I rebuilt a 4R100 to replace my Diode transmission over a year ago. I only installed it a couple of months ago. It has the full Transgo Tugger kit installed. I used a good quality kit with Borg Warner clutches and adjusted the clutch packs to middle-to-tight with selected parts. I air tested the pistons/seals before I installed the valve bodies, with no leaks.

I've noticed that it is pretty weak in reverse, while I haven't noticed any problem in forward gears. Reverse gets worse the warmer the fluid gets, while I notice no difference in forward gears because of fluid temperature.

I finally put a pressure gauge on it and here are the results:
Cold (80* F)
Idle psi (Factory spec.):
Neutral - 80 (50-65)
Drive - 80 (50-65)
Man. 1st 85 (70-115)
Rev. 90 (70-100)

Stall psi (Factory spec.):
Neutral 95 (None Specified)
Drive 90 (136-156)
Man. 1st 90 (175-210)
Rev. 125 (220-240)

Warm (150* F)
Idle psi (Factory spec.):
Neutral - 82 (50-65)
Drive - 80 (50-65)
Man. 1st 82 (70-115)
Rev. 80 (70-100)

Stall psi (Factory spec.):
Neutral 95 (None Specified)
Drive 91 (136-156)
Man. 1st 92 (175-210)
Rev. 107 (220-240)


The idle pressures seem OK cold. I have not measured them warm yet, so they could be low when the fluid is hot.

Stall pressures are way too low. I am suspecting the pump. When I rebuilt the tranny, the pump seemed like new, with no wear or distortion showing. The other possibility is that I did something wrong in rebuilding the pump. In addition to the Tugger parts, I also installed a Sonnax drainback valve kit in the pump.

I installed these Sonnax parts in the transmission: Cooler Bypass Kit, Center Support Ring, Center Support Shim Pack, and Clutch Feed Seals.

Does anyone know what pressures I should be expecting when using the Tugger kit? They claim to "double" the Low/Reverse clutch pressures in the 1 position, but don't give any pressures in the directions. It would seem that pressures in Reverse should be pretty high as well.

From the pressures I see, the Reverse pressures are higher than the forward pressures, so the valve body seems to be directing the pump correctly. At least the Boost Valve is trying to jack the pressure up.

Does anyone have more tests to try before I drop the transmission and replace the pump?

 

I added warm (150*) pressure readings to the original post.

 

Anyone????

 

I am wondering if the pressure loss in those gears could be related to the Coast Clutch. It is a applied during each of those applications when the pressure is lowest and my have a leaking piston seal. IIRC, there is test of the Coast Clutch by getting up to ~45 mph (3rd gear shift) and then manually shifting into 2nd while letting of the throttle. You should feel a "braking" effect when the Coast Clutch is applied. Transmission diagnostics are not my forte', but that is my thought on this.

 

Thanks for the response Roland!

I have noticed that there is no engine braking going downhill in "2", but haven't tried to see if there is a change in drag when engaging. I'll try that today.

 

Mind you I am no expert when it comes to tranny's but thanks to brother Roland I do know how to build one and have a basic understanding of how it works. Now it sounds like you paid attention to the details when building it but I have a few questions. Did you check the end play of the output shaft after installing the reverse/ 1st clutchs? If so what was the end play of the shaft? After reading what you wrote I was thinking the same as Roland as far as a damaged piston. Or the case to valve body might have a leak due to torqued feed bolts. Did you check the case to make sure it was true after torquing feed bolts before valve body bolt up?

 

BDK, I didn't check the case after torquing the feed bolts, but I did install the Sonnax shims between the center support and the case that are supposed to prevent that problem. I did check the end play on the output shaft per the Ford manual. It was in the middle of the specification.

I will be pulling the valve bodies soon to air test the clutches again. If there are no leaks, I'll check the valve bodies for flatness and the internals for proper assembly and sticking. If those inspections go well, I'll reassemble and if it still has a pressure problem it looks like I'll have to pull the transmission and look at the pump again.

 

Honestly I didn't think the output shaft end play could cause your issue but it could cause some kind of issue if out of spec. So that is a none issue. Also I would rule out the reverse/ 1st piston being damaged because if there was a nick in the seal you would have a slow engagement in both reverse & 1st. The only other piston would be like Roland said the coast clutch. But personally I am thinking it has to do with the feed bolts and the flatness (straight) of the case at the valve body.

Now installing the feed bolt shim at center support is very tricky. I had to cut my shim down to .183 to fit correctly. Also if I recall the case where the valve body bolts up is to be no more than .0015 distortion out of true after the feed bolts are torqued. Because over torquing the feed bolts can cause problems too. That is why John Woods torques the feed bolts and uses a planing hone to make sure the case is straight.
http://s3.amazonaws.com/sonnax-dev/u...6743-01-IN.pdf

Also before you pull the valve body refer to ATSG page 111 about the manual valve sticking out past the valve body casting .050 with the gear shifter in reverse. And is this the Sonnax Center Support Seal kit #3642424k you used ??
http://www.sonnax.com/parts/2063

Hopefully you won't have to pull the trans to solve this issue. If you do I have a few more mods you might want to do to the pump.

 

Yes, that is the kit I used for the Center Support Seal. I also filed the Center Support shims so that they fit snugly without distorting the case.

Notice that I have corrected the stall factory specification for Drive in my original post. I had mistakenly used the idle pressure. This points out that the stall pressure is low on all positions, not just the Reverse and Manual Low ones.

Taking this into account, the factory manual troubleshooting has one thing in common: 7A100 Main Valve Body. Or the pump can't hold full pressure because of internal problems.

 

Jock sounds like you did everything right and I am kinda at a loss of what it could be??? But when you drop the valve body still check to make sure the case is straight. Now on the valve body I found the valve body bore where alittle wore and the valve were sticking alittle and I ended up honing the bore with home made tools but Sonnax sells a valve body bore tool to correct that problem. I hope for your sake it is in the valve body. If it is the pump I would replace the Pressure Regulator Valve and the Pressure Regulator Valve Boost Valve with the Sonnax valves. I replaced all pump valves and pump gears with Sonnax parts.

 

I know this is an old thread but I am having the exact same problem and can't figure it out I was wondering if you ever found what the problem was