Dexron Auto Gearbox

herbie

herbie

Member
Hello All,

Have just been to the Le Mans Classic in the P6, which performed faultlessly and cruised at 70-80mph on a 770 mile round trip (who said SC Auto's were slow!)

Before I left the Rover was at the local garage having the rear bushes changed and the guys kindly checked a few bits for me in preparation for my journey. The problem is the gearbox oil was low and was subsequently topped up with Dexron fluid, since then it has held onto gear, thumps into reverse and doen from 2nd to first when approaching traffic lights etc.

Obviously I need to change the oil, will this cure the problem or has damge been caused, I know that when changing the track rod ends whilst it was with them that a lot was partially dismantled from the bulk head could this also have caused the prob interms of cable adjustment etc??

Many thanks

Richard.
 
I have sorted the problem with the thumping and late drop down, the cable for the gearbox was not located properly at the throttle linkage and now all is fine again.

Is it still necessary to change the gearbox oil?
 
Dexron is designed to cause clutch and band slip to smooth out the changes on boxes that it was desighned to be used in. Slip = heat, so the BW boxes (which weren't designed to use it) run permanently overheated with Dexron in them. If you want to remove the Dexron and replace with the correct fluid you'll need to do 4 drain/refills with use in between to be pretty sure of getting most of the Dexron out.
 
Thanks Harvey, I will need to get it all out as gearbox was re-built 4 years ago and I wouldn't want that expense again! The Rover is used a lot so I will aim to do it every 1000 miles? or sooner would you think?
 
herbie said:
The Rover is used a lot so I will aim to do it every 1000 miles? or sooner would you think?
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You don't need to leave it anwhere near that long, all you need is to get a reasonably even mix between the two types of fluid, so if you had the inclination you could do the 4 changes in the same day. I reckon all you'd need is a good length road test between, say 5 miles. A lot of fluid will be moved around in that distance. Alternatively do a change every weekend after using the car during the week. If you make sure the level is correct before you start, you can save time and effort on each change by measuring the amount that comes out and putting the same amount back. Just recheck the level after the last refill. The longer you leave it draining the more you'll get out each time, but you can't drain the converter, hence the need for multiple drain/refills.
 
Afer a second reading of the OP. Do you know how much Dexron was added to bring it up to level, and do you know for certain that it had the correct fluid in it before it was topped up? If it had the correct fluid in there, and only had a pint or so of dexron added, I'd be less worried than if it was totally filled with Dexron.
 
It had the correct fluid in it previously, I'm not entirely sure how much went in, one of the chaps has emailed me back to say that it didn't actually say Dexron on the bottle it just said 'suitable for Ford'??
 
herbie said:
, one of the chaps has emailed me back to say that it didn't actually say Dexron on the bottle it just said 'suitable for Ford'??
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If it's suitable for early Ford, then it should have M2C-33F or G on the bottle, and if that's the case, panic over!
 
Do you know who rebuilt the box? It is possible that was rebuilt with Dextron compatible bands and clutches. The aftermarket kits from Australia use Dextron compatible bands and clutches. The BW35 was manufactured in Australia into the mid to late 80's with Dextron compatible parts. Hence the aftermarket parts manufacturers make kits that are Dextron compatible. To make things more confusing these boxes went into Ford cars, but these cars only were sold in Australia as far as I know.

If in any doubt, change the fluid to M2C-33F, as per Harvey's instructions. I have seen the internals of a box which had been topped with Dextron, and the bands were starting to flake after not many miles. I had been advised at a parts store the Dextron was okay in a BW35 box, which is only true if you know the history of the gearbox.
 
Very true J Radcliffe. The specifications changed during the late 1980's here in Australia. Both Ford and Castrol changed the requirements accordingly.

Ron.
 
We've just had our BW35 reconditioned by an automatic transmission specialist who refilled it with Dexron III, which they recommend. I hope they've used Dex3 compatible components. They claim they have had no problems with this in all the BW35s they have done on Fords and have given a lengthy warranty.
 
idexnz said:
We've just had our BW35 reconditioned by an automatic transmission specialist who refilled it with Dexron III, which they recommend. I hope they've used Dex3 compatible components. They claim they have had no problems with this in all the BW35s they have done on Fords and have given a lengthy warranty.
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I had some work done on my BW35 a year back by a "gearbox expert" here in Auckland."Yes mate know the 35 back to front ".
A minor problem which involved refilling the gearbox.
I arrived back to pick up the car and fortunately they were late with the job and about to refill the box with dextron. An argument ensued and I went "nuts" and the mechanic reluctantly went off and did a google search. He refilled with typeF , not dextron. Then he had to outsource the oil . Bloody experts!! They would have charged me to stuff the box.
Trust no one with ya baby !!
 
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