1964 vintage velvet drive gearbox problem

stuhaynes

stuhaynes

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Twin engines by Thornycroft (based on Fordson major tractor engine). I think that they are about 2.3 litre diesels. One engine recently lost both forward and reverse. On checking the gearbox I found a plate on the top of the gearbox with the following info on it:-

Velvet Drive
AS 771
1.91 1278
CM 31781

The plate was difficult to read so there may be an odd letter or number incorrect. I would have expected to find Borg Warner mentioned somewhere but didn't find any reference

The selector shaft runs sideways across the top of the box and is not siezed. On selecting forward or reverse the shaft turns okay but there is no 'clunk' to suggest anything engaging internally.

Anyone got any thoughts? :confused:
 
vintage is the right word. I'm not sure I would want to put to see replying on 50 year old kit, andy more than I would happily drive round the M25 in a Morris Oxford.
 
As L'escargot says, first thing to check is the ATF level. Next to the little plate is a threaded cap with a T bar on top. Unscrew it and you will find a dipstick.
If there isn't enough ATF then the hydraulic pump wont be driving the vanes - no drive.
Topping up will restore drive - or it did on my BW Velvetdrive 71C - but it would be an idea to find out where the fluid is going.
The lost likely excape route is through the gearbox cooling heat exchanger - the fluid can leak through the core into the cooling water and exit via the exhaust.
By the way, when you replace the dipstick make sure the cap is fully screwed down. There is a cone shaped seal under the cap which must be air-tight.
 
Bosun Higgs said:
vintage is the right word. I'm not sure I would want to put to see replying on 50 year old kit,
Click to expand...

Why ever not ? Do explain your reasons why.

If this is the model im thinking of then there is also a filter low down on the right hand side which may be blocked. You really have to look hard to see it.
 
My experience of Velvet drives is that they are all hydraulically operated. A search through Google may find the manual for your model. For example: -

http://www.marinepartssource.com/velvetdrivepb/188early.asp
http://printfu.org/read/documents-m...S69LZsOHf29mx0-Pmytrgx-nW1Nq819PpydGe4s3UlqHy

The second link is for a series 71 gearbox. It indicates that there is an indent for each of the three positions: F N R and that the selector lever must be in the indent position for it to work. Perhaps the indent is not working and thus the lever is slightly out of position and hydraulic oil is not getting routed correctly.

Also check on http://www.cruisersforum.com/forums/f54/ and ask here. This is an American sight and the Velvet Drives are very popular over the pond. I have found this site to be good.

Good Luck,

BlowingOldBoots
 
Bosun Higgs said:
vintage is the right word. I'm not sure I would want to put to see replying on 50 year old kit, andy more than I would happily drive round the M25 in a Morris Oxford.
Click to expand...

There are plenty of 2 year old boats that break down and plenty of boats way over 50 years old that are serving their owners well. In any event this particular boat is on the inland system (canals) and will never see an ocean. :rolleyes:

My camera is out of action but I'll see if I can borrow one to post a pic on here.

Thanks everyone so far. :)
 
fisherman said:
Doubt if it's worn out: sometimes just rubber ringseals gone in the pump, if not low oil.
Click to expand...

Thanks for that Fisherman. An earlier site link on this thread has given me a load of information. The box appears to be a Velvet Drive 71C 1.91:1. At this stage I too think it's a low oil problem. The box is not on my boat, but I did try to check the oil, but no way could I get the plug out! I'll check it again with heavier tools. :)
 
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