Lucas transmission fix fluid in A750F tranny? (1 Viewer)

[chrisbruck]

Has anyone used the Lucas Transmission Fix additive in their A750F tranny ('03 / newer 5 spd)?

Good, bad, no difference???

I'm chasing an intermittent downshift clunk from 3rd to 2nd (I think). Upshifts are smooth, usual downshifts smooth, manual shifting smooth. Just have this pesky harsh clunk at times.

Had a major fluid leak, replaced one of the solenoids / tranny filter and WS fluid is full at the proper level. Didn't have any issues before. Tempted to add a bottle of the Lucas and see what happens but I don't want to make anything worse.

 

[94SRUNNER]

No comment in regards to the Lucas treatment.

Have you looked at some of the other sources of the clunk (CVs/flanges, diff bushings, etc...), which are well documented here on the forum?

 

[OregonLC]

I seem to remember from years ago someone had a shift issue when braking and it was due to low fluid level that sloshed forward and starved the pump. I'm sure you're good on this, but just to confirm the WS fluid level was filled to overflow with engine running and at the prescribed temps?

 

[Mike NXP]

Has anyone used the Lucas Transmission Fix additive in their A750F tranny ('03 / newer 5 spd)?

Good, bad, no difference???

I'm chasing an intermittent downshift clunk from 3rd to 2nd (I think). Upshifts are smooth, usual downshifts smooth, manual shifting smooth. Just have this pesky harsh clunk at times.

Had a major fluid leak, replaced one of the solenoids / tranny filter and WS fluid is full at the proper level. Didn't have any issues before. Tempted to add a bottle of the Lucas and see what happens but I don't want to make anything worse.

Where and how did that leak start?

Who repaired it and topped off the fluid?

Review the FSM and make sure you are checking it at the proper temperature / procedure. If you check your fluid with the proper procedure, it looks clean and is up to level then this isn't your transmission failing.


Typically when you are slowing down and feel the lower end of things clunk then your driveshaft needs a good greasing, specifically on the slip joints. If I were you I wouldn't use any additive in the transmission at this point.

 

[NE Snowman]

Where and how did that leak start?

Who repaired it and topped off the fluid?

Review the FSM and make sure you are checking it at the proper temperature / procedure. If you check your fluid with the proper procedure, it looks clean and is up to level then this isn't your transmission failing.


Typically when you are slowing down and feel the lower end of things clunk then your driveshaft needs a good greasing, specifically on the slip joints. If I were you I wouldn't use any additive in the transmission at this point.

First place I would start is checking fluid level via FSM specs than I’d move to the driveshaft, common clunking problem. Check other rubber while you’re under the 100.

 

[Mike NXP]

First place I would start would be the driveshaft, common clunking problem. Check other rubber while you’re under the 100.

That was my thought as well. But the problem didn't exist for OP until there was work done on the transmission.

I'd be more curious as to what failed and why , who fixed it, and if the fluid was topped off properly.

Few shots of grease in the DS should be done anyway just to help troubleshoot

 

[NE Snowman]

That was my thought as well. But the problem didn't exist for OP until there was work done on the transmission.

I'd be more curious as to what failed and why , who fixed it, and if the fluid was topped off properly.

Few shots of grease in the DS should be done anyway just to help troubleshoot

Yeah just edited my post I didn’t catch the fluid problem at first

 

[chrisbruck]

It's definitely a shifting issue and not the driveshafts. The lower transmission cooler hose popped loose and got cut by the fan resulting in a major leak and the tranny to quit working. Dealer fixed the hose and refilled with WS fluid. Later started throwing P2714 code and I replaced the offending solenoid, transmission filter and refilled. I followed the FSM and updated TSB's on the proper temperature to check it. Confident the tranny is filled properly.

It's only the 3 -> 2 downshift, typically when cruising along between 20-40 and then reach a hill where it needs to downshift. Then the harsh shift or clunk as I call it may occur.

Just curious if the Lucas product may help this harsh shifting out.

 

[Rhetoric]

Honestly given your situation why not try? Nobody will be able to tell you as that's a very unique use case.

Report back here once you give it a shot so the loop can be closed.

 

[OregonLC]

Dang. Note to self to replace that last trans cooler hose.

 

[Mike NXP]

It's definitely a shifting issue and not the driveshafts. The lower transmission cooler hose popped loose and got cut by the fan resulting in a major leak and the tranny to quit working. Dealer fixed the hose and refilled with WS fluid. Later started throwing P2714 code and I replaced the offending solenoid, transmission filter and refilled. I followed the FSM and updated TSB's on the proper temperature to check it. Confident the tranny is filled properly.

It's only the 3 -> 2 downshift, typically when cruising along between 20-40 and then reach a hill where it needs to downshift. Then the harsh shift or clunk as I call it may occur.

Just curious if the Lucas product may help this harsh shifting out.

Bummer, did the hose just come loose. Yeah gotta check mine now =]
This is a doozie, maybe it is worth a try? I prefer seafoam products but I'm not really basing that on much. I just like the fuel and hydraulic addative. The trans tune is worth looking into.

Hopefully someone with more knowledge on these transmissions can chime in on these symptoms.

 

[NE Snowman]

I know the T4R guys use the Lucas stop on the v8 4Rs for the rumble strip feeling, certain grades and the right speed make the truck feel like it’s going over rumble strips. I don’t think you anything to lose at this point.

Failures like this are my biggest fear, depending on your drive you won’t notice and when you do it’s too late.

 

[sunfic]

Has anyone used the Lucas Transmission Fix additive in their A750F tranny ('03 / newer 5 spd)?

Good, bad, no difference???

I'm chasing an intermittent downshift clunk from 3rd to 2nd (I think). Upshifts are smooth, usual downshifts smooth, manual shifting smooth. Just have this pesky harsh clunk at times.

Had a major fluid leak, replaced one of the solenoids / tranny filter and WS fluid is full at the proper level. Didn't have any issues before. Tempted to add a bottle of the Lucas and see what happens but I don't want to make anything worse.

When you say proper level, did you use the temperature in FSM? you should use lower temperature based on these TSB. in other word, add in more fluid.

 

[chrisbruck]

Yup, once it got close to 100 deg I checked the overflow tube and let a little out.

 

[YotaWagon]

Yup, once it got close to 100 deg I checked the overflow tube and let a little out.

Did you ever try out the Lucas product? I'm curious how it turned out.

 

[chrisbruck]

Did you ever try out the Lucas product? I'm curious how it turned out.

I did... have probably a couple thousand miles on it now... did it work???

Can't say for sure. It seems to be a little better. Could just be all in my head and I may have adjusted how I drive since I can tell pretty much when it would do the harsh downshift.

It certainly didn't harm anything and frankly I wouldn't mind adding another bottle next time I drain some fluid.