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No engine brake in 1st gear


 
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MikeJak
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Joined: 28 Mar 2022
Posts: 71
Location: Herts

PostPosted: Fri Jun 17, 2022 9:52    Post subject: No engine brake in 1st gear Reply with quote

Hello…trying again to pick some brains wiser then mine… I’m getting to know my vehicle and it’s behaviours and I while I get good compression braking dropping in second gear I don’t seem to get any braking at all in first gear on my Colorado petrol auto in L not much difference in h, hl or ll when in first gear/L it just rolls away and I have to ride the brakes.
From reading the manual I should get engine brake when dropping below 31mph when in high and 6mph when in low. I tried stopping completely and starting moving in L which the transfer in LL and it still picked up speed  up to 20 mph… a bit too fast for steep descents!
It definitely engages first gear.
I thought it may be a defective gearbox solenoid but I checked codes from the ecu but get no codes/continuous blink so that should exclude the solenoids..

I noticed my kick down cable was is a little slack, I sorted i to spec last night but don’t think that should affect engine braking…
Any experience or ideas would be much appreciated.

The auto box was fully rebuilt two years ago and runs very smoothly.
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PostPosted: Fri Jun 17, 2022 9:52    Post subject: Google Ads keep this community free to join!


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modvrs
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Joined: 03 Oct 2013
Posts: 260
Location: Southampton

PostPosted: Sun Jun 19, 2022 18:58    Post subject: Reply with quote

I jammed my auto V6 into 1 in high range today at just under 30mph and got lots of engine braking. I forgot you'd mentioned trying it in low range so will try that on the next trip out.
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1997 Toyota Land Cruiser Colorado 3.4VX
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MikeJak
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Joined: 28 Mar 2022
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Location: Herts

PostPosted: Sun Jun 19, 2022 20:24    Post subject: Reply with quote

Hi Modvrs, yes, that’s the behaviour I would expect too.. hi or low gears will just change the multiplier so the speed the code compression  brake will keep.
I’m a bit confused as if it is a problem with my torque converter I should have some gear slippage and  imprecise shifting and likely no braking in 2 either. Shifting is smooth and responsive without delays.

I tweaked the kick down cable but, as expected no difference, the gear change happens a touch earlier now. No difference on the compression braking in 1st.
Level of atf fluid was maybe a touch low, I find it a bit tricky to get a reliable hot reading not knowing the actual temp.

As I said no codes suggesting solenoids malfunctions… quite frustrating to just coast with nearly no resistance in 1st..
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modvrs
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Joined: 03 Oct 2013
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Location: Southampton

PostPosted: Sun Jun 19, 2022 21:30    Post subject: Reply with quote

I looked in the FSM A/T troubleshooting section and it says for no engine braking in L look at the "low coast modulator valve". It didn't give any further details. There are references to the valve on the IH8MUD forum but their problems seemed to be related to reversing under load and clattering noises. I'm well out of my depth on auto transmissions.
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1997 Toyota Land Cruiser Colorado 3.4VX
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MikeJak
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Joined: 28 Mar 2022
Posts: 71
Location: Herts

PostPosted: Mon Jun 20, 2022 9:25    Post subject: Reply with quote

Hey modvrs, thanks for the pointer!
Auto trans are totally over my mechanical skills but that’s a great pointer… I found what the low coast modulator valve is and where it is…seems there are two in the lc90 trans and could be the cause if the spring is out of range/lost it’s memory…
I think I found the topic on ih8mud, was it a mention in an 80 series reverse issue?
Looks pretty deep surgery unfortunately. I will eventually look into it I suppose but may have to wait a while… parts are really cheap but getting in there looks time consuming and complex. I don’t think the trans needs to come out but pan needs dropping and filter and valve assembly taken out… will talk to my trusted mechanic and see…

I will check the throttle cable too, apparently if the throttle doesn’t close fully when accelerator is released that could also cause loss of engine braking in 1st… that would be an easy fix but I’m pretty sure it’s wishful thinking on my part..😅

Where did you find the FSM? I have a Haynes manual but there is no mention of a/t troubleshooting in there…
Thanks again, really appreciated!
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MikeJak
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Joined: 28 Mar 2022
Posts: 71
Location: Herts

PostPosted: Mon Jun 20, 2022 10:13    Post subject: Reply with quote

mmmh acually just found what the modulator valve does:
The Low Coast Modulator Valve reduces line pressure from the manual valve to reduce shock when the gear selector is moved to the L position. The low coast modulator pressure pushes the low coast shift valve down and applies the 1st and reverse brake to buffer shock.

doesn't actually seem to be the issue I have...arrgh... who knows... likely a job for a specialist...
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modvrs
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Joined: 03 Oct 2013
Posts: 260
Location: Southampton

PostPosted: Mon Jun 20, 2022 21:29    Post subject: Reply with quote

Just had a re-read of the manual, there are two sections in troubleshooting for no engine braking in low gear, I'd stopped when I'd read the first one which relates to on-vehicle repairs which refers to the low coast modulator valve which can be accessed by dropping the valve body out if the trans. The second section refers to off-vehicle repairs and says to check the 1st and reverse brake.

I guess the most likely part to wear out at higher mileages is the brake band rather than the valve that actuates it but I'm only guessing, as you say it sounds like a job for an expert.

I've collected dozens of service manuals from the Internet in the ten years I've had my car, they pop up all over the place and I squirrel them away.
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MikeJak
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Location: Herts

PostPosted: Tue Jun 21, 2022 7:14    Post subject: Reply with quote

Thanks for checking the manual again, really appreciated.
Still not sure if that could be the issue as a worn brake apparently would give some slip and noise or difficultly in engagement/jolty changes… weird thing all changes of gear up and down are really smooth. Will chat to the mechanic next week and pick his brain and see if there is a reliable auto specialist local.
I’m still not 100% convinced is gear box related…but hey…what do I know 🤣
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modvrs
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Location: Southampton

PostPosted: Thu Jun 23, 2022 9:17    Post subject: Reply with quote

I'm wondering if it was an error on the transmission rebuild, maybe a spring was left out or the wrong spring inserted. It will be interesting to see what the experts say.
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1997 Toyota Land Cruiser Colorado 3.4VX
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MikeJak
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Joined: 28 Mar 2022
Posts: 71
Location: Herts

PostPosted: Thu Jun 23, 2022 16:07    Post subject: Reply with quote

It did cross my mind too… not a vital function if you use the truck as a mall crawler…
I have the invoice to the previous owner for the full rebuild (2500£ !!) and I will contact the trans specialist that did it but doubt they’ll have any details 2years down the line… next Tuesday I am seeing my mechanic for fitting the lift kit and will pick his brain…
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