BW 35 stuck in 1st gear

willem

willem

New Member
Hello,
I have a Rover P6 from '71 with a BW35 gearbox.
It has a problem, It will stay in 1st gear when the 2nd is engaged.
I can drive in L position. If I select D1, it pulls away, until 2nd gear is engaged, then it slows down until it switches back, then the process repeats again.
When I try to drive away in D2, not much happens, the car moves with a lot of resistance.
The problem has suddenly occurred after a few days of downtime. It worked fine (for a BW35), but after a few days the problem appeared right away. I noticed lately that it sometimes took a little longer before 2nd was engaged, when I stopped and just selected all the gears it functioned normal.
The oil looks good, as new actually, though I did notice that the oil I topped up with was incorrect (misread the label).
Do you have any idea what might be going on here?

Regards Willem.
 
Do you have a PRND2D1L selector pattern? If so that can't be original as by 1971 they had PRND21.

If I understand your description of the problem correctly, and you have a lot of slip pulling away in D2, and a reluctance to shift into SECOND when driving in D1, then that is a front band fault, either a problem with the band itself, or the servo that actuates it. The servo adjuster locknut may have come loose allowing the servo to go out of adjustment, or one of the servo seals may have failed. The servo can be removed, overhauled, and refitted without removing the gearbox.
 
It has PRND2D1L, and L works, so not original I guess.
The box does shift into 2, but I get the impression that it does not release the first gear at that moment. The car slows down (pretty hard), until a speed is reached where it shifts down (releases the second gear). Then it goes up again until it shifts into 2 again, and slows down again.
I returned home in L.
It does not slip while trying to drive in D2, it just won't go, and the revs stay low.
 
When you are in D1, and still in first gear, before it tries to upshift, do you have engine braking if you lift off the throttle?
 
Yes, I just tried it, it brakes quit severely and makes a bit of a whining noise. When it is almost stopped, it releases again.
 
If you have engine braking in D1 while in first gear, then the rear band must be jammed on. In D1 first gear it should coast when you lift off the throttle. If the rear band is jammed on then when the box shifts into Second gear, the front clutch, front band and the rear band will be applied at the same time, and that will lock the box up. The rear servo piston may have come out too far, jammed, and locked the band on.
 
Ok, you mentioned that the servos can be fixed with the box in place, but if the servo came too far out the band will probably need to be replaced. Can this also be done with the box in place (I guess not)?
 
The box needs to be removed to replace the bands.

If you're confident that the diagnosis fits the symptoms then I would suggest you drain the fluid and remove the sump, and you should be able to see if there is a problem with the rear servo. If so, you can remove the servo and repair or replace as nesessary, and providing you haven't put too much load through the bands while trying to drive it when it had the fault, the bands will be OK, and refitting the rear servo correctly will cure the problem.
 
The diagnosis fits the symptom perfectly, I know what to do now.
Thank you very much for this information!
 
If you drop the sump, and see a problem, then if you can take a pic and post it before you remove anything I'd be interested to see it.
 
Because it was behind the rear servo, the shape of the pieces, and the fact that the servo has been the problem, the chances are that all the debris is from the rear band. The band being applied when it shouldn't have been has most likely stripped all the friction material off.
 
Ok, this means the box has to come out.
That would be my first overhaul of an automatic gearbox.
Is there a workshop manual you would advise on?
 
The factory workshop manual is pretty comprehensive, although IIRC it breaks things up into dismantling and overhauling individual components rather than dismantling and rebuilding in sequence. If you intend to overhaul the box, you're going to have to be on top of your game as they're not easy to do, and there is plenty to trip up the unwary, plus there are some special tools that you can't do it without. On the other hand, if you want to just repair the problem you have (and inspect/replace the clutches without replacing the seals and take the risks that involves) you can do that relatively easily, quickly and far more cheaply.
You may find that the shredded band has damaged the outside surface of the gearset that it runs on.
 
I'll do the minimal 'overhaul', the box worked fine anyway until this happened. Except for some leakage, which I'll try to solve also.
I hope the surface has not damaged, but I'll see to that when I get there.
 
I'm rebuilding the box, replaced the clutches and bands.
Only, I found the front band being of the old rigid type, while I ordered the flex type.
According to the seller they are interchangeable, so I went on.
But now the pushrod is too long (.215), it already applies pressure if I tighten the front servo.
I think there are three things I can do:
- get a shorter rod
- get the rigid band
- get the front servo which belongs to it, maybe of the self-adjusting type
What would you do in this case?

bw35-f-servo.jpg
bw35-frb.jpg
 
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