New Modulator on BW-8 Auto Transmission

[hogman63]

(I just posted the same question on the binder bench forum. Maybe this forum has readers who don't frequent the binder bench forum. Just trying to get more feed back.)

I just installed a new modulator valve on my 1966 bw-8 auto transmission. I removed the old modulator, noting the amount of turns required to remove it. Re-installed the new modulator, setting it to the same number of turns in. Reconnected the vacuum line from the intake manifold. First thing I noticed was a change in the engine idle. Made ajustment to idle jet to speed up idle.

Then I put selector in gear, but the tranny would not engauge unless I reved the engine. Made two reveloution in and out adjustments respectively on the new modulator, without much change. It did seem to engauge at lower rpm the farther I screwed in the modulator. I did not attempt to drive the pickup as I was afraid I had too much pressure, and could do some damage. Decided to reinstall the old modulator and get it to a transmission shop and have them install and adjust. Old modulator behaves just as it did. I do know the old modulator is not holding a vacuum. The diaphragm is shot.

What is logically happening with the new modulator? Is the idle speed decreasing because I plugged a vacuum leak? Is the old modulator holding a high pressure and letting bands engauge better? Would a band adjustment along with the new modulator solve my problem. Or is the transmission due an overhaul?

Just give me your best educated quess if you are not sure.thanks for any help. It is much appreciated.

 

[Michael Mayben]

I've never run diagnostics on one of these trannys. So I'm tossing out some "stuff".

As for the take-off modulator not holding vacuum, what you have described is exactly the scenario one would expect with a very healthy vacuum leak. No doubt the engine tuning (idle mixture and curb idle speed) was compensated for that at some point in time. So now you've eliminated that particular vacuum leak and the tuning needs to be re-visited! The modulator runs off manifold vacuum, so any leakage in that system (including the plumbing) would significantly affect the carb setup. So you have addressed that in a correct manner!

As for the "slow to engage" condition for the trans...using the appropriate section of the service manual for that trans, I'd suspect that the front clutch is a goner. By increasing control pressure with the modulator adjustment, it does have an effects you have described, but if the friction materials on the clutch discs are toast, then it simply can't make a friction engagement in the clutch pack.

Does placing the shift lever in "1" position (manual low) make any difference in initial engagement? After it's run for awhile and gotten hot while playing with it, does it then make an attempt to engage and move but slips badly in breakaway?? If so, you might make an attempt at band adjustment and see if that has any affect.

Do you have the appropriate service manual for that transmission? And I don't mean one for a Ford fmx semi-clone? The IH service manuals are very good regarding diagnostics and service on these units.

I have one (Scout 800 4x4) myself that certainly needs to be rebuilt, but I'm not gonna put the resources into it unless I have a buyer for it, there is simply no demand for these units in the IH enthusiast community. They are excellent transmissions when working and very rugged.

I'd have no issue at all with expending the capital to build one.

 

[hogman63]

I've never run diagnostics on one of these trannys. So I'm tossing out some "stuff".

As for the take-off modulator not holding vacuum, what you have described is exactly the scenario one would expect with a very healthy vacuum leak. No doubt the engine tuning (idle mixture and curb idle speed) was compensated for that at some point in time. So now you've eliminated that particular vacuum leak and the tuning needs to be re-visited! The modulator runs off manifold vacuum, so any leakage in that system (including the plumbing) would significantly affect the carb setup. So you have addressed that in a correct manner!

As for the "slow to engage" condition for the trans...using the appropriate section of the service manual for that trans, I'd suspect that the front clutch is a goner. By increasing control pressure with the modulator adjustment, it does have an effects you have described, but if the friction materials on the clutch discs are toast, then it simply can't make a friction engagement in the clutch pack.

Does placing the shift lever in "1" position (manual low) make any difference in initial engagement? After it's run for awhile and gotten hot while playing with it, does it then make an attempt to engage and move but slips badly in breakaway?? If so, you might make an attempt at band adjustment and see if that has any affect.

Do you have the appropriate service manual for that transmission? And I don't mean one for a Ford fmx semi-clone? The IH service manuals are very good regarding diagnostics and service on these units.

I have one (Scout 800 4x4) myself that certainly needs to be rebuilt, but I'm not gonna put the resources into it unless I have a buyer for it, there is simply no demand for these units in the IH enthusiast community. They are excellent transmissions when working and very rugged.

I'd have no issue at all with expending the capital to build one.

I did not try the 1 (low) position. I also was running cold, as I had let the truck set a few hours before changing out the modulator. I was concerned about running the transmission very far as the service manuals I have state I need a pressure gauge to read the internal pressures. I do not have such a test gauge. Thought I would leave that up to the transmission shop.

I do have the cts-2000abc (1957-63 pickup), and the cts-2312 (1962-71 travellall/pickup) service manuals. Since this bw is out of a 1966 1000-a pickup, I purchased the cts-2312, although I havent detected a difference in the bw auto transmission service pages from one to the other.

One other thing I didn't mention was a high pitch hum when the selector is in reverse. It has diminished in loudness after I put a quart of trans-x in it last week. It is barely audible now, but I can still hear it if I stop the vehicle motion.

Would your transmission fit my bd220 engine, and what would you want for it rebuilt? I have a transmission shop about 75 miles from me that has a tech that knows alot about these bw transmissions. I am concerned about parts availability.

Thanks so much.

 

[JimKoz]

I was in a similar situation when I got my bw-8 rebuilt. It has a much longer modulator pushrod than the other borgs and isn't very easy to stab into the right position.

The transmission shop installed my modulator, but after it wouldn't engage without slipping, I decided to take the pan off so that I could see what was going on. Once I got the modulator installed properly, everything was fine.

Glad to hear that your borg hums. Mine does that too, but in both low and reverse.

 

[hogman63]

I was in a similar situation when I got my bw-8 rebuilt. It has a much longer modulator pushrod than the other borgs and isn't very easy to stab into the right position.

The transmission shop installed my modulator, but after it wouldn't engage without slipping, I decided to take the pan off so that I could see what was going on. Once I got the modulator installed properly, everything was fine.

Glad to hear that your borg hums. Mine does that too, but in both low and reverse.

I wondered about that, but after I reinstalled the old modulator. It returned to working as before, with the old modulator. Maybe I got it lined up better on the re-install of the old modulator. The pushrod is 1/32" short of 4" long.

 

[hogman63]

I was in a similar situation when I got my bw-8 rebuilt. It has a much longer modulator pushrod than the other borgs and isn't very easy to stab into the right position.

The transmission shop installed my modulator, but after it wouldn't engage without slipping, I decided to take the pan off so that I could see what was going on. Once I got the modulator installed properly, everything was fine.

Glad to hear that your borg hums. Mine does that too, but in both low and reverse.

Well this one has me shaking my head. I think my binder is playing trickery with me. Logic seems to be lost to me on this one.

After bench test comparisons between the old modulator and new modulator, after consulting two different transmission shops with bw experience, after consulting and searching the forums, I just couldn't understand why the new modulator wasn't performing. As stated before, I uninstalled and reinstalled each several times. Always the new would fail to perform, yet the old would perform. (I.e. The gears would engage at normal idle vs. Higher engine rpm.)

the bench test showed that the old modulator moved 1/16" under 18" of vacuum. The new moved 1/2" under same vacuum. A manual compression of the modulator springs indicated identical travel of the pushrod. Only diffenence was new modulator was slightly stiffer in the spring, but not by much.

Logic told me that I couldn't be hitting the pushrod paddle in the trans. On the reinstall of the old modulator 100% of the time, and then missing the paddle 100% of the time on the install of the new modulator. I went through at least 5 uninstall / reinstall cycles as I gained more recommendations from above sources.

It was only after I broke the pushrod on a bench compression test, and made a new 1/4" longer pushrod, that I could detect I was hitting the paddle during install of the new modulator. The initial engagement returned to normal once I installed the pushrod in the correct location on the paddle.

I made the pushrod longer because logic told me that since the old modulator was retracting 1/16", and the new modulator was retracting 1/2", I needed alonger rod to actuate the paddle the same. So I added 1/2 that amount. I did a final reinstall after shortening the pushrod back to the original 4" length. I missed the paddle again, but got it right after another try.

Transmission now shifts what seems to be fairly normal. I now have a vacuum induced downshift when I punch the accelorator. I have yet to hook up the kickdown switch, but will do so over the weekend.

Btw, the bench test on the kickdown switch showed me that the the pushrod extends by about 1/8" so by logic, I assume that the quick acceloration causes a reduction of vaccum to the modulator, thus lengthening the travel of the pushrod, causing the upshift to 2nd gear.

Please excuse the ramble, but thought this might help someone else. Thanks to all who advised. I'll be back with another question soon. You can count on it!

 

[Michael Mayben]

Thanks for posting your findings!! That's in the best spirit of ihon where we deal in fact and not bs!

You are now our go-to dude for borg warner slushbox issues!

Several years back when this same kinda stuff came up on another forum I frequented (and no longer do so), I did some extensive research on the bw "modulator" subject. At the time, there was still a bench man (long since retired) at a local tranny shop that I could go to and pick his brain. Seems that between us we figgrd out there were at least five modulators and variations of the pushrod used in all the different applications of that trans, from studebaker to jaguar. So you can see it's real easy to get all this stuff mixed up when swapping parts around. No doubt some of the combinations are simply not available and the selection as been reduced to only a couple of part numbers. Therefore, the pushrods have gotten mis-matched during the exchange. Once folks hit a dead end with making 'em work, they simply park the "project" and someone comes along years later and picks it up, not knowing what caused the rig to "park".

And the ihc applications of the bw box are just one of many variations, while they are all of the same family, they certainly are not "all the same" as the novice gearhead normally states!

I wish I had the experience with the bw boxes that I have with the torqueflites!