• Register Today It's free! This box and some ads will disappear once registered!

^^Searches ExplorerForum.com^^

4R70W Rebuild Diary - Part XX - Friction Material Discussion


EF Tranny Guru
Moderator Emeritus
February 8, 2003
Reaction score
City, State
Sacramento, CA 95827
Year, Model & Trim Level
1992 XLT


In an automoobile we utilize friction material in various places. The obvious one is brakes. Also a clutch in a manual transmission. Friction plays a part in the AC clutch too. (Though it is metal on metal). Also in the transfer case, and the torque convertor, and in spades in the automatic transmission.

As better explained by Jerry W. in his definitive (if slightly dated) article on the www.tccoa website - entitled "Transmissions 101", in a wet environment (meaning saturated with automatic transmission fluid) there are two important types of friction "stopping" power. One relates to how fast and strongly the friction material, when pressed between steel plates, can arrest rotation. This is called "Dynamic friction." This one, according to Jerry, is more a function of the friction material. The second one, called "static friction" is related to the ability to hold the rotating part stationary. He says this is more related to the properties of the fluid as anything else. I am going to assume that he pre-assumes you have a decent friction and adequate pressure holding it between the plates (how about that 2 assumptions in one sentence!)

Often we assume that stock is innately inferior to some aftermarket whiz bang product - just because it is stock. Tell me guys, how many of you have had your auto trannie last longer in a rebuild than it did stock?

In this case, stock deserves serious consideration. reading Jerry's threads only emphasized that. The other thing that I took away from reading his threads was that the non-grooved frictions needed a fairly strong and quick apply to prevent the hydroplaning that could lead to overheating, whereas the grooved frictions did not exhibit this tendency. Certainly makes sense to me, just empirically.

The other thing we need to do is evaluate what each clutch we build will be expected to do. Some mainly are ON in forward gears and hold. Others engage in lower gears. But the idea is KNOW what is expected of the clutch, and when. With that you are better equipped to consider friction material. Is this clutch more dynamic, or static? (Also tells you something about fluid changes!!)

Some might be inclined to think... "the most heavy duty I can get is the best." Well, maybe NOT. Why ? Because if the hydraulic apply pressures needed for some of those frictions cannot be brought to bear and fast (can you say HARD shift?) they will slip. Slipping is not a good thing. So we face grooved versus non gorrved. Non Gorrved have more surface area.....BUT ! If the stock.. grooved plates will hold JUST as well, and you lose 5% of the surface to grooves, have you really lost anything worthy of worrying about? My point? Unless you are building something all out race, be careful in upgrades..... and for this tranny there are a lot of them out there.

Kevlar. Well by now you know my views. Since I rarely see a need to replace a band because of a loss of friction material, I am not sure Kevlar is all that necessary in a street tranny. Again, I'd want to max out the apply force... higher chance of band breakage. In the end I decided against Kevlar in this 4WD towing transmission. (Now I do want to build an all out race 2WD version, but it will have to be pre-ordered - I am not gonna spec one of these again - putting a ton of money into rebuilding a tranny I "hope" to sell is not something I plan on doing anymore - even when the tranny is one of a kind, or maybe especially when it is.) I digress.

Jerry gave some parts numbers for frictions. In the case of the intermediate, his numbers have been superceded by a newer part (And I will assume better - more assuming).

He gave the FORD part number of F75Z-7B164-CA for the lower horsepower (under 450HP ) frictions, and F3LY-7B164-A for the higher horsepower ones. Today I bought a set of intermediate frictions for a 1999 (A year picked at random) 4R70W and they were FORD part no. XW1Z-7B164-AA. The parts man said they were a newer part. They are grooved, and were not cheap.... as frictions go.... $9.21 each.

Now, I have an ALTO upgrade kit for this clutch.... Kolene steels and ALTO red plates... non-grooved. What to do?

I am concerned that the HP upgrade really should have an accumulator to match....(can you say apply NOW and HARD?) and I do not want my shifts THAT hard for normal use. Right now I am thinking I will use the intermediate Kolene steels from the ALTO upgade kit, and the expensive stock (grooved) plates, in lieu of the ALTO smooth ones.

I notice that ALTO likes their smooth plates set up with less clearance. Undoubtedly this is to help ensure a faster "stop" of rotation, but it will come at the expense of drag between the frictions and steels - can you say "HOT" ? Grooved frictions can be set a little farther apart and there will be less parasitic drag during non-engagement periods. Less drag = less heat. Tradeoffs.

Is this making sense? Custom tranny building is all about choices, especially in something as popular as the AOD/ADOE/4R70W. BUT, and this is a big but, you have to make them intelligently. Friction material (and numbers of frictions) is one of those choices.

I will try and show some comparisons as best I can in upcoming comments here.

(more to follow)