LH150 Reverse gearbox - No reverse

[JaimeManero]

Hello, Ive been helping out a friend whose lh150 won't engage in reverse. Ive been reading for the last couple of days other topics about this transmission and it was of great help to understand the different components and working principle of this gearbox, thank you for all users involved. Apart of previous experience with my own BMC 1.5, it was the first time dealing with a different type of transmission.

 

Just a bit of context, Im helping this person for free so I can only help her with the diagnosis or a repair that doesn't involve too many work hours or replacements, but of course this is not written on stone. I dont want to get suck into the "ok, ill help you out for free it shouldn't take long" rabbit hole that many people might be familiar with 😅.

 

    She told me, transmission got stuck in forward when they were boating, as I understood this the default position  for this transmission after a hydraulic loss of pressure. This is a safety feature that ironically, made her owner crash into a lock landing. When they checked the engine there was transmission fluid on the bilge. They never could figure out where the leak was. They also had other people trying to figure out the issue but as i understood they didn't had much idea of what they were doing. They refilled the oil for the reverse box and didn't leak again 

 

So this is the information I could gather after being at her engine bay:

 

1. Lh150 engages forward and neutral. There's a around a 2 second delay from selecting neutral and the shaft going into full stop. It won't engage reverse.

 

2. The oil level for the reverse box is way over the maximum limit, probably 3 times more. Also she couldn't confirm that EP 80/90 was used, so it might be any other random oil. The level for the reduction gear is within limits

 

So the fact that it engages means there hydrolic pressure, what I don't know if manages to reach enough to engage reverse. Im happy to get a oil pressure meter if necessary.  My other thought might be the reverse band being broken.

 

Any insight will be appreciated. Thank you 

 

 

 

 

 

 

 

[Tony Brooks]

OK, my thoughts, and thanks for trying to help a fellow boater.

 

I doubt overfilling the LH150 would be a problem when cold and i think it started life requiring SAE 30 engine oil, so unless the iol is a stupid synthetic very thin oil I can't see that being a problem re diagnosis.

 

I don't think that you can take the fact that it will go into neutral can be taken as meaning the hydraulic pressure is OK. The reverse brake band operating piston is smaller than the neutral piston, so ideally you would check the hydraulic pressure via the screw in the centre of the neutral piston cover. The "triangular", 3 bolt thing on the back of the box. However, you need a pressure gage and a suitable adaptor to fit into the hole to do that.

 

It is possible that the reverse brake band needs adjusting but don't have a manual to hand to copy the procedure but from MEMORY

 

Take the cover off and use one of the cover bolts through the bolt hole in the centre of the neutral piston cover to jack the piston forward to put the box in neutral.

Hold the slot in the threaded brake band rod where it comes through the reverse piston and tighten the nut on the rod until the box locks into reverse. You may have to turn the engine or shaft coupling to see when.

 

Unscrew that nut until you can turn the box without the  brake band rubbing in the drum. I am sure there is an X number of turns for this, but I can't remember.

 

Replace all parts and try it, you may be lucky.

 

@bizzard and @RLWP can you confirm or put me right.

[JaimeManero]

Hey Tony,  thank you for your answer.

 

Good to know the oil is not the culprit. Of course if repair is successful, will be flush and replaced with suitable oil. 

 

My next step is to get the oil pressure gauge and run a test. I remember it was around 260psi for neutral and 320psi for reverse from what I can remember from other topic in canalworld. Should I fit the tester into the same screw hole for forcing the neutral position?

 

If the pressure is correct, Ill start following your instructions. I got the part of the screw to lock the neutral on the 3 screws cover. But just to be sure, is the "threaded brake band rod", the part that is directly underneath of the "bulge" on right of the main top cover (looking from the stern)?. 

 

Is there a risk of damaging the gasket when removing the top plate?  Should i have a replacement ready?

 

What's the torque for the bolts of that plate?

 

Also if you know where I can get the handbook manual ill really appreciate it. I googled it without much success. 
 

 

[Arthur Marshall]

34 minutes ago, JaimeManero said:

 

Also if you know where I can get the handbook manual ill really appreciate it. I googled it without much success. 
 

 

Hope the above helps. I'm pretty sure I've got Lister SR2 manuals as PDFs somewhere if they are any use - pm me an email address if they are. the page above is from a PDF too.

I also had an odd problem with the gear box, in that it wouldn't stay in neutral but slipped into forwards, in one case leaving a lock without me when I really wasn't expecting it. No-one ever managed to work out why, but it did turn out that the gearbox had been overfilled, and lowering the oil level solved the problem, again though the engineer couldn't understand why it might have done so.

[Tony Brooks]

9 minutes ago, Arthur Marshall said:

No-one ever managed to work out why, but it did turn out that the gearbox had been overfilled, and lowering the oil level solved the problem, again though the engineer couldn't understand why it might have done so.

 

That is why I specifically said when cold. It should not affect it going into reverse at that time. It may allow the oil to overheat and thin too much, so as the OP says it will need sorting once it seems to work.

 

I think your instructions may be missing a paragraph, because as shown the box would be locked in astern.

 

48 minutes ago, JaimeManero said:

Hey Tony,  thank you for your answer.

 

Good to know the oil is not the culprit. Of course if repair is successful, will be flush and replaced with suitable oil. 

 

My next step is to get the oil pressure gauge and run a test. I remember it was around 260psi for neutral and 320psi for reverse from what I can remember from other topic in canalworld. Should I fit the tester into the same screw hole for forcing the neutral position?

 

If the pressure is correct, Ill start following your instructions. I got the part of the screw to lock the neutral on the 3 screws cover. But just to be sure, is the "threaded brake band rod", the part that is directly underneath of the "bulge" on right of the main top cover (looking from the stern)?. 

 

Is there a risk of damaging the gasket when removing the top plate?  Should i have a replacement ready?

 

What's the torque for the bolts of that plate?

 

Also if you know where I can get the handbook manual ill really appreciate it. I googled it without much success. 
 

 

 

Yes under the bulge.

 

if someone has lued it in place with gasket goo, but it was, I thin, a special rubberised fabric rather than paper sp if you are carefull they will usually come apart without damage.

 

Torque - no idea, use a normal spanner and tighten it using two fingers, that will be  about right.

 

Note, I have a concern that Arthur's instructions may not be complete.

[Arthur Marshall]

4 minutes ago, Tony Brooks said:

 

Note, I have a concern that Arthur's instructions may not be complete.

Sorry if they are - you are the expert in this, not me, I just seem to have that PDF. If it's of any use, I've uploaded the full SR2 manuals onto my website at https://www.arthurmarshall.co.uk/lister.html and I think there's much more complete instructions in there. there's certainly a section on the gearbox.

 

Tony, if you are sure my original PDF is wrong, I'll take it down before it causes any problems.

[Tony Brooks]

7 minutes ago, Arthur Marshall said:

Sorry if they are - you are the expert in this, not me, I just seem to have that PDF. If it's of any use, I've uploaded the full SR2 manuals onto my website at https://www.arthurmarshall.co.uk/lister.html and I think there's much more complete instructions in there. there's certainly a section on the gearbox.

 

Tony, if you are sure my original PDF is wrong, I'll take it down before it causes any problems.

 

Trouble is that I don't know, been 60 years since I worked on them, but basic principles say that with no pressure in the system (which you won't have with the top off) the band needs to be just clear of the drum. Otherwise, the box would lock with both ahead and astern engaged. I think there should be another paragraph saying "undo the lock nut by X turns". No idea what X would be.

 

That is why I pinged Bizzard and Richard. Maybe @Tracy D'arth will know.

Edited April 27, 2024 by Tony Brooks

[Arthur Marshall]

I'll leave it there for now and amend if necessary. It appears to be all I've got.

 

[bizzard]

After tightening anti clock wise the astern gear adjustment screw until the brake band is felt to be tight on the drum then slacken the screw clockwise 6 complete turns and then lock the nut. It's important the the top plate gasket is in good nick as the hydraulic passageways are under it.

8 minutes ago, bizzard said:

After tightening anti clock wise the astern gear adjustment screw until the brake band is felt to be tight on the drum then slacken the screw clockwise 6 complete turns and then lock the nut. It's important the the top plate gasket is in good nick as the hydraulic passageways are under it.

That's the final part of the adjustment Arthur which is missing on your post, add it to your notes

Edited April 27, 2024 by bizzard

[Tony Brooks]

24 minutes ago, bizzard said:

After tightening anti clock wise the astern gear adjustment screw until the brake band is felt to be tight on the drum then slacken the screw clockwise 6 complete turns and then lock the nut. It's important the the top plate gasket is in good nick as the hydraulic passageways are under it.

That's the final part of the adjustment Arthur which is missing on your post, add it to your notes

 

Just found my manual and it says undo three complete turns, I actually don't think it will matter that much, but I would err towards six and tighten it a bit if reverse slipped.

[bizzard]

5 minutes ago, Tony Brooks said:

 

Just found my manual and it says undo three complete turns, I actually don't think it will matter that much, but I would err towards six and tighten it a bit if reverse slipped.

Yes. I've always used the 6 including my own box, but I expect 3 to be ok too.

[JaimeManero]

Thank you all, I feel more confident to tackle the job. So in the next step ill remove the top plate and follow the instructions and let you know how it goes. To adjust the band should I also lock it in neutral as Tony indicated ?  I guess this is for feeling when the band is holding the drum? Or ill be able to feel it when adjusting? Sorry for so many questions. 

 

I shouldn't worry too much about ordering the meter and measuring the pressure before hand right? If this doesn't solve the issue ill know it has to do with the hydrolic part. 

 

Arthur thank you so much for the screenshot and the link to the manual, the cross section diagram and the instructions are very helpful, and they are nowhere to be found in Google.  I always like to understand how things work before tinkering with them. 

[Tony Brooks]

For information. I have had one of these boxes that did not operate properly and found that the screen around the oil pump inlet had clogged up with fibres and muck from the worn brake band and ahead clutch, causing low oil pressure.

[Arthur Marshall]

59 minutes ago, bizzard said:

After tightening anti clock wise the astern gear adjustment screw until the brake band is felt to be tight on the drum then slacken the screw clockwise 6 complete turns and then lock the nut. It's important the the top plate gasket is in good nick as the hydraulic passageways are under it.

That's the final part of the adjustment Arthur which is missing on your post, add it to your notes

Thanks Bizzard, will do.

[bizzard]

Also to count the number of full turns when turning that astern screw anti clock wise for the band to grip the drum. When unscrewed to the 6 full turns the difference will be a guide to how much wear on the band.

[Arthur Marshall]

Sorry to be a pain, but I want to check this is now correct before I leave it on the website! I've added the sentence, with a bit of luck in the right place..

[bizzard]

2 minutes ago, Arthur Marshall said:

Sorry to be a pain, but I want to check this is now correct before I leave it on the website! I've added the sentence, with a bit of luck in the right place..

That's it Arthur.

[Arthur Marshall]

1 minute ago, bizzard said:

That's it Arthur.

Many thanks.

[Tony Brooks]

Sorry to go on about this, but here is the cut and paste of the instructions I have:

 

We know the instructions have been altered, so Bizzard may be quoting the latest, but perhaps it is an earlier version. I would say adjust it as above and if the band did not totally free it would wear prematurely, whereas six turns is far more likely to free it and if it did slip in astern it is easy to tighten it a bit.

[john.k]

Never use a "Friction Modified" engine oil in a boat gearbox .

[RLWP]

On 27/04/2024 at 21:28, JaimeManero said:

 

 

I shouldn't worry too much about ordering the meter and measuring the pressure before hand right? If this doesn't solve the issue ill know it has to do with the hydrolic part. 

 

If it doesn't work, it's more likely the reverse band has gone.

 

You've got forward so the forward clutch is OK.

You've got neutral so the pump is working and pulling the clutch out against the springs. 

 

We have bands in stock

 

Richard

 

Richard

[JaimeManero]

Hello, thank you so much for the help. Im just letting you know that I haven't forgotten about this topic, I just havent had time to check the transmission. Will update you about the results when I have time 😁

[Tony Brooks]

Take note of what RLWP said. When you take the top off the box use a torch to have a good look around inside the box. You might see the remains of the brake band lining in the oil.

 

The brake band outer is steel and is probably still in place and looking OK, the linings are fairly thin (say 2mm) and are stuck to the inside of the brake band. They do break up and they also wear. You might get an idea of its thickness by tightening it onto the drum and assessing the gap between the drum and the steel part of the band.