirodale]

Hi Tom, John Crawford here commenting on your failure. We import Shamrocks with jag rearends. What I see here is that the shortening of the lower swing arms were shortened in the wrong place and then where they were shortened was never reinforced. If you can see the Shamrock Jag rearend, you'll notice that where its shortened on both the axel as well as the lower swing arm are sleaved and welded on both ends of the sleave. We've talked with our manufacturer on this issue and they have tested the rearends to 700hp with out failure using street tires. Obviously with this kind of hp and racing slicks, you're bound to break something. The original Jag that these rearends come out of weigh around 4600 lbs. Our Shamrocks complete weigh 2600 lbs. Then with shortening them only adding strength from the original. So my thoughts are on your failure came from whoever shortened your components and the only other opinion as to the failure would be if the shocks and springs were extremely to rigid for this application and not allowed to flex with the weight of your car. This is a very unfortunate failure but definitely not the norm. Nice car though. Good luck
John Crawford
Shamrockautocraft.com