Transmission doesn't shift

75Travco · November 09, 2008, 10:41 PM

Sent: 7/1/2007 10:05 AM

The transmission in my 1975 Travco (on a 1973 RM-350 chassis with 440 engine) doesn't shift properly. With the selector in "D", it starts out in 2nd gear and stays there, even at 65 mph. Putting the selector in "2" gives the same results. No shift occurs when moving the selector from "2" to "D", or "D" to "2", at any speed. "L" seems to work OK, will easily climb a very steep grade, but it will not downshift to low unless the vehicle is stopped. Reverse works fine.

I rebuilt this transmission last summer, so it is definitely possible that something wasn't assembled properly. Just driving around the neighborhood everything seemed to work OK, but now that I'm using it more it's clear that second gear doesn't handle all situations. Sluggish acceleration from a dead stop, and a noisy engine at highway speeds!

Yesterday I removed the valve body and carefully went thru the assembly per the service manual, no change in performance.

Any suggestion on what to check next?

MSN Member · January 08, 2011, 05:27 PM

From: firehart2
Sent: 7/1/2007 11:17 AM

Could a plugged up torque converter cause this problem?

ontheroadagain · January 08, 2011, 05:28 PM

Sent: 7/1/2007 2:31 PM

did you check the downshift linkage that goes to the carburator it might have fell off or needs adjustment

75Travco · January 08, 2011, 05:28 PM

Sent: 7/1/2007 2:58 PM

The kickdown linkage has been been adjusted and checked several times, wide open throttle pulls the kickdown lever to it's limit. Don't know how to check for a plugged up torque converter, this part seems to work OK as the vehicle pulls pretty well.

I made some of the hydraulic pressure tests that are outlined in the service manual. Line pressure is low - 30 psi vs. 54-60 psi, and 60 psi vs. 90-96 psi with the kickdown lever in full throttle position.

ontheroadagain · January 08, 2011, 05:29 PM

Sent: 7/1/2007 3:34 PM

heres a link i found that might help you to figure the problem
http://www.allpar.com/mopar/transmissions/torqueflite-tom-hand.html

Slantsixness · January 08, 2011, 05:30 PM

Sent: 7/2/2007 1:04 PM

Bands adjusted too tight?
upshift servo adjustment off? (it is inch-pounds... sometimes I forget and grab the wrong torque wrench!.. but usually the trans wont budge at all is it's that.

Did did you replace the converter and pump? are they both for the right year/ model 727?

Is there any restriction in the cooling lines? (this will cause low pressure at the valve body, and never shift out of 2nd until like 3500 rpm...ouch!!!)

Tom

75Travco · January 08, 2011, 05:31 PM

Sent: 7/3/2007 2:20 PM

Yesterday evening I bypassed the transmission cooler & lines with a short loop of rubber hose. No change; line pressure still 30 psi, increasing to 60 psi as the kickdown linkage is pulled to the full throttle position.

Bands adjusted 2 turns from tight, plenty of clearance. I didn't replace the converter and pump when the unit was apart.

Today I plan to check the operating pressure for the reverse servo, which should be around 260 psi. If this checks OK, I'm guessing the pump is OK.

75Travco · January 08, 2011, 05:32 PM

Sent: 7/4/2007 12:23 PM

The old Travco is now shifting the way it should. Turns out the governor valve was stuck, which made the governor line pressure much higher than it should be. Normally governor pressure is zero when the vehicle is stopped, and smoothly increases with vehicle speed. Using the diagnostic routine from the service manual, I found that the governor pressure was around 30 psi with the vehicle stopped, which was much too high. Must be 2 psi or less to enable downshifting into low. Fairly straightforward fix as the transmission didn't have to come out, only had to remove the extansion housing.

Learned another lesson. Found that the pressure gage used for the initial measurements was reading 30 psi low, so the line pressure was fine from the beginning. Can't take anything for granted.

denisondc · January 08, 2011, 05:32 PM

Sent: 7/5/2007 5:31 PM

Thanks for your feedback. Its valuable for those of us who will be rebuilding our own 727s in the future.

rcaircraftnut · January 08, 2011, 06:58 PM

I have rebuilt a few transmissions but Im no expert. I will give this thought as it is very pertinent. If you are going to reuse any part in an auto trans, you must 1st very carefully restore it to looking and functioning as new. If not you will run into issues like this. Sticking valves, govenors, bent band struts and the like are an easy cure. Since you are there anyway, go ahead and replace the band struts and the band anchor with quality after market ones. This will beef it up a loot. Remember these are very heavy vehicles and the trans really takes a beating. Also on the older 727 there was no part throttle kick down you literally have to go to full throttle to get it to drop into second and go. You can make things much easier on the drive train and your wallet via the mileage increase of not ever having to mat it, by using the later year valve bodies. These have a part throttle kick down and make the driving experiance much nicer. It will also allow it go into 1st gear sooner without having to almost come to a stop. Also I highly recomend a shift improver kit as it will firm up the shifts and slow down wear and slipping during shifting helping to keep heat buildup in check when towing and pulling hills. Hope this helps and if you have any other questions Ill be happy to try to answer them.

DaveVA78Chieftain · January 08, 2011, 07:48 PM

rcaircraftnut,
For reference - Originally this site was located on MSN Groups. When MSN shut down the site was moved here.
If a post starts out with something like "Sent: 7/1/2007 10:05 AM" then that is one of the system admin people migrating posts from the old MSN site to here and is not a current issue. This way we do not lose old information. Adding additional information is great though. Just putting all this into proper context for you as this posting is from 4 years ago.

Dave