Big issue with Auto gearbox

[wattg]

Hi guys

Was away for the weekend in the bongo and began getting a few gear change issues which got worse today on the way home.

On the way up I would describe it as feeling like a slipping clutch. Changed fine from first to second then into third. When you pushed the throttle a little o accelerate you got lots of revs and no speed increase. If I held in the hold button just before accelerating it dropped down fine then and accelerated. Just when I arrived at destination it decided to rev loads when asked to accelerate at all with no acceleration. So went out yesterday, and continually free revving when asked to speed up even slightly but fine if I put hold in first. But today I left to come home. 100 mile drive. Just after leaving found fine in first gentle throttle change to second gradually up to 25 mph and just as you think it should change up you get no more change in speed and just revs right up above 4000 rpm. Hold in hold button and a little bit better but not much. So changed into S on gear lever and was able to accurate up to 40 mph but the poor thing was really revving hard. As soon as I tried D or D and hold it just revved and no acceleration. So had to come all the way home at 40 mph in S drive with hold on for any slight inclines. Finally got home. Checked oil level and it seems fine but it is a bit black and burned smelling. Any suggestions on what could be wrong. Was thinking it was kaput all the way home. Have also noticed the speedo on odd times going about 20mph if you take foot off throttle the speedo needle will go right round to 100mph then settle back at the right speed?????

[dave_aber]

Firstly, if the oil looks burnt or smells like burnt toast - change it.

What is the setup of your speedo? Is it an original KM/H unit with a converter chip in-line, and the KM/H changed to M/H?

If so, then a malfunctioning converter chip would account for the wayward readings - and there have been posts on here previously about speedo chip failures affecting gearbox operation.

Certainly worth disconnecting the chip (if one is fitted) and seeing if it settles down, and change the oil too.

[wattg]

Hi

Not sure about the conversion but the speedo has had the K part of the KP/H replaced by M/H. Where would the inline chip be located if this was the case?

G

[dave_aber]

Almost certainly has a chip in there somewhere then.

If you pull the clocks out, you will find that the speed sensor wire to the instruments has been cut, and a pulse correction chip wired inline. They are usually small (20mm x x20mm - ish) and are just taped to the wiring, or left dangling about in behind the speedo.

If I remember right, the speed sense wire is on the right hand (as you look at it) connector block, and it's a blue/white wire. Should be obvious, as it's the only one which has been cut.

[mikeonb4c]

Firstly, if the oil looks burnt or smells like burnt toast - change it.

What is the setup of your speedo? Is it an original KM/H unit with a converter chip in-line, and the KM/H changed to M/H?

If so, then a malfunctioning converter chip would account for the wayward readings - and there have been posts on here previously about speedo chip failures affecting gearbox operation.

Certainly worth disconnecting the chip (if one is fitted) and seeing if it settles down, and change the oil too.

Not engine oil, but the automatic transmission fluid, just so you check the right one.

[wattg]

So guys just replacd the auto gearbox oil and disconnected two wires on the SpeedM8 conversion chip one that was on the blue/white wire to speedo and also a connection to the green/red wire on the rear. So took it out a run and still the same issue. Ch ages fine every time 1st to second and goes along fine in second until time to change gear where it then revs right up above 4000 rpm when it should be changing and vehicle speed doesn't increase. Anything else guys you think I should be checking there are still a couple of connections from the Speed M8 chip into the rear of rev counter connections which I have not removed yet. Any suggestions??

Strange sensation looking at the speedo now in KM/H !!

[dave_aber]

Oh well, it was a cheap check to do, but it sounds like the issue is more related to transmission internals - i.e. the oily / expensive bits.

As I understand it, there are a system of clutches and bands in the box which between them lock out the gears which are not in use, and thus select the actual gear in use. A quick google around, and it looks like clutches are in play when the gears are being changed automatically, and the bands when selecting gears manually - which may indicate that as you have drive in S, there is a clutch issue with the 4th ratio?

There is a member on here by the name of Alacrity who is an auto transmission specialist by day - it may be worth sending him a PM, however I'm not sure when he last posted / visited the forum. (Edit : only 6 days ago, you may be in luck!)

The not-so-bad news (I was going to say good news, but it hardly qualifies) is that the Bongo transmission is much more bread & butter to any (decent) auto-transmission place than for example the engine & cooling system is to any (average) garage.

[dave_aber]

Here's some bedtime reading

[mikeonb4c]

Oh well, it was a cheap check to do, but it sounds like the issue is more related to transmission internals - i.e. the oily / expensive bits.

As I understand it, there are a system of clutches and bands in the box which between them lock out the gears which are not in use, and thus select the actual gear in use. A quick google around, and it looks like clutches are in play when the gears are being changed automatically, and the bands when selecting gears manually - which may indicate that as you have drive in S, there is a clutch issue with the 4th ratio?

There is a member on here by the name of Alacrity who is an auto transmission specialist by day - it may be worth sending him a PM, however I'm not sure when he last posted / visited the forum. (Edit : only 6 days ago, you may be in luck!)

The not-so-bad news (I was going to say good news, but it hardly qualifies) is that the Bongo transmission is much more bread & butter to any (decent) auto-transmission place than for example the engine & cooling system is to any (average) garage.

Alacrity (Geoff) would be excellent. Try googling 'solenoid pack' or searching on here as that is one slightly less expensive thing that can go wrong with Bongo autoboxes.

[Alacrity]

I'm afraid your high clutch has burnt out. there are different clutch packs that come on for different ratio's. The high clutch is a common failure item on these transmissions, so every time a gear is selected that needs this clutch you will get, effectively, a neutral. Its a gearbox & converter rebuild I'm afraid or a good used transmission. Don't let anyone tell you otherwise. It's shame I didn't see this post earlier as I would ave saved you the cost of the oil change as that was never going to fix it.

The reason I don't visit here very often is because I have been worn down by the armchair 'experts' that contradict most of the professionals on here that dare to post a fix that costs more than a few quid. There are also people on here that insist auto transmissions never fail, but I have been rebuilding & repairing them since 1979 so I'm not sure what planet they come from!

I'm sorry you trans has failed, but you will have to get it rebuilt/changed to get you moving properly again.

Geoff