A-518 No Reverse

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lhearold

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Finally getting ready to get my Dart out of the shop. Installed the A518 tranny and found out it has no reverse. When I pulled it last year to redo the car it had reverse with no problem. Now its as if reverse is not there. All other gears work fine, shifts great, all linkages are adjusted properly. Pulled the pan and adjusted the bands (again) to make sure everything was right. Anyone have any ideas?

For info, its a 94 A518 tranny bolted up to a Magnum based 408 stroker. MP 2300-2500 stall converter (made for the 518).

Thanks,

Larry
 
Larry there are 3 components that cause reverse to happen. The front clutch assy., the low/reverse band and servo, and the valve body. If all 4 forward gears work properly you can rule out the front clutch assy cause if it didn't work you wouldn't have 3rd and 4th gear. That leaves the valve body and low/reverse band/servo. First thing to do is a pressure test to see if the vb is applying pressure to the low reverse servo. I attached 2 pics for reference. Their from a 727 but the items were dealing with are nearly identical so the ports are in similiar locations. The first is of the outside of the case and shows the test port for the low/reverse servo. Hook a gauge up to it that goes to 500 psi, warm the engine and trans up and select reverse and see what the pressure is. It should be approx. 230-300 psi. If it's low (and it probably will be) it's possible the low/reverse servo seal has blown and is leaking past or the other possibility is a valve is stuck in the valve body. In any case the valve body will have to be removed. When you remove it you can do an air pressure test by applying 30-40 psi of air pressure to the port that leads to the servo. If it's working right the air pressure will apply the rear band firmly. If you hear air leaking that means the seal is blown and the servo will need disassembled and seal replaced. If all seem well with the rear servo/band apply the problem is in the valve body. Possibly a stuck valve.

727 pressure test ports 2.jpg


727 Air test ports 2.jpg
 
Also check to be sure that the rear band apply links are properly installed. IIRC, one piece is just out of square, and installing it incorrectly (turned 90 degrees) can cause the rear band to not apply.
 
Rear band apply strut is on correctly. No leaks in the servo with 40 PSI pressure. Applies right away without any lag or stutter and releases as soon as pressure is removed. Only about 60 lbs pressure on the reverse/low servo test port with engine at normal operating temp and in reverse. I am assuming that pressure should be present if the valve body is operating correctly.

I think that the problem is in the valve body itself. We installed a MP shift improver kit for the A518 and it had a replacement seperator plate that went between the upper and lower halves of the valve body. Prior to the shift kit being installed (way last year) the tranny worked correctly but the kit was installed during the setup of everything to go back into the car. The instructions that came with the MP kit were crap and I'll bet that there is something in the seperator plate that isn't right. I have the valve body out and am going to tear it apart again tomorrow and see.

All forward gears work fine. Real crisp shifts on 1-2 and 2-3. OD and TC lockup functions are present and work without any problems so the only thing I can think of is that there is a hole or holes missing in the MP plate.

Thanks to all for the assistance. Will let you know what happens.

Larry
 
This is at 1600 rpm copied off chrysler service
  1. Pressure should be 145 - 175 psi (1000-1207 kPa) with throttle lever forward and increase to 230 - 280 psi (1586-1931 kPa) as lever is gradually moved rearward.
 
Larry it wouldn't surprise me to see the problem with the Mopar Perf. shift kit. I used one back in the mid 90's on a 518 and it caused all kinds of shifting problems. 1st to 2nd gear overlapped terrible so bad when it shifted it bucked and about threw you into the windshield. 2nd to 3rd gear shifted real sloppy. I took it out and put a Trans-go kit in it and it worked great.
 
I had that problem also with my 94 Ram 1500. It was like 2d gear applied before 1st gear released. I can't remember what brand I replaced it with. When I was shopping around for a kit for this tranny I talked to several people that had good luck with the MP kit and I called the MP tech line and after getting thru the snob that answered, was told that they had changed some things and it didn't cause the problems any longer. Maybe they reallymeant it didn't cause the "same" problem!
 
lhearold said:
I had that problem also with my 94 Ram 1500. It was like 2d gear applied before 1st gear released. I can't remember what brand I replaced it with. When I was shopping around for a kit for this tranny I talked to several people that had good luck with the MP kit and I called the MP tech line and after getting thru the snob that answered, was told that they had changed some things and it didn't cause the problems any longer. Maybe they reallymeant it didn't cause the "same" problem!
Click to expand...

That's called overlap and that's what mine did. It was so bad that when I first installed it (the Mopar perf. kit) and tested it on the jackstands when I ran it through the gears when it shifted from 1st to 2nd the rear wheels almost completely stopped turning before they took off again. On the road it bucked like a mule when it shifted from 1st to 2nd. I took it out after about 1500 miles and it had a bunch of friction material in the pan. I feel that if I would have left it in the trans wouldn't have lasted long at all and at that time it only had about 38,000 miles on it. After I removed the junk Mopar kit and put in the Trans-go kit it worked perfectly and I ran it until it had over 90,000 miles on it then sold it to a guy and he ran it until it had 150,000 miles on it before the tranny went.
 
Jack the back end up and fire it up and have somebody put it in reverse while you watch the driveshaft. If it turns really slow and you can stop it with your hands you may have a cracked or broken reverse servo piston.
On the overdrive trannies they are aluminium and will crack the edge off and there goes your apply pressure.

Don't ask how I know of this problem........
Don't nail throttle in reverse trying to back a Dakota R/T up a steep driveway with Dart on trailer.
 
Well, got the valve body off and apart. Traced the passage for the reverse fluid flow and low and behold, a check ball is there. Went back to the MP instructions and sure enough it says to take a ball from another spot and put it in that spot. Anyway, removed the ball, reinstalled sverything and it has reverse now! I wonder how many cups of rice they paid the guy to write up those instructions. Must not have been much since they were WRONG!

Thanks again for all the advice though.

Larry
 
Good deal Larry. Glad you got it. Too bad it cost you so much work though. I think if it were me I'd call Mopar Performance's tech line and let them have it. Come to think of it I did the time mine didn't work right.:-D
 
lhearold said:
Finally getting ready to get my Dart out of the shop. Installed the A518 tranny and found out it has no reverse. When I pulled it last year to redo the car it had reverse with no problem. Now its as if reverse is not there. All other gears work fine, shifts great, all linkages are adjusted properly. Pulled the pan and adjusted the bands (again) to make sure everything was right. Anyone have any ideas?

For info, its a 94 A518 tranny bolted up to a Magnum based 408 stroker. MP 2300-2500 stall converter (made for the 518).

Thanks,

Larry
Click to expand...

Well the reverse problem is cured. NOW it doesn't have any 3d gear. Does the 1-2 shift just fine but never gets into 3d! Cure one problem and find something else.....

Larry
 
lhearold said:
Well the reverse problem is cured. NOW it doesn't have any 3d gear. Does the 1-2 shift just fine but never gets into 3d! Cure one problem and find something else.....

Larry
Click to expand...

Reverse is the front clutch appliedand the rear band applied , 3rd is the rear clutch applied and the front clutch applied , if you truly have reverse then it's a valvebody issue .

When you removed that miss placed check ball didyou put it back where it was originally or just toss it all together ?

Did you go for a test drive after you did that checkballectomy before ?
 
JohnRR said:
Reverse is the front clutch appliedand the rear band applied , 3rd is the rear clutch applied and the front clutch applied , if you truly have reverse then it's a valvebody issue .

When you removed that miss placed check ball didyou put it back where it was originally or just toss it all together ?

Did you go for a test drive after you did that checkballectomy before ?
Click to expand...

Ha, test drive? Yep, in between the ice storm and 3 snow storms I took it from the shop to my garage at home to work on during the winter. Thats when I found the 3d gear issue. I still have the extra (?) ball. Looked at the MP shift kit instructions again and all the balls are in the correct place except for the one that caused the no reverse. Of course that was true before but the instructions were WRONG! The ball that caused the reverse issue was part of the kit and the instructions said where to place it. Well, that was the reason for the no reverse. Don't know if the 3d gear issue was present along with the reverse issue before since I didn't drive it with no reverse. Never again will I use a MP shift kit for a A518! But, as much snow as there is on the ground I'll have plenty of time to sort it out before its decent enough to drive it again!

Larry
 
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