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Insufficient Drop Arm Spline Engagement Issue

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Hello all,

1988 110, PAS, 4 Bolt Box, Proof i'm not being crazy and it is a RHD adwest 4 bolt pas box...



Bit of an odd one to me this one, brief background, had a loose ball joint on the drop arm, no problem, just swap it in situ, in the process the old upper cup for the balljoint simply just came out with no pressure, new balljoint cup was loose, assume it's spun and worn. So, new drop arm.

Old arm came off fairly easily, bit of puller pressure and off it came. Procured the new arm for the 4 bolt PAS box a QFW000020. Went to fit it and push it on by hand, this is all the engagement I got...



So assuming it was just 'newness' and paint etc, tightened the nut up to see if that was it, definitely not, engagement about 8mm shy of what it needs to be.

Old one, slips straight on no issues



So i've ruled out the obvious, splines are all clean, rust free and in good condition.

Old and new arm have all the right splines however the old arm taper is very very slightly larger than the new arm. Also the splines in the old arm are 'sharper and thinner' while the new arms are 'blunt'. Lastly the alignment 'slot' on the back of the old arm does not accept a 8mm bolt, the new arm does.

Been to a land rover parts place near me and compared my new Britpart arm to another new allmakes arm, identical and both measure the same, confirming that my drop arm is indeed different and it's not a defect. The old arm has a casting number of BD2295604 but that doesn't seem to mean much really.

So my current thinking is this. I somehow have a gemmer 6 bolt output shaft inside my 4 bolt adwest box so I need the old RTC6398 arm. The box was reconned about 15 years ago and has very little play in all that time.

I do know that if you accidentally fit a 6 bolt gemmer arm to a 4 bolt box, it will fit, but is guarrenteed to loosen over time, which would make sense with my logic above. But from what I can see, this is unique. Also I have found other forum threads of 6 bolt owners with arms that don't engage fully which seem to be because they have been sent 4 bolt arms, which again follows with my assumption.

Thoughts, do i have a confused steering box that thinks it's a hybrid?



Edited by Adam001
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Your logic is sound.  I would suggest talking to Adwest.  It may be they deliberately use 6 bolt shafts?  That being the case, they should be able to supply arms that fit.

Either way, Britpart or Allmakes would not be my first choice for something so safety critical.


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Thanks for the offer, but i've got one coming from Paddocks in the morning. This mini saga has cost me quite a bit of on road time!

I considered converting mine to the disco setup at the start but i already have sumo bars and im glad i didnt as it wouldn't have fitted anyway!

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I'm sure I've looked at the "sector" shafts of a 4 and 6 bolt PAS box before and they're not interchangeable.  - I'd echo simonR - not sure i'd be buying Britpart/Allmakes stuff like that.

The manufacturing tolerances on Britpart parts is just abysmal.


For the price I'd be probably buying genuine.

Land Rover Defender Steering Box Drop Arm & Ball Joint RHD Genuine Adwest | eBay

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Hear all the genuine mentions, i do get it, but its not like land rover manufacture them theirselves, they come from someone, granted, not britpart.

The britpart and allmakes i looked at measured identically, taper and spline profile both different to my old arm.

Received the RTC6398 from paddock, unsure of the manufacturer as it came with a ball joint and no brand sticker and their picture does not have the balljoint (not complaining there!), appearance wise of the casting does not look like normal aftermarket, looks more like the original. It has the same casting numbers as my old arm and this one has no alignment slot, odd.

Left to right, my old arm, the 4 bolt arm then the 6 bolt



Measurement wise, none are exactly the same, but i am using verniers manually, the 6 bolt arm is very close to my old arm and has similar splines but the spline length is 1mm less, the 4 bolt arm is markedly different to the other 2.

Fitted well, freely fitting, no pressing etc. tightened and loosened it a few times to be sure it's seated, fits up to what i would say is correct.



I've paint marked all joints and will keep an eye on it for a little while, if anything seems off, i'll swap the whole box.

Edited by Adam001
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  • 1 month later...


Also just to note, the nut came loose on mine after about 200miles, retightened and it hasn't changed after a further 1700miles. Nut came to rest around 45degrees further on than before.

Edited by Adam001
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Do you have the tab washer fitted?

Do you still have the one that did not fit? If so could you do me a favour? I am looking at fitting an Adwest arm to my Rover P5 power steering box on my S1 and the RRC arm is too large a diameter. From your comments it seems like the Adwest one maybe the correct size.

If possible can you measure the top and bottom inside diameters from the bottom of one spline to the bottom of the opposite spline?

The easiest way is to use the two splines either side of the registration spline with a vernier if you have one?




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