stangrcr1

I have read a bunch of the threads about these, and since I have an extra rear diff, I decided to take a look inside.

My interest in this is not drag racing, etc. I have experienced too many times of spinning the front tires in the rain and nothing from the back to help get going. Living in Seattle, the rain is prominent come Fall, Winter... Plus going up in the hills, snow. My 97 CRV is my daily driver, so I am doing things to it to make it better all around.

I have read threads about people using these diffs in EG, etc conversions, but not a lot on how to mod them. I have seen some have tried shimming the clutches, and shimming the relief valve, but not much else.

Has anyone considered just how small the feed hole is to the clutch apply plate? Then how much of that goes to the orifices bleeding off that pressure? Seems to me that if you can't get the fluid to the apply plate, it won't create much forward push in the rear diff.

I measured the supply orifice at .046". The bleed orifices are smaller, approx .018", two of them in series.

The diff I am working on supposedly had about 140k miles on it, and the clutches are barely worn. Sure it could have been grandma driving, but I would have expected a little more wear. This tells me the stock setup really doesn't do much...

What I am considering doing is opening up the supply to the apply plate a few thousandths, shim the relief a little, and see what happens. This should not affect any other mode of operation, but...

Any thoughts on this?

stangrcr1

Simple fluid dynamics. If the fluid can't fill the apply chamber, it can't engage the clutches.

I have built many transmissions and a quick look at this setup tells me the restriction is getting enough apply pressure. Between opening the supply and increasing the -pressure to it, there should be a noticeable difference.

OneBadTurboCRV

Yes, this is on my eventual to do list. My issue is the potential for full time engagement if you mess it up. Since you have rebuilt many transmissions, you already know that a minor change in orifices can lead to disastrous results. Given, this is your spare (I have a few myself) but I keep mine as backups LOL!

If you want schematics out of the Factory Service Manual I would be more than happy to provide them AS LONG AS you share your results. You will see in the schematics that there is a little more to the circuitry in this simple pump than you might think. It operates off of dual pump pressure differentials.

stangrcr1

I was hoping you would chime in. I have a factory manual and have been studying the circuits in the manual and in the pump itself.

I have rebuilt more transmissions than I can remember.

While it is true it is "dual pump", the second pump seems to be more of a release than a pump.

The size difference of 2.5% makes me want to swap them....

But really what we want here is some engagement on takeoff. By the nature of traction, the front tires will slip as they start to pull. Not much, but a little every time. This little difference should be enough to engage the rear. Maximum traction is actually around 10% slip. More and white smoke, less than that you need more power. Don't believe that? Go watch some slo-mo drag racing takeoffs and see the tires slipping.

Slow takeoffs won't engage it. Mat the pedal and the slight slippage on takeoff should be enough and this is the area I have been looking at. Pressure is low with the relief. It never really gets high enough to engage the clutches. Looking at my clutches, they look almost new after 140+k.

So how do we increase apply pressure? As I stated above, the orifice supplying the apply piston is small. Very small. Once filled, it should not take much to get the piston moving, but here is the problem. The apply piston bore is 4.465" diameter, being fed from a .046" orifice. It is going take some(long) time for the chamber to fill. As such the vehicle is probably already moving, and the pumps equal out, plus the orifices bleeding off pressure in the apply chamber. To get the apply piston moving faster, it needs to fill the apply chamber faster.

I am not worried about it being engaged full time with the bleed orifices. They are a good thing to prevent exactly that.

stangrcr1

And don't worry. I will share results.

The reason I bought the spare diff is the diff in the CRV has one of the two forward stud mounts cracked off. It has been like that for apparently years. I bought the CRV like that. Got a discount on the price because of it.

Back to topic.

Honda made the system simple. Like most of what they do. The problem is they should have copied Subaru. How I long for symmetrical AWD. Since that will not happen here, we make do.

The fluid flow chambers around the apply piston orifice are big. .275" wide and .128" deep. Maybe drill to .125" to the apply piston?

The spring pressure on the relief and control piston is key then. Too stiff and too much pressure equals broken parts, stock and it may make no difference.

Time to drill.

OneBadTurboCRV

Let me start off by saying I am not trying to attack you in any way. Please don't think that. The last time I looked into modification of the rear diff was probably over two years ago. I never said I didn't believe you on anything yet. We are all well aware there is a slip / delay in the system. There are even a few YouTube videos showing this in the snow...

There have been a few that have shimmed the relief check on these. Fast2CamCiv and Draggbody are the first two that come to mind. I wasn't that impressed with the results from shimming. In my opinion it only increased the pressure upon activation equalization and did not shorten the time it takes to activate. The only option would be to mess with the apply area or the orifice / feed galleys. Obviously the orifice is the easier route. I personally was running different size tires to get activation to happen quicker, but got away from that more recently.

I agree and disagree about the second pump. The reason being reverse activation (pages 15-7 & 15-8). If you go off of all the diagrams, you can see why they made the pumps different sizes. I am not sure is switching them would be a good idea (or if it's even possible - IDK).

So, since it's been a while, I was thinking backwards on where the orifices were. You even stated it, but I read it in a hurry so please accept my apologies. On page 15-6 the lower feed port is definitely the one I would enlage. If anything, the bleed orifices should be closed up a bit to up the apply pressure but should be left alone for the time being IMO. The pressure shouldn't change severely as all you would be doing is increasing flow to the clutch piston. One would assume the reason they restricted the flow is the same reason most automatic transmissions undersize holes from what they "should" be - smoothness. People would probably complain if the rear end firmly activated.

It's been too long since I have had a pump apart. I definitely am interested now. I won't be able to get into one until Wednesday at the earliest though. It sounds like you already know what's going on though, not sure why you wanted a second opinion? Or did you just want to call me out?

PS - Yes, I would drill 1/8" then. The bleed orifices should be your safety net. The relief shouldn't need to be touched I wouldn't think. The only reason is that is essentially your safety as there is fluid loss after the bleed orifices anyways. HHMMM, maybe shimming the relief was stupid after all...

stangrcr1

I am not looking for a second opinion, let me get that straight. I already know what I want to do, and this is sharing with the community. We are good and I wanted this banter with you.

I am looking at 15-6 and not sure which port you mean. There is only one port that supplies the apply piston, between check valves E and F. As far as 15-7/8, nothing gets changed there.

Shimming the relief is nothing. If you can't get the fluid into the apply chamber, it means nothing.

You can't switch the pumps as they are different in how they engage the shafts. Just threw that out there...

Yes, the orifices are sized for the average consumer. That is not us. Hehe.

Back to the pumps. The front pump is the one we are worried about, It will provide the pressure we want to engage the clutches. I look at the rear pump as riding along to take away some of the pressure we could otherwise use applying the clutches.

You say about shortening the time to activate. That is because the orifice supplying the apply piston is too small. Takes too long to fill and by the time it does, you don't need it anymore. Same with most auto trans making the shifts long and soft. Its about the average consumer.

I want to do a time trial for this, but my CRV is mostly stock. Guess it will be butt dyno.

Shimming the relief was not a bad idea, it just needed a drill bit to go along with it. Size to be determined....

OneBadTurboCRV

My reference to 15-6 was just the normal activation mode - when the vehicle moves from a stop. Top diagram (yes, the diagrams are all the same but different flow paths) I am talking about the "lower port" as in the supply port, yes. Just saying lower to coincide with the picture. I apologize and will try to choose my description wording better from now on.

My reason for bringing up pages 15-7 & 15-8 was if you desire to have the RT4WD active in reverse and also as a response to your pump switching comment. For all we know, the restriction in the feed line is for reverse activation. Given, looking at the circuits it shouldn't make a difference, but there isn't much information to go off of here as far as exactly what pressures and flow rates are in this system (at least not that I have knowledge of).

As previously stated, I don't see the front pump as being a focal point. The system operates in both forward and reverse. Myself personally, I am only concerned with forward as I don't typically drive it any other time than the summer. I would assume by your first post that you are concerned with any and all situations. Also, just going off circuitry desgin it doesn't matter what's going on between which pump when it comes to apply piston pressure feed. We are downstream of all that.

To expand on my reason for the relief valve being a waste of time is that is your safety from breaking things. Then again, it does lubricate with the bled off oil... so maybe raising the relief pressure would force more oil for lubrication? Technically if you want more apply pressure you want to decrease orifice bleed size. The thermo-switch could be considered the ultimate fail safe though assuming it is set to go off before the fluid starts to break down from temperature. So in that regard, shimming the relief may not matter for reliability comcerns.

You could take an action camera of some sort and do some grass acceleration to clock activation speed changes. Unfortunately as far as testing goes, my CRV is still down due to waiting on a a few parts and my rear disc brake conversion brackets. I haven't gotten extremely involved yet, but this has been my goal to improve the rear end for quite some time now. I am working on a possible LSD solution right now too, but it is looking like it's going to have to be a PhantomSlip style... Keep up the good work man.

Sorry for what seems like I am rambling or unorganized, but there are too many ideas rattling around in my tiny brain. Talking theories gets me pumped and motivated to actually work on my pig. I had planned to do a write-up on my findings on all these modifications, but I am more than fine with someone beating me to it since I take forever LOL!

stangrcr1

Baby steps. I drilled the apply orifice to .070" and chamfered the edges. The is a 131% increase in the orifice area.

Yes, you could decrease the bleed orifices, but since they are already .018" or so (hard to measure, used some tiny drill bit I have to gage it). I think it makes more sense to fill the apply chamber faster. The relief is still going to limit overall pressure. And as far as lubrication, when applied, the lube to the clutches is whatever comes from the relief, and a reason why not to increase the pressure too much. If the relief is set too high, the only lube to the clutches is through the .018" bleed orifices. At cruise the lube comes from the rear pump through the center control valve.

Yes it works in forward and reverse, but it always looks at the difference from the front pump to the back, with the front pump always in lead since that is where the power comes from. If the rear pump spins faster due to small tires, etc. that is the same as forward deceleration, and no pressure to the apply chamber.

At the top of 15-6, what is the rear pump doing? It is along for the ride. That's it. The rear pump does not really do anything for acceleration. Only cruise or deceleration.

And this brings back the fact that once the vehicle is moving and both pumps equalize, we are back to front drive only. Without more mods or maintaining larger tires on the rear, we will only get help on initial acceleration.

And after typing this, I can only see one bad reason for making the orifice even larger, it would fill the chamber too fast and create a shock load breaking something. But only if the relief was set too high.

Will put this diff back together and get it into the CRV. Going to find a gravel road and see what happens with a side view camera and the butt dyno.

OneBadTurboCRV

LOL!!! Yeah, good call... I honestly didn't do the math before to consider what I had said about going 1/8" off the bat... that's like a 640% increase in size! Then again, other than the apply piston, what could it break? There is always the issue of premature clutch failure but I have broken WAY more u-joints than anything and have yet to explode a rear differential.

In any event I was running wider and taller tires in the rear. The exact percentage difference I don't recall right now, but those were my thoughts before.

I am going to have to look again at that schematic because I could have sworn the arrows showed the lubrication being provided before the relief valve.

Definitely interested in the results either way... I have a feeling filling the chamber faster is only one part of the equation that is going to be needed to be dealt with. I am also very interested in any change in sound as well.

stangrcr1

Sound? Is the diff going to make noise?

My thought on breakage is the stock axles are quite small. The clutch is awesome with all those discs, but get that locked up and it would probably be more torque than the axles were designed for. The other issue is the small coupler between the clutch basket and the front pump. The tangs on it are pretty small.

One other thing I did is flatten the pump plates on 1/4" plate glass and fine sandpaper. There was some warpage over time. This also tightened up the pump clearances. Might make a difference.

Back when I took the case apart, I used an impact to pull the bolts and one broke off in the case, so it will be a little bit before I get it back in the CRV.

stangrcr1

Another thought occurred to me. Do the pumps bleed down when the vehicle is stopped?

OneBadTurboCRV

If you throw enough power at them they will scream at you. My noise concern stems from if the apply piston is slapping the clutch pack upon engagement if too much fluid flow is there / too firm engagement. Given, you probably wouldn't be able to hear it anyways with proper preload / clearances, but a GoPro strapped underneath might if there is something there to hear.

I have broke the rear tire loose at 40-50ish MPH with a 2nd gear clutch dump a handful of times. Nothing broke LOL! Where I break most of the driveline is standing launches (accidentally slipping out the clutch too fast) and shifting hard. A inline flow control helps tremendously here. The stock rear axles seem to be stronger than they look. In a stock powered CRV I wouldn't be concerned with those. The U-joints on the other hand... leave way too much room for concern.

The tangs for the pump shouldn't be a concern IMO. You aren't doing anything that would increase stress on them when it comes to turning the pump aside from the potential for line pressure rise. Fluid viscosity stays the same (unless changed of course) and input speeds are the same as well. Most of the shock to the system from being modified should be after all of that. Definitely makes you wish there was a line pressure test port of some sort.

I would assume the pumps bleed down based off my conversations with "draggbody" on here when he did his air locker rear end. Obviously air is a lot "thinner" than the dual pump fluid, but even that fluid is pretty thin in viscosity. Not only that but the "slip" design of the dual pumps being able to freely draw through each other. Essentially the entire system is designed around leaks LOL!

forcfedcivic

iTrader: (3)

Love all this tech.....you guys are awesome, please keep us updated!

OneBadTurboCRV

Ok, so a few days ago I had some time to pull a couple TCD apart. The feed orifices on both of the ones I tore apart are definitely bigger than a 0.046" (3/64) drill bit. I don't have a pin gauge that fits good either, so I would have to guess it is 0.050"+ or so. After looking the system over I decided on a ~200% increase to a 0.094" (3/32) drill size. For now I am going to leave the bleed orifices alone with skepticism as well as the relief.

The pump gears are the same in everything but overall height. They most likely can be shaved down, but with everything else the same it is pointless to even try. So at that point that's where I am at. I won't be able to test anything until I get the pig back together, eventually. Freaking machine shops take their sweet, sweet time these days. Extremely annoying!!!

gokart95

This is very interesting. Looking foward to the results.

stangrcr1

I haven't forgotten about this, just not much time to work on the CRV...

And I still need to get the broken bolt out of the case.