BW35 control cable "calibration"

gbvona

Member
The short version of the story is that my 1970 NADA P6 suffered a carb swap (to HIF6's) and when I got the car the accelerator linkage was a total bodge. The BW35 tranny cable was not even connected.

I have made efforts to rationalize the carb linkage, which required fabricating a crank arm from the accelerator rod (that rotates when you press the pedal) to the carburetters. I guessed at the length of said crank and have apparently guessed wrong. The crank on the rod for the tranny cable is the original bit and I am using the original manifold casting.

Clearly there must be some coordination between the opening of the throttle and the distance of pull on the tranny cable. At present I have it set so that the tranny cable (which closes the pressure valve at idle) starts to pull out when the engine just gets off of idle.

Even so, the tranny tends to hang in lower gear too long and shifts abruptly. (Note that I have thoroughly cleaned the tranny, replaced the wear parts and adjusted the adjustments as per the shop manual, and am using the correct juice). To my thinking the pressure is too high at a given level of throttle.

I need to make a new crank arm for the carbs that reduces the pull on the tranny cable (giving a lower pressure) for a given throttle opening. It would help immensely if someone could make a measurement of how far the tranny cable is pulled out (from idle) with the throttle wide open (WOT). This would at least give me a ballpark estimate of the relationship between the length of the two arms (the tranny arm and the throttle arm), in that I could fabricate a carb arm that would match WOT with this distance of pull on the tranny cable.

As always, thanks for your advice!

gbvona
 
I would suggest using the OE parts as they will fit only needing the cable setting for it to work correctly. If you make your own bracket then unless it is exactly the right length, and sits at the same angle as the original, it won't give the correct pressures throughout the rev range, which is the problem you're experiencing it would seem.
Post pics of the carbs and manifold and I should be able to tell you which parts you need, and possibly even sell them to you.
 
I would suggest using the OE parts as they will fit only needing the cable setting for it to work correctly. If you make your own bracket then unless it is exactly the right length, and sits at the same angle as the original, it won't give the correct pressures throughout the rev range, which is the problem you're experiencing it would seem.
Post pics of the carbs and manifold and I should be able to tell you which parts you need, and possibly even sell them to you.

OK, here is a picture of the current rig. I am told that the HIF carbs are not correct for the manifold (which originally used HS carbs) but cannot confirm that. The original linkage had some kind of roller affair riding inside a fancy lever arm attached to the HS carbs. Now there is just a ball coupling on the HIF carb, crudely linked to the homemade lever on the accelerator rod.P1070025a.jpg

Thanks for any advice you can offer.

gbvona
 
The flat surface on the very top of the manifold should have the type stamped in it. From that angle I can't see whether it's HS6 or HIF6. I can't see the kickdown bracket either. but it looks like the forward end of the later short cable BW35 set up. I can see the bit you've had welded on, and I may have one of those somewhere.
 
The flat surface on the very top of the manifold should have the type stamped in it. From that angle I can't see whether it's HS6 or HIF6. I can't see the kickdown bracket either. but it looks like the forward end of the later short cable BW35 set up. I can see the bit you've had welded on, and I may have one of those somewhere.
It is highly unlikely that the manifold is an HIF model. This is the US where parts like that are very hard to come by. My educated guess is that it is simply what came on the car originally, which for the US market had HS carbs and the dreaded AED. In any case, the only numbers stamped on the top of the carb tower seem to be a date code of 19/9/69 (or maybe they are inverted). There is also "T1" stamped in a boss on the rear near the top (you can kind of see it directly behind the choke link). The fabricated lever for the carb linkage is attached to the accelerator rod via a welded-on ring that secures with setscrews, so fiddling with this is easy.

I attach another picture showing the kickdown lever and such.

P1070027a.jpg

Thanks for your help!

gbvona
 
If the manifold tower has a large bore pipe on the front face, or a plug where the pipe was, that marks it out as HS6 with the provision for the AED. That kickdown bracket assembly is all correct for late BW35 short cable. The only problems are the fabricated link on the front end, and the fact that the carbs will be sitting in a different position if they are HIF6s on a HS6 manifold.
 
Yes, it does have a plugged large bore pipe on the front of the tower. Yes, the problem is the fabricated link. I don't have any idea how long it should be (between the centers of rotation of the accelerator rod and the connecting ball). That is why I asked how far the cable pulls out with wide open throttle on an original linkage. I can figure out the rest, I are a engineer ;). I figure that if I get the end points right, it can't be too far off in the middle. It can't be as bad as it is now.

Thanks

gbvona
 
gbvona

I am only a mere newbie here but I have a 1972 2 owner auto car that has not been too messed with, after work I can measure the kickdown cable movement for you if that is any help.

Mark
 
I am picking up a parts car in the next week or so... let me know if you need any bits and I'll see what I can do for you.
 
gbvona

I am only a mere newbie here but I have a 1972 2 owner auto car that has not been too messed with, after work I can measure the kickdown cable movement for you if that is any help.

Mark
That would be absolutely swell, thank you!

gbvona
 
OK from idle to WOT the clevis on the end of the cable rises by @ 32mm, its a job to get in there !
Also the lever that is welded on your car is @ 55mm from pivot to ball on my car.

Hope this helps.
Mark
 
OK from idle to WOT the clevis on the end of the cable rises by @ 32mm, its a job to get in there !
Also the lever that is welded on your car is @ 55mm from pivot to ball on my car.

Hope this helps.
Mark
Got it, thanks so much for the information!

gbvona
 
Made a lever that gave me right at 32mm of cable pull at WOT. FYI, with the confused rig I have (HIF carbs on an HS manifold) the distance from the center of the accelerator rod to the center of the ball is 1.5". On a brief test drive the tranny was much more civilized, smoother shifts and shifting more or less when it was supposed to.

Thanks to all for collective help!

gbvona
 
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