BW35 slipping out of 3d gear

[scherts]

I was hoping to get some advice on the following. My BW 35 shifts very smooth to 2, but for engaging 3d I have to depress the gaspedal.

Also, once in third gear, above 45 mph the autobox falls out of gear and revs like hell until I depress the gaspedal again. The kickdown cable is at it's loosest setting. All other settings result in the car not shifting to 3. I also checked if I have the right kickdown cable which is the case. The fluid level is ok. No burnt fluid or particles. Does this sound like an overhaul job or could this be solved with a specific adjustment or repair without removing the transmission?

[harvey]

When you say "depress" the throttle, do you mean lift your foot off the pedal, or press it down further?

Low fluid level can cause it to drop out of TOP gear, how are you checking the fluid level?

Do you have any problems at all with REVERSE?

[scherts]

I have to lift my foot from the pedal yes. I check my fluid by driving the car until hot, then I put the gearbox in park and read the dipstick within 30 seconds. Also reverse is smooth unless I give full throttle... then I hear some disconcerting noise but for the rest it runs very smooth in R and 1, 2

[harvey]

If you're having problems with loss of drive in TOP, and noise under hard throttle in REVERSE then it could be a rear clutch problem.

[scherts]

After a busy period I did some more problem solving efforts.
I adjusted the rear brake band. Now I can throttle in reverse like there is no tomorrow and it doesn’t slip or make noise. So I am hoping it’s not the rear clutch. Possibly it’s the kickdown cable which is triggering kickdown from 3 to 2 at higher speeds (50 mph). I think so because it only shifts as it should when I have the cable at the loosest setting and that requires removing the locknut for the adjuster and a sloppy cable. When I adjust to the setting as in the workshop manual (both the cable stop and the cam are in the right position) it shifts from to 2 very late at very high revs and does not shift to 3.

[enigmas]

I think you're winging it 'scherts' with regard to the BW35's control cable adjustment. Harvey has provided you with good advice. You need to remove the trans pan and visually check the throttle cam and cable operation. It's not hard just a bit messy if you're not careful. The throttle cam should be at rest with your foot off the throttle...and there should be no slack in the cable.

The picture below is of a (modified) Mk3 BW35 valve body (slightly different to yours) but the throttle cam position (at rest) should be the same. Top left hand side of the image.

[scherts]

Thank you. Yes I double checked the setting but it doesn’t solve the problem. When I disconnect the kickdown cable it doesn’t slip out of 3d gear anymore. So that supports the theory that more throttle triggers kickdown in 3 above 50 mph. Actually it was not slipping but shifting back to 2. However the slipping in reverse reappears under hard throttle with the kickdown cable disconnected. I am really puzzled by this problem! I have a theory that my car has a late valve block and early cam because it has also the late type filter and with the car came a cam in a different shape which I tried but doesn’t fit because it gets stuck under the selector shaft in kickdown. Is that a possible explanation?

[harvey]

Jul 31, 2019 11:47:04 GMT scherts said:

However the slipping in reverse reappears under hard throttle with the kickdown cable disconnected. I am really puzzled by this problem!

That is exactly what will happen. With the cable disconnected there won't be any increase in line pressure to match the throttle opening, so it will slip.

Jul 31, 2019 11:47:04 GMT scherts said:

I have a theory that my car has a late valve block and early cam because it has also the late type filter and with the car came a cam in a different shape which I tried but doesn’t fit because it gets stuck under the selector shaft in kickdown. Is that a possible explanation?

There are (at least) 2 different types of cam and brackets. Early brackets were cranked so they cleared the selector shaft, later ones were flatter, and the selector shaft was turned down so thewy didn't come into contact. Fit the later cam and bracket with the earlt selector shaft and they will foul. I have seen the brackets bent downwards so that they clead, but then it's impossible to get the cable adjustment set correctly.

[scherts]

Thanks so much Harvey! I will install the later cam and selector and let’s see what happens.

[enigmas]

Scherts have you removed and cleaned the Valve body and Governor valve?

Throttle Cams.
Note the difference in profile.
The Cam on the left is an early BW35 cam and works in conjunction with the small 2 - 3 valve shift plug.
This version does not provide a part throttle shift.

You also need to check these valves in the event someone (who doesn't know what they're doing) has done some mixing and matching on the valve body.

Note:
The throttle cam on the right of the image below is adjustable for position and must be positioned correctly using a .010" feeler gauge.

The one on the left is not and has a fixed position.



I've cross posted this info from here: roverp5.proboards.com/thread/10658/bw35-tech-miscellany
2 - 3 Shift Valve Plug

The post also includes a disassembled Governor Valve so it may be worth your while checking it out as they can/stick if the box has been left unused for lengthy periods or the fluid is dirty/contaminated.

Ever wonder why some BW35s will part throttle shift or drop back into 2nd gear at light/moderate throttle...not kickdown.

It's partly due to a redesign of this plug, providing a larger surface area. Note the difference in diameter between the 2 plugs. The smaller plug is the early version as fitted to the MK3 and P5B (AFAIK).




Sited in the upper removable section of the valve body.

[scherts]

Very interesting, it seems there is a huge variety in parts. Maybe my automatic is a mix of several generations  
The governnor, doesn't this involve removing the whole gearbox. This is in the rear housing isn't it? 

[enigmas]

Aug 1, 2019 10:35:30 GMT scherts said:

Very interesting, it seems there is a huge variety in parts. Maybe my automatic is a mix of several generations  
The governnor, doesn't this involve removing the whole gearbox. This is in the rear housing isn't it? 

In answer to your 2 questions.

No...it can be done in situ by removing the rear gearbox extension.

and

Yes...it is within the rear gearbox housing fitted to the output shaft.

* My 2 cents worth...I'd remove the valve body first and check that for correct assemblies, springs and valves before attempting to remove the governor.

[scherts]

Jul 31, 2019 12:09:36 GMT harvey said:

There are (at least) 2 different types of cam and brackets. Early brackets were cranked so they cleared the selector shaft, later ones were flatter, and the selector shaft was turned down so thewy didn't come into contact. Fit the later cam and bracket with the earlt selector shaft and they will foul. I have seen the brackets bent downwards so that they clead, but then it's impossible to get the cable adjustment set correctly.
[/quote]


Is it possible to grind a sleeve in the shaft of modify the cam so it fits? Or replace the shaft with a later one?

[scherts]

Can the cam that has been fitted be the source of all problems? It has been bent and looks very different than the cams enigmas showed.

Attachments:

[harvey]

The cam and bracket fitted to the valve block is supposed to be cranked like that, it's designed to clear the early selector shaft that isn't turned down to a smaller diameter on the inside of the box, but the cam doesn't look like it is coming fully back and laying up alongside the valve. The loose cam and bracket is designed to fit with the turned down sector shaft, so if you have the turned down selector shaft (which you should have with that 303 valve block) then you can try that bracket and see what happens. The trouble is that during the 45+ years since the last cars were made, all sorts of parts get put into all sorts of gearboxes.

[scherts]

Both cams are coming fully back. In the picture the spring was not set up in the right way but in the car it was. 
So both cams work more or less the same I suppose and use the same kickdown cable?
I can obtain the right selectorshaft but I think it's quite a challenge to replace it with the transmission in the car because of that spring ball. And is this the solution? 

I still am puzzled why the car drives 70 mph in 3 without kickdown cable and not faster than 50 mph (in 3) with the kickdown attached. Time to check the governor? The 2-3 valve was not sticking. I am willing to have the unit overhauled but not convinced it's necessary.

[harvey]

Aug 2, 2019 14:53:22 GMT scherts said:

Both cams are coming fully back. In the picture the spring was not set up in the right way but in the car it was. 
So both cams work more or less the same I suppose and use the same kickdown cable?
I can obtain the right selectorshaft but I think it's quite a challenge to replace it with the transmission in the car because of that spring ball. And is this the solution? 

All the cams work in a similar way. There are 3 different types of cable, long, short, and short 303, but they are all interchangeable.
I wouldn't attempt to change the selector shaft in-situ, just use the cam and bracket designed to work with the shaft you've got.

Aug 2, 2019 14:53:22 GMT scherts said:

I still am puzzled why the car drives 70 mph in 3 without kickdown cable and not faster than 50 mph (in 3) with the kickdown attached. Time to check the governor? The 2-3 valve was not sticking. I am willing to have the unit overhauled but not convinced it's necessary.

Are you sure you're getting into TOP with the cable connected? If you aren't it won't want to go much more than 50 in SECOND. With the cable disconnected you will have low line pressure, so it's easy for the governor to build up enough pressure to trigger the 2-3 shift, but with the cable connected, line pressure is higher, so if the governor isn't building up enough pressure then it won't trigger the shift into TOP. If you haven't looked at the governor already, (and TBH, even if you have) I'd be looking at it now. If you are getting into TOP with the cable connected, and it won't do more than 50 it sounds more like an engine problem than a gearbox problem.

[scherts]

I get in top without and with the cable connected. But in the latter case... despite the fact my engine is in excellent condition, it’s not fun on the big road driving in second gear faster than 50 mph. A rather noisy and freightening experience. Thanks again. No escape possible anymore to check the governor!

[enigmas]

Scherts AFAIK there may be relative differences in the position of the Throttle Valve at rest with either of those cams in place. It is an easy otion to swap them whilst the valve body is on the bench and take a measurement of the Throttle Valve at rest (this means the cam is at rest too...no rotation.)

Both should have the Throttle Valve 'at rest' at the same distance. If not the 'cam' that holds the Throttle Valve further in is the incorrect one to use.

See image below.



For reference only.
3 images below of the modified valve body (BW35) on my MK3 (V8 hybrid)

Note the position of the throttle cam.
This particular cam is adjustable for position.
Note that there is a nut fitted between the valve body and its adjustable mount. Leaving this nut out/off would affect its function!

Both your throttle cams looked to be the early fixed positional type (non adjustable) but obviously only one is the correct option for your valve body...although both may have the same stroke. The stroke from rest to full throttle and kickdown needs to be measured to confirm which one is correct.







Hope this assists.


PS. Looking at the relative positions of the cable attachment point on the 2 cams...they look to be at different positions when at rest.

If you've fitted a different inlet manifold the lever/linkages that operates (draws out) the transmission kickdown cable may be incorrect for the current setup. This is quite easy to check with the trans pan removed and the valve body and cable fitted.

[scherts]

I’ll pick up used BW35 for almost nothing Tuesday. Somehow they are always for sale in the Netherlands for cheap. I can fit the correct valvehouse and cam and meanwhile check the governor. But maybe this is a waste of time. As per Rover p5 manual there are 3 possibilities for unvoluntary high speed 3 to 2. 
- fluid level
- oil tubes missing or not installed correctly
- rear clutch slipping due to worn plates or faulty check valve in piston. As was the initial diagnose from Harvey.
The first two options I rule out. But because shifting to 3 was also difficult with the kickdown cable attached I will start with the governor.

[scherts]

I fixed my gearbox problem. The valve block was very sludgy. Also the governor was not that loose, but I wouldn't call it stuck either. The real culprit was in the kickdown cable. The crimp was located in the wrong place so not matter how much I would turn the screw in, it wouldn't matter. So I removed the crimp and now it shifts perfectly and I can go as fast as I want without the unvoluntary shift from 3 to 2 at higher speeds.

[harvey]

The crimp is only a guide, and it's only as accurate as the person who fitted it, who most of the time, don't have a clue.

[enigmas]

Aug 8, 2019 18:34:45 GMT scherts said:

I fixed my gearbox problem. The valve block was very sludgy. Also the governor was not that loose, but I wouldn't call it stuck either. The real culprit was in the kickdown cable. The crimp was located in the wrong place so not matter how much I would turn the screw in, it wouldn't matter. So I removed the crimp and now it shifts perfectly and I can go as fast as I want without the unvoluntary shift from 3 to 2 at higher speeds.

I hate to say this scherts but you seemingly weren't reading or acquiring the info offered in the posts made to assist your issue.
To be more specific...simply removing the trans pan and observing the function/operation of the throttle valve cam would have made it evident that the cam was not being fully returned to its 'at rest' position. The cause of the trans malfunction all the while seemingly being an improperly positioned and clamped ferrule...a 5 min fix. I imagine a very dirty/contamined valve body would have also added to the conundrum. Good luck.

[scherts]

I have a steep learning curve indeed and thought the cam was sufficiently in. Somehow I couldn’t conceive the possibility of such an error in the cable. Anyway many thanks for the assistance!