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I got this trans second hand. It was not used for long - 5,000 miles maybe. Maybe a couple races behind a 400 HP 355. Trans is supposed to have all the upgrades. Sonnax parts are evident from the outside. Otherwise I'm not 100% on the build list. I was told heavy duty clutches, 5 pinion planetary, and all billet servos, etc. Has a 3000 stall non-locking converter.
The trans sat for about 5 years in dry storage after the car (83 Malibu drag wagon) was parted out. The guy lost interest in it and bought a Vette I'm told.
All of the information I have is reliable, if second hand. The builder is local and well respected though I wasn't his customer, and it's long since expired any warranty it might have had. I don't wish to bother him, or pay him. I'm willing to buy whatever tools and gain whatever knowledge is necessary to effect repairs and/or upgrades.
The TV is properly adjusted, and the I'm very happy with the trans in forward years. It's got very nice part throttle behavior (after going back to a stock weighted governor), and shifts very hard under WOT. Burns rubber from every stop, and chirps hard into second.
When cold the reverse action is pretty firm and locks up ok. When warm it's delayed, it shudders especially backing up hill, and under WOT in reverse it slips.
I have changed the fluid, and filter, and made absolutely sure there's good seal between filter and pump, etc.
Seems to be slowly getting worse. I changed the filter yesterday and on top of the old filter was a bronze/brass/yellow light dusting. Very little on the magnet for the drain plug but some.
What should I be looking for when I open it up? I'm planning to do a basic rebuild on the old trans and swap it in, then see what I need to change out in the race trans - hopefully not a full rebuild but address whatever issue is causing the reverse slippage.
Re: Drag race built 700R4 reverse slipping when hot.
I tried talking to them once before and all I got from one of his lackies was "bring the car in and we can do it for you." Which ain't gonna happen. I'm a shop owner and have never brought a car into someone else's shop and I'm certainly not going to start now. Invariably whenever I trust that some part was done right by the last guy it wasn't and I end up having to do it over myself. If you want it done right....
But yeah they have no helpful information for me. It's long out of their warranty and I'm not the guy they sold the rebuild to so I'm not likely to get anything from them. I would rather put down $1k on tools, books, and my own labor to be better informed and learn a new skill than get a black box back that has been " fixed".
GD
Last edited by GeneralDisorder; 09-07-2017 at 08:53 PM.
Re: Drag race built 700R4 reverse slipping when hot.
Pressure should be apx. minimum 200 - max. 275 psi. in reverse, when giving It throttle. The TransGo .300" intermediate/reverse boost valve is one way to go.
Re: Drag race built 700R4 reverse slipping when hot.
Sonnax is .283 (but with an o-ringed spool), TransGo is .300, and TCI has a .400
What are the benefits and drawbacks of the different sizes? I'm going to order the TransGo I'm just wondering why all the different sizes and what it means if I find other-than-stock in there already.
Also while I'm there, should I also swap the TV boost valve?
Re: Drag race built 700R4 reverse slipping when hot.
Need to measure the valves that are already in place. They may be stock (bad), or the builder may have already upgraded them (good).
When you drop them keep them in order as they were installed. That will help to know whether they were incorrectly installed.
Note that the pressures I listed above are at 1000 RPM and minimum TV. The ones that ProBuilt listed would be at 1000 RPM and maximum TV. I referred to the '92 FSM for these values.
You can also check the line pressure in manual 1st and 2nd. The intermediate boost valve also comes into play at those times.
Re: Drag race built 700R4 reverse slipping when hot.
I'll check line pressures before I drop the valves out.
So 1k RPM..... I should check it with TV cable disconnected and then with TV cable pulled to max by hand I assume? That's how I get the two different readings. I assume you want to see a nice smooth progression in pressure as the TV cable is pulled?
Re: Drag race built 700R4 reverse slipping when hot.
Results:
1000 RPM for all tests.
Park/Neutral/Drive: 90-100 psi @ min TV. 185 psi @ max TV
Reverse: 130 psi @ min TV. 140 psi @ max TV
I used a very accurate mechanical gauge. Old school Acetelene regulator gauge. 0-400 psi. US made, brass backed, etc. Super nice unit.
Based on these results, am I likely looking at a low reverse boost valve problem that I can potentially solve by taking out the boost valve line up and installing upgraded parts? That is what I'm reading from the results and my limited understanding of how this system should be operating. Am I right in thinking the boost valve raises the pressure and that's not happening in reverse, but it is happening in Drive, therefore the pump, etc is capable of the necessary pressure but it's not being boosted by the low/reverse valve?
Also - the information I've seen refers to the spool not sealing well to the pump housing. The Sonnax version, while smaller than the others, addresses this with o-ring seals on the spool. The others do not - are they compensating for spool leakage by making the valve larger? The design choices here are interesting. My inexperienced observations of the Sonnax parts suggest a keen eye for engineering solutions like their smart shell, etc. Any thoughts appreciated.
Re: Drag race built 700R4 reverse slipping when hot.
We used the O-rings vs. non O-rings on the main boost valve and there was virtually no difference (2-5 pounds???). At 1,000 rpm the pressures at WOT will have the gauge needle bouncing around. So only do this for a couple of seconds. Try it at 1,500 rpm and see what happens here. The reverse pressure is way low from your results. When measuring the diameter of the intermediate/reverse boost valve there will be "two" lands. Measure the smaller diameter land. From 1987 on there are .283"and .296" I/R boost valves from the factory. Replace the boost valve snap ring and install it with the sharp edge of the snap ring facing you on installation. Make sure that the snap ring is in its groove completely. Hot idle pressure in neutral should be 70 - 80 psi. at apx 750 rpm. Make sure the TV cable is tight at WOT.
Re: Drag race built 700R4 reverse slipping when hot.
I went to remove the boost valve line up, and it was not having any part of coming out. So I left the snap ring out, put the pan back on with fluid, and ran it through the gears revving it a bit. Boost valve didn't come out but it moved just enough that I could grab it with a really strong magnet and it came out.
So apparently they used a factory 0.296" reverse boost valve, and the Sonnax 0.500" TV boost valve, but rolled and cut the upper o-ring upon assembly. This did not happen during disassembly because the boost valve was noticeably difficult to move and sticky even before I removed the snap ring.
I installed the .300 and .500 TransGo parts, but the reverse slipping persists. I haven't checked line pressure again but I may do that later tonight.
So either this o-ring damage caused a bunch of leakage or blockage that led to low pressure and damage to some clutch pack, or this simply isn't the problem and the o-ring is unrelated.
At this point it looks like a tear down is in order, but what am I looking for?
Anything in the valve body that could be bleeding off pressure?
GD
Last edited by GeneralDisorder; 09-14-2017 at 10:04 PM.
Re: Drag race built 700R4 reverse slipping when hot.
I'm sorry about your transmission GD but, thank you for your replies to my previous post. I think I am having the same problem as you currently. When cold reverse engages as it should but, while warm it slips. I took a video with my phone earlier and uploaded it to YouTube. Does this look anything like what you are experiencing?
Re: Drag race built 700R4 reverse slipping when hot.
Yes that's similar to what I'm experiencing. It delays slightly unless I give it gas and it goes in soft. Then it won't lock in hard. It will shudder and slip when backing up. When cold it goes in nice and solid and will roast the tires in reverse. Slips when warm or hot.
Re: Drag race built 700R4 reverse slipping when hot.
Did you ever find the problem, GD? I'm taking mine back to the shop for the third time in Wednesday. I'll let you know the findings as soon as I can incase it may help.
Re: Drag race built 700R4 reverse slipping when hot.
No I haven't found the issue. Only that the reverse line pressure is low. I'm probably going to do a rebuild on my old factory transmission and swap it out so the race trans can be torn down.
Re: Drag race built 700R4 reverse slipping when hot.
Update - swapped the trans out for a nice unit from arcticwhiteZ (Thanks Jeff!), and tore it down for inspection. This is what I found on the low/reverse clutch piston seal:
As usual - if you want something done right, do it yourself. This is the work of the owner and master builder of a prominent local transmission shop.
09-04-2017, 01:15 AM
