Now that we've gone front to back with the internal hard parts, it is time to compare the friction bands (three total in each transmission), servos (two in each), and associated hardware (levers, pins, anchors, etc.).
I'll start at the back and work forward. This means the first thing is the parking prawl and spring. They look the same to me. The only difference I can see is that the one from the A4 is marked with an indented "N" on one side and the one from the 5R is marked with a raised "N" in a depressed circle. There is a picture below with all of these small metallic parts.
Next is the low/reverse band. They are the same. I don't mean kind of the same...I mean the exact same part number. I think that they have been making this band the same since '83 (from the part number). Here it is (this is off the 5R - chosen because the numbers showed better in the photo):
Now the reverse piston that actuates the low band. Both had close to the same part number. They both have the same diameters for both o-ring seals. There are a couple of differences, but at this point I'm not sure this is an as-manufactured condition or the result of some damage. I'll update this part when I get them torn apart and see what's going on.
Moving forward in cases we get to the intermediate and overdrive servos. These are the pistons that apply force to the friction bands that stop the intermediate drum and overdrive drum from spinning. Each servo has an apply side and a release side. The servos are made in different sizes, denoted by a two letter code, and work only with their own specific sized cover. Here is what we know: BB is 1.945" in diameter, AB is 2.100", and ZC is the largest with a diameter of 2.300". There are five smaller sizes, but as far as I'm aware, they weren't used in the 4.0L version. The larger the piston, the more force is supplied by the piston (if the pressure is the same). In the A4, the BB sized servo was used on the intermediate (further back), and the AB sized servo was used on the overdrive (further forward). In the 5R, the AB sized servo was used on the intermediate, while a ZC was used on the overdrive.
Here's a picture of the servos with their covers on in the 5R case:
Here's a picture of the A4 case without the servos installed:
Here's a picture of the 5R intermediate servo cover installed in the case (note the AB on the cover):
Here's a picture of the 5R overdrive servo cover installed in the case (note the ZC on the cover):
More servo pictures will be posted later.
When the servo is activated, it applies force to a lever, and in this case both sets of levers had the same lever distance, denoted by the letter A on all of them. One of the things I noticed that was different was that the levers from the 5R didn't show as much wear where the servos applied force. The A4 had 125K miles and the 5R only had 90K, but the difference in wear is still an outstanding factor. I believe that the levers from the 5R are different in that they use a hardened steel (not sure if it is case hardened, through hardened, or an alloy, but it takes more force from bigger pistons/servos with a lot less wear). Here is a picture of the parking prawl and spring, band levers, anchors, and accessories (A4 stuff on the left, 5R on the right):
Here is a closeup of the wear marks on the levers (A4 on the left):
Now that we've looked at the levers, let's look back at what pushes on the levers - the servos. Here's a picture of a typical servo and what seals against what:
Notice that there are two seals on each servo. The one that seals agains the cover applies force to the lever (engaging it), and the one that seals against the body moves it in the opposite direction (disengaging it). Fluid gets between the servo and the servo cover through the hole in the stem (or rod) and flows through the hollow stem up to a hole in the top.
Notice that I have them arranged starting from the left with the largest (ZC on the cover) and going to the left with the smallest (BB on the cover). It is the seal that seals between the servo and servo cover that changes, as the seal to the body of the transmission as well as the stem sizes are the same.
I only have two springs from the A4 showing, but I'll show the other spring when I get it removed from the 5R case. These springs help to push the servo out into the deactivated position.
Here's a pic of the inside diameters of the servo covers (ZC on left):
Here's a pic of the three sevos next to each other (ZC on the left front, BB in back):
Here's a shot of the sides of the servo covers (ZC on the left):
Notice that the cover also has a o-ring seal to keep fluid in the case.
Now we'll take a look at where these servos fit into the case.
Here's a pic of a servo bore in the case (they are pretty much the same in both locations on ech case, and the same case to case):
Here's a pic of the intermediate servo locations in the case:
Here's a pic of the overdrive servo locations in the case:
Notice that both have a drain that appears to be located where the pan gasket sits. The intermediate drain is smaller than the overdrive drain (the intermediate servo has more pressure, therefore more potential leakage and larger drains). The pan gaskets and the pan are the same for the A4 and the 5R, and both have small channels cut into the pan gasket to let the (supposedly small amount) fluid that gets by the servo/servo cover seal drain back into the pan (and it is this leaked fluid which the o-ring on the servo cover serves to contain).
Here is a picture of where the pan gaskets have channels in them for the drains:
(Update 2)
Each servo has a spring to help push it back into the cover. This might just be a safeguard so that if you kill the engine in a gear where a band is applied, when you start it, the band is disengaged. Here is a picture of the springs:
I noted the colors that I had, but just FYI Glacier991 had some different colors for his spings in his A4 rebuild (as documented in the A4LD rebuild diary).
(end of Update 2)
Next is the intermediate and overdrive bands. I'll post more here later after I take some more pictures.
(Update 1)
Overdrive and Intermediate Bands
The bands function the same for all transmissions: they selectively apply pressure around a drum to get it to come to a stop and keep the drum from rotating when required. There have been two distinct band styles for the A4’s, namely a double-wrap design (for a short period) and a single-wrap design. The single-wrap kinds are the only ones I have to compare data on, but to see a picture of the double-wrap design, look here at Glacier’s A4LD rebuild diary - part 3, page 4 (top of this link):
http://www.explorerforum.com/forums/showthread.php?t=103666&page=4&pp=20
I have in my possession six bands: two of the Ford originals from the A4, two of the Ford originals from Jefe’s 5R, and two Borg Warner aftermarket replacement bands (same box part number but quite different). I’ve measured thickness and mass data on each one listed below, and only one stands out from the rest as being superior (IMO). I don’t have any data on the Raybestos brand bands, so I can’t vouch for their properties.
So what makes for a good band? Two things stand out above the rest: having enough friction material to outlast the other parts between rebuilds and not breaking into two parts.
All friction material is meant to wear down. This wear is the sacrifice of being able to dissipate energy (reduce the rotational inertia, a form of kinetic energy). This opposing-force energy is created by molecular separation, where in the best case (least wear) a single molecule is pulled from its adjoining molecules, and in the worst case (most wear) where chunks of material is ripped away (leaving the bonds internal to the chunk of material intact). Either way, it involves separating molecular bonds. With this concept (roughly) explained, heat is the byproduct of this molecular separation. If there is no heat generated, there is no braking force applied. For example, if the metal plate or drum next to the friction material is so smooth (glazed) that there isn’t enough “bite†to wear away friction material then the opposing force is reduced (and slipping could occur).
Now, I’m pretty well set-up in my garage, but I don’t have the capacity to quantitatively measure the molecular properties of the friction material used in these bands, so I’m going to have to compare them on the basis of thickness of friction material an ASSume they have the same friction properties
. Since this friction material is weak in tension, it is bonded to a metal band in all locations, but there are lubrication cannels (and holes) in the bands where I can accurately measure the thickness of the metal band. That means that in order to get a thickness value for the friction material, I measured the entire thickness and subtracted off the metal, so it is a derived value (as opposed to a direct measurement).
The thicker the metal band, the more tension it can take without breaking and the more heat it can sink (before transferring it to the tranny fluid), but there is a limit on how much thicker the band can be because the thicker the band, the stiffer and less conforming (to the shape of the drum) it is. The ends of the bands have anchors that are attached with rivets, and the thicker the metal band is, the more force the band can sustain without rivet pull-through (where the rivet head pulls through the band metal). If the friction material is worn away to where the heads of the rivets are ground off, it doesn’t matter how thick the metal band is, it is pulling apart (example picture below).
O.K. – time to compare some bands. Here are the six bands that I have:
The first band end – the broken overdrive band from my A4:
The second band friction material – the contaminated intermediate band from my A4 (metal particles embedded in the friction material):
The third and fourth band backs (steel) – the 5R overdrive and intermediate band:
The fifth band back (steel) – the first Borg Warner band I received:
The sixth band (steel) – the second Borg Warner band I received:
The fifth and sixth band’s friction side (fifth or first band on top):
Here's the data on the bands:
* - value isn’t valid due to the existing damage
Something that should be mentioned is that while the A4 and 5R bands were previously soaked in fluid (which might add to the mass value slightly), the Borg Warner bands were completely dry. Another thing to consider is that the A4 bands had 125K miles on them, and the 5R bands had about 90K miles on them.
You can see which one I like the best, and for Frankentranny I’m going to try to get a second band with the big “5R55†letters printed on the band (I only have one at the moment). The two Borg Warner bands were ordered as the same part number from TranStar, so I’m not sure if the change was a running production change or what the deal is there. One had a date code of early August and one had a date code of late August on the box, and the first band cleaned out their stock on hand, so it is possible that when distributors run out of the first kind, the second kind will be what is dealt.