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4R70W REBUILD DIARY - Forward Clutch


EF Tranny Guru
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February 8, 2003
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Sacramento, CA 95827
Year, Model & Trim Level
1992 XLT
4R70W REBUILD DIARY - Part 10 - Forward Clutch


In every automatic transmission there is a forward clutch, or something akin. This clutch is engaged in all forward gears, and so can be more aptly described as a holding clutch for 95% of it's life. As we discuss in the frictions section, a holding clutch relies on the properties of the fluid to a great extent. Jerry W. in the TCCOA article opines that the stock friction material is just fine for this clutch. I believe him. I purchased new stock frictions....


the part no is: F8AP-7E311-AA, which is newer than Jerry's post. They smell very much like phenolic material. Probably last forever.


I paid about $3.50 each from FORD.

At the back of the clutch is a "wave plate"... see Jerry W's article for a discussion. I am using a 3 wave plate in this transmission... there is a thinner 5 wave plate, used in the 5.4 liter applications, giving you a little more room in the clutch. In fact you can do more or less like we did with the direct and sneak in an extra plate using this wave plate and omitting the top pressure plate and instead using a steel. Worth considering depending on your use.

I have been concerned about the shift feel using a 5 wave, but am assured you won't notice. (In fact some claim you hardly notice it running with NO wave plate except now and then on 4-3 downshifts).

FORD Part No. F6AZ-7E085-A.. list is $8.95




(5 Wave plate is FORD PN ____________________.)

This goes into the clutch assembly first, followed by a steel plate.


My steels are coming from a donor. Steels, absent a major catastrophe in the transmission, are clearly reuseable. I like to always rough mine up using 220 grit carbide paper....


I try and end up with a random pattern to rough them up... I start out just doing them on one direction..... more or less... the top one I shave started on the bottom is a used one untouched.... it is actually smoother than the pic suggests...


And then I try and randomize the patterns....same comparison


It takes but a few minutes and I think is well worth it. Details.

While this may one of those "overkill things" I think it is important enough I do it anytime I use ANY steel, new or used, except Kolenes.

Number of Frictions

The stock Forward clutch has 5 plates. You can add plates, but it requires you to remove the wave plate. The wave plate is like an accumulator, it reduces the suddenness of apply pressures. Jerry W. in the TCCOA threads says the 5 plate forward is ok up to about 450 HP.

Plate number is always a tradeoff. More equal greater holding, and also equal more heat. Heat is a tranny killer.

All too often people want to have the monster killer trannie, yet run it behind a less than monster engine. Like the Tim Allen character in "Home Improvement" and the Binsford 5000!

Let's all step back and take a collective breath.

The forward clutch is a holding clutch. If 5 plates can hold up to 450 HP.... well... why lose the benefits of the wave plate and add a 6th? Why have unnecessary heat? Well, I'm not gonna do that.

This tranny will do JUST fine with a 5 plate forward. That is what it is gonna get.

I guess my message is "THINK" when you are building trannies....think real. Think actual usage. Do I want to build a super duper full race tranny? Hell Ya! But only for someone who will use the features - and can stand the awful shiifts necessary to lock them up...


This is a good place to talk about these guys because this drum presents us with some difficulties when using the standard compressor. The typical compressor can be had for about $40 and it looks like this:


You can see pics of it in use elsewhere in this thread.
It requires that the clutch be open in the middle so it can be installed.

The other, more expensive kind, clips into the snap ring groove, and can be used on a clutch where there is no middle opening for the other kind to go through. This forward clutch is just that kind... no center opening to use the cheaper compressor..

Here is that "other" compressor installed in the clutch. Was quite a long assembly, what between it's length and the fact this clutch also has an input shaft on it!


Assembling the Forward Clutch

Ok. It's getting late and I am a little tired. You have watched me put seals on pistons, you have watched me using seal protectors and vaseline to install the pistons... for now I am not going to repeat that here. Your know my views of care of lip seals. These seals are lip seals and you need to make sure the lips point DOWN. You SHOULD use seal protectors and lots of vaseline to install them without damage. I did that here.

Next we need to install the piston spring and retainer. In the cse of the FWD clutch is this tranny the spring is ONE roung BIG spring! The compressor needed snaps into the snap ring groove. Here is a pic of it all pre-crunch down.


Notice how the compressor snaps into the groove for the snap ring and how the "fingers" are on the retainer... You compress it down by twisting the handle and once you have the groove exposed add the snap ring to the center shaft (something else I have done in pics ad nauseum.... I'll repeat it if you think you need to see it again.... but have not for now...)

Here is the finished assembly, piston, retainer and snap ring...


Notice the snap ring installed and the BIG honkin' spring under the retainer!

Another view

Ok, piston is in...it is time to add the plates... first the wave plate..


Then a steel plate


After that it is a soaked friction, then a steel, another soaked friction, another steel etc.... until 5 frictions and 6 steels are in. I did not photograph this because I was messy with ATF from the frictions but you get the idea.... the top plate is the pressure plate, and then you add a snap ring... easy to do by hand.

Last step is to gauge the pack for proper clearance.... here looking for about .075... (Spec is .050 to .090, Jerry W. seems to like it around .080).This is not as easy thing to do because of the geometry.... I tried and tried and in the end more or less approximated and hoped. Flat feeler gauges didn't work, so I ended up using a wire type spark plug gauge, but it wasn't optimal. I'll come back and use a dial type indicator later.

Front Clutch Hub

The front clutch hub is like most hubs.. splines and a center hub for a gear or something... (In this case a sun gear shaft end)


The clutch plates engage the hub.... that connects via the sun gear shaft to the planetary gearset. I recommend you align your clutch plates on kind of a "dry run" using the hub before you do anything else. It will make installing the hub and bearing easier in the next step. Here are the plates all aligned in my clutch... count em... 5...


Anyway there is a torrington that goes into the hub.... it is one of those that you cannot put in backwards... one way works, one way doesn't. Also this one does not come apart (interesting) so soak it in ATF as start up lube. Here it is, right side up..


I have added some vaseline "glue" to add it

and here it is installed


The assembly goes into the plates we installed, and fits flush.....


The brownish looking cast on the center is an photographic artifact.. it is in fact bright shiny steel.

The larger set of splines you see engages the sun gear into the planetary gearset. The smaller one engages the big end of the stub shaft, which couples the direct drum to the forward drum. They spin in locked motion relative to one another.

The Forward drum is DONE!

1948 ford

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December 16, 2016
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1998 mercury mountaineer
I just took apart my 4r70w and the forward clutch lip seal has 5 little bite marks in it like piston was traveling at an angle up and rubbing holes in the top of lip seal . Also where the steels notches travel looks like some of them hung up in the drum put little grooves in it? Should I sand the tips of the steels so they all have soft edges to travel in drum? Is that the solution or have you heard of this happening? Thanks Chris