Expedition 80 Series Build

[Julian Voelcker]

I am still not convinced about the merits of plumbing into the airbox versus the security it offers in wading but that's just me For my money exposing the diff/gearbox/t-case oils to reduced pressures everytime you run the truck versus the once in a lifetime prospect of submerging the truck deeply enough and long enough to flood raised breathers in the engine bay doesn't seem a good trade-off. But I accept that you do this professionally and have worked on way more 80s than I will ever touch, so a neat solution that obviously works in practice is fair enough.

[Remember lower pressures reduce the vaporisation (boiling) point of oils, so this will generate more oil vapour than keeping the oils at atmospheric pressure.]

I could get all technical and measure it, but I am pretty certain that the negative pressure that builds up in a standard axle with the standard breather is much higher than what you would get in the air box - when you pop the breather hose off you get quite a loud hissing noise that takes a few seconds to subside on early 80s with the smaller hole in the breather union and maybe a couple of seconds in a post '92 80.

If it was such a big problem, why would Toyota and other manufacturers run their rocker cover breathers into the inlet pipe work- it's the same sort of thing.

 

[Andrew Prince]

If it was such a big problem, why would Toyota and other manufacturers run their rocker cover breathers into the inlet pipe work- it's the same sort of thing.

Not the same thing at all - they do it intentionally because it's advantageous to run the engine (valve cover and crank case) at as low a pressure as possible to assist oil flow and reduce pressurising of valve seals etc! Formula 1 engines are fully sealed and dedicated vacuum pumps for this precise reason.
Engine designers recognise the low pressure zone of the air-box, particularly in turbo-charged engines and utilise it accordingly. My point about diff & gearbox breathers is that they are presumably not intended to run at negative pressure.

As I said before, if it works in practice, then my theoretical musings are nothing more than that Anyway, I am not trying to start an argument - just adding my 2c.

 

[Julian Voelcker]

OK, see what you are saying, however ;-)

My point about diff & gearbox breathers is that they are presumably not intended to run at negative pressure.

With the one way valve arrangement on the factory breather and the expulsion of air when hot you cannot avoid negative pressure in the axles or gearboxes as they cool.

I've looked briefly at the maths and from winter cold (5 degrees) to running hot (say 80 degrees) around 25% of the air in the axle is expelled through expansion so when it cools, particularly in winter, it can lead to a reasonable pressure drop in the axle.

I assume Toyota have factored this into their designs because this level of negative pressure doesn't present any problems for normal running.

I have also run with a vacuum gauge on my truck linked up to the air box and on a scale of 0 to -30 inches of mercury the dial doesn't move off zero at all, not even when on full boost on a steep incline so the negative pressure in the air box is pretty insignificant.


In terms of live testing, my truck actually had the breathers installed when I got it and as far as I know in over 100k miles of motoring with the setup it has never caused a problem with any of the seals.

 

[james-c]

I'd like to pipe my diffs into the airbox as I've had an issue with the front breather getting stuck. What kind of tubing / hose do you recommend for this?

Cheers
James

 

[Andrew Prince]

I take your point about the empirical evidence - the set-up works

I've looked briefly at the maths and from winter cold (5 degrees) to running hot (say 80 degrees) around 25% of the air in the axle is expelled through expansion so when it cools, particularly in winter, it can lead to a reasonable pressure drop in the axle.

I did the calc using 15 and 60 deg C and estimated just under 16%, so I'm with you in your example. The one point I would make though is the cooling is not instantaneous and the "seal" is unlikely to be perfect so I doubt the pressure differential is anywhere close to that amount, as some air will seep in. If the pressure differential was too severe, I imagine air would been drawn in through the inner axle seals.

 

[David Killough]

Not sure about all the vacuum stuff you guys are tossing about, but, it would require a TREMENDOUS amount of vacuum to suck heavy oil all the way up those pipes. Far more than is being offered by that airbox. The benefits for me far out weight the ever so miniscule possibility of having a wee bit of gear oil spray in the airbox. The places I work at in Africa typically have no infrastructure and require crossing rivers and such. Keeping the diffs/gearbox/t-case breathing in those instances without having to plug them while crossing is quite handy. So, thanks Julian for your help!

 

[Julian Voelcker]

The one point I would make though is the cooling is not instantaneous and the "seal" is unlikely to be perfect so I doubt the pressure differential is anywhere close to that amount, as some air will seep in. If the pressure differential was too severe, I imagine air would been drawn in through the inner axle seals.

One of the first 80s I ever worked on was up on axle stands outside my house for nearly four weeks and the axles were the last thing we did - when we popped the breather off there was a distinct sucking noise that lasted a couple of seconds so that axle had held that negative pressure for four weeks so the seals are pretty good. (especially since when we pulled the CVs they didn't have any grease in them despite having being changed by the dealer 18 months before)

 

[Lorin]

Lorin had problems with this set-up - the suction caused the oil seals in the t-case to fail IIRC and he had other oil leaks related to the breathers.

That is precisely what I thought had happened. Essentially after the front axle was fully rebuilt and the breather plumbed into the airbox, I was getting diff-oil in the airbox which it transpired was coming from the front axle breather. It also developed a front diff-pinion leak and was subsequently found to have a considerable amount of water in the diff oil which I assume can only have come past the new axle seals.

Covered this a couple of times before, but here goes again......

In Lorin's case the suspension was lowered by removing spacers, but we didn't clean out the props - (having never had to lower suspension before it never occurred to him or us).

Lowering caused the props to be compressed but with old grease in there this can lead to hydraulicing issues putting extra pressure on the pinion seals and T/Case output seals leading to the leaks which is the most likely cause of the problems.

Thanks for the explanation, Julian I wasn't aware of the diagnosis of Lorin's problems.

I was also not aware of this diagnosis Having subsequently had to have the front axle fully rebuilt again and having removed the breather from the airbox the diff-oil has remained clear of water ingress and no oil has made its way into the breather tube, despite numerous wadings and no work having been done on the props. However, the front diff pinion seal continues to leak oil despite being replaced Does this mean I should get my props looked at Julian?

 

[Lorin]

I was also not aware of this diagnosis

Correction - went back and looked at the original thread on this topic and Julian did suggest this as the cause of my issues. Still wondering whether I need to do something about my props though

 

[Jon Wildsmith]

the front diff pinion seal continues to leak oil despite being replaced Does this mean I should get my props looked at Julian?

May just be that the flange surface has a ridge worn on it and needs replacing, or the fitting of the seal didn't go to plan e.g. the spring has come off the back, best pull the flange off and see what's going on, doesn't take long

 

[Julian Voelcker]

Correction - went back and looked at the original thread on this topic and Julian did suggest this as the cause of my issues. Still wondering whether I need to do something about my props though

Yes, I would pull them off and mark the two halves and then split them and thoroughly clean out the slip joint - might as well fix the pinion seal whilst at it.

I was getting diff-oil in the airbox which it transpired was coming from the front axle breather.

As have said, we have found that with shorter pipe runs on the front axles you can get a small amount of diff oil in the air box, particularly with older axles that run a little hotter. It's a case of the axle blowing it out, rather than the air box sucking it in, there just isn't enough negative pressure there to do that.

It also developed a front diff-pinion leak and was subsequently found to have a considerable amount of water in the diff oil which I assume can only have come past the new axle seals.

I would be extremely surprised about that, as I say there isn't the suction there to suck water in past knuckle housings 3/4 full of CV grease and then into the diff.

Was the CV grease contaminated?

Was there also CV grease in the diff oil?

Were you getting diff oil flowing out the of the ends of the axle as well?

It is more than likely that the water in the diff oil would have come past the pinion seal - the original seal would have taken quite a hammering with the lowered suspension and would have easily been damaged enough to let oil out and water in.

Additionally when the original seal was replaced the initially loose pinion may have been tightened further which has helped the current seal last longer and only only allows the diff oil to seep out slowly.

 

[IRLGW]

Very interesting topic guys and as i'm going to be fitting a snorkel I was interested in the arrangement./ However if the diff breathers are fitted with non return valves is it necessary to extend the breathers at all?

 

[nivapilot]

Very interesting topic guys and as i'm going to be fitting a snorkel I was interested in the arrangement./ However if the diff breathers are fitted with non return valves is it necessary to extend the breathers at all?

YES, What happens is that the axle gets hot, naturally, and when plunged into water the cooling effectly contracts, and causes a negative pressure on the air in the axle...and as you have non return valve on the breathers....air, and water, is drawn in through the oils seals....not good

That is why the non return valves are removed and tubed to a higher level...air is then sucked out and in with no adverse effects.

 

[Graham]

Interesting,

Didn't some one with a 120 extend the breathers?
Gary or Crispin maybe?

On the rear diff, etc, is it all the same thread when one removes the one way existing valves?

Gra.

 

[nivapilot]

I'm sure I read somewhere of someone?, pressurising the axle with compressor, just so that the water couldn't get sucked in.