Transmissions having problems changing up

[JamesC]

Hi all . . after my successful post regarding my locked side door, I have another issue for you guys. My Bongo is delaying in changing up to higher gears. Also, when it is in top gear on the motorway, it intermittantly slips down to a lower gear, the revs shoot up and I have to slow down, until I can get it to change up again.

The garage I use have altered a setting, so it now seems to be changing up, but only at very high revs. It sometimes needs to go over 4000 revs to change up into top gear. Also, if I am reving high, I can often get my van to change into top gear by lifting my foot off the gas momentarily and then reaplying the gas.

I have seen some similar issues mentioned in the Q & A section in the Clinic area of the site, can anyone confirm which of the answers is likely to best fit my problem.

Finally, this problem started when I let the transmission fluid run to almost empty before topping it up.

I hope you can assist . .cheers

[wonkanoby]

first thing i would try is changing the fluid

inc dropping the sump

you will be amazed at the sludge in there

and washing out the gauze filter you find under there

its awkward unless you have a pela pump

as you need to keep sump level

or its going all over you or road

[missfixit70]

As said above, drop it clean it out & clean the filter - http://www.igmaynard.co.uk/bongo/forum/ ... =3&t=30096 or there's a fact sheet in the members area.
Did you fix the leak that allowed the fluid to get that low? It could be that you've bu66ered something in the gearbox by letting it run low? But I'd have thought you'd have a fault code flashing up if that was the case?
Have you checked the level with everything warmed up, ranged through the gears & check the level in D with brakes on & chocked?
Did you fill with Dexron III ATF?
Sounds like the garage may have adjusted the TPS?

[mikeonb4c]

Not heard of a garage altering a setting like this before, but if they have done and you're convinced the behaviour has happened as a direct result, then I'd ask why they changed it and/or if they could change it back? Wouldn't do any harm in the meanwhile to check fluids as advised above. But personally, I would be inclined to speak with the garage before I did anything much that allowed them to think the behaviour could be down to what you did rather than what they did.

[You've Been Bongod]

if you need a new box i have an exellent 2wd for grabs

[Alacrity]

Can't see how changing the oil can effect gear chage points as they are electrically shifted. It may change shift feel - & that I question but many here believe it does. The only thing the garage can have altered is the TPS adjustment, which will of course change the shift points but they don't normally need adjusting unless they are faulty, then they should be changed. As I have said before on this board you will only get a flashing hold light for an electrical issue with these crude electonic transmissions, they cannot detect slip so would consequently could not pick up a low oil level scenario.

So long as it is downshifting on the motorway & not slipping then you have a control issue - either TPS or speed senor but the most likely scenario is that, for some reason, the engine is down on power, this would give EXACTLY the symptoms you describe. I won't go into details here as to how or why as I have explained this in several previous posts - do a search on my posts or search 'gearbox' & 'transmission'.

[Alacrity]

OK I can save you the trouble searching as I have found my previous post:-

"The two basic inputs required by any auto trans are throttle position & road speed & from this the ECU (in the case of an electronically controlled transmission like the Bongo) can determine when & how to shift. If the engine is, like yours, down on power it will change gear late & downshift/kickdown all the time as you are having to give the engine more throttle to make the vehicle move at the same speed as you would normally. So for example you may drive on a light throttle up to 40mph with, lets say, 25% throttle opening normally (good engine power), to get the same speed with an engine down on power you will probably be at 50% + so the gearbox will late shift. Of course as soon as you feather the throttle, it upshifts as you have reduced the throttle opening. If you use even more throttle then it will downshift or kickdown, expecting the engine to then pull up to high revs, in this situation because the engine is not making its power that doesn't happen so you end up with loads of revs & no go.

This is a very common scenario & one we see quite a lot when car are either miss-diagnosed by garages or the power loss has been gradual (as in mass air flow meter issues) & the owner just doesn't become aware until the odd shifting makes him/her aware."

[dandywarhol]

Beat me to it Alac............... Does the engine feel as powerful as it shouldbe/was?

A faulty TPS won't show up as a dashboard light fault but should be stored in the memory of the ECU. If the engine performance is up to scratch I'd be looking at a TPs fault.

What year is the Bongo?

Alacrity - I've experienced harsh, slightly late upshifts, especially when the 'box was cold and changing the fluid/cleaning the strainer transformed it immediately.

[missfixit70]

Sounds like you're probably right Alacrity , my response was based on what had already happened & eliminating possibilities first.
IMO if you know the gearbox oil is not still leaking (level had dropped - why?) the correct grade, clean, with a clean filter & to the correct level, that's a good starting point . The question that was in my mind (incorrectly?) was whether the TPS had been adjusted because the gear changes were iffy because of problems with the oil level, flow, possible leakage, blocked filter, overheating etc? Thus introducing another "problem". Hence why most of my post was questions, I am no expert on autoboxes, so it's good to have the input of those that are

[bigdaddycain]

We could do with a few more details from the OP to pinpoint this one. Was the throttle position sensor adjusted because of the erratic gearchanges? Was the erratic gearchanges down to a lack of hydraulic assistance because of low oil? Was the low oil situation remedied, yet the TPS was left in it's adjusted state? I'd get the original guy that adjusted the TPS to sit with you for a road test, adjusting the TPS to suit, then look at (if) the power delivery problem form the engine if the adjustments don't return the gearchanges back to normal.

[Alacrity]

I completely agree with all your logic Kirsty. Oil leaks must be sorted or you will have a big bill from someone like me!

I wish my harsh 1-2 shift could be helped by an oil change. I do mine anually (as I tow a lot) & it never make a bit of difference - same on the last Bongo. I have thought of changing the solenoid pack - has anyone had an success with doing this to help the thump?? If not I may give it a try just to see. Nuthin ventured etc. etc.

[dandywarhol]

I think they inherantly lurch a bit from 1 - 2 and I'd doubt if you would feel any difference if you change th eoil annually - i don't know when/if mine had ever been changed and was pretty slimy around the filter gauze so a clean and change of fluid made mine different.

If the shift is too harsh when towing you could always use 1 hold and manually shift to 2nd then let the 'box do its own stuff................

[bigdaddycain]

A harsh gear 1-2 change? I don't recall experiencing that.

[Alacrity]

A harsh gear 1-2 change? I don't recall experiencing that.

I think you may be in a minority of one there then!!

[francophile1947]

A harsh gear 1-2 change? I don't recall experiencing that.

Try going above 2000rpm Ste Mine is quite harsh if I'm giving it a bit of welly, but not too bad if driving economically.