Go Back   Ford Truck Enthusiasts Forums > Misc. > Clutch, Transmission, Differential, Axle & Transfer Case
Sign in using an external account
Register Forgot Password?


Reply
 
 
 
 
LinkBack Thread Tools Search this Thread
  #1  
Old 06-11-2008, 01:28 AM
Qizzar Qizzar is offline
New User
 
Join Date: Jun 2008
Posts: 21
Qizzar is starting off with a positive reputation.
1988 Ford F250 Diesel Transmission Acting up

Thanks in advance for any tips and suggestions.

About a month ago I purchased a 1988 Ford F250 Diesel Truck.

Everything seemed great. It was running smooth and shifting great.

Yesterday the transmission started acting up. It seems to be shifting late into gears. Where my rpms will reach around 3000 and then when I let off the gas as the rpms go down the truck will shift into the next higher gear.

And the shift isn't as smooth as it was the previous in the month, but I am assuming that is a result of the higher rpms.

The only other symptom I notice is that while in 3rd gear even on level road, the truck seems to downshift into second gear early. This sympton resembles the same feeling you get if you are towing a heavy item and start driving up a hill while also hitting the gas pedal hard, because it will downshift but then the rpms shoot up.

Any tips or suggestions are appreciated or if you have any questions to ask that might help clarify further what is occcuring...ask away

Thanks
Reply With Quote
  #2  
Old 06-11-2008, 01:25 PM
Lazy K Lazy K is offline
Post Fiend
 
Join Date: Jan 2005
Posts: 8,402
Lazy K is a name known to allLazy K is a name known to allLazy K is a name known to allLazy K is a name known to allLazy K is a name known to allLazy K is a name known to all
I assume your trans is a C6 so the shift points are vacuum controlled. As your truck is a diesel the vacuum source is a vacuum pump driven off the crank pulley. So have you got plenty of vacuum? A good indication is if the power brakes work good. If you have good vacuum this is supplied to the C6 via a modulator valve on your injector pump. The vacuum finally ends up at a modulator diaphram on the C6. So check all the vacuum pipe work. The pipe going to the injector pump and leaving the injector pump and running down the frame rail to the trans. If this all checks out pull the vacuul pipe at the trans and see if any red fluid is present, this would indicate a faulty diaphram. Good luck. I should add that if you have had any work done on the injector pump the vacuum modulator valve may be out of adjustment. Good luck.
Reply With Quote
  #3  
Old 06-11-2008, 02:12 PM
Qizzar Qizzar is offline
New User
 
Join Date: Jun 2008
Posts: 21
Qizzar is starting off with a positive reputation.
Thanks for the suggestions Lazy K...

The brakes work excellent so my vacuum must be ok. I'm headed out now to check the pipe work and your other suggestions..hopefully it will be this simple...

I'll let ya know...

Thanks again
Reply With Quote
  #4  
Old 06-11-2008, 03:44 PM
tjc transport's Avatar
tjc transport tjc transport is online now
i ain't rite
 
Join Date: Mar 2005
Location: Marlboro Mental Hospital
Posts: 33,848
tjc transport has a superb reputationtjc transport has a superb reputationtjc transport has a superb reputationtjc transport has a superb reputationtjc transport has a superb reputationtjc transport has a superb reputationtjc transport has a superb reputationtjc transport has a superb reputationtjc transport has a superb reputationtjc transport has a superb reputationtjc transport has a superb reputation
anything less than 17 inches of vacuum, and your trans will start to act up.
preferably, you want more like 20 or 21 inches of vacuum
__________________
Tom
Moderator of the "not wrapped too tight forum"
rarely in life do you meet a person that will drop everything to help a stranger,
and give the shirt off his back to a friend.
Steve Price was that kind of person.
Godspeed "window licker", the short bus will never be the same with you gone.
Reply With Quote
  #5  
Old 06-11-2008, 07:50 PM
stuart1 stuart1 is offline
Postmaster
 
Join Date: Jun 2003
Location: Somewhere Saskatchewan
Posts: 2,741
stuart1 has a good reputation on FTE.stuart1 has a good reputation on FTE.
hmmmmmmmmm

I could be wrong but didn't some of them have hydraboost vs vacuum brakes?
Also have a look at the kd linkage, it may be stuck.
__________________
Wrench twister since 1957.
Journeyman since 1964.
Transmission builder since 1964.
Reply With Quote
  #6  
Old 06-12-2008, 07:55 AM
Lazy K Lazy K is offline
Post Fiend
 
Join Date: Jan 2005
Posts: 8,402
Lazy K is a name known to allLazy K is a name known to allLazy K is a name known to allLazy K is a name known to allLazy K is a name known to allLazy K is a name known to all
Stuart1, surely the hydraboost was on the F350?
Reply With Quote
  #7  
Old 06-12-2008, 08:06 AM
stuart1 stuart1 is offline
Postmaster
 
Join Date: Jun 2003
Location: Somewhere Saskatchewan
Posts: 2,741
stuart1 has a good reputation on FTE.stuart1 has a good reputation on FTE.
Right

I just looked it up and the hydraboost was on some 350's and some had vac boosters.
__________________
Wrench twister since 1957.
Journeyman since 1964.
Transmission builder since 1964.
Reply With Quote
  #8  
Old 06-13-2008, 12:03 AM
Qizzar Qizzar is offline
New User
 
Join Date: Jun 2008
Posts: 21
Qizzar is starting off with a positive reputation.
Status

Well, I did a visual inspection of all the vacuum lines and all looked good except one which was cracked at its end. So I cut it a little shorter and reconnected it.

I also pulled the vacuum modulator at the transmission and inspected it. I didn't see any fluid, but to replace it was only $10.00 so I went ahead and purchased a new one.

After installation I noticed a major improvement.

It still seems to shift at a high RPM and between 33-35 mph if my foot isn't on the excelerator the truck downshifts...enough so that you hear the engine rev up.

The truck still has a semi-hard shift unless I am heavy on the excelerator. If I am heavy on the excelerator the shifting seems to go smoother.

The instructions for the vacuum modulator said it has an adjustment screw on it to compesate for older vehicles. On quick inspection I wasn't able to locate this screw......it must be a really small screw. But this will be my next modification....

Thanks for all the replys thus far!!!
Reply With Quote
  #9  
Old 06-13-2008, 12:51 AM
stuart1 stuart1 is offline
Postmaster
 
Join Date: Jun 2003
Location: Somewhere Saskatchewan
Posts: 2,741
stuart1 has a good reputation on FTE.stuart1 has a good reputation on FTE.
The screw is in the end where the vacuum line hooks up to.

Turn it back a couple of turns will lower and soften the shift a bit.
Plus there are several different lengths of modulator pins.
__________________
Wrench twister since 1957.
Journeyman since 1964.
Transmission builder since 1964.
Reply With Quote
  #10  
Old 06-13-2008, 03:49 AM
Qizzar Qizzar is offline
New User
 
Join Date: Jun 2008
Posts: 21
Qizzar is starting off with a positive reputation.
Thanks for the advice...I'll give that a shot and see what happens..
Reply With Quote
  #11  
Old 06-13-2008, 01:45 PM
Qizzar Qizzar is offline
New User
 
Join Date: Jun 2008
Posts: 21
Qizzar is starting off with a positive reputation.
update

Well, I backed out the screw first a half turn (counter clockwise) and didn't notice any real change.

So I did an additional full turn counter clockwise and it seems to have made a difference in the shifting not kicking in as hard.

I don't know if its just me (which is possible) but it still seems to be late in shifting and adjusting the screw didn't seem to have any affect as far as that goes.

I know I read somewhere that mentioned not to turn the screw in (clockwise) more than 4 turns from the original factory settings. If I keep backing out the screw (counter clockwise) another turn or two will that affect the late shifting or will the trans just stop shifting all together?

and how many rotations is it safe to turn the screw (counter clockwise) from the original factory settings

Thanks
Reply With Quote
  #12  
Old 06-14-2008, 08:03 AM
Lazy K Lazy K is offline
Post Fiend
 
Join Date: Jan 2005
Posts: 8,402
Lazy K is a name known to allLazy K is a name known to allLazy K is a name known to allLazy K is a name known to allLazy K is a name known to allLazy K is a name known to all
I think you are going to have to check what vacuum you actually have, as suggested by TJC T. If you have around 20in. then you will have to adjust the modulator valve on the injector pump. However first establish your vacuum reading.
Reply With Quote
  #13  
Old 06-14-2008, 05:27 PM
timcos timcos is offline
Senior User
 
Join Date: May 2008
Location: Bentonville, AR
Posts: 202
timcos is starting off with a positive reputation.
Anyone have a diagram for all of this...can't seem to find it in my manuals (Chilton and Haynes).
Reply With Quote
Old 06-14-2008, 05:27 PM
 
 
 
Reply

Similar Threads
Thread Thread Starter Forum Replies Last Post
Diagnosis procedure for Escape XLT 2008 CD4E trans when P0732/P0734 codes surface cchighman Escape & Escape Hybrid 4 09-11-2014 10:15 PM
Transmission issue? downshifting at odd times mpally 2009 - 2014 F150 2 05-31-2013 01:26 AM
Transmission HELP vlietracer64 6.0L Power Stroke Diesel 7 09-29-2011 02:33 AM
F350 7.3 diesel SES light on no power CaminTX Super Duty & Heavy Duty 0 10-09-2010 12:26 PM
Not shifting correctly eakanator 1987 - 1996 F150 & Larger F-Series Trucks 13 07-09-2002 02:22 PM


Go Back   Ford Truck Enthusiasts Forums > Misc. > Clutch, Transmission, Differential, Axle & Transfer Case

Tags
1986, 1988, 88, adjust, clutch, diesel, f250, f350, ford, modulator, pump, slip, transmission, vacuum, valve

Thread Tools Search this Thread
Search this Thread:

Advanced Search

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is On
Trackbacks are On
Pingbacks are On
Refbacks are On

Forum Jump


Participate In The Forums

Create new posts and participate in discussions. It's free!

Sign Up »





All times are GMT -5. The time now is 07:04 PM.


Powered by vBulletin® Version 3.8.7 AC1
Copyright ©2000 - 2014, Jelsoft Enterprises Ltd.
Advertising - Terms of Use - Privacy Statement - Jobs
This forum is owned and operated by Internet Brands, Inc., a Delaware corporation. It is not authorized or endorsed by the Ford Motor Company and is not affiliated with the Ford Motor Company or its related companies in any way. Ford® is a registered trademark of the Ford Motor Company.

vbulletin Admin Backup