Torque convertors and lockup

[OG.]

Seem to have a weird issue with my auto box. Actually a couple of issues... 1. It seems reluctant to keep the TC locked up. The TC wont lock sometimes but if I manually shift to second then back (or engage kickdown) it will lock the TC but then slowly lose lock. Once lock is lost I have to drop it to second again to re-engage it. 2. The OD button seems to do very little. If its on (as in overdrive enabled) and I disengage it the revs rise about 100 rpm and return to where they were. Operate the switch again and it does exactly the same. Any ideas...? Its a 90 series 3.4 V6 2001 model.

 

[wobbly]

What state is the atf ?

Right age for the rad fluid / atf fluid to have mixed - the resultant goo destroys the clutchs inside the box.

Pete

 

[OG.]

Just drained a small amount of fluid out and its dark but not full of water. Smells slightly burnt but not overly bad. Have ordered 6l of ATF from the local garage and will be changing it all tonight. I plan to change it once, then drive a week or two and change it again and see how it goes.

Interestingly enough the fluid appears fine on the dipstick when checking.

 

[fridayman]

Do yourself a favour and get 12 litres then flush it out using the autobox pump - pump out 2l then top up, and repeat until atf coming out is clear red.. On the diesel the fluid is pumped back from the rad/cooler on the drivers side.

 

[OG.]

Too late.... drained fluid and refilled. Seems marginally better but won't know for sure till the morning run to work. Will repeat the job this weekend perhaps. Looking at the oil its dark, not gritty at all and seems water free.

 

[wobbly]

Hopefully you shouild see an improvement.

 

[OG.]

Well there has been a definite improvement but its still not entirely sorted. I'm starting to think there may be two separate issues - one with the lockup and another with the o/d switch function. It does use all gears but the manual override doesn't work though the switch itself seems fine.

One think I have found is the transmission cooler can't be getting water in it as a previous owner has bypassed it with an separate unit with its own fan.

His weekend will see the pan removed, strainer cleaned and another refill of ATF.

 

[wobbly]

Thats a good modification, an improvement on the original setup.

 

[OG.]

The Colly has now had a complete fluid change and pan removal/clean and filter removal/clean. The lockup issue is gone but it still wont drop to third when the O/D button is pressed. Everything appears to function but it doesn't change gear - i.e. the OD off light comes on (so we know the switch works), it seems to try to change gear but then goes straight back into 4th. Any ideas? Aside from that the gearbox seems to function normally going up through the gears from 1st to 4th then into lock then back down again. Its just the manual overide isn't working.

 

[goodoldboy]

to me it sounds like its working correctly as mine dose exactly the same - try switching the o/d off going down a step hill & see if you get better engine braking

 

[OG.]

No.... I dont get any extra engine braking at all. With OD off my understanding is that it will never go into 4th, but mine does irrespective of the switch location or the light on the dash being on or off.

 

[wobbly]

I had a run out in the Prado today, its a 3.0 Diesel so revs wont match up, but I found:

With O/D off, the box runs through all the gears, and goes into 4th at about 2400-2500rpm.

When I press the O/D button, the revs drop to just over 2000rpm.

If I release the O/D button so its off, the revs go back up to 2400rpm.


I may be wrong in this, but I dont think that the O/D actually controls the gears, it is an additional facility to reduce the revs for better economy, a sort of electrical operated gear. So if you are in 4th and swith od off, it stays in 4th but the revs go up.

What may confuse the issue slightly is that if you switch od off, then the revs rise to the point that makes the gearbox kickdown a gear? This would feel like the od is making the box drop a gear, but in reality its the kickdown doing it.

Cheers

Pete

 

[OG.]

I've been doing loads of research on this and have managed to find a very detailed description of how the Colorado auto box works (I can post links if anyone is interested).

It seems there are 2 sets of planetary gears. Each set in theory giving 3 ratios. In practice one set is for 1st, 2nd and 3rd whilst the other is for overdrive (4th). These are controlled by a set of clutches and two solenoids attached to the valve body.

Depending on the combination of solenoids operated the 4 gears can be selected.
There is a third solenoid responsible for torque convertor lockup making it feel like there is a 5th gear. Lockup only operates in fourth gear.

I suspect that in my case what is happening is the 4th gear clutch pack is losing hydraulic pressure causing it to slip. Once pressure is lost the gearbox thinks it is in 4th but has in reality dropped back to third even though the solenoids are still in the 4th gear state (4th is third on the first set of planetary gears engaged in conjunction with the second set of planetary gears so no pressure on the 4th gear clutch will drop out the second planetary gear set).

I suspect this will mean a gearbox strip down and overhaul as the fluid flush will likely only be a temporary fix.

 

[OG.]

Well things have got worse. Fourth gear has now failed entirely and an auto trans specialist has suggested the clutch pack has likely failed. Looks like a box rebuild is on the cards.

Even my Land Rovers have been more reliable in their first month of ownership than the Colorado.

 

[wobbly]

You've only owned it a month?

Got to say, I'm always suspicious when there are major issues appear so soon after a purchase - who did it come from?

Looking on the bright side, the Landie normally breaks down every month

And your diagnosis was correct !

Pete

 

[silvercruiser]

Well there has been a definite improvement but its still not entirely sorted. I'm starting to think there may be two separate issues - one with the lockup and another with the o/d switch function. It does use all gears but the manual override doesn't work though the switch itself seems fine.

One think I have found is the transmission cooler can't be getting water in it as a previous owner has bypassed it with an separate unit with its own fan.

His weekend will see the pan removed, strainer cleaned and another refill of ATF.

Sorry to hear your news, the clutch pack in the auto box could of failed due to water contamination, as you stated earlier that the cooler has been bypassed so to me points out that the rad/cooler failed on the previous owner who then had the external cooler fitted and the fluid changed but the damage had already been done.
Just my two cents worth.

I hope once fixed you have many happy miles.

Joe

 

[fridayman]

Yip, sounds like previous owner had the rad/cooler fail and the damage was probably done then.

 

[OG.]

Had it confirmed today. The box has to come out to have the internals inspected and replaced. The thought is that the 4th gear clutch pack has worn or that the seals operating the clutch are shot. Either way its a rebuild.

Got a quote for £1200 + VAT for the whole job including a rebuilt torque converter and a 12 month unlimited mileage warranty. Sounds reasonable to me. Any thoughts?

 

[wobbly]

Expensive job, having auto boxs rebuilt, so doesnt sound ott.

The garage doing the job have to be A1 standard.

I agree with Joe, previous contamination messed the clutchs up. Once rebuilt though, should be fine as the system is modified.

Pete

 

[OG.]

Guy I spoke to seems to know all about them and knew of the contamination issue. Asked all the right questions and came up with what seemed to be the right answers. Negotiating with the seller regarding their contribution to the cost at the moment (it was bought from a dealer). So far they've been OK about it.