Transmission Fluid Leak

#21
BW35 Trans Fluid Leak/noisy reverse gear - PROBLEM SOLVED

Dear Rover friends,

just to give you an info, he Problem is finally now (I hope) solved. I bought an rebuild BW35 which is now installed in my car.
I did not have too much time to test now, but until now it drives fine, losing just somedDrops of oil (parking).

Kind regards
Richard



In that case it may be that the converter has drained back into the gearbox itself, artificially raising the fluid level, and causing some fluid to leak out.

Hello P6 friends,

- my BW35 is still losing much oil (Bw35 was rebuild in circa 2010 by Rover Club Austria) and again in 2013 (reverse gear did not work anymore),
but it seems, they did not do a good job, because it is still losing much oil. my workshop said, the oil is not draining back from converter. (?)

- since a few weeks, the reverse gear of my BW35 sounds very rough and loud.
- I must fill up auto trans fluid now every 80-100 km, because the trans starts to slip.

OIL: what is the secret, to solve the problems? is it just a seal? (I am always using castrol TQF fluid)
NOISE: I am worry about this noise.

do you have any advice? I am scary to have again an auo trans box damage. :shock:
kind regards, richard
BW35 Trans Fluid Leak/noisy reverse gear

In that case it may be that the converter has drained back into the gearbox itself, artificially raising the fluid level, and causing some fluid to leak out.

Hello P6 friends,

- my BW35 is still losing much oil (Bw35 was rebuild in circa 2010 by Rover Club Austria) and again in 2013 (reverse gear did not work anymore),
but it seems, they did not do a good job, because it is still losing much oil. my workshop said, the oil is not draining back from converter. (?)

- since a few weeks, the reverse gear of my BW35 sounds very rough and loud.
- I must fill up auto trans fluid now every 80-100 km, because the trans starts to slip.

OIL: what is the secret, to solve the problems? is it just a seal? (I am always using castrol TQF fluid)
NOISE: I am worry about this noise.

do you have any advice? I am scary to have again an auo trans box damage. :shock:
kind regards, richard
 
#22
BW35: I suddenly experienced the same leak. One day there was a small pond on the floor. After refilling everything is honky-dory until the car has been standing for xx hours/days. Harvey states that the check valves very often do not work, but then most of us should experience the problem. Or?
Besides is the any cure apart from total dismatling? If not so I better replace with my somewhat younger spare engine with BW65. That is, if only I can find a rear mounting and a selector cable...
 

harveyp6

Well-Known Member
#23
The check valves in the valve block don't work very well. Some BW35/65/66 have a valve in the cooler return line and you could fit one of those if you can find one, or if not ISTR someone I know made a few.
 
#24
Good idea. Who might that be?

Besides I came to think: Where would the overflow typically come out. Is there a breather of some kind somewhere or is it by some some spindle - speedo drive - shift rod - anything?

An engineer (I) come to think "communicating vessels": If the (un)inteded breather is further up, the fluid wiil stay in the system and simply be pumped back to where it should be next time the engine is started.
 

harveyp6

Well-Known Member
#25
Solid dipstick tubes have a metal breather tube and there were problems with early ones which led to a modification to move the breather pipe up the tube. Later flexi tubes have a plastic breather pipe which ends around the gearbox main case/tailshaft housing joint.
 
#26
There may be something there. I shall check when back at the garage. If the breather tube does NOT pass/end over the top level of the converter, spills may/will occur if air can anyhow slip into the converter when the car is left standing idle...
 
#27
Parts catalogue illustration: According to the engine number my car should have this version. Later ones are quite similar. As can be seen the engineers clearly thought about communicating vessels. Even if the check (non-return) valves are inoperative the 'up-and-down' breather will prevent spills, but only if the 'up' part is completely airtight. I now know where I shall start fault-finding.
 

Attachments

#28
I found my leak: It comes dripping out from the sleeve around the bottom end of the kickdown cable. So nothing wrong with the breather. But if the breather tube (communicating vessels) should be of any benefit, the bottom end of the kickdown must be airtight. And is it really supposed to be that? Nevt, at the same level or just a cm. up comes the shift linkage and the inhibitor switch. Same thing: Supposed to be sealed and tight???.
 
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#29
BW35 and mysterious leaks while parked - a possible explanation.....
----------------------
After forum reading, catalogue study, and thinking, I have come to this belief: Correct me if I am wrong or missing something.

We may consider the system as a box with a fluid pan and a pump that sends the fluid up in two loops. The first one is the converter. The next one is the cooler which is integrated in the water radiator. The first one is pressurized, but leaving that it is a free flow through the second back to the pan.

There should be a check (non return) valve somewhere. I cannot find it in the parts catalogue.

At the very first this model explains why the fluid level must be checked while running: Only then will the pump ensure everything is filled to operating conditions. Fluid level may be higher while stopped.

On the left hand side of the box casing are three holes where moving parts are passing through: The kickdown cable, the inhibitor switch and the PRNDL-shifter. All are threaded, sealed and above normal fluid level. The breather tube is sitting even higher and has a top "Neck" further up high. The speedo drive on the rear extension is attached higher.

Now, if air can enter either of the upward loops (converter and cooler) when parked, fluid will flow back to the pan, raising the level up above the three holes, or even the breather entry point. This is no problem if all gaskets are OK: First time the engine is started fluid will be pumped back where it should be - converter and cooler. Level correct: Drive off.

If any of them have a leak, fluid will disappear out of the system.

1) The converter is pressurized while operating, so any leak will be VERY obvious, but only with a started engine.

2) I would rather suspect the cooler circuit - interconnected pipes and tubes. Let us just imagine you had the radiator out and one of the joints is no longer fully sealed. You will not notice it with a started engine: this part is not pressurized. But stop, and air will start entering. Btw. you cannot see the bubbles, because you would have to sit inside the pipe.

Remedy?

1) Ensure there are no leaks in the piping. Difficult. Best you can do is ensure all connections are clean and properly and solidly assembled.

2) Find the leak where fluid gets out. You will need litres of new fluid, so buy it. The three primary candidates are very close to each other, so clean and dry with a rag and pour some fluid in the box. Remember the fluid level is flush with the leak, so just a cup of fluid will reveal the leak almost immediately (the time you use to to get under the car should be sufficient).

3) Fix it - gaskets, seals, PTFE-tape, inhibitor switch, kickdown cable..

4) Harvey mentions possible availability of external non-return-valves. Consider asking him where to get them, where to install and in which direction.

5) Refill. Happy Rovering :)
 

harveyp6

Well-Known Member
#30
We may consider the system as a box with a fluid pan and a pump that sends the fluid up in two loops. The first one is the converter. The next one is the cooler which is integrated in the water radiator. The first one is pressurized, but leaving that it is a free flow through the second back to the pan.

There should be a check (non return) valve somewhere. I cannot find it in the parts catalogue.
Almost, but not quite. The fluid is split into two, but the low pressure side supplies the converter, and the outlet of the converter runs through the cooler and back to the sump. The high pressure side runs the box.

There is a pic of the check valve in the cooler return in the WM IIRC, but it's in the BW65 section, not the 35. It was never fitted to the 35, and TBH I don't ever remember seeing on on a Rover 65 either.
 

harveyp6

Well-Known Member
#31
The return line check valve is shown in the parts book in the BW65 main case page. RTC0035, same as fitted to the Stag, but they are NLA.
 
#32
Well, I only considered the front pump. I know there is a another rear one, and I can see the check valve for that in the parts book. But then my assumptions for the front circuit so far still seem to be correct and able to explain those leaks.
 
#34
Yes, of course the rear pump is high pressure and the front one only to provide flow. And sure enough RTC0035 is not in the P6 Parts Catalogue.

Then bottom line: Mysterious slow spills - several litres - when the car has been standing for hours/days/weeks are typically due to air ingress in the two loops (converter and cooler) causing fluid flow back to the pan. The main suspect is the second one (cooler) due to external tubes and pipes and connections that may have been opened. The first part (converter) is only rarely touched. Even though it is a low pressure flow, leaks in that will most probably disguise themselves when running because fluid will be centrifuged out into the converter case. No dripping: No leak there.

This will only cause a problem if the three openings on the front left side are not sealed.

By the way: Simple hydraulics knowledge will show that if return line check valves can be found, you will need two. They should both be sitting directly where the pipes to the cooler enter/leave the box. Only this will ensure fluid to stay if the leak is in the cooler loop. If the leak is in the converter loop the fluid from that can still flow back. Hopefully this then is not enough to raise the level above kickdown/inhibitor/shift/breather whichever let the fluid spill out onto the floor.
 

harveyp6

Well-Known Member
#35
Yes, of course the rear pump is high pressure and the front one only to provide flow. And sure enough RTC0035 is not in the P6 Parts Catalogue.
Front pump supplies the converter and the fluid to operate the box, the rear pump was there so that the car could be towed or tow started. RTC0035 is in my parts book, but on the BW65 main case page.
 

harveyp6

Well-Known Member
#37
Maybe that valve was a later addition after your book was printed, or your book is later than mine and it was deleted as a cost saving measure. Either way it's in my book and not yours. In my experience the 65 never suffered as much with the drain back problem as the 35 did. Maybe that was because the design of the box was better as far as that problem was concerned, or the problem still happened but the box was a bit more oil tight so the excess fluid was contained rather than escaping.
 
#38
My cure was this: Remove the kickdown cable. Get rid of the damaged plastic on the lower 5-6 cm. Cut the cable in the middle of the free section at the top. There was ca 1,5 cm between the end bracket and the pressed on stop. Get heat shrink tube (glue type) down at the exposed/leaking end plus the bottom attachment. Heat. One more layer. Heat again. Put a solderable sleeve over the top cut (used one from a stainless steel pop rivet). This was also conpressed. Put everything together. Adjust. Bottom oil pan on box. ATf in. Now the oil pan gasket was leaking instead: Rats! New thread.
 
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