> BBE AUTO BUILDS AND TESTS A TOUGH TH350 FOR OUR LX TORANA HATCH
A CLASSIC street machine like our giveaway LX Torana hatch calls for a classic transmission, and thatís precisely what a Turbo- Hydramatic 350 has become. Of course, itís not the only choice available; adapters or modifications make it possible to fit almost any transmission to a 308 Holden V8 these days.
The Trimatic, for example, is a good trans but it isnít as robust as a Turbo 350. In standard form it will start to suffer beyond about 400hp, though with the right components that figure can be extended to as much as 600hp. For heavy-duty applications thereís the classic Powerglide, and these can be built to handle any power level, but for regular street use there are better choices than a two-speed transmission.
The three-speed Turbo 400 is tough enough to handle most street applications and is certainly strong enough for this car. However, the 400 is unnecessarily heavy and its extreme toughness just isnít needed behind this engine in a car of this weight. True, it would be bulletproof, but so is a Turbo 350 in this application. In fact, a well-prepared 350 with the right components is capable of 600-700hp, which is considerably more than our Torana is turning out. Although it has some clout, this hatch is a cruiser rather than a dedicated bruiser, so a Turbo 350 is perfect.
John at BBE Auto in Elsternwick, Victoria agreed to help us get a strong, fully tested 350 into our giveaway Torry for the lucky winner to enjoy.
So what exactly does Ďfully testedí mean? Well, BBE Auto actually has an Axiline transmission dynamometer, which they use to test and verify the operating integrity of virtually all transmissions before they leave the building (see sidebar p134).
Removing the original TH350 sump revealed a world of pain.
Fortunately, BBE Auto was always going to fit the replacement valvebody shown
Thankfully the upper side of the valvebody, which is cast into the transmission case, was able to be cleaned up after the lower section was tossed away
The direct drum also showed some signs of corrosion, but this was also replaced
The OE clutches were worn, and you can also see where water had caused the friction material to start detaching from the backing. Itís not any fault with the friction material, itís just that clutch frictions arenít meant to see water. Note the wear on the original speedometer drive gear (inset, on the left)
This is a factory sprag. Getting these replaced in higher-powered applications is essential. The rusty material has been transferred in the dismantling process
Here are all of the new parts BBE Auto supplied and fitted for the Torana transmission. The cooler a transmission is while in service, the longer it will last, so BBE Auto also supplied a trans cooler
Replacement bushes should always be fitted in a press. This ensures theyíll be aligned to the bores in which theyíre located. All the apply pistons have rubber seals.
New seals from the rebuild kits are fitted using special transmission assembly lubricant
Some of the components, like this clutch pack, are assembled into sub-groups and then fitted into the case. Clutch pack clearances are meant to be between about 0.020 and 0.090in. Most rebuilders set them at about 0.008-0.010in for friction plate. The clearance is adjusted by each friction plate. The clearance is adjusted by fitting different-thickness intermediate steels, usually referred to as just steels
Pump side clearance is also essential. This is measured using a straight edge and a feeler gauge as shown
Where there are double ring seals as on this pump shaft, the gaps in the rings should be set opposite each other, much in the same way that pistons rings are installed with the gaps at opposite sides
When it comes time to start filling the transmission case, you are working from back to front. If you were ever to attempt the job at home youíd really need a good manual or plenty of experience.
Naturally the guys from BBE Auto have plenty of both
Some clutch packs are assembled directly into the case along with the planetary gearsets, which are the core of any automatic transmission.
Most components in automatic transmissions canít really be misaligned; if they are, the next components just wonít fit
The direct drum carries the heavy-duty replacement sprag (under the gold coloured plate). Here, Gilbert is fitting the apply band for it. This also has uprated Kevlar friction material
This apparatus is used to set longitudinal freeplay.
The central measuring rod is dropped until it makes contact with the thrust bearing, and the gasket must be in place for this as shown.
The measuring rod is then transferred to the case, above the direct drum in the transmission. The distance between the thrust washer and the tip of the rod should be between 0.020 and 0.045in, and then the pump can be installed
The marks around the edge of the case are from the water, but theyíre just that, marks. The surface is completely smooth and will seal perfectly after the new valvebody lower half is fitted. A number of gaskets are supplied with each rebuild kit. The holes in the gasket must match the holes in the valve body separator plate
OF COURSE, the transmission had to be built before it could be tested. The original unit we were going to fit turned out to be beyond salvage, so BBE found the one pictured on page 130 for us. But it also had some problems. When the sump came off, Gilbert, whoís been rebuilding transmissions for over 20 years, said heíd never seen a valvebody with this much rust on it.
Valvebodies can be refurbished by boring out valve bores and fitting oversized valves and other replacement parts. But pretty clearly, this valvebody was way beyond that. In any event, the rust didnít matter too much because it was always going to be converted to a fullmanual trans, so an aftermarket BTE valvebody and separator plate were always part of the plan. The rust hadnít penetrated too far and the internals cleaned up quite well. Most of the rust you can see on the parts in the dismantling shots was transferred during the valvebody removal.
The factory direct drum was also rusted, but it too was scheduled for replacement. The direct drum carries a sprag-clutch, and the factory unit is a particular weakness in the Turbo 350, as the outer races on these sprags tend to break at around 350hp. There are aftermarket races available, but John isnít keen on them. Rather, he feels itís best to replace the entire drum with an aftermarket performance version. In addition to being thicker and stronger, these drums come with a 36-element high-performance sprag that can hold as much as 1000hp.
Obviously, the clutches in any transmission undergoing a rebuild are replaced. Not surprisingly, the used ones out of this transmission looked worn, but things werenít as simple as that.
Gilbert said that the loss of friction material looked more like it was from moisture rather than straight wear, pointing out that parts of the material were flaking off the backing steel rather than simply wearing away.
Finally, the sump is bolted in place and the Torana transmission is ready to go on the dyno. There are many more steps involved in both dismantling and re-assembling a Turbo-Hydramatic 350; weíre simply showing you an overview rather than how to rebuild a transmission
PUTTING transmissions back together properly is as much about diagnosing worn components as it is about fitting new parts. If the old parts arenít diagnosed properly problems could be missed and may recur when the transmission is back in service.
John suggests that friction material for automatic transmissions is often misunderstood. Sure, it needs to be highquality, but it needs to be matched to the application. Friction material designed for higher-performance applications is harder and may not work as effectively under less demanding conditions. Surprisingly, harder friction material may result in a slower, softer grab because of the lower temperatures and pressures. Softer friction compounds work much faster and can grab virtually instantly, but if the material is too soft it will wear very quickly. Originally, our idea was to fit Raybestos blues because of their reputation, but after John explained all this to us we followed his advice and fitted the regular Raybestos tan types.
Clutch engagement speed is vital for performance, but holding power within a clutch assembly is just as important. Obviously, increased holding power is achieved by increased pressure within a system. Standard pressure within a TH350 might be something in the order of 120psi. If an apply piston has an area of, say, four square inches, the clutch pack on which it acts will have a clamping pressure of 480lbf/in2. Line pressure in this transmission was upped to 180psi, so clamping pressure would also rise to 720lbf/in2. That will hold quite a bit of torque.
While increasing pressure in the main circuit will push the clutch plates together more tightly, it doesnít do much for the speed of engagement. Making things happen more quickly calls for valvebody modifications. There are a number of aftermarket valvebodies available and these also should be matched to the correct application.
The final modification to our Turbo 350 was fitting a deep castalloy sump. This serves several purposes. First, it simply holds more transmission fluid, so operating stresses are dispersed through a greater amount of fluid. The increased fluid volume can also absorb more heat. Also, because the sump is finned, it has a greater surface area than the smooth factory unit pressed from steel sheet. Greater heat rejection through a larger surface area also helps keep operating temperatures low.
One more feature of the thick cast-alloy sump is that itís much more rigid than the pressed factory unit. This bridges the void in the underside of the transmission case with a strong structural member, which strengthens the case and resists torsional strain. s
THE Axiline transmission dynamometer tests elements of a transmission that would be difficult or impossible to assess after installation. The dyno runs the transmission through the gears under a variety of simulated operating conditions.
Simple noises are a case in point. The operator can stand right next to a running transmission and listen to it without engine noise while visually checking it from every angle. Hearing exactly when any noises are present in a trans is an invaluable diagnostic tool. A high-pitched noise may indicate a worn pump. A noise from the converter can be confirmed by listening to when it occurs. If, for instance, thereís no noise in Park or Neutral but there is in Reverse and Drive, itís likely a turbine bearing fault. When gears are engaged, pressure increases and the two halves of the converter tend to separate, which loads the bearing and increases noise.
Pressures, shift points and speeds, down-shifts, converter lock-up characteristics, stall speeds and more can be tested, logged and recorded. Vacuum circuits on older-style transmissions like the 350 can also be tested, as can solenoids and modern electronic control systems.