This spring I pulled the jag out of storage and found a broken bolt on the floor. Hoisted up the car and found the rear subframe is missing the right front bolt, I read "Rear Subframe mounting bolt" post from daro31 from 2017 and it looks like a difficult job to repair. Is there any further advise someone can offer? I am still driving the car, any safety concerns?

Bolt found on the floor, appears to be snapped in half.

Head of the bolt

Bolt came from this area , rear subframe front right side.

Close up view, front right side. Doesn't appear to have any access holes to reach in.

 

Here's the link to the previous thread https://www.jaguarforums.com/forum/s...-bolts-181392/

My concern would be if that one just fell apart the other three are going to do the same.

 

Is that a bottle of Kaluha in the background? I think you need to drink that before you go to the mechanic. Unfortunately I see PIA in your future.

 

Yes I can see this being a pain in my a**. I wanted to redo the rear suspension so I guess now would be the time to do it. The Kaluha is next to a bottle of Voka both are used to make a Black Russian drink, one of my favorites. I will start this job in the fall and that's the drink I will have when the car is back down on all fours.

 

From the above post it appears that there is only one more problem bolt to get out. That's good I was thinking there might be three others. I want to redo the rear suspension this winter so that will be easier to do if I remove the rear subframe. Then I can take care of the bad bolts too. I will cut a hole in the floor ( inside) and heat head of nut and hopefully it will spin out.

 

Safety concerns. Don't drive the car until it is fixed. If one bolt is broken, it will put more strain on the remaining ones, which may also be weakened. If the subframe breaks loose... The accident investigators will blame you for continuing to drive an unsafe car. Providing no-one died, you may be able to escape jail time, but I wouldn't risk it.

I had a rear joint let go on my old Alfa 164. It led to a head-on collision. Luckily both parties were wearing seatbelts. I got two broken ribs but didn't go through the windscreen. My lovely irreplaceable car was a write-off, but it could have been so much worse. The guy I hit had an airbag and wasn't driving too fast. So he only got a smashed van and whiplash. It shook me up and I don't take chances on cheap parts anymore.

 

I replaced the three remaining bolts with new ones. The three didn't look bad and came out easy. I still plan to remove the broken one this fall and redo the rear suspension at the same time.
I am no metallurgist but I know of Hydrogen Embrittlement and the one bolt that fell apart could be do to a bad heat treat process. A Hydrogen Embrittlement failure requires a heat treated part and the part under stress for a long period time to fracture for apparently no reason (which was my case).

Three bolts remove and replace with new one, three look good and came out easy. The fourth one (broken) I found laying on the ground.

Fourth bolt could have failed do to Hydrogen Embrittlement.
For those of you that have a 2000 S-type you may want to keep an eye on your rear subframe bolts. If my bolt fracture is indeed do to Hydrogen Embrittlement there may be more out there.

 

It's rust not hydrogen embrittlement.
Just plain old rust.
.
.
.

 

I agree. The road spray ate away at that bolt and that second one that was on the verge of breaking as well. That third bolt also was deteriorating! So wow you were lucky that broken piece fell out where you could see it and you were smart not to ignore it! That road salt is a killer!

but I also agree with the post about not driving until its fixed. Driving with one missing bolt could be multiplying the forces on the other bolts in ways we cant readily perceive or imagine without performing a stress analysis. The configuration of the mounts and the weight distribution all play a part in the loading of those bolts and its not as easy as saying the other three bolts not take on an additional 33% load. One might actually take on a much higher load than the others making the car very risky to drive. Id drive it home and park it till its fixed

 

Farmer John, I am in a similar situation, except the bolt that failed is the forward left, of the rear sub frame.
Looks like you will have to remove the rear sub frame complete to access what is left of the broken bolt.

If you notice the removed bolt end threads (the 4 off threads exposed at the bolt end) of the other three bolts, the thread tops are all stripped of thread. Stripped while removing them no doubt.

See (below) the photo of the bolt top in the access hatch which DARO 31 posted in his thread.
The exposed threads of the bolts, inside of the tube void space would appear to be corroding due to ? and causing difficulty in removing the bolt.(s)

So this little difficulty will have to be overcome. i.e the over coming of the corroded exposed thread portion of the fractured bolt during removal. While your removed bolts (3 off) at the top look in fairly good condition, as does the underneath of your 2000 4 Ltr. There was enough rust corrosion on the exposed threads to cause the stripping of the exposed threads and thus making the removal difficult on the broken bolt.

I do not think you will have much difficulty, given the application of heat and intermittent vertical mechanical force (application with 2lbs hammer) on the fractured bolt end during removed to ensure the thread end is freed and allowed self cleaning by rotation down and backing up during the removal. If mole grips fail to give enough rotational torque, then welding on of a suitable nut to the protruding bolt shaft will assist.

I would be looking to avoid the cutting out and the installation of a new pillar tube for this bolt at all costs.

Quote from DARO31 post.
"Has anyone had the back seat out of their Stype to see what is at the top of these subframe mounts. There is a threaded tube welded in an you will see in one of the attached photos where I was able to get some heat in. Even though I got the tube cherry red I have still only got another half inch of thread out. The interior in my car is pristine and dove and I really don't want to remove it. Has anyone got any idea what I will find on the interior side of that threaded tube?

The bolt acts like it has rust at the top that is being drawn down with the bolt as even when I turn it back in it binds after a 1/4 turn. I have gotten it this far with a back and forth motion with vice grip and heat for about 2 hours, and now it is totally frozen."


From the above the bolts would appear to be in a more corroded condition than yours, but best to proceed carefully.

Also, from your post.

"The three (bolts) didn't look bad and came out easy"... Can you define: easy?

 

Can you please explain the difference?
As previously mentioned, park the car up until all 4 bolts have been replaced. I totally agree. Even with 3 new bolts the car could be dangerous. It was designed with 4 for a reason. If it was perfectly safe with only 3, Ford/Jaguar would have designed it that way.

 

hydrogen embrittlement suggests the individual part was faulty due to improper plating or something went wrong during manufacturing that caused the bolt to be weaker than a similar bolt processed correctly. That fault would suggest theres not an inherent problem with all the bolts and may only be a fault in a group of bolts processed during a specific time period or lot. That would allow for someone keeping the other bolts and not replacing them. In other words, not an inherent defect

rust as the fault would mean youd be able to inss as pect for the defect and replace as necessary. Also allows for corrective action to prevent future reoccurrence by taking steps to avoid the oxidation. No oxidation, no rust, no more broken bolts due to rust

 

Yes rust is a contributor to the failure but I believe not the root cause. I replaced the three I could and feel safe driving the car until I can repair the 4th this fall. Cars are designed with a safety factor. If one bolt will do the job then install two for a 100% safety factor, if a 10mm bolt will do the job then use a 12mm bolt. Of coarse some common sense will also be used but things are not design on the edge of failure.

 

I am sure the top threads were not stripped off during removal of the bolt. It appears to me that is the way the part was manufactured. What is known as a "dog point" bolt to help installation in a blind operation such as this. It also appears that the treads below the dog point are thread tapping so the bolt makes it's own threads during the initial installation. That would make sense because of the blind operation similar to a seat belt anchor bolt which usually goes into an extruded hole.

 

I can't agree, I don't believe those are dog points, they look to be stripped probably as the protruding section was corroded, which would raise the concern that the thread in the captive nut or whatever
they screw into may also have been damaged.
Hopefully you were able to check those before you put the new bolts in.

 

I will take a closer look at the bolts tomorrow and will attempt to get a picture as well. New bolts are already installed, the top of the captive nut can not been seen.

 

If you inspect for rust, all bolts will be bad and is very subjection, one rust pit or two, 0.5mm deep or 1.0mm. Inspection for hydrogen embrittlement is impossible to check in the field. If other 2000 Jags have a similar 12mm harden bolt failure then just replace all bolts for that assembly.

 

Please see below, the Dog Point type bolt, these are off a 2005 S type, C2Z 2226 ish the part number will change with the VIN/year etc. M12 x 165mm length.


Dog bolt end not fully threaded. C2Z2226

C2Z2226 M12 x 165mm Judging from the thread discolouration the top 4 threads protruding are subject to corrosion.





This bolt is more fully threaded, and not a dog point bolt, as the sheared threads are clearly visible at the top of the bolt.


Why Jaguar would want to have this extended thread protrude into and passing through the bush, I am not clear. Later bolts would appear to have the dog point, shorter thread lengths and still manage to protrude 4 threads above the locking nut, which apparently are susceptible to severe corrosion.

Looking at the Vin, part number and price, the later bolts are much cheaper, the earlier bolts being 4 x more.

 

There are many styles of self tapping dog points. I cleaned off one of the jag bolts and I still believe the top 3 thread are not stripped off or corroded , I am sure it was manufactured that way. You can see the cutting notch on the first couple of threads. I believe the nuts they go into are good. I will check them when I remove the sub frame. I had a couple of other bolts in my tool box that shows a similar design example2 is most like the one used on the 2000 jag. Once the threads are formed in the nut there is no need to use a thread cutting dog point. I replaced with a standard harden bolt (non-dog point) much cheeper $4 instead of $40.

 

Project update May 2023:
Dropped the rear subframe and removed the broken bolt. Now I will redo the suspension.