Transmission to Transfer Case By Pass Hose Concern (2 Viewers)

[doug720]

Recently I saw several threads about using a hose connecting the transmission fill plug to the transfer case fill plug. The theory is this hose will save you transmission and transfer case if a seal connecting the two goes bad, and one or the other forces oil into the other case, leaving that case dry.

Even though my case seals were not leaking, the theory sounded good, so I made a nice SS braided hose with cool AN fittings and threaded adapters.

We recently made a 6 hour round round trip to the mountains, with another few hundred miles of driving while there. This was the first trip with the hose.

While driving home, I noticed the shift to third gear was a little "Notchy", something the H55 had never done before. We had been driving for an hour or so, and I thought maybe it was time for a transmission oil change.

Yesterday, I got around to doing the transmission and transfer case oil change.

When I removed the transfer case end of the hose, gear oil came pouring out the hole. That was odd, so I let the gear oil run out the fill hole and collect in the pan. Once it stopped, I measured the amount that came out...Almost a quart!

I next checked the transmission fill plug, and found it was low! I measured the gear from the trans and found it was just over 4 qts, about 1 qt low! Likely explains the notchy shift to third gear!

When I installed the hose, both cases were full. Both transmission and transfer case vents are extended to the engine compartment and are clear and free flowing. So it appears the gear oil was collecting in the transfer case, which has a the fill plug that is lower than the transmission fill plug.

This hose, in hindsight, may not be such a good idea - At least if the seal between the gear boxes is good. It allowed my transmission gear oil to be about 1 qt low.

My connector hose was not blocked, so it was just liquids finding there own levels.

I removed the hose and will not be reinstalling it.

Just my experience, your may be different...or maybe not?

 

[JMJA]

Your theory seems to be contagious cause I did the same thing as preventive maintenance. I purchased the hose from a Mud member and after a few days of installing it, my transfer case began to leak from the front and rear. It wasn't leaking before the install. I had to purchase a gasket kit from Georg at Valley Hybrids. I have a H55F and stock transfer case. I removed the hose, also!

 

[dkyuss]

Thanks for the info. I just finished a Tcase and transmission rebuild, seals were all replaced and have been wondering if I should reinstall or go back to factory setup. Obviously with new seals I should not need it, I will remove the hose and just monitor fluid levels!

Maybe this bypass hose should not be confused with preventive maintenance, only a short term fix IF you have the pre-existing issue (oil being pumped from Tcase up into tranny).
Or maybe you two are the only examples???

 

[SteveH]

Good to know of this issue. Glad you caught it before real damage...

I still contend that venting the transfer case to free air (meaning, ditch the Toyota spring-and-flap seal and run a hose up the firewall) is the best way to keep those oils in their respective cases. The transmission is vented through the shift tower. By doing this, the seal between the two boxes sees no pressure on either side, to speak of.

 

[hj 60]

I made the hose a few years ago but never installed because I did not trust it to work one way (lowest) when seal is fine, thanks for the info
Just agree if it aint broke don't "fix" it. Very important because I never read about someone questioning the hose idea as preventive.

It just looks odd, if the seal inside is oke oil will never flow upward trough the hose, only down (splattering)
, and only if the seal is broken oil can flow back (horizontal)

Would a fluid sensor work? There is no pressure to measure, and fluid level sensor might work but I can not find anything that is designed for this
M18x1,5

This is about it, but might dissolve in aggressive gearbox fluid, oil might be to heavy slamming, stupid idea?

Found a sight glass! that makes it possible to do a visual inspection
part from kipp K0448.241815
KIPP - Oil level sight glassesaluminium

Housing, transparent, high mechanical stability, non-ageing, temperature resistant with oil up to 100 °C, with water up to 70 °C; resistant to solvents but not to alcohol.
Flat seal, asbestos-free. White reflector.

And for sale:
HYDRAULIC OIL/FILTERS & ACCESSORIES - M18 X 1.5 POLYMIDE OIL LEVEL SIGHT GLASS 1
HYDRAULIC OIL/FILTERS & ACCESSORIES - M18 X 1.5 POLYMIDE OIL LEVEL SIGHT GLASS 1


Ordered two Can anyone find the inch size for M18x1,5 because it seems there is a lot more from motorcycles in aluminum for sale but I don't know the size in inch"

Thank you for your purchase

You will receive an email confirmation shortly, Estimated delivery between Monday, Mar. 7 and Friday, Mar. 11

 

[mongoose2231]

The hose fix works only if the seal is bad. All the above is correct.

 

[crashn]

The hose fix works only if the seal is bad. All the above is correct.

Could you please explain how this works when the seal is bad? Does the T case somehow push oil up to the transmission when the vehicle is traveling. If it just works on the gravity feed then it will stay in the T case because the fill hole is lower than the one in the transmission. I have this situation and I would like to understand the problem a little better. Thank you in advance.

 

[Output Shaft]

I'll pipe in my 2c.
The oil can flow either way with a bad seal. Up or down. More often if flows from the transfer to TMS, but it can also flow the other way depending on how much you drive and the condition of the TFR vent.

The reason that doug720's (Op) TMS drained into the TFR is because when the TMS is spinning, it's slinging oil all over the place inside the case. As its slinging oil along the sides of the walls of the TMS, that oil drains down past the fill hole and some of it will drain back down the hole via the bypass hose if the fitting isn't angled upwards.

I've personally experienced this in my h55f too from a SOR bypass hose. IMO, these bypass hoses can be dangerous. They might work for some transmissions with leaky seals, but there's no guarantee. And that being the case, you've still got to check the oil levels frequently.... So what's the point?

 

[cruiserpilot]

I'm glad I found this thread. I have a bypass hose I bought as my vent was leaking oil, but I think I am
better off to attend the vent, than install the bypass hose.

 

[crashn]

Output shaft, I appreciate your taking time to explain the action going on in the TMS. When I checked the H55 fill hole I couldn't touch the oil, so when I slow and carefully removed the fill plug in the T case I drained an extra 1 1/2 guarts of gear oil out. I suspect the seals are bad and It doesn't help the it sits for long pirods of time between outings. Thanks again for your help.

 

[darthvincor]

The way I understand this hose, is that it is a temp fix for a bad seal between the gearbox and the transferbox. And if the seal is fine, there is certainly no need for this hose.

I'm curious, are the filler holes at the same height?

 

[Matty f]

My FJ62(h55f) had an notchy shift when I bought it.
Checked levels and the box level was low and Transfer Overfull.
Grabbed a bypass hose without thinking much about it

Later thinking in my case how will a hose help fluid run uphill from Transfer to Gbox and equalise levels but fitted it anyway and yes it hasn't done much I still drain Transfer and refill Gbox.

But if your seal was bad and was pumping fluid into Gbox . Then maybe the bypass hose would work well by gravity feeding it back down to the Transfer and equalising levels??

 

[Varty Yo]

Noticed today in my 42 the seal must be bad. When i pulled the gear box fill off it poured fluid.

I think ill be haveing a hose made up locally.

What is the fitting i need for the fill plug? Maybe ill just take the plug in so they see it 1st hand

 

[Output Shaft]

Transmission to Transfer Case Bypass Hose

 

[Willard]

So I will pipe in here.
I bought my FJ60 last year. It never leaked. I drove it around and I found oil in my garage. Dropped the skid plate and to my surprise i had the bypass.
Now this was NOT leaking, but the speedo gear was. replaced the o-rings and all is well again.

From the looks of it and from the receipt from Man-A-Fre this has been on the FJ60 for about 8 years. I still have the 4-Speed so not sure if that matters but mine is not leaking one drop and the seal must be gone as the level looks to be about right when I checked the fluid for a change.
I put it back on.

So not all are troublesome. Yes fixing the seal is the way to go, but that will happen with a 5-speed swap.