I hope my recent learning experience can help someone cause I didn't see any info on the web related to my issues.

My sister-in-law recently reported that her 97 Grand Caravan 3.0 with the A670 trans started slipping in 1st and reverse. She noticed it when first attempting to drive on very cold mornings. I recommended that she change the fluid ASAP but it didn't make it 3 days before getting completely toasted. I have no idea how bad it really was or for how long. I went to the local pull-a-part and hunted for the newest looking trans in on the lot hoping to find a rebuilt unit. I thought I got lucky and spent only about $85. However, only after I pulled out the original, did I realize that trans I pulled from the local yard (also from a 97 Grand Caravan) did not have the rear transmission mount. Not sure if two versions were offered or if that was a replacement error. As a result, the replacement trans became a parts donor. Tearing into the original trans revealed that the rear clutch was destroyed. Tearing into the donor trans revealed that the front clutch was bad anyway. I was able to put the two together to get all good parts....so I thought. So I got everything back together and took it for a test drive... STILL SLIPPING! Suspecting a sticking valve in the valve body, i completely disassembled and cleaned the valves. In doing so I found several valves sticking that would have prevented proper operation. Especially the pressure regulator valve which boosts the line pressure from 60 to 200+PSI for reverse. After reinstalling, I found that this corrected the reverse slip but did nothing for the 1st gear slip. When test driving in LOW, it even seemed to be severely dragging and wouldn't coast like it should. I studied the flow diagrams in the ATSG manual and concluded that the accumulator piston might be leaking. Since I'm a mechanical engineer and not a mechanic, I took a stab at inspecting the accumulator piston and BINGO! Not only was it leaking but the piston was made of plastic and broken in two pieces. I thought I had a spare in the donor trans but guess what?? Yep, plastic accumulator piston broken in two pieces. As a result I've concluded that the broken pistons were the source of both failures by causing low hydraulic line pressure and/or by possibly engaging multiple gears simultaneously. When I called the local Dodge dealer, I was told that this part is on national backorder with no ship date offered. I found an aftermarket aluminum piston, installed it, and problem solved. After 4 weeks, still going strong. If you were to catch this soon enough, you might be able to save your trans.

Most importantly, DO NOT ATTEMPT TO REMOVE THE REVERSE BAND or OVER RUN CLUTCH WITHOUT SPECIAL TOOLS!! In order to remove the reverse band, the over run clutch must be removed because there is a pin boss on the housing that is in the way of removing the band without first removing the clutch. When you remove the over run clutch (one way clutch), there are several little rollers and springs that go B-O-I-N-G and you absolutely cannot get them back in place properly without the special tool....and I'm pretty creative. Instead of paying the $50 for this tool, I took a sledge and beat the pressed in inner over run drum out of the old trans and used it as the tool. It worked just fine.

Also, Be careful with the trans pan bolts. 50% were stripped out from a botched previous repair before I even started.

I hope this helps some other DIYer.

 

I found this information: All 1996 and newer minivans have the rear mount on over the diff. It would be nearly impossible to have a pre 1996 3.0 670 trans in a newer van because none of them had the provisions for a crank sensor.

 

Maybe, but my initial investigation indicated that the A670 trans was used in anything from the Neon to the Grand Caravan. Below is a pic of the donor trans removed from the 97 Grand Caravan. Note the missing rear mount and crank sensor.



So I believe this confirms the saying "Give a Red Neck a wrench and he can do anything."

Most likely an incorrect replacement was used in the donor. I was pretty selective about choosing the trans and was specific to a 97 Grand Caravan because I didn't want any compatibility issues. I also chose one that looked to be rebuilt since the odometers are all digital (no power on the lot). However, I failed to take into consideration the phrase above. Ultimately my fault.

Here is a pic of the two failed accumulator pistons. I have no idea whether they are the factory units or a aftermarket replacements since both trannys were rebuilt at some point.



CHECK/CHANGE YOURS BEFORE IT LEAVES YOU STRANDED!! It's not too difficult and can be done without removing the trans. Remove the pan, valve body, and a snap ring and it's otta there.

 

I know exactly what happened there. That is a reman trans. When these vans first came out in 96, they had a lot of problems with blowing differential pins. There was a few companies making brackets allowing old style transmissiont to mount on the trans diff housing to allow it to bolt up on the rear mount. Your fly-by-night trans shops would hack these in because the new case design was hard to get from junkyards. I can see that there is no boss where the crank sensor is. Someone just drilled a hole in the case. Have a close look at your correct transmission and that's exactly what was done. It was a cobbled installation.

 

Makes perfect sense and only confirms my bad luck. Thanks for the explanation!

 

thanks for your post i have a low pressure problem slipping and slipping reverse.

 

A transmission replairman told me to use CDC TRANS-X to fix my transmission shifting problem. After installing it into the fliuid and driving the van around 3 weeks, my transmission was fixed. 50,000 miles later it is still working. Reason, O rings sealing internal transmission pump get hard and start leaking air causing low pump pressure to shift gears. CDC TRANS-X Restores seals to soft conditions which reseals them creating restored transmission fluid pressure. Its worked in my 2003 and 2007 Caravan transmissions, costs $15 at Autozone.