BW35 Valve Body interchangability.

#1
Hi gang,

As no doubt those that have worked on bw35s before will know, '35s come in different sub models.

My question for the collective is... Is a 7FU box interchangeable with a 303 valve body?

I've two boxes out. The 303s bands are done. But the 7FU, although freshly built has an incorrect kick down fitted.

I do, however, have the correct kick down for the 303 cam. Which leads me to think I could swap the bodies over?

Fraser
 

harveyp6

Well-Known Member
#2
You can swap the valve bodies, but you need to use the snorkel type filter to go with the 303 body. You could just swap the cam and bracket. The only possible problem I can foresee is that there are two types of selector shaft, the early type is the same diameter through to the inside of the box, and can mean that there are certain types of kickdown cam that will foul on it. If you cam braket is bent downwards that could be why. Later shafts are turned down and won't foul.
 
#3
I won't be using the 303 box. I have currently installed 303 valve body installed, inclusive of cam, filter housing which appears deeper (though I'm not so sure what you mean by snorkel type filter housing).

Effectively the entire 303 valve assembly, undone by three bolts is now attached to the bottoms of the 7FU.

I am also using the 303 kickdown and cam.

This should be ok to start up in the morning?
 
#5
Hopefully, these help you. This is the valve block which is now currently fitted to the 7FU. These pictures are of it sitting in the 303 in situ while I tried to suss out what was wrong.


WP_20190115_03_50_17_Pro.jpg WP_20190115_03_50_17_Pro.jpg WP_20190115_03_49_49_Pro.jpg WP_20190115_03_50_12_Pro.jpg
 

harveyp6

Well-Known Member
#6
OK, so that looks like a 303 valve block, but it's fitted with the wrong (flat) filter. That will make it behave as though the fluid level is too low. Also the front servo isn't self adjusting, which the 303 should be, (and so should the 7FU if it's a later one come to that) so the dogleg pipe should have a restrictor in it at the valve block end. It's not fitted with a 303 bellhousing either.
 
#7
so a self adjusting servo and a revised filter should get this back on track?

I may have a self adjusting servo, those servos I'm question were out of the 7FU and I was swapping them over in these photos.
 

harveyp6

Well-Known Member
#8
I'd definitely fit the correct filter, but the front servo would be OK especially if it has a solid band. Servos can be fiddly to fit on the car, best way would be to juggle the self adjusting parts onto the servo without removing the servo itself. You also need the pipe without the restrictor if you fit the self adjusting mechanism.
 
#9
gotcha.

I suppose another way to do this would be to refit the 7FU valve body and then fit the 303 cam and kickdown?

This box now installed has two solid bands. The 303 had a flexi band and getting the servo back in and the .215 metal piece was certainly testing.

I'm regard to this restrictor. Is that in the actual steel pipe or within the valve body? If in the pipe, is it easily identified?
 

harveyp6

Well-Known Member
#10
It's in the pipe. It's a reduction in bore size of the pipe to about 1/8" diameter, for about the last 1/8" of the pipe. I wouldn't change the valve block again. The manually adjusted servo will work fine with a solid band. (And with a flexi band as well come to that, although they shouldn't be used in that combination, I've seen plenty that have. As the last boxes went in the cars over 40 years ago they've had time to get all sorts put in there).
 
#11
So get hold of the filters and see how we go? Is this restrictor pipe diameter change internal or external? If internal is there anyway to tell it apart?
 
#13
I hadnt noticed that. I'll have a look at the pipework I have left over.

I'll look at ordering a filter before the weekend. Would a overfilled sump suffice for the next few days?
 

harveyp6

Well-Known Member
#14
You could raise the level by about 3/8" over the HIGH mark when HOT and that should do no harm in the short term. TBH so many people have trouble setting the level correctly anyway there must be loads of boxes out there that are overfilled, and probably by a lot more than that.
 
#15
I guess thats part of the 'evolutionary' process these boxes have had over the years.

Thanks for you help Harvey, its appreciated. I can see myself getting quite into figure these boxes out as a side project.
 

harveyp6

Well-Known Member
#16
They are a very clever box, all mechanical (no electronics), controlled by just 3 inputs, and giving various options, fully auto, first gear start, second gear start, hill start, and kickdown to name a few. There's a lot to learn. I've been trying to figure them out for about 45 years.....:)
 
#17
I'd imagine you've seen some weird and wonderful things done to them over the years? Is there a gearbox you've come across that's stood about as bizarrely built or the likes?

As we finish here. I drove it to the petrol station today briefly. It was slipping out of gear. I added a few more litres of type F and it seems to have stopped. I assume this is the need for the snorkel filter you talk of? And jumping out of gear the symptoms of low fluid?

Also, I haven't connected the speedo cable properly. Is that a 'getting back under the car' job or can it be done with an access hole in the trans tunnel?
 

harveyp6

Well-Known Member
#18
I'd imagine you've seen some weird and wonderful things done to them over the years? Is there a gearbox you've come across that's stood about as bizarrely built or the likes?
I've seen all the normal faults, and some not quite so normal, trouble is I can never remember them. Sometimes something will prompt a reminder, then 'm good to go.



As we finish here. I drove it to the petrol station today briefly. It was slipping out of gear. I added a few more litres of type F and it seems to have stopped. I assume this is the need for the snorkel filter you talk of? And jumping out of gear the symptoms of low fluid?
Low fluid level gives delayed engagement, and can cause slip and loss of drive, particularly when cornering.

Also, I haven't connected the speedo cable properly. Is that a 'getting back under the car' job or can it be done with an access hole in the trans tunnel?
There's a grommet in the tunnel that gives access.
 
#19
Well last night was actually a marked improvement after filling the box up with another couple of litres of ATF. I was pretty happy with the results and wizzed around the place before parking it up for the night

This morning, however, I drove it to work and it wouldn't jump up into Third. Instead opting to sit on second? This wasnt an issue yesterday. I have noticed that the shift from First to Second is a little sharper than my previous box. Are these potentially related?

Yesterday night it actually drove very well and I was very happy with it, this morning outside of no third gear, it pulled away very nicely. Is there a set of norms that cause it to lose third?

Reverse is also fine btw.

Fraser
 

harveyp6

Well-Known Member
#20
Can you get it to change into TOP if you take your foot right off the throttle? If so the cable needs adjusting correctly. If not it could be the governor sticking if the box has been unused for some time, or possibly the 2-3 shift valve sticking, but as this is the valve block from your other box which wasn't exhibiting the same problem, I doubt it.
 
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