Took the engine apart, now no reverse

[dieseldave71]

I have an '87 GN that suddenly won't go into reverse. It worked fine the last time I drove the car a few months ago before taking the engine apart to replace a piston. Now it's back together and running but it won't back up. I can feel a slight bump when reverse is selected, and the wheels will spin if the car is jacked up but there's not enough power to make it move. I had the engine oil pan and the driver side head off to replace the offending piston, but I can't imagine how that could have afffected reverse gear in the trans? The car was on jackstands- front end only- for a couple of months while it was apart, and a friend suggested that maybe an o ring or seal dried out in the trans? A long shot, to me, but then again I have no explanation at all... Anyone have any ideas about what the trouble is and how to fix it?

 

[1985WH1]

dumb idea but check the trans oil level, than can leak when sidding due to the converter draining and over filling the pan, if the fluid is now too low it might not engage reverse

 

[dieseldave71]

dumb idea but check the trans oil level, than can leak when sidding due to the converter draining and over filling the pan, if the fluid is now too low it might not engage reverse

That was the first thing I thought of, too- that maybe sitting tilted back it had lost some trans oil- but it's full of nice clean oil, unfortunately. Wish it was that simple! I picked up a pan gasket and filter for the trans, I'll pull it this week and see if I see anything. Anything in particular I should be looking at, or are there any tests I can perform? I'm wondering if maybe a check valve or something got stuck? I refuse to believe that my trans blew up while the car was sitting with it's engine apart

 

[SSedan64]

TV Cable adjustment, Manual Shift Linkage, Throttle Valve Binding, Reverse Boost Valve are easy to check with pan off.

 

[DR BOOST]

check the linkage on the steering column and tv cable

 

[justin84]

Fluid is my first guess. T.V cable close second because it had to be tampered with but more would be wrong if it we're in fact the T.V cable....by that I mean you would notice RPM spikes and delayed shift or so on on on

 

[dieseldave71]

TV Cable adjustment, Manual Shift Linkage, Throttle Valve Binding, Reverse Boost Valve are easy to check with pan off.

How do I go about checking the above? Is there a thread here somewhere or a manual that I could get that would give me a more or less step-by-step process? I'm not a transmission guy, that's for sure.

Thanks everyone for your help so far!

 

[SSedan64]

TV cable connects to Throttle Body & left side of Trans.>> http://www.tciauto.com/Products/Instructions/instructions/gm_tv_cable_adjust.htm
Throttle Valve is in the Trans Valve Body on passenger side of Trans.
Reverse Boost Valve is in bottom of Pump on driver side of Trans.
An ATSG Manual or Chris @CKPerformance has a Manual also.
Shows TV/ThrottleValve location>> Sonnax Transmission, Torque Converter, Performance, Driveline Parts :: Transmission :: 65754-03K :: Part Summary TV is behind spring in Valve Body, plunger can also bind.
Shows TV Boost Valve>> Sonnax Transmission, Torque Converter, Performance, Driveline Parts :: Transmission :: 77917-04K :: Part Summary & Reverse Boost Valve>> Sonnax Transmission, Torque Converter, Performance, Driveline Parts :: Transmission :: K77898A :: Part Summary there's an instruction link on pages that shows a little more.
CK's Manual etc..>> www.CKPerformance.com
Todd

 

[dieseldave71]

Todd, Thanks for all the info! Very helpful, at least I now know what I'm looking at.

I have the trans pan down now. It was full of fluid, trust me The TV cable is connected and moves with the throttle. I take it that the valve body has to come down to check the throttle valve and the boost valve?

 

[SSedan64]

The TV Boost Valve and Reverse Boost Valve are in the Pump. These can be removed & checked. Have to remove the snap ring.
The Throttle Valve in the Valve Body can't be removed without dropping the Valve Body.
Maybe it will be something easy to fix.
You're Welcome,
Todd

 

[WE4]

My take...

It is not boost valves.
Fluid level could definitely be possible. TV cable, NO way. It would still engage and back up . Are you SURE you got the converter in all the way? If not, pump may be the issue. Are all the other gears fine or just reverse. That is the magical questiion....

Are They?
Then if so we move on to step 2... If not, your issue is fluid level or converter/pump rotor related.
I would also run a pressure test just to see what it is doing.


Bruce
WE4
Performance Transmission Services

 

[dieseldave71]

It is not boost valves.
Fluid level could definitely be possible. TV cable, NO way. It would still engage and back up . Are you SURE you got the converter in all the way? If not, pump may be the issue. Are all the other gears fine or just reverse. That is the magical questiion....

Are They?
Then if so we move on to step 2... If not, your issue is fluid level or converter/pump rotor related.
I would also run a pressure test just to see what it is doing.


Bruce
WE4
Performance Transmission Services

Bruce, Here's the situation in a nutshell: The car needed a piston but still ran, so I backed it out of where it was sitting (it went right into reverse and backed out no problem) and drove it into the shop. The weekend before that I had it out to a local cruise night and it shifted fine, both forward and reverse. So, I drive it into the shop, jack it up, pull the oil pan (engine oil pan, not the trans) and driver side head, replace #3 piston, and button it back up. At no time did I have the engine, trans, or TC out of the car, so there's no way it could be a converter engagement issue. Once the engine's back together I fire it up, go to head out for a test drive, and the car won't back up. First thing I do is check the fluid- I never saw any leak out while it was in the shop, and it's in the xxx's on the stick with the engine running, so it isn't that. Next I wonder if I knocked the linkage out of adjustment, but it doesn't seem likely because I feel reverse engage when selected- a tiny "bump" and the car drifts back a couple of inches, but no positive engagement. I adjust the TV cable, but that makes no difference. I haven't driven the car yet because I'm afraid of tearing the trans up even worse if it has a mechanical issue.

Soooooo, do I push it out of the shop and take it around the block to see if it mysteriously lost any other gears while it was sitting immobile on jackstands in my shop? What are the chances of hurting it further?

 

[justin84]

Ok, I am not being a dick here, but it sounds like the Ebrake is on or something. No I am not stupid but I know him well. I have seen dumber stuff!

 

[Otto J]

Ok, I am not being a dick here, but it sounds like the Ebrake is on or something. No I am not stupid but I know him well. I have seen dumber stuff!

If the shifter is engaged in reverse and its not there now,pull the trans and figure out why.
on another note in most instances if your ebrake is on it actually moves in reverse easier than forward.

 

[dieseldave71]

Ok, I am not being a dick here, but it sounds like the Ebrake is on or something. No I am not stupid but I know him well. I have seen dumber stuff!

No, nothing that simple. I'm not saying I couldn't do something dumb, but I'm a certified diesel and heavy equipment mechanic, plus I've built and worked on cars and motorcycles all my life- not bragging, but I'm not a complete idiot. Also, I've had other guys here at my shop look at the car to verify what I'm seeing, just in case a little bit of idiot slipped in there somewhere The trans fluid is fine and the e-brake isn't on- the trans has a mechanical and/or hydraulic issue.

If the shifter is engaged in reverse and its not there now,pull the trans and figure out why.
on another note in most instances if your ebrake is on it actually moves in reverse easier than forward.

I probably will have to pull the trans, but I want to make it isn't something simple first. But what drives me crazy is how could it blow the trans sitting up on jackstands? Imagine if it were a customer's car that came into your shop, how would you explain it? "Well, we fixed the engine and it runs fine now, but the trans blew while it was up on the lift..."

 

[LOT]

Maybe I missed it but

While on jack stands will the forward gears work as they should? Auto and manual? If not take one of the trans line loose @ the rad. (top line out of trans is supply to cooler)--start eng. and see if fluid flows--this will tell you if the pump is pumping.

 

[Otto J]

your unattested proof that it CAN happen.
although trying to make a customer believe it is another thing

 

[dieseldave71]

I pulled the reverse boost valve and checked the other things as best I could without dropping the valve body. Back together tonight and filled with fresh fluid, but no change in performance- it will try to back up just a little bit and then quit. One thing I did notice is that in reverse it make a sound that sounds to me like pump cavitation. What would make it cavitate in reverse only? I'm going to drive it tomorrow, see how many forward gears it has.

LOT, I'll try the homespun pump test tomorrow

Otto, I have a feeling I'm going to learn all about 200R4 innards very soon. I'm not especially thrilled about it, but I am genuinely thankful that it's my own car and not some side job I took in to make some $$$. I've had some similar situations in the heavy equipment repair industry and it's a difficult thing to resolve.

 

[dieseldave71]

Fixed it

I got my reverse back today I was just about ready to drop the trans when I decided to try one more thing- unhooked the TV cable and cycled it through it's travel while my dad had the car running at 1000-1200rpm in reverse with his foot on the brake. Nothing at first, then after maybe a dozen times back and forth the car suddenly went into reverse. Good thing dad had his foot on the brake or it would have shot right out of the shop! Hooked the TV cable back up and now it's fine. Sooooo, what was the problem? TV cable binding? I don't think so, because while I had the trans pan down I had someone work the gas pedal while I watched the trans end of the cable and it seemed to move the lever it's attached to smoothly through it's full range of motion. TV cable adjustment? No, because I didn't readjust it once the trans started working again and it works ok now with it hooked back up. I think there was something stuck in there from sitting- a valve, check ball, etc.- that finally decided to break loose or reseat or whatever. Whatever the reason, I'm glad to be able to back up again:biggrin:
Thanks to all who took the time to respond to my questions!

 

[justin84]

I'm glad it's fixed bud! Had all of us really puzzled!!!