Leaking ARB

[Dave W]

This is a long standing problem I've had with my rear ARB diff (RD56) for a couple of years. Over that time I've tried everything I can think of to cure it with no real success.

The problem is that the diff leaks air when it's engaged BUT it only does it when it's off road, it never does it on the drive, for example. The air leaks into the axle and exits via the axle breather above the cab. Sometimes it'll work fine for a while but it seems that once it starts leaking it'll leak all the time until you get back onto, say, a gravel track between sections, at which point it'll work fine again for a while.

Initially I tried replacing the O rings, first with standard rings and then with the square section X type rings. Neither set made any difference off road.

I tried replacing the bearings following a discussion with someone who had had a similar problem. No different.

I had the diff rebuilt by Crown who replaced the top cap and changed the copper pipe routing slightly and, again, fitted another new set of O rings and bearings. No different.

I came up with a theory that maybe the pressures were wrong so I changed the pressure switch after testing it showed it was maybe 10 PSi out. No different.

Soooo... I'm open to suggestions/ideas as to where the problem may lie !

[T1G UP]

axle flex?

[Hybrid_From_Hell]

Is this the early type (with 3 bolts holding air collar on the side) or the later RD56 with the spring clip ?

I'm hoping you say spring clip type

Nige

[Dave W]

It's the spring clip type.

[Hybrid_From_Hell]

AH

A mate had one that defied efforts to get it not pressure up the entire axle all the time

numerous rebuilds, used black O rings, brown ones and the later square one - Nope

Got bits (From ashcrofts I belive) to convert to earlier 3 bolt stylee, belive some machining

took place but was 100% OK from then, I think it is / was on the clip type a toleraqnce issue

coupled with seals, the seals weep under load - possibly being things flexing a micron with the wabbly

spring system, also belive Jim Marsden at Gigglepin may be worth a call as he also has expereince of these

being PITFA So I have heard ?

Nige

[Dave W]

If it helps, this is a pic of it after it was rebuilt last year...

[Dave W]

A mate had one that defied efforts to get it not pressure up the entire axle all the time

numerous rebuilds, used black O rings, brown ones and the later square one - Nope

Got bits (From ashcrofts I belive) to convert to earlier 3 bolt stylee, belive some machining

took place but was 100% OK from then, I think it is / was on the clip type a toleraqnce issue

coupled with seals, the seals weep under load - possibly being things flexing a micron with the wabbly

spring system, also belive Jim Marsden at Gigglepin may be worth a call as he also has expereince of these

being PITFA So I have heard ?

That sounds worth a try, I'll give Jim a ring tomorrow. Flex would make sense given that it only seems to happen when off road and, I think, it's worse in cross axle situations.

[simonr]

I had pretty much the same thing with the earlier (bolt on) type. Went through several sets of O rings - to no avail.

Eventual solution was to feed it through a small regulator, just turning the pressure down until it stopped leaking but still operated.

Si

[Soren Frimodt]

I had the exact same problem with my RD128 in the back of my series. When I really hammered it up hills or through mud, the compressor pumped more often than if I was just crawling along with the lockers engaged. A LR mechanic told me it was because i had too much slack in my bearings. But on inspection there was nothing wrong. I eventually sold the locker. But my mate runs the same locker in the back of his 90" and it does the same thing when he is really hard on the throttle. So to me there is no doubt about the fact that it is some sort of deflection that causes it. But I didn't find the problem that annoying so I have not looked further into it.

[Dave W]

Thought I'd update this as I think it's finally fixed !

Having changed/repaired/reconditioned everything else the only thing left untouched was the axle tube. Changed that last week, went for a play at the weekend and NO LEAKS !

I think the rear axle must be slightly bent, causing the air seal to twist and leak under load. It was noticeable that, when replacing the drivers side half shaft, it went into the new axle tube easily whereas on the old axle tube it was slightly stiffer as it located into the diff. I must have bent it on the OBC in 2008 as it was working fine then but has been giving me problems ever since it arrived back in the UK.