I told you guys this would take awhile and i cant thank you guys enough for the transmission school seminar this weekend. So this is how it went.
As Bill explained to me one of the most challenging parts of building the Chrysler transmission is that the Cummins makes a tremendous amount of torque at the low rpms and the Chrysler transmission is designed for higher rpms. At DTT as we have mentioned in the past pressure testing is not something we do for fun it is more like a religion.
Lets start with the TC, the oem factory system has a tremendous amount of leakage, if guys started pressure testing their tc’s they would find out exactly what we are talking about.
A 10 % leakage is considered excellent. 10-20 % leakage is considered good. 20-30 % is considered average.
For us when we pressure test the oem systems and our competitors 30 % and above is quite normal. One of the best-kept secrets by DTT is that we have changed the lockup clutch system. People are always amazed that how we can handle 800+ hp with a single disc clutch. According to Bill it’s not such a great feat at all.
Pascal’s law is:
(P. S. I. )Pressure = FORCE(LBS )
_ _ _ _ _ _ _ _ _ AREA ( SQ. IN. )
According to PASCAL’s law the lockup clutch system is over 70% stronger than 3rd gear. The problem with the oem factory system is that it has so much leakage.
If you want to pressure test your own lock up system it is quite simple.
Cooler line pressure vs overdrive pressure will give you your lockup clutch pressure within 4-5 %. That is counting on the fact that your od circuit is sound. ( not excessive leakage in od. ). To do a more accurate test you would have to modify the valve body and take readings from the switch valve.
So if you are running 100 psi at 2000 rpms in od locked up you should be also running 100 psi in the cooler lines during lockup. OEM + and – specs are the major reason for a lot of the reason for these transmission and tc failures and also why you see a lot of aftermarket transmission failures. .
The quality of the work you get done is not only dependent on the parts but the quality of the technician doing the work. If he does not pay attention to the specs in simple terms you are playing roulette.
A lot of people think you need to add a front cover to prevent your tc from ballooning.
Advocates of that mentality have obviously not pressure tested a tc in the Dodge Cummins Diesel. If they had they would know that the Chrysler converters are not even remotely close to ballooning.
In our testing DTT has run the pressures as high as 200 psi and did not balloon the tc .
Obviously Chrysler feels the same way as in the 48RE’s they have changed the pump assembly to add more pump volume by 20 %.
Another area that DTT has spent a great amount of time and resources is on the transmission case itself, since 1993 the quality of the machine work on the Chrysler transmission cases have continued to deteriorate. To try and compensate for this Bill spends between 10-20 minutes prepping the transmission cases where the vb bolts on to the transmission case. Again this is where the technician working on the truck comes into play.
If he doesn’t pay attention to these smaller details you could end up with more problems than you started with. This is the main reason we developed the valve body to transmission case gaskets. Transmission cases will still need prepping even with the vb gaskets but the gaskets show an increase of 5 – 6 psi on a good prepped case.
3rd gear is the weakest link in this transmission according to Pascal’s law. At DTT we changed the factory piston for 3rd gear to a billet piston to get rid of any leakage in that area, we have changed the sealing rings that feed the 3rd gear clutch pack, we have changed the front servo, now according to some people snap valves will help protect you from a 2-3 bind up. According to Bill they must be smoking some pretty good cigs if they are seeing snap valves on the Chrysler transmission as Chrysler does not use snap valves for the 2-3-shift valve on the 272,518, 47RH, or the 47 RE transmissions.
If you guys look in your Chrysler manual you will notice that the 2nd gear apply pressure is not exhausted when the transmission shifts into 3rd. Its 3rd gear pressure build up that releases the 2nd gear band it takes 28% less pressure from 3rd gear to actually release 2nd gear. So the 2nd gear band does not release until there is a 28% difference in the force between release and apply . Again this is not rocket science according to Bill but you know for you and I we have to really concentrate. Again this is Pascal’s law at work. The release side of 2nd gear servo has a greater surface area than the apply side of 2nd gear. But the pressure is never released on the apply side. I used my Chrysler 2000 service manual as a reference , Section 21 page 465 , compare that with Section 21 Page 466 .
You will find that this is why Chrysler does not like to have a 3-2 downshift and when you are slowing down the Chrysler transmission tends to go from 3rd -1st. Its not taht the technology does not exist to produce the 3-2 downshift but you must modify the 3rd gear release system in order to facilitate the 3-2 dowhshift. When we developed the smart controller we were forced to modify the 3rd gear release system.
If guys pressure tested the circuitry they would know this that Chrysler tends to vent 3rd and 2nd at the same time producing a 3-1 shift during the down shift. As a matter of fact Chrysler puts in a kick down limit valve that prevents a 3-2 downshift at higher speeds.
The technicians that know this circuitry will actually be able to build a transmission that will eliminate or reduce a 2-3 bind up shift. You can bet these guys are not going to be waiting for any imaginary snap valves to take care of the 2-3 bind up. Their knowledge will dictate how they set up the trannys.
To further prove what i have said if you are wanting another source other than the Chrysler service manuals think of all the guys that have had problems with their trannys not wanting to shift into 3rd gear while the transmission was cold. Why do you guys think your that your transmission does not shift back into 1st gear when the 2-3 shift valve had already stroked, but rather stays in 2nd gear until he lipseal in the front drum swells up enough to capture 3rd gear oil . When you are in 4th gear locked up your first gear clutches, your 3rd gear clutch pack , your od clutch pack and your lockup clutch must all hold equally. Slippage in any one area will cause transmission failure. Again the technician that can set up your trans properly is the key to a good transmission.
Contrary to popular belief in some circles, changing your od direct from 8-10 has no bearing when you are in 4th gear locked up as this clutch pack is actually released when you are in 4th gear locked up.
For the record, 1991-1993 Dodge rams with the 518 transmissions came from the factory with 8 od direct clutches, 1994 –1995 or the 47RH transmissions had 9 od direct clutches, 1996 –2003 47 RE transmissions came from the factory with 10 , again the od direct clutches have no bearing what so ever when you are in 4th gear locked up going down the highway, Whether you are at 1600 or 3000 rpms they couldn’t care less as they are on a holiday doing nothing.
If you want a transmission where you can run it between 1600-1700 rpms on the highway and still maintain good transmission holding capacity the technician building your transmission as well as your transmission parts are equally important, the edge will always go to the technician that knows how to use a pressure gauge.
As far as locked to locked shifts are concerned it is only a matter of time before you burn out the transmission clutch packs or break and input shaft or hub or pump stator. We are trying to load some pictures up for you guys, we had 2 guys come in our shop this past week with these parts broken on their trucks that others told them that it couldn’t happen.
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One was a 1995 Dodge Ram, he successfully did locked to locked shifts for about 3 years with 350 hp, one of Piers crazy customers. He took out his pump assembly, input shaft, and his transfer case all in one hit. He even lost his transmission case.
On top of that he had a 200-mile tow bill. The other was a 2001 truck he was more fortunate, he merely ripped the splines out of his input hub. He only had a 60-mile tow bill to his local Chrysler dealership. He brought us the transmission in pieces in a box as Chrysler wanted $ 4000 from him. Locked to locked shifts will eventually catch up to you, its just a matter of when.
It seems that the guys really advocating the locked to locked shifts are the guys running the factory torque converters or the milled stator torque converters.
Ok, now that that is done, i am going back to working on the race car. As Chris ripped the front strutt off the car , my mom made Bill
buy new ones,
I guess she figured at 160 + mph it was time for a change. Something about safety.
