Type 35 Gearbox Converter Check Valve (Anti Drain Back Valve)

[stagdriver]

I am a 1975 Triumph Stag owner and have been reading with great interest the Rover technical articles on the Borg Warner type-35 gearbox; it would seem that both cars suffer with the same problem of leaving transmission fluid on the garage floor. The Triumph Forum has very little on this subject hence this asked for help from you Rover chaps. My gearbox have leaked oil for several years but other that it works fine, after reading the various articles on the Rover forum I diagnosed that the gearbox selector shaft seals were the major contributor to the leaking problem, a secondary leak area was the breather pipe connection to the gearbox. I have replaced the seals on both ends of the selector shaft and installed a longer breather pipe secured on the gearbox with a clip.
After reading about the function of the converter check valve I decided that as I had the car on the ramps I might be prudent to see if my car has one fitted, I could also clean or replace the gauze filter and adjust the bands if needed. After removing the gearbox sump the valve block was very simple to remove and strip down on the bench, you will probably not be surprised that the “check valve was not fitted”. There is another similar ball valve located in the middle of assembly which is called the ( 3-2 Shift Restrictor Ball and spring ) it’s has an extremely weak spring not sure what is does as I could not find any technical reference to the items function in the two workshop manuals I have.
I have read several technical manuals and none of them give the principles of operation of the check valve, I do know however from the forum that it was to stop drain back from the converter.
I am also missing the magnet that is supposed to live somewhere in the sump area, can someone tell me where it should be located.

Now the 64K-Dollar question:-
Can I make a homemade check valve with a suitable steel ball and spring? The pressure in the hydraulics must quite high, the spring would have to strong enough to stop the fluid draining back but not too strong to interrupt the correct function of the Converter, The ( 3-2 Shift Restrictor Ball ) is ¼” in diameter and fits in the Check valve pocket all I have to source is another 1/4” steel ball and a suitable spring that puts just enough pressure on the ball to stop the fluid leaking.
It begs the question why do so many gearboxes have the check valve missing, did Borg Warner stop installing them because of technical improvements or did it cause other problems? It has been reported that it was never was 100% effective.
Any thoughts would be greatly appreciated; I might just be wasting my time even thinking about installing one.

Attachments:

[enigmas]

The BW35 if carefully built doesn't have to leak or weep ATF. The trans sump being a steel pressing is often distorted..so it doesn't seal properly against the mating flange of the transmission. Spend some time with a good flat file, a steel straight edge or ruler to ensure that the mating surface really is flat and true before refitting it to the trans.

The 3-2 dump ball is a one way valve that allows a fast ( virtually instant) 3 to 2 manual selector downshift.

Not all BW35s have the drain back ball and spring in place. Usually the early versions had them. BW40s and BW51s (the last iteration) did without the convertor drain back check ball and spring.

Both springs are very light and can be easily pushed in through the separator plate orifices with a scriber or fine tip screwdriver

The pix below are of my Rover P5 Mk3 valve body. It also utilizes a rear pump and has the 3 to 2 dump ball added to the separator plate

[johnwp5bcoupe]

You mean a Anti Drain Back Valve.

i.postimg.cc/mkQK4SvH/IMG-08861-zpsoaxgiyue.jpg

[harvey]

^^^^^ That's the kiddie the OP needs. The check valve in the valve block will never stop the converter draining back though the cooler return, only back through the valve block on the converter supply side. Stag's BW35 were supposed to have them as standard, as were P6B BW65, but in practise I've not seen many of them fitted at all.

[eightofthem (Andy)]

Stag driver said
the 64K-Dollar question:-
Can I make a homemade check valve with a suitable steel ball and spring? The pressure in the hydraulics must quite high, the spring would have to strong enough to stop the fluid draining back but not too strong to interrupt the correct function of the Converter, The ( 3-2 Shift Restrictor Ball ) is ¼” in diameter and fits in the Check valve pocket all I have to source is another 1/4” steel ball and a suitable spring that puts just enough pressure on the ball to stop the fluid leaking.

Read more: roverp5.proboards.com/thread/11152/type-gearbox-converter-check-valve?page=1&scrollTo=89898#

If you do then you need to drill a small hole in the bottom of the valve body as a relief drain, and if your top half of the valve body does not have a notch then it will need one.

Enigmas said

The BW35 if carefully built doesn't have to leak or weep ATF. The trans sump being a steel pressing is often distorted..so it doesn't seal properly against the mating flange of the transmission. Spend some time with a good flat file, a steel straight edge or ruler to ensure that the mating surface really is flat and true before refitting it to the trans.

The Stag boxes have an alloy sump pan( MK2 ) the early ones MK1 have a steel pan, the alloy being better to seal.
Read more: roverp5.proboards.com/post/new/11152#ixzz5knhRWJdu

And if you really really want one then here is one.
Item number
273802725664. E bay.

[stagdriver]

Thanks everybody for your comment and especially the photos from enigmas in Australia, it would seem that the valve block on the Rover although very similar to the Stag are different, I have highlighted these in my photograph, After some digging on the internet it would seem that the later type Stag Type-35 gearbox was never fitted with a front pump so never required the two valves that balance the pressure between front and rear pumps, the check valve was also made redundant. At least now I am not chasing my tail trying to fit a part thatnever was fitted.                                                                                                                         
I do have another question for the forum, The adjustment of the rear band to 13.5 Newton Meters was very straight forward, the front band however is proving to be quite problematic, with the 0.250 inch shim inserted behind the servo body I cannot obtain the required torque, the adjusting screw just keeps on winding inwards I am afraid something will snap if I keep going. Thefront lever is made from aluminium and the rear lever is made from steel, I wonder if the aluminium lever is bending as I am adjusting the screw.

Any thoughts on the subject ?

[harvey]

You can set the front band without the spacer plate, just torque up and then back off the screw exactly 4 turns. Remember the torque setting is 10lbin, not 10lbft.

All BW boxes have a front pump, it was the rear pumps that were deleted, at which point so were the pump check valves, and the converter check valve was also moved.

[stagdriver]

Harvey has spotted my mistake about the pumps, I did mean to put the rear pump but got side tracted with front and rear bands discussion.I totally missed the difference in the torque settings between the front and the rear bands, no wonder the front bands did not like 10-lbft being applied.

Thanks again.

[stagdriver]

I could not believe that I missed the correct torque settings for the front Band so Last night I went into the Garage to check The Triumph Stag Service Manual that I have been working with and quess what," it incorrectly lists the setting as 10-lbft", when I checked the Borg Warner Manual it correctly list it as 10-lbin, I suppose there is a lesson to be learnt somewhere.

[eightofthem (Andy)]

You were very lucky not to split the servo body in two.