42RH advice needed

-
H

Headintheclouds

Well-Known Member
Joined
Dec 27, 2021
Messages
83
Reaction score
30
Location
UK
I have finally installed a 42RH in place of my 727 and all seems well when driven in traffic at moderate throttle. Driving at about 50MPH I tried kickdown. It seemed to shift down but the engine revved very high without the anticipated surge forward - so much so that I was worried about the engine.
This morning after driving for a few miles to warm it up I tried a full throttle standing start. Again i saw crazy high revs without much forward motion and I took my foot off the accelerator immediately, but it took a second or two for the revs to drop.
As both transmission and torque converter are unknown to me I don't know whether to investigate transmission adjustment or if I have an issue with the torque converter.
Please can someone suggest what checks I can make to find out what's going wrong?
 
How's the fluid look/smell? Adjusting the kickdown band might help but usually if it's slipping that badly it's to late....

Rear clutch is applied in all forward gears, if it were slipping you should notice it in high gear... OD direct clutch is backed up by the OD sprag so I doubt that's giving you a problem...

Try adjusting the front band & don't expect much...
 
Most of the fluid was drained for shipping before i got it but it didn't look too bad. It has new fluid in it now.
What is most likely to be worn out?
 
Headintheclouds said:
Most of the fluid was drained for shipping before i got it but it didn't look too bad. It has new fluid in it now.
What is most likely to be worn out?
Click to expand...

If the trans did what you described with the new fluid it would smell like a forest fire.
Drop the pan and post a couple of pics.
That will tell a lot.

Sounds like a burnt forward clutch to me, and possibly the front band.
 
What's the new fluid look/smell like? If it's slipping bad it could already be burnt...
What are you using for kickdown linkage? Try adding pressure...
 
Thank you for the speedy and helpful replies. It did smell a bit...
Kickdown linkage is rod all the way. Is it possible that this wasn't adjusted right when the transmission was installed and has caused the issue or more likely that the transmission was tired as purchased? The car has been driven less than 100 miles since it was installed. I got a very good deal on it so I was expecting to have to do a rebuild.
I was hoping to run the transmission as is to test overdrive and lockup operation before a rebuild but it's looking as if it might not last too long. It will be a week or two before I can get it in the workshop and wire up the switches as there is another project in there I'm doing with my son. Nearly finished with that one - just need to fit seat belts. Starting from scratch as it's from 1959 and doesn't have any mounts for them.
 
TrailBeast said:
If the trans did what you described with the new fluid it would smell like a forest fire.
Drop the pan and post a couple of pics.
That will tell a lot.

Sounds like a burnt forward clutch to me, and possibly the front band.
Click to expand...
Forward clutch is applied in high gear... Not first or second.... If you apply the forward clutch & the front band at the same time bad things happen....

Try increasing the length of the kickdown rod 8MM...
 
1WildRT said:
Forward clutch is applied in high gear... Not first or second.... If you apply the forward clutch & the front band at the same time bad things happen....

Try increasing the length of the kickdown rod 8MM...
Click to expand...

He says the engine revs but the car doesn’t seem to accelerate.
It’s either slipping or the converter is trashed.
Either way it warrants a pan drop as an inspection.
 
1WildRT said:
Forward clutch is applied in high gear... Not first or second.... If you apply the forward clutch & the front band at the same time bad things happen....

Try increasing the length of the kickdown rod 8 mm
Click to expand...
The forward clutch is applied in all forward gears. The direct clutch is applied in high gear and reverse gear. Kim
 
Last edited:
What am I looking for when I drop the pan? I replaced the pan with a deeper aluminium unit when the transmission was installed less than 100 miles ago. I replaced the filter and fitted the Sonnax valves that allow the TC to fill in Park.
Remaining fluid in the trans when I got it was dark red not brown and no significant amounts of friction material in the pan. Also not much metal on the magnet.
 
Sounds good to me! I would call light "sediment" normal. If that makes sense.
 
I can’t help you much with the diagnosis part, but if you determine it’s time for a rebuild, I found the following information helped me.

I ordered the how to rebuild your 904 and 727 book by Tom Hand. Lots of good information on the forward part of the Transmission.

As recommended by some folks here, this video was good to watch. He is rebuilding the larger 518/46RE, But they are similar, and the same processes. Overdrive portion is identical.



This guy is working on a 42 Rh, but watch through it first Because he makes a few slip ups and hast to go back and redo things. Not major, but it might save you some time.


Measuring the overdrive unit was confusing to me until I watched this guy’s video
 
Last edited:
Headintheclouds said:
What am I looking for when I drop the pan? I replaced the pan with a deeper aluminium unit when the transmission was installed less than 100 miles ago. I replaced the filter and fitted the Sonnax valves that allow the TC to fill in Park.
Remaining fluid in the trans when I got it was dark red not brown and no significant amounts of friction material in the pan. Also not much metal on the magnet.
Click to expand...

From the sounds of what you described something should be fairly obvious.

Or, maybe a better description is in order.
 
@67Dart273 is the one that sent me the link for the 42RE class video, Thanks to him & that video-gave me the confidence to tackle my transmission. Just now getting it back on the road because of other unrelated family medical issues.

I bought a small shop press at Northern Tool for this project since I've occasionally had need for one anyway. Using this would come with the warning I also got in my thread from @rbkt65 "Front half of the trans is similar to 904. Back half is where you will need the special tools. Grab a fsm for 92 up truck and look at it. DO NOT ATTEMPT TO REMOVE SPRING, IN THE OVERDRIVE UNIT, WITHOUT SPECIAL TOOLS. IT IS UNDER 800 PLUS LBS OF TENSION. YOU COULD HURT YOURSELF. If the overdrive clutches are burnt up, the od unit WILL HAVE TO COME APART. As said above, there are upgrades that can be incorporated into the rebuild. Also, there are rebuild od units on internet fairly reasonable."
 
Make sure your kick down linkage is correct before you tear anything apart. That is cheap to free. Make sure your kick down arm ss all the way back when the carb is all the way open. There are lots of great comments here, but chech the cheap/free stuff first.

Cley
 
Headintheclouds said:
What am I looking for when I drop the pan? I replaced the pan with a deeper aluminium unit when the transmission was installed less than 100 miles ago. I replaced the filter and fitted the Sonnax valves that allow the TC to fill in Park.
Remaining fluid in the trans when I got it was dark red not brown and no significant amounts of friction material in the pan. Also not much metal on the magnet.
Click to expand...
The Sonax valves may not have been installed properly or were defective. Show us some pics and the instructions. I assume u changed the manual valve and what else? Kim
 
What is called the "forward" clutch isn't the front most one as mounted in the trans, that would be the high,/reverse. The "forward" clutch which is engaged in all forward driving gears is actually the rearward mounted one in position within the case. There are 2 clutch packs in that overdrive unit, I believe one is engaged all the time you're moving forward as well. I know that if one of the clutch paying the OD is bad you won't have reverse.
 
Approaching retirement with way too many projects part done so I paid a garage to change out the transmission. The mechanics seem really switched on and made a very good job of the linkage. I think they compared kick down actuating arms from 727 and 42RH and chose the better option. I need to make sure the end stops match WOT and idle on the carb.
I supplied the Sonnax instructions with the valves so I hope they got that right.
These were Manual valve 22771-09 and Pressure Regulator valve 22771A02K. I had a quick look at the instructions and it looked pretty straightforward so I would be surprised if they got it wrong.
 
I managed to get the car in the workshop for a few minutes today. It looks as though the kickdown operating arm is very slightly longer than I need for this application. With the throttle closed the kickdown lever is about 1/8" back from fully forward and at WOT the lever could still travel another 1/4". Would that be enough to cause the slip?

I drained a bit of fluid from the transmission and it looks a good red colour. I can't smell any cooking smells.
 
The lever is about 2" from centre of shaft to where it joins to kickdown rod.

Idle.jpg


WOT.jpg
 
Update on my issue. I had done all my checks underneath the car with it in Park. When I moved the selector to the other end of its travel the problem became clear. The kickdown arm was fouling the gear selector. With the selector in Drive - or worse, second, and the throttle pushed hard down, the kickdown was just able to push the gear into neutral.
As far as I can tell no harm done. The gear selector arm has now been bent down and now all linkages seem to play happily together.
When I started to bend the gear operating arm I did it cold. This was a mistake as it started to crack. A brief application of the welding torch followed and now all is well.
 
Headintheclouds said:
Update on my issue. I had done all my checks underneath the car with it in Park. When I moved the selector to the other end of its travel the problem became clear. The kickdown arm was fouling the gear selector. With the selector in Drive - or worse, second, and the throttle pushed hard down, the kickdown was just able to push the gear into neutral.
As far as I can tell no harm done. The gear selector arm has now been bent down and now all linkages seem to play happily together.
When I started to bend the gear operating arm I did it cold. This was a mistake as it started to crack. A brief application of the welding torch followed and now all is well.
Click to expand...

good thing you found that before taking it all apart :) hope it's working good now
 
I think I am on the home straight with my upgrade from 727 to 42RH but could still use a little advice. Overdrive seems to be working fine but I'm not sure about lockup. All seems pretty smooth with no juddering.

I have separate relays for overdrive and lockup operation through pressure and vacuum switches. I have wired indicator lights up so that I can tell when these are grounding the two circuits as I found that delay in operation was making it difficult to set the pressures.

Part of the problem is that I haven't driven a vehicle with one of these transmissions so I don't know what to expect.

I see a significant drop in revs when overdrive comes on but not when the lockup light comes on. Are there any simple checks I should run with the car at rest? Should I be able to hear the LU solenoid click if I ground the rear wire with the car on the ramp? Anything else I should look for?

Also, when speed drops enough for overdrive to disengage and I'm on light throttle I don't see any drop in revs but next time I put my foot on the gas the revs pick back up so it's obvious overdrive has disengaged at this point. Is this normal? I am used to old manual transmissions with Laycock overdrives that jump out as soon as the power is removed from the solenoid.

How long should it take from grounding the overdrive solenoid to overdrive coming in and should it come in with a positive clunk or a smooth flow?

Thank you for your help.
 
You must log in or register to reply here.
-

Back
Top