Xj Bump stops

[Jaymz]

This is probably a silly question but one I can't seem to find a definite answer for.

I have lifted my XJ with a 2inch lift. How much do I need to adjust my bump stops? 2 inches as well?

Cheers.

[Hamsteh]

Bumpstops are usually required for two reasons: to prevent damage to shocks as a result of over-compressing them and to accommodate larger sized tyres (stop them from hitting body/flares etc).

As a result, you need to adjust bumpstop length if:
Your shock absorbers have a longer minimum length, or
Your tyres are larger and are at risk of hitting body etc

[junglejuice]

The third reason is to stop the springs from over compressing, a 2" lift will most likely require around a 1" extension max, when I was running the OME shocks they had the same compressed length as the stock shocks did so stock length stops were ok...

[Jaymz]

Hmmmm seems I'm getting slight tire rub on my flat flares under flex so I will adjust to fix that first... now I just have to find a way to flex it up in my garage safely so I can measure how far to extend them.

Any hints on how you guys flex to measure bump stops?

[Raisins78]

build some ramps? or use a really high jack maybe?

[UKXJ]

Hmmm, well that's something I've learned - I think.

My XJ had 2"" lift fitted by P.O. x several, back in 2003, but still runs stock (probably original) shox and one thing that occurred to me was that the bump stops serve no purpose and had in mind some 2" square tube under the rears & rubber hammer heads (thanks Gojeep) in the front but seems I needn't bother, unless/until I replace the shox - with anything other than OME's.

[Wooders]

Bumpstops are usually required for two reasons: to prevent damage to shocks as a result of over-compressing them and to accommodate larger sized tyres (stop them from hitting body/flares etc).


I'll ague the symatics of this all day long.
The correct way to determine a suspension setup is to start with the desired coil height, then fit bump stops to protect the COIL from being over compressed.
Then with the bumpstops defined you can select the optimum shock length.

Sure the bumpstops can be adjusted further for tyres/shock changes - but the PRIME job of bumpstops is to protect the coil.


How to determine how much:
Ok now we'll assume the factory R&D has determined a good starting point.
1. If fitting coil spacers, you are effectively "raising" the bumpstop by the entire amount of the bumpstop with the same spring. Also the coil spacer is 100% non-compressible lifing "space". So to maintain correct bumpstop gap the stops should be adjusted by the same amount.

2. If fitting new coils then the ideal method is to compare the original wire thickness & wraps, compare to the new coil wire thickness & wraps. the total difference between the 2 should be the minimum change in bumpstop. or you risk coil bind which can result in premature sag and in extreme cases failure of the coil.

Rear leaf pack is a different beastie, but the bumpstops will still help prevent a number of problems that might occur.

[Jaymz]

Thanks for the info guys. I actually understand what the stops are there for now. Now just to work out a way to flex it up enough to measure what I need.

[Kirky]

I understood that front bumpstop length was also pretty important with a lift kit to stop the drivers side upper control arm from whacking the sump and the autotrans cooling lines. This happens when driver side is under compression and passenger side wheel falls in a hole.
PK

[junglejuice]

I understood that front bumpstop length was also pretty important with a lift kit to stop the drivers side upper control arm from whacking the sump and the autotrans cooling lines. This happens when driver side is under compression and passenger side wheel falls in a hole.
PK

That is how I set my bump stops which also coincided with the compressed length of the shocks and also prevents the over compressing of the springs.
In the rear I have also extended the bump stops but this was mainly due to the airbags having a reduced travel then what the suspension allowed, to me the airbags are a higher priority then the extra 40mm of travel that I lost....