XJ XJ6 / XJ8 / XJR ( X350 & X358 ) 2003 - 2009

Rear Subframe Captive Nuts

 
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Old 05-13-2019, 03:44 PM
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Default Rear Subframe Captive Nuts

Hi

Recently tried to replace a rusted through NVH brace which is secured by the front rear subframe bolts ,when trying to undo the bolts the captive nuts started spinning inside the chassis mounts .
the bolts and captive nuts are rusted solid and it is virtually impossible to get access inside the mounts , the subframe bolts are now loose , any info on how to overcome gratefully received .

Mark

x350 2007

Captive Nut Inside subframe mount is spinning
 
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Old 05-14-2019, 08:56 AM
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Cutting looks to be your only option, the best way is the real question.
Grinder with cutting disk if there is room, is easier than a reciprocating saw.
Cutting torch around the gas tank is kinda iffy.
Unless your real careful, things could go up in smoke.
 
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Old 05-16-2019, 05:01 AM
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The more i look at mine, am thinking the whole steel rear frame section will have to be removed.
Wondering just how big a job that would be, once the rear suspension, & all are removed.
If your lower brace is this bad, does rest the frame it bolts to look much better?
If the four bolts that appear to attach the frame to the body, from the drawings.
Are accessible from the trunk, it SHOULD be similar to removing the bed from a pick up truck
Not all that bad a job, after everything necessary, is disconnected, & or removed.
My 07 has this same situation starting, but not nearly as advanced as yours.
Spraying used A T F on it slows it down, but more is need to stop it.
Am looking and asking myself, as well as others, is this a project, you can do yourself???????????????
Used parts are around, blasting, then painting before replacing, would be the best solution.
Someone here, has probably already done this, and will respond.
 
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Old 05-16-2019, 12:22 PM
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If you are contemplating removing the subframe then I suggest you take a look at the rear brake pipes while you are at it.

About 18 months ago I had to have the rear brakepipes replaced on my 2004 Super V8 ( in the UK ) due to corrosion .In order to do this they actually removed the rear subframe and the fuel tank. They also found the captive nuts were really seized up, the technician spent a lot of time sorting the problem but managed it in the end. My rear Brembo callipers had seized bleed nipples so I sourced a pair of used callipers and they were swapped out at the same time.
 
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Old 05-16-2019, 12:45 PM
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Saddle fuel tank, a new fixing bolt shown, and the subframe when it was on the floor !
 
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Old 05-16-2019, 02:02 PM
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The exposed heads on all the bolts on mine look fine.
But if torque is applied and one or more were to break.
Or to break the nut loose, on the other end.
That i'm guessing is spot welded, or underneath the gas tank, of all places?
If total rear frame removal is required, is the removal of the fuel tank really required as well?
Unless i'm mistaken only the heads are visible on mine, none of the bolt is exposed.
Just realized this is inside the trunk???
Thought this was from underneath the car
That would make sense, of the picture to me
Now i see after looking at roviw's pictures of what made no sense to me.
On what the issue is
 

Last edited by Wingrider; 05-17-2019 at 07:31 AM.
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Old 05-19-2019, 05:17 PM
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I can understand why roviw s technician would have spent so much time resolving this issue
The previous photograph of the seized captive nuts was through a small opening in the aluminium subframe support as shown by the green arrow in attached photo , it would seem the only way to replace the seized captive nuts is to cut the exiting bolts to allow the subframe to be dropped , then somehow get the old captive nuts out through this small opening and then replace with new captive nuts and bolts ( if new ones are available )
roviw - any clarification on the actual detail of how this was carried out when they replaced yours

Arrow showing opening in subframe mount
 
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Old 05-21-2019, 05:48 AM
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Those type of captive nuts are a nightmare, they are just a nut which is held in place by a metal "spring", once the bolt rusts up any pressure on th ebolt causes the nut to force its way out of the spring and just spin. had this a lot on ford Mondeo front subframes, and Vauxhall's, Vauxhall's were relatively easy as you can see the nut, so a bit of heat and some vice grips usually did the trick, Mondeo's were inside the chassis leg and the method i used was to cut a square out for access , then heat and vice grips, replace, and weld a plate over the hole. Lately I have an inductive coil heater which works a treat.

This looks a bit more tricky, definetly need heat, an inductive coil might help, but it looks like it would be difficult to even get it over the nut, not a lot of room there. If you could get access with a mig welder, you could tack weld the nut in place, the heat of the weld, might also help to free up the bolt. Of course if it's steel to Alu, then you have more trouble.

A few years ago, I had a ford in with siezed spark plugs, alloy head and steel plugs, so a danger of damaging the head, no movement on the plugs whatsoever, I created a little dam around the plug with plastecine/putty and filled it with vinegar, left it for a full day, replenishing the vinegar a few times, and the plugs came out like it was in finger tight.
 
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Old 05-21-2019, 04:30 PM
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Originally Posted by Mark One View Post
I can understand why roviw s technician would have spent so much time resolving this issue
The previous photograph of the seized captive nuts was through a small opening in the aluminium subframe support as shown by the green arrow in attached photo , it would seem the only way to replace the seized captive nuts is to cut the exiting bolts to allow the subframe to be dropped , then somehow get the old captive nuts out through this small opening and then replace with new captive nuts and bolts ( if new ones are available )
roviw - any clarification on the actual detail of how this was carried out when they replaced yours

Arrow showing opening in subframe mount
Sorry but I do not have any further details as to how he did the job, the actual technician has since left my local Jaguar dealer so I cannot even pop in and ask him.
All I remember was they were telling me there was going to be a lot of extra time involved in the various work at the time. It was part of a service, MOT ( road safety test in the UK )and various other things. The car was with them a month, I had told them there was no hurry and to work on it whenever they could.
I have been using the local main dealer for 30 years and they look after me very well, so I help them whenever I can and they , in turn, help me out when the invoice is prepared.
This particular visit amassed a job sheet with 36 hours on it !!
I did supply a pair of used rear Brembo Callipers, a new hand brake motor unit and cables and a few other parts, they also provided a few new items as well.
I told them the car was a keeper so he did say he put loads of grease/copperslip whatever to minimise the nuts seizing again .
 
 
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