If you would like to join the DLOC, please visit the Club's website https://www.dloc.org.uk/
Please don't post someone's email address. Some people don't want to risk it being harvested by spambots and GDPR regulations discourage it.
Always look at "ACTIVE TOPICS" which gives all posts in date & time order if you can't find a post or "Your Posts", as topics are sometimes moved.
Reg. nrs. Please add reg. nr. when posting a photo or anything about a car as this will help searches. Don't add punctuation next to nr. as this negates search.

250 saloon auto transmissiion problem

Post Reply
tom.harding
Posts: 2
Joined: Mon Mar 25, 2019 9:19 pm
Location: Hereford UK

250 saloon auto transmissiion problem

Post by tom.harding » Mon Mar 25, 2019 9:51 pm

My 1968 250 saloon has developed an auto transmission problem, it will no longer change gear!
Starting in D1 gives first only, D2 gives 2nd but it will never go into 3rd. Reverse is fine.

The fluid level is correct and looks a clean pink colour. I tried adjusting the downshift cable with no effect.

Over the winter I had the radiator re-cored to fix an overheating problem.
Although I was careful to block off the transmission pipe unions at the bottom of the radiator, I suspect that something has found its way in the auto box.

Looking at the fault diagnosis section of the workshop manual, the most likely problem seems to be a sticking governor valve.
Does this seem likely? What other possibilities are there?

Thanks in anticipation

Tom

tjt77
Posts: 467
Joined: Wed Mar 23, 2016 7:01 pm

Re: 250 saloon auto transmissiion problem

Post by tjt77 » Tue Mar 26, 2019 1:13 am

your first check should be to be sure the fluid level is where it is supposed to be, and second step is to check condition of fluid.. it should be red in colour and clean ..if it is not red but looks dirty or brownish, drain fluid, remove the sump from the gearbox and check for residue and crud in bottom and and condition of filter .. dirty fluid indicates a problem ..its usually caused by contamination by fragments of the clutches in there, but there is quite a bit of leeway and even when the clutches are worn slightly, the gearbox should operate fine as long as it can get sufficient oil pressure ..the symptoms you describe are typical of low fluid press and commonly the cause is a choked gearbox filter.. very often a through service with new filter and fresh fluid will resolve the problem..

tom.harding
Posts: 2
Joined: Mon Mar 25, 2019 9:19 pm
Location: Hereford UK

Re: 250 saloon auto transmission problem

Post by tom.harding » Sun Apr 07, 2019 8:45 pm

Firstly, thanks for your suggestions.
I drained the fluid (nice clean red colour) and removed the sump. No debris and the two filters looked fine. Also, very little on the magnet. Checked the downshift cam operation and it seemed fine.
I replaced the sump and refilled with new fluid (Comma AQF). Did a road test and all seemed fine, changing up OK and kickdown working from 3-2. I came back, left it a while and tried another run - no gear change, just as before!
I connected a pressure gauge to the pressure takeoff at the rear of the transmission, but as soon as I started the engine the pressure went right up to 8 or 9 bar, basically off the end of the scale! What am I doing wrong?

Post Reply