4HP22 post mortem ...Dr Ashcroft to pass judgement please..

[justinC]

I finally got round to dropping the pan on the 4HP22, and found most of the clutches and possibly even lock up clutch material in the bottom of it..

There was even fairly big material particles in there, we're talking gritty sort of plate crumbs etc. Thats clutch plate, not dinner plate.

I'm off to pick up the '84 RR I bought on Sunday. I'll slot the LT95 in and get it back on the road.

A question for ' DR' Dave Ashcroft if you are reading this:

Dave, As you may have read in previous posts, I have had no luck with getting a 4HP22 to last behind my 3.9 4 cylinder Isuzu diesel, which is turboed and intercooled and conservatively putting out about 400Nm of torque, at about 2000rpm. The torsional vibration from this engine is huge - at idle, the dash shakes and the tyres on the vehicle vibrate. I have had 2 identical trans failures to date, and one snapping/ destruction of a sprag due to too much boost and right foot. I have reached the conclusion that the engine is going to keep vibrating these autos to bits, and I'm better off with a manual box like the LT95 which appears behind these engines in our military Landies. I want to keep the autobox eventually though, and I'm looking at the Allison AT540 which was designed for a diesel motor in the first place. I guess my question to you is do you think I'm barking up the wrong tree, or is the vibration issue a possible cause?
Thanks, JC

[Maggot4x4]

Hi JC,

I don't know if this is possible or would even help but just an idea, what about a second set of engine mounts? May help reduce the vibration.


The other thing I have done recently is raise the idle a little bit as I have a problem with bolts on the motor becoming loose regulary.

Just a thought.

[justinC]

Hi Ash,

Yeah, have tried the idle trick, but apart from having no brakes at the bottom of hills when in low range, when you select drive, the converter drops the RPM anyway, and loads the box up. I don't know whether the low stall converter made things worse, but I'd say it didn't help.

JC

["CANADA"]

Hi JC,

I don't know if this is possible or would even help but just an idea, what about a second set of engine mounts? May help reduce the vibration.


The other thing I have done recently is raise the idle a little bit as I have a problem with bolts on the motor becoming loose regulary.

Just a thought.

raising the idle on mine about 100 rpm has stoped alot of the massive vibrator effect

[up2nogood]

Engine mounts from Mercedes cars are excellent vibration dampers as well. Much more impressive than LR ones.

And are about $75.00 each. Just replaced a set in the wifes '89 300E.

Just a thought.

[ashtrans]

I have had 2 identical trans failures to date, and one snapping/ destruction of a sprag due to too much boost and right foot. Thanks, JC

were both failures due to one of the one way clutches failing ?

if so do you know if it was the rear one way clutch or the 'C1/C2' ?

if the rear one, you can fit the larger diameter 4HP24 one and we 're-cam' them to make them even stronger, from our web site :

A common problem with all ZF 4HP22/24 boxes is the failure of the one way "sprag" clutch. Once the cams in this one way sprag clutch "flip" the unit will slip both ways resulting in the vehicle only pulling off with the shifter in position "1" not "D" and driving OK when shifted up to position 2,3 and D until you stop then you need to pull it back to "1" to start off again. It is not feasible to change this unit in each rebuild as this one part is approx £ 400. By disassembling the "sealed unit" we were able to examine the profile of the cams and understand how they work, from here the challenge was to find another cam from another type of autobox that would fit and had the correct profile to make the unit stronger by not allowing the cams to flip. After quite a lot of searching we found one, "re-cammed" some of these clutches and thoroughly tested them, we have not had one fail since. This is an example of how we are able to use our engineering background to understand a problem and cost effectively make the unit stronger without having to raise our prices.

if the problem is the C1/C2 you can fit the larger, much stronger one as part of the 4HP24 upgraded internals, the 22 ones fail all the time, I have not seen a 24 one fail,

I have no experience with the Allison trans. I don't think fitting would be easy.

[Bush65]

Changing engine mounts can reduce the movement of the engine and transmission due to torque reaction. This may have some affect on the reliability of the transmission. Radius arm bushes make the best engine mounts IMHO.

IMHO, the main cause of transmission problems with the 4BD1 and 4BD1-T, is torsional vibration combined with the high torque at low revs. This can different to the movement due to torque reaction and is mainly a result of the characteristics of the torque pulses from a large 4 cylinder diesel engine.

Torsional vibrations are difficult to deal with. The vibration damper pulley on the front of the crankshaft is one way to reduce the torsional vibrations. If the rubber element in the pulley has deteriorated, it could result in failure of the crankshaft or drive train.

The 4BD1 is known to be severe on stock LT85 gearboxes. Maxi-drive has modifications for the LT85 as a result, but they still fail.

[justinC]

Thanks for your reply David.
Only one failure was the result of a rear sprag failure, and was my fault as I was trying too hard with 15 psi and heaps of fuelling. At this point the vehicle was able to spin one front tyre from stand still...And Idiot was holding it with the brakes on to get a pyrometer reading! Snap.

The other two were identical in their symptoms. There was a shuddering lack of drive and intermittent complete loss of reverse. In any gear, 1,2,3 or drive the shudder was the same Finally no drive at all and heaps of buzzing cavitation type of sounds.
When the pan was removed, it looked like several clutches worth of friction material were in the bottom of the pan, and large bits were evident too. Funnily enough, the symptoms were quite sudden. I drove the car to work in the morning with no symptoms at all. Several hours later, I got in the vehicle to go to town, and on the highway there was no lockup clutch operation. Then by the time I had turned around and got back to work there was almost no drive.
It happened quite quickly.
LT95 goes in this week, and the quest for possible LT230 adaption to a Allison AT540 begins. I require utmost reliability, or it'll be staying manual.

JC

[justinC]

Hi John,

Yes, the crankshaft generated torque forces/ pulses are immense, and the LT85 that originally came with this motor had had a few mods and was on its second rebuild. I'm picking the LT95 as a replacement for its simplicity and ease of repair, although I'll be trying to source a taper roller transfer kit for it if it stays in there.

I REALLY want an auto trans behind this motor, as it really performs under boost in sand and up hills, but you can use all that torque idling around in low rtange all day. Also saves the coarse axles and standard CV's from destruction(!)

I'm hopiing the AT540 will be suitable, as they are an isuzu fitment, and even though they are only fitted to 6 cyl engines, the vibrations from them can be pretty huge too.

The bellhousing bolt flange looks OK so far, its just a problem fitting the LT230 to the back of them properly, as there is very little to mount an adapter to.


Thanks for your reply.

JC