Rebuilt 700r4 lost reverse

[UKSquarebody]

Evening all,

I am after your thoughts on this please.
I have a 700r4 in my 87 long bed (with 350 motor).
I have had it rebuilt early this year.
Got it on the road two months back.
It drove great as a daily truck for 3 weeks. Engaged all gears fine, no delay in engaging, no slipping - all good.
Then, it lost reverse.
No warning - it just went.
The firm that rebuilt it took it back under warranty.
They have stripped it, and - after 5 weeks(!), told me the reason reverse failed is that it was 1ltr short on fluid, which has cooked something to do with reverse.

I am struggling to get my head around that.
In 25 years of running lots of cars, low fluid has always resulted in slipping between gears, slow to engage, scavenging pump etc.
There was no oil leak - and I put 11ltrs of fluid in when I reinstalled the trans.

Do you reckon they are trying to shift blame and get out of standing by the warranty?!

Chers,
Keith

 

[Vbb199]

Did it have low/first gear

 

[NickTransmissions]

Evening all,

I am after your thoughts on this please.
I have a 700r4 in my 87 long bed (with 350 motor).
I have had it rebuilt early this year.
Got it on the road two months back.
It drove great as a daily truck for 3 weeks. Engaged all gears fine, no delay in engaging, no slipping - all good.
Then, it lost reverse.
No warning - it just went.
The firm that rebuilt it took it back under warranty.
They have stripped it, and - after 5 weeks(!), told me the reason reverse failed is that it was 1ltr short on fluid, which has cooked something to do with reverse.

I am struggling to get my head around that.
In 25 years of running lots of cars, low fluid has always resulted in slipping between gears, slow to engage, scavenging pump etc.
There was no oil leak - and I put 11ltrs of fluid in when I reinstalled the trans.

Do you reckon they are trying to shift blame and get out of standing by the warranty?!

Chers,
Keith

Hi Keith, one liter low may or may not have burnt the low reverse and/or reverse input clutch pack but I have my doubts as I've owned several vehicles over the years equipped with 700r4s and 4L60Es and have, on occasion, been that low with no discernable impact to any of the applied elements inside the case (occasional harsh shifts / engagement typically accompany a mild low-fluid condition).

Loss of reverse can be caused by one or more of the following:

- Low fluid or severely overfilled system
- Incorrect throttle valve cable adjustment and/or incorrect TV geometry (bracket-cable relationship is flawed)
- Worn filter pick up seal and/or partially clogged filter
- Worn valve body (wear in the manual valve bore at the reverse position)
- Worn pump assembly/pr valve/reverse boost valve and sleeve - this will result in delayed, soft engagements into reverse
- Torn/lacerated low-reverse piston machine cut rubber seals - there's three of them and the middle one is usually the one rebuilders nick up due to insufficient assembly lube or failing to get the piston square in the bore before tapping it into position
- Incorrect low-reverse clutch pack clearance - many 700r4s and some 4L60Es have 'selective' steels which are thicker than the standard flat steels that go into that clutch pack - if that steel isn't installed, clearance in the pack can be excessive
- Failure to tighten and torque the auxiliary valve body-to-case bolts to spec (95 inch lbs) - this will create a massive cross leak out of the reverse circuit and usually presents immediately upon engaging reverse for the first time since installing the transmission and filling it w/fluid
- Torn pump stator shaft teflon sealing rings - these seal off the reverse input clutch apply circuit and fluid lost here will burn the reverse input clutch (I have only seen this a handful of times in my 15 years of rebuilding these transmissions)

Next Steps:
- If you haven't pulled the trans out already, perform a line pressure test to ensure your line pressures at idle-minimum TV and full TV (you pulling on the cable itself) are within spec, especially for reverse
- If the pressures are within spec, drop the pan and see if the aux valve body bolts are loose - film this so that you have evidence the bolts being loose, which would be a workmanship error on the part of the builder
- If everything is tight and nothing obvious is amiss, contact the builder and make arrangements to bring it back under warranty

 

[UKSquarebody]

Did it have low/first gear

Yes. Perfectly. Smooth engagement, no lag

 

[UKSquarebody]

Hi Keith, one liter low may or may not have burnt the low reverse and/or reverse input clutch pack but I have my doubts as I've owned several vehicles over the years equipped with 700r4s and 4L60Es and have, on occasion, been that low with no discernable impact to any of the applied elements inside the case (occasional harsh shifts / engagement typically accompany a mild low-fluid condition).

Loss of reverse can be caused by one or more of the following:

- Low fluid or severely overfilled system
- Incorrect throttle valve cable adjustment and/or incorrect TV geometry (bracket-cable relationship is flawed)
- Worn filter pick up seal and/or partially clogged filter
- Worn valve body (wear in the manual valve bore at the reverse position)
- Worn pump assembly/pr valve/reverse boost valve and sleeve - this will result in delayed, soft engagements into reverse
- Torn/lacerated low-reverse piston machine cut rubber seals - there's three of them and the middle one is usually the one rebuilders nick up due to insufficient assembly lube or failing to get the piston square in the bore before tapping it into position
- Incorrect low-reverse clutch pack clearance - many 700r4s and some 4L60Es have 'selective' steels which are thicker than the standard flat steels that go into that clutch pack - if that steel isn't installed, clearance in the pack can be excessive
- Failure to tighten and torque the auxiliary valve body-to-case bolts to spec (95 inch lbs) - this will create a massive cross leak out of the reverse circuit and usually presents immediately upon engaging reverse for the first time since installing the transmission and filling it w/fluid
- Torn pump stator shaft teflon sealing rings - these seal off the reverse input clutch apply circuit and fluid lost here will burn the reverse input clutch (I have only seen this a handful of times in my 15 years of rebuilding these transmissions)

Next Steps:
- If you haven't pulled the trans out already, perform a line pressure test to ensure your line pressures at idle-minimum TV and full TV (you pulling on the cable itself) are within spec, especially for reverse
- If the pressures are within spec, drop the pan and see if the aux valve body bolts are loose - film this so that you have evidence the bolts being loose, which would be a workmanship error on the part of the builder
- If everything is tight and nothing obvious is amiss, contact the builder and make arrangements to bring it back under warranty

Thanks Nick,
I took it back to the builders and they have stripped it and apparently fixed it.
They want to ‘chat’ tomorrow as they have decided it failed as it was a litre short on fluid.
I was told 3 weeks ago it was stripped on the bench. Then, two different people reported seeing my truck on the road 2 weeks ago (C10’s are not common around here!).
It all feels a little suspect to me. If it was being Road tested 2 weeks ago - what’s been happening since?!