Author | Topic |
thesaabologist V4 Fanatic
319 Posts | Posted - 15 Jun 2017 : 21:03:58
| My bullnose 3 speed gearbox has recently developed an interesting fault.....
When left running in neutral, for example at the lights, when I select a gear (could be forward or reverse), it is as if the box is still in neutral, despite the fact the gear stork is firmly in gear and the gear has been selected on the column. No amount of changing, clutch depressing etc has an effect. However if I put the selector back to neutral, switch the engine off and then on again and then select a gear, the drive engages as normal.
Any ideas on what the fault could be?
--------------- 1974 Sonett III 1964 Bullnose
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UK_Sub V4 Guru
United Kingdom 2555 Posts | Posted - 15 Jun 2017 : 21:31:38
| Have you tried it with and without the freewheel engaged? | |
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melle V4 Guru
United Kingdom 3830 Posts | Posted - 15 Jun 2017 : 22:09:05
| Sounds like a worn freewheel mechanism (it doesn't actually matter if freewheel's engaged or not, if it's worn you'll loose drive).
www.saabv4.com | |
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chris steeden V4 Fan
United Kingdom 163 Posts | Posted - 15 Jun 2017 : 22:21:04
| It is a sound idea to try UK Sub's suggestion first and maybe use a flushing oil in the gearbox. If no luck check your timing and distributor. You might find that it is 180 degrees out. This simple mistake can make two strokes play up and can cause reverse gear happening when you select first gear. It is possible with incorrect timing for the engine to 'reverse rotate' and to be honest, all sorts of box problems. | |
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thesaabologist V4 Fanatic
319 Posts | Posted - 16 Jun 2017 : 09:04:37
| Thanks all - good suggestions. So far I've not opened up a gearbox - if the issue is the freewheel is there anyone in the UK still repairing these boxes / is the repair a DIY repair?
--------------- 1974 Sonett III 1964 Bullnose
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Derek V4 Guru
United Kingdom 2187 Posts | Posted - 16 Jun 2017 : 10:40:23
| Off the wall but have you got the tickover speed set VERY low? If it is a quite a bit lower than the freewheel engagement speed you will indeed appear to be in neutral It's possible that when you do the restart the base revs are just a bit higher so free wheel then works normally. Tickover can take a while to fall back to its minimum after a start or restart in this case. More speculation, but with a 2 stroke the whole pumping action can get very inefficient at low speed which tends to gradually slow the tickover down even more. Agree with Simon, just lock out the freewheel and see what happens. | |
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andydeans3 V4 Guru
United Kingdom 1994 Posts | Posted - 16 Jun 2017 : 12:14:18
| Saabologist My money would also be on the freewheel mechanism. If it is, I wouldn't say it's a DIY job to check it out. There is a special tool required to re-build it, and it is, I believe, quite impossible, to re-build the freewheel mechanism, without it.
Lots of springs and ball bearings that have to be loaded sequentially, while holding in place the ones previously loaded. I know a guy in Fife who has this tool, and does know these boxes. I could speak to him if you want.
Andy
1978 LHD SAAB 96 1978 MGB Roadster 2008 LHD "Classic" Renault Twingo | |
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thesaabologist V4 Fanatic
319 Posts | Posted - 16 Jun 2017 : 14:38:04
| Derek you may be on to something - I have been running the tickover very low because I found the dynamo was over-charging the battery and thought a fast idle might have something to do with it. I'm going to try the various suggestions and will report back.
--------------- 1974 Sonett III 1964 Bullnose
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GeoffC V4 Mad
United Kingdom 507 Posts | Posted - 16 Jun 2017 : 15:32:45
| Just put a freewhel together I found in a box of bits! All you need is a strong elastic band and some patience!! However for the rest of a box rebuild it's setting all the gear back lash and clearences and I haven't managed that yet! So if you find another gearbox builder I have one that needs doing as well sometime! | |
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melle V4 Guru
United Kingdom 3830 Posts | Posted - 16 Jun 2017 : 16:51:06
| quote: Originally posted by GeoffC All you need is a strong elastic band and some patience!!
Yes, it's a fiddly job, but not all that difficult.
The problem is that the bore the freewheel spins in wears, I believe this is what causes it to slip. I've replaced the shaft, but kept the old 6-roller freewheel when I had this issue about ten years ago and that worked fine. You could measure the bore with an internal micrometer (or a telescopic gauge and an external mic), but I'm not sure of the spec. I didn't bother back then as I didn't have micrometers at the time. Maybe stronger springs or longer "push pins" could also cure the problem?
www.saabv4.com | |
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Fliptop V4 Fan
United Kingdom 154 Posts | Posted - 17 Jun 2017 : 22:44:28
| 99% the freewheel is slipping.
Running and bodging Saabs since the dark ages... | |
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thesaabologist V4 Fanatic
319 Posts | Posted - 08 Jul 2017 : 17:53:13
| quote: Originally posted by Derek Off the wall but have you got the tickover speed set VERY low? If it is a quite a bit lower than the freewheel engagement speed you will indeed appear to be in neutral It's possible that when you do the restart the base revs are just a bit higher so free wheel then works normally. Tickover can take a while to fall back to its minimum after a start or restart in this case. More speculation, but with a 2 stroke the whole pumping action can get very inefficient at low speed which tends to gradually slow the tickover down even more. Agree with Simon, just lock out the freewheel and see what happens.
Tickover was set on the low side and increased tickover speed has certainly improved the situation - almost a full cure - it was doing it all the time and now just every so often.
--------------- 1974 Sonett III 1964 Bullnose
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Derek V4 Guru
United Kingdom 2187 Posts | Posted - 09 Jul 2017 : 11:31:54
| Maybe a bit more tweaking will cure it, perhaps another 50rpm. Being a two stroke, getting the tick over both slow and smooth not so easy. Refilling the gearbox with ATF and running it in gear with the wheels off the ground for a while will clean out the internals and is sometimes used to improve the freewheel action. Just an oil change might be enough.
At tick over or say under 1k revs a dynamo won't normally be putting out much charge so overcharging more likely down to the voltage regulator not working properly. | |
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fuling Starting Member
Sweden 32 Posts | Posted - 16 Jul 2017 : 15:29:36
| 1: Have you tried it with and without the freewheel engaged? 2: What do you have for oil in gear box?
3-shifted gear boxes are usually bulletproof.
If a ball bearing on diff is broken. Sometimes it drives and sometimes does not work. Similar to the problem with freewheel. Changsen is very small, but I have experienced it.
"The drill the freewheel spins in wears" I do not believe in it. I have seen drill that badly worn. Rusty and more. With a clean and good freewheel, it works.
quote: "Refill the gearbox with ATF and run it in gear with the wheels off the ground for a while Clean out the internals and is sometimes used to improve the freewheel action. Just an oil change might be enough."
I have not tested myself but heard it as used disel for flushing. (With the wheels off the ground)
There are 3 different freewheel. 6 roller and 2 10 roller
6-roller -1968 (3 & 4 gears) 10 roles 1969-1974 saab no 719 431 10-roll 1975-1980 saab no 871 181 Do not take the years exactly, but about
I prefer 6-roller with a little stiffer springs, seem to work forever. (Rally, race) Next 871 181 Last 719 431, but it also works. (standar cars)
Freewheel tools can be manufactured. A pipe, a lathe, a saw and a file. Think even you could do plastic. Measurements can I fix if someone is interested.
Without tools, it goes with 6-roller. 10-roller I would not even try. | |
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melle V4 Guru
United Kingdom 3830 Posts | Posted - 21 Jul 2017 : 12:38:29
| quote: Originally posted by fuling "The drill the freewheel spins in wears" I do not believe in it.
That's fair enough. I think the problem is that the standard springs aren't strong enough to compensate for a worn bore.
www.saabv4.com | |
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fuling Starting Member
Sweden 32 Posts | Posted - 22 Jul 2017 : 17:43:24
| I have measured a number of drills. (New and old) Separates max 0.1mm. What it gives to reducing the spring force I do not know. But that's a little bit. And the springs themselves do not lock the freewheel. It's the sloping planet that forces out, locks, rolls. | |
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