Hi guys, A few days ago I removed and replaced the right rear shock and reassembled the unit using a new "top hat" bush with the new shock. Apart from the old top hat (which had crumbled to pieces), the lower bush (spherical joint) of the old shock was worn to the point that it could be wiggled around with a little finger, so replacement was well overdue.

When I ordered the new shocks, the supplier listed the shocks as Bilstein MNA3540AA's which are apparently the OEM equivalent replacement for the original units on these late models with the X300 type rear suspension.

However, when the shocks were delivered I was surprised to see that the model number was not MNA3540AA, but Bilstein 24-018586. My first thought was to return them, but after checking out the model found that these 24-018586's suit early X300 VDP's with the comfort suspension setup, so I decided to fit them.

The first difference I noted with these 24-018586's was that the rubber material used in the MNA3540AA lower bushes had been replaced with what appears to be polyurethane, but the main difference was the arrangement and size of the foam isolator bushes, lower washer and metal spacer used at the upper mounting plate - the lower isolator and washer were considerably larger than the MNA3540AA parts and both the upper and lower isolator apertures were also quite a bit bigger and made to suit the spacer supplied of the 24-018586's (roughly double the thickness of the MNA3540AA's).

Now as I didn't have any new "correct" upper isolators/spacer/washers on hand and that the new spacer wouldn't pass through the new "top hat", I decided to re-use the original foam isolators as I had to get the car reassembled and out of the garage the same day. Needless to say, even though the isolators were not too bad and still fairly uncompressed, that was probably the wrong approach as the test-drive later that day confirmed ...

Checking the arrangement on JHP I noticed that the XJ40 "top hat" bush had been eliminated entirely on the X300 suspension and indeed the spacer, washer and isolators matched the components of the 24-018586's. From the illustrations, it looks like the extra thickness of the spacer takes up the slack and replaces the top hat on the upper mounting plate - I checked the part numbers of the upper mounting plate and it's the same on the late 40 and the X300, so I'm assuming I could have fitted the new isolators after all ....Oh well, I guess if a job is worth doing, it's worth doing twice?

I'll be doing the left rear in a few days and see how the new arrangement fits. I was concerned at first that the recess for the top hat in the upper mounting plate would be a problem (gap) but thinking about it, the increased diameter of the lower isolator probably takes care of the issue - especially as the X300 top plate is identical to the 40. If it all goes together properly on the left side, I'll pull the right again and replace the top hat arrangement.

here's a few pics, more later when I pull the left side.







Hope this is of some help to anyone contemplating the same job on a late 40!


Larry

 

Today I decided to remove the right side shock once again.

I'd spent all weekend wondering how the space created by removing the "top hat" bush in the upper mounting plate could be accounted for by using the X300 bushings. Even though the metal spacer sleeve on the X300 shocks is considerably thicker, it's still about 1/4" less in diameter than the aperture normally filled by the top hat in the "original" top plate arrangement. I was concerned that without a bush between the upper shock shaft and the plate, there would be nothing to prevent the shaft spacer from moving to one side and contacting the plate, very like the symptom of top hat bush failure.

After re-checking that the X300 and XJ40 top plates were identical (same part number) I realized there WAS something in the design of the new arrangement that allows the shock upper shaft to be self-centering without using a bush. As I re-assembled the shock to the plate with the new isolators and washers, I saw that the spacer sleeve was slighly shorter than the thinner "old" sleeve and that the upper concave washer was also a different shape, slightly more of a "V" than a dish. It also had a a definite "flat" area at the bottom that mated with the top of the new spacer sleeve. When the nyloc nut was fully tightened I finally saw how the engineers had overcome the top hat issue. The V shaped upper washer, isolator and shorter spacer sleeve work together to self-center and isolate the shock absorber shaft from the upper plate without any need for the "extra" top hat bush.

Tomorrow I'll re-install the right side and start on the left.

I'll take a few shots of the differences in the new/old parts and upload them soon.

Larry

 

Re-fitted the passenger side shock using the new bushing arrangement and removed the driver's side and fitted the new unit. I'll install the driver's side tomorrow.

As promised, here are some pics comparing the old and new parts.















As you can see, the X300 system is quite different from the stock 94 XJ40, but fits perfectly.


Larry

 

The first thing I noticed after fitting the new shocks was that the car stayed more "upright" on a sharp corner, handling was definitely better.

It still seemed a bit bumpy over potholes so I upped the tire pressures (running Kumho Excstas 225/60/R16 98W's) up to 31/33. That did improve the rough-road feel a lot.

Before the swap I was running the Kumhos at OEM Pirelli "comfort" level in the 28's range (I know the book says no if not Jag Pirellis) thinking the lower pressure would give me a softer ride over the bumps, but that was all wrong - I think I must have been bottoming out fairly often because the hub was pretty shiny where the bump stop hits.

I finally got out on the highway today and the car behaved beautifully, better than I expected, really controlled. I'd had this annoying intermittent minor tapping/shimmy/vibration in the left rear - the new bushings/shocks seem to have sorted that out too, so all good.

On to the next job!

Happy motoring

Larry

 

I've just found out that the springs on my car are replacements and are the wrong springs for the late suspension, so the rear shocks will have to come out again!

Due to a broken spring some time ago, a PO replaced the springs with JLM11382's - the springs for the earlier type of suspension where the spring sits on a collar on the shock.

The correct spring for the late model 40 with the X300 arrangement is JLM12257.

JLM12257 is quite a different animal and has more coils than the JLM11382 as you can see in the pics below:

Incorrect JLM11382 spring currently fitted



Correct spring for late XJ40, JLM12257


The JLM12257's illustrated above are the actual springs I bought to originally replace the old units, but when the old ones came out I chickened out because they didn't match the old ones (which I assumed were OEM at the time )

One more point - the old springs had 2 height adjuster shims fitted, problem is I've no way of knowing if these were added when the incorrect springs were fitted or if they were originally in place when the car was new ...any ideas on this?

Thanks

Larry

 

Hay Larry,when I installed KYB's in Cin's ride,I noticed things like # of coils,diameter of steel rod used,and coil diameter.
nothing looked like the stuff that came out.
put it in anyway.

The ride is a little stiffer than stock,but wayy sportier!(she loves it!]

The new springs in your pic look like fronts.check the diameter of the winding
and the length ,
sounds like it's workin good tho..

think ill' work on Cin's car tomorrow,parts are HERE!!
Hopefully someone else knows more....
Let us know what you see..Cheers
Jim and Cindy

 

Hey Jim - Good news on the parts!

I don't think they're front springs mate! - take a look at these springs in this video of a guy replacing the rear shocks on an X300 (same suspension as mine)


good luck with the fuel system re and re tomorrow!

all the best

Larry

 

Replaced the rear springs and fitted the JLM12257 units.

Old spring had a part number impressed, CCC6536 however a search on JHT for that number came up with no match ...curious!

here they are side by side, old spring on right:



Larry

 

Hi Larry,

Did the rear ride height change, and if so are you happy with it? And how's the ride?

Thanks!

Don

 

Hi Don, Ride is much improved, I think a bit firmer but well controlled.

Height of car (rear) is 27" to the top of wheel arches at both driver and passenger sides.
Prior to change, measurements were different side to side, 26-1/4" on left, 26-1/2" right ..I removed one of the two 6mm spacers previously fitted on each side.

Here's a pic I just took of the new level trim, seems fine to me!



cheers

Larry

 

Larry,

I really like that slight increase in rear ride height! It gives the stance a more aggressive look that is a big improvement. I wonder if I could fit those springs to our '93 with the pre-X300 suspension???

Your car is a real beauty!!!

Cheers,

Don

 

Thanks Don!

I don't know whether they'd work on your 93 - I went with the JHT OEM part number for 94MY when I selected them - the greater number of coils is theoretically a softer ride but how they would work in a shock mounted situation ...not sure! If it's any help, the free length of the JLM12257 is 14" (35.5cm) and they have 7 active coils as opposed to the ones I took out which have 5.
Unless the old ones are compressed with age, they appear to be about 1/2" or so shorter. If you wanted to increase the rear height without changing springs, a couple of 6mm spacers under the upper spring pan may be the answer?

Dennis (Grooveman) made up a couple of spacers he fitted between the body and the upper shock mount which gave the car an even more "aggressive" look, but he tells me he also runs larger aspect tires on the back, so no doubt that contributes quite a bit to the "look".

Dennis had a chart for spacer size v. ride height and Bryan N figured out that in all cases a spacer increases the ride height by 150% of the thickness of a given spacer. A 1/4" spacer will give you a 3/8" rise, 2 will get you 3/4" etc.

Pics of Dennis's approach and result are in the Grooveman album over on jaglovers if you want to check it out.

To get the look you want (if you don't mind swapping out the units a couple of times) I guess it's no problem to experiment if you've got extra parts around - spacers are cheap but OEM springs are up there and if you're not in the UK, shipping will be a killer.
In some ways I was pretty lucky when I did mine. First of all the springs were from a low mileage Californian X308 (and not one from near the Ocean!) and the ebay seller had them up for a $45 b.i.n so it didn't cost me too much to have a shot at it. Once I bought the springs I had to think about spring compressors and bought a pair of heavy duty ones for another $20 on ebay the same night. The big conical donuts at the top are OEM and were pretty reasonable too.

Doing the job, the spring compressors were indispensable. The ebay ones have a good quality feel for them, heavy castings and heat treated thread. I read in the CD to mark the position of the compressors on the springs if you have to remove them and I can see why - there's not a heck of a lot of room to get the shocker/spring out and if you install the compressors in the same position as when it came out, at least you know it must be able to go back in!
Of course, when you fit new springs, there's no way to mark them so best make pic or note of where they were placed when you took the shocks out and orient the new springs the same way - the springs on the late suspension fit into a thin rubber gasket in a cast socket on the control arm, molded to the profile if the spring's base. Spring can only sit in this one position and because of the space limitations, it's nigh impossible to rotate the spring if the compressors are in the wrong place.

The ebay compressors are a bit long for the rears of the car so I took a chance and had a pal cut about 2"-3" off the thread. I was on the right track though as the guys in the x300 forum confirmed that short was the way to go with the X300 rear springs.

Another thing that made the job easier was to remove the 4 subframe mount bolts by the diff. That helped the control arm to drop lower so I didn't have to play prybar/armstrong quite as much as my first attempt!


happy motoring

Larry

 

Groove and I have talked about his spacers and I even purchased some plastic starboard material he recommended to make my own, but I also found a couple of sets of OE Jaguar spacers of different thicknesses, so the next time I have a reason to remove the rear shocks I plan to experiment. The springs are known to sag with age, and the large "donut" upper spring isolator bushes compress over time, so it's too common for an XJ40 to develop a sagging rear. Not attractive!

Cheers,

Don