Jump to content
If you value this forum's future please support us
CraigM

Transmission shudder.....

Recommended Posts

Help please, guys. My son has got a 91 LR 3.9v8 auto which has developed a bad shudder. It only happens on take-off. Feels like a clutch slipping. If I pull away really gently, it doesn't do it, but if I pull off normally it shudders like hell. 

I'm afraid I'm a bit lost. Anyone got any ideas? 

Share this post


Link to post
Share on other sites

It could be the transmission brake not releasing fully ? does shudder or clunk when coming to a stop ? Also does it then change up/down through 2/3/4 cleanly?

What does the oil on the autobox dipstick smell like ?

cheers

 

Steve b

Share this post


Link to post
Share on other sites

Thanks Steve b. Firstly, I should have said it was an RRC. Secondly, I drove it home from work tonight carefully and it's pretty bad. Finally It lost "D"  - just revved like it had slipped out of gear, but it ran in 3, 2 and 1. So definitely transmission, but not sure what...

Share this post


Link to post
Share on other sites

It could be the chain jumping , or maybe the viscous diff locking , but first check the auto box oil level , warmed up and in park , ticking over ,having been shuttled between D & R . The symptoms suggest oil issues , level and/or quality or possibly a blocked  pickup filter

 

Steve b

Share this post


Link to post
Share on other sites

Most auto box problems are down to the oil.

First try topping up.  If that doesn't help, change the filter (take the sump off to find the filter) and the oil.

My guess at the cause of the shuddering is the band brakes (the equivalent of clutches) slipping.  This usually happens (initially) due to low hydraulic pressure due to low oil or blocked filter.  You need to fix it quickly as the slipping heats the oil up to the point of burning (going black / dark brown) and damaging the friction surfaces permanently.

Si

Share this post


Link to post
Share on other sites

Possibly a torque converter issue, especially if it does it in higher gears.  Slipping clutch packs would cause the same problem, but I find it unlikely that they'd all fail at the same time (I believe there are three packs in a ZF 4 speed with reverse).  Replacing the torque converter is cheaper than rebuilding the box, so would be a good start point if replacing the fluid and filter (filters are rarely replaced by most garages) doesn't sort it.

 

There are some very good videos on youtube explaining how TCs and autos work, so you'd see how worn clutch packs would cause this.  They are the Achilles heel of the auto transmission, but also (with the TC) the reason why you can't shock and overload an auto...

Share this post


Link to post
Share on other sites

On it's own, a vibration could be the flex plate on the torque converter has cracked.  It's not uncommon and I think Ashcroft's now make a spring steel one as an upgrade.

 

As a warning, if an old autobox suddenly get some TLC in the form of new oil, the detergent in the new oil lifts ingrained dirt and carries it to the governor, which acts like a centrifuge.  It's again not uncommon for this to result in a gearbox failure, such as sticking in second for example, as the governor sticks.

 

So if the box is suffering neglect I'd suggest a couple of changes of oil over the coming weeks, drop the oil without staring the engine too as the muck will settle in the sump.

Share this post


Link to post
Share on other sites

It's the sprag clutch.  Common enough that Ashcroft redesigned them for their own units and gives the exact symptoms you describe - slipping in D but fine in 1, 2 and 3.

Share this post


Link to post
Share on other sites
Posted (edited)

From Ashcroft's website:

Q. I have a 4sp ZF, when I select "D" the vehicle won't move, when I select "1" the vehicle moves off. I can then select "D" and continue to drive normally. If I stop I have to start in first again. Why?

 A. A sprag clutch has "inverted" and will need replacing. No further damage will occur if you continue to drive but you will need to select "1" every time to start moving. A rebuild is required to correct this.

http://www.ashcroft-transmissions.co.uk/frequently-asked-questions/4hp22-faq-s.html

Edited by paintman

Share this post


Link to post
Share on other sites

Create an account or sign in to comment

You need to be a member in order to leave a comment

Create an account

Sign up for a new account in our community. It's easy!

Register a new account

Sign in

Already have an account? Sign in here.

Sign In Now




×