26 GEARSMay/June2008

What does it take to rebuild quality torque converters? There are several things you

can do; one is to remain as informed as possible on the latest tech and trends facing the industry. And one of the best ways to do that is to get involved with

your trade organizations (shameless TCRA plug).

Going to trade seminars and read-ing articles like this are key. One of the best ways of keeping up is to maintain an open line of communication with your customers and learn from them;

they’re a great resource for keeping up to date and finding out when something isn’t right.

This is even more important when you’re working on a new converter; one where there is no information — no “playbook” — available. In cases like

these, your only choice is to use your best judgment, make your mistakes, and make sure you learn from them.

This happens to every-one: Sometimes these are the best lessons because they’re the ones you’ll probably never forget. And this is where it’s so impor-tant to have great relation-ships with your customers, because they’re the ones who’ll be in the best posi-tion to provide you with that critical feedback on your rebuilds.

Of course, one of the

Rebuilding the Late Model ZF with a Captive Clutch Torque Converter

by Joe Rivera

Figure 1: Exploded view of late model ZF "captive clutch" torque converter.

Cut Open Process

“Captive clutch” simply means the lock clutch plate is held captive by the

pressure plate and lock up is an “always on” system and oil pressure is needed

to take the lock up off.

GEARS May/June 2008 27

great benefits of an industry association such as ATRA or APRA is they allow you to learn from the mistakes of oth-ers. So here are some tips I’ve learned from my mistakes while rebuilding the late model ZF torque converters found in everything from Audis, BMWs, Range Rovers and Jaguars.

Many of the torque converters coming out of today’s ZF transmis-sions have what has been described as a “captive clutch” (figure 1). By “cap-tive,” we mean the converter clutch plate is held captive by the pressure plate. Lockup is normally applied; the system applies oil pressure to release the converter clutch.

There are several different styles of captive clutch. Some have snap rings holding the pressure plate in place. Others have the pressure plate crimped in place. The most difficult of all is when the pressure plate is welded in. Think about that for a minute: Imagine you’re rebuilding a transmission. You disassemble the unit and when you go to open the clutch drums, they’re all welded shut!

What do you do now? Well some torque converter rebuilders have found a way to open these unserviceable little stinkers, repair them, close them back up, and make them usable again. But not without their trials and tribula-tions… and taking a few lumps along the way. Here are a few lumps you might want to avoid:

Potential Problem 1The first place a mistake can creep

in is way before you attempt to rebuild the unit, when you first open the torque

Figure 2: ZF5HP30 Converter with Closed off Orifice

There are several different styles of captive clutch. Some have snap rings holding the

pressure plate in place. Others have the pressure plate

crimped in place. The most difficult of all is when the pressure plate is welded in.

28 GEARSMay/June2008

Figure 4: Seal FailedFigure 3: Bad Clutch and

Engagement Tabs

Rebuilding the Late Model ZF twith a Captive Clutch Torque Converter

converter. In the ZF 5HP30 in the 7-series BMW, there’s an orifice at the very bottom of the converter. If you fail to maintain this orifice size, or if you close the hole by applying too much pressure with the mandrel, you’ll build in an entirely new problem.

This orifice is the passage for con-verter clutch release oil. If you close this orifice down (figure 2), the engine will want to stall when you put the car in gear. This is because there isn’t enough oil passing through the hole to hold the converter clutch off.

What if you only close it down a little… not enough to make it stall? When it happened to us, the engine only stalled when the transmission got hot. Which of course led everyone to believe that it couldn’t be a converter problem. Even the transmission shop was sure it couldn’t be the converter.

How did we find the problem? After checking everything else and finding nothing wrong, we decided to replace the converter; the problem went away immediately. Then we took the converter apart again and found the orifice problem. We opened the orifice back up to normal size and the converter worked fine: Lesson learned through proper communication. Not an easy lesson for either shop but a valu-able one.

Potential Problem 2

Cutting the converter open can be one of the most demanding parts of the rebuild process. Many converters can be damaged by open-ing it the wrong way, damaging splines, seals and bushings.

Think of it like this: The best cake starts with the best ingredi-ents, and all of those ingredients are important. Your cutting process is as important as your rebuilding process, which is just as important as your weld-ing process.

Potential Problem 3Another common mistake is not

opening the captive clutch, and simply hoping that everything inside is okay. This is the “roulette” rebuild procedure, and the odds against you winning are pretty much the same. In fact, they may be even worse: Every clutch we’ve seen was worn, delaminated or just plain failed (figure 3).

So if you’re looking for a gamble, take it to the tables, not your rebuilds.

Always open the captive clutch, and replace it as necessary.

Potential Problem 4The next common mistake is to

reuse the seals. A lot of rebuilders have tried this, simply because the seals haven’t been readily available. This is a big mistake, because these seals always fail (figure 4).

While we’re on the subject of seals, there’s a medal clad seal in this unit that you need to be careful installing: It’s very easy to install upside-down (figure 5). I’ve seen this several times in failed rebuilt converters from other rebuild-ers that have made their way into my shop.

Figure 5: Seal Installed Upside Down

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30 GEARSMay/June2008

Potential Problem 5Another seal you don’t want to

forget is the o-ring. While that may seem beyond obvious, it’s important to remember not just to replace the seal, but to make sure you don’t damage it during the welding process.

An all-too-common way to dam-age the o-ring is to weld the converter housing too hot. Using too much heat in the welding process will burn the o-ring and cause premature converter failure (figure 6).

Potential Problem 6Avoid the temptation of reusing the

clutch plate. Every one we’ve opened has been damaged to where it shouldn’t be reused. I’d recommend replacing every converter clutch, even if you can read the printing (figure 7). Some of these clutches are available from the usual converter parts suppliers; some aren’t.

But whether you reline the clutch, or even if you’re going to roll the dice by reusing the original clutch, always pay close attention to clutch release clearance. The clutch release clearance is only 0.010” and the available travel on these pressure plates is only 0.040”. If you use the wrong thickness lin-ing, the converter clutch won’t release properly.

If you do choose to reline this clutch, check the engagement tabs and

make sure they aren’t worn. If they’re worn, they’ll make a noise.

The key to identifying converter problems and making sure they don’t recur is to keep an honest, open rela-tionship between the converter rebuild-er and the transmission shop. Working together will make what seems like an impossible job a whole lot easier.

Special thanks to Scott Johnston at Fairfield Transmissions, Fairfield, CT, and Nat from Eriksson Industries, Old Saybrook, CT, for keeping those lines of communication open.

Joe Rivera owns ProTorque, a torque converter company focusing on high quality rebuilt torque converters located on Long Island, NY and can be reached at www.protorque.com.

Joe is a member of the TCRA board of directors and his primary goal is for the TCRA to improve relations between the torque converter and transmission industries. You can find this article and other important information about torque converters at www.tcraonline.com

Figure 6: Using too much heat in the welding process will burn the O-ring; causing premature converter failure.

Figure 7: 6HP Jaguar Segmented Clutch Failed * note the printing still on it

Rebuilding the Late Model ZF twith a Captive Clutch Torque Converter

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1607-PRE-053 Gears Magazine April 2008, January 2008 T: 8.125 x 10.875 B: 8.375 x 11.125 4C

1607PRE-8.125x10.875-053 2/26/08 11:41 AM Page 1