What is normal torque converter slip?

How they work, how they don't work, and how to fix them

Moderators: Greenleaf, BC847, Richie O

What is normal torque converter slip?

Postby ByronRACE » Mon Feb 24, 2014 6:45 pm

Hey Guys,

I took the engine/transmission out of a donor '92 Dodge Cummins and put it in my '74 Grumman Kurbmaster Stepvan/RV Conversion. As far as I know, the engine and converter is stock. The transmission has been rebuilt.

I have a question about torque converter slip in this transmission. It's a non-locking A518 4spd with the electronic overdrive in 3rd.

I wired the OD to a switch. It functions.

This truck has 4.88 rear end gears and 32" tall tires.

Flat out in 3rd gear on the governor it does 45mph. I did the math, and assuming a 2600RPM governor limit, that works out correctly for this gearing and shows me that I'm getting 250RPM converter slip under those conditions.

Flat out in 4th gear on the governor it does 58mph. Assuming the same 2600RPM governor limit, that works out to 600RPM converter slip to achieve that speed.

Does that sound right? For this to be correct, that means I have more than 2X the amount of converter slip between 45mph/3rd and 58mph/4th in a vehicle with probably 3x the frontal area of a dodge pickup. I find that surprising, but maybe that is normal with this much load. Are these converters that slushy?

I do not have a tach on this engine. The RPM is a guess based on where I think the governor is supposed to do its thing. I do think I'm riding the governor in both gears, especially since the math works out pretty close in 3rd gear and the engine feels like it noses over.

I do not have a pyrometer, or boost gauge or fuel pressure gauge. They are coming. The speedometer is correct and has been verified with my GPS.

Does this converter slip sound normal? If so, I need to change my rear end gears sooner than later. I have a dana 70 that can be put in this truck, I just didn't plan on doing that right now. I need to be able to cruise down the freeway, and if the converter slips this much...gearing it is the only solution.

Thanks for any input!

Byron
ByronRACE
fuel screw!!!!
 
Posts: 38
Joined: Fri Nov 01, 2013 9:12 am

Re: What is normal torque converter slip?

Postby tim curran » Mon Feb 24, 2014 6:54 pm

If it is the torque converter then time for a new one. When I stretched my last torque converter out sled pulling it was doing the same thing. Stock converter only good for stock light trucks. I put a bd in my truck much better. It still slips some but that is the nature of a none lock up. :alien:
1993 w250, 3200 RPM springs, maxed fuel screw, industrial inj. Fuel pin, Dynamite diesel 75 horse inj., ind inj stage 2 pump, 60 lbs valve springs, ARP head studs, Banks ram air intake. 4 inch diamond eye exhaust,16cm turbo housing, 60 mm comp. Housing, BD tourqe converter, billet flex plate, Banks gauges, 212hp 608 tourque, old smokey and worn out.
tim curran
fuel screw!!!!
 
Posts: 83
Joined: Mon Jan 11, 2010 1:49 pm
Location: Poland ME.

Re: What is normal torque converter slip?

Postby ByronRACE » Mon Feb 24, 2014 9:24 pm

I guess what I need to know is how fast a stock '92 dodge diesel pickup can go in 3rd and 4th gear, what rear end ratio it has stock, and what the tire diameter is.

That, plus the stock governor rpm and I should be able to calculate whether or not what I'm seeing is normal.
ByronRACE
fuel screw!!!!
 
Posts: 38
Joined: Fri Nov 01, 2013 9:12 am
Top

Re: What is normal torque converter slip?

Postby ByronRACE » Mon Feb 24, 2014 10:29 pm

This is what I'm experiencing I think:

Image

Does this look like realistic converter slip for a non-locking A518 in a 10,000lb step van with 7' x 8' frontal area?

Looking at some of the other "how fast can you go" posts, it looks like normal loaded slip up top is around 300-400rpm in a pickup truck at the top of 4th gear. Can anyone confirm this?
ByronRACE
fuel screw!!!!
 
Posts: 38
Joined: Fri Nov 01, 2013 9:12 am
Top

Re: What is normal torque converter slip?

Postby Philip » Tue Feb 25, 2014 6:44 am

Most stock 1st gens start defueling at 2450 RPM.
93 W350 Club/cab w/duals, buckets & console, B&W flatbed, G56, 6 spd, 3:07 rears, gages, HX40/16, 4" exhaust, 6X.018 sticks, rear air ride suspension
User avatar
Philip
14mm rotor
 
Posts: 1954
Joined: Mon Jan 08, 2007 10:50 am
Location: Indiana
Top

Re: What is normal torque converter slip?

Postby ByronRACE » Tue Feb 25, 2014 10:15 am

Thanks for that, I guess my next step is to figure out how to wire the crank sensor to a tach. If it's only turning 2450RPM, that explains a lot.

The reason I'm dwelling on this is I have a decision to make about where to put my money next.

I don't mind the slushy converter. In fact, I think it's pretty great in this application. This truck is very heavy; about the equivalent of towing a car and car trailer behind your pickup all the time; and I think it is a great cushion to protect the transmission under these loads. I'd rather keep the slush and handle the heat problem with coolers than sink 4K into the transmission to make it handle more abuse. That is, assuming the behavior I'm seeing is normal and not indicative of a converter about to blow up.

I don't mind spinning the engine a few hundred more RPM than you would in a pickup as long as this won't hurt it. Should I be concerned about running the truck wound out on the governor going down the freeway hours at a time? If not, how bad will this hurt fuel economy versus running it at 2000-2100rpm?

I don't mind a 60mph speed limit. This truck shouldn't be moving faster than that anyway. It's huge, has 4 drum brakes, and no sway bars. 60 is plenty. In fact, 55 is plenty, as long as that doesn't mean 35 on the hills.

I like the way the 4.88 rear end gears moves this truck from a stop. It's effortless and accelerates like a car. I don't think it'll drive as well around town if I change the rear end to 3.73s or 3.54s.

I don't mind losing a little fuel economy because of the increased RPM. But how much am I losing? I have not driven the truck far enough to know what the fuel economy is.

Is it safe to climb large grades in 4th gear on an A518? How about towing? 3rd gear is a much stronger gear isn't it? 3rd gear is wound out at 45mph. It's presently not usable for freeway duty. If I changed the rear gears to 3.54s, I would be near 55mph wound out in 3rd, making it usable for towing and climbing grades without impeding traffic. If 4th is strong enough, I don't need it.

I have a Dana 70HD with the same width and bolt pattern that I can swap in, and that rear end will allow me to change the gearing to as high as 3.54. To do that, I'll need to modify my driveshaft ($150), rebuild the brakes and bearings ($200), and have a ring and pinion installed and whatever else it needs ($500?), and either move the spring perches on the differential or fabricate spacers for my leaf spring frame mounts. The spring pads are 1" further apart than the rear I have now. It's quite a job. I have a feeling that I'll need to do this, but perhaps not right away.

If anyone knows the answer to any of my questions above, it would sure help me make a decision.

Thanks!

Byron
ByronRACE
fuel screw!!!!
 
Posts: 38
Joined: Fri Nov 01, 2013 9:12 am
Top

OK, that was stupid!

Postby ByronRACE » Tue Feb 25, 2014 1:17 pm

OK, so I don't have a ballooned converter or a bad transmission or big frontal area causing too much load, or too much weight or any of that other crap I thrashed around with yesterday...

I have...shudder...a 3/4 open throttle at WOT problem.

Pretty lame huh? Yeah, well all I have to say is when you're sure it's not something...check it AGAIN.

I had another symptom, and that was the truck wasn't making the 14+psi of boost that it should be making, so while I was investigating potential causes for that problem I read a thread about a guy that discovered his throttle wasn't opening all the way and when he resolved that, he not only produced more boost but more top end on the freeway.

So I went out and looked...and yep, I somehow managed to build my throttle assembly such that it doesn't open the throttle all the way. I resolved that, took it for a drive and holy crap, it's a whole new engine...14lbs of boost and 66mph on the governor just like the math said it should.

The rear end can wait. I love the way the truck accelerates with the low gears. I think 2200rpm at 55mph is probably fine for a big heavy truck. I'm going to run it like this for a while and see how it goes.

Thanks for listening, and not beating me up too much.

Byron
ByronRACE
fuel screw!!!!
 
Posts: 38
Joined: Fri Nov 01, 2013 9:12 am
Top

Re: What is normal torque converter slip?

Postby dazedandconfused » Tue Feb 25, 2014 1:30 pm

If it was mine I would probably drop to 4.10 gears. It would still pull out good and gain you some mpg.back and get the engine down in its power band a bit more.
Big Andy
1983 Dodge D150 that has been repowered with a 93 Cummins/518 running gear AKA The Ugly Duck! I would much rather build them then buy them.[
User avatar
dazedandconfused
14mm rotor
 
Posts: 6119
Joined: Thu Apr 05, 2007 6:25 pm
Location: Walton, Kentucky
Top

Re: What is normal torque converter slip?

Postby PToombs » Tue Feb 25, 2014 6:13 pm

FYI, stock 1st gen tires are about 31 inches tall. My thoughts on gearing it up is that you will have more converter slippage on the highway.
Glad you found the throttle problem. Did you back out your high idle screw? I'd back it flush with the casting or remove it completely. You may notice a little more rpm again.
pete

Just enough power to break everything behind the crankshaft.
User avatar
PToombs
14mm rotor
 
Posts: 11367
Joined: Sun Jan 07, 2007 6:13 pm
Location: Syracuse NY. Snow central!
Top

High idle screw

Postby ByronRACE » Tue Feb 25, 2014 8:23 pm

No, I have not touched the high idle screw. I'll read about that.

Right now I need to figure out where my fuel leak is. It's leaking diesel somewhere between the injection pump and the filter assembly, and only under hard throttle. Odd. It's not the IP or filter assembly...both are dry. It's in the middle. Strange.
ByronRACE
fuel screw!!!!
 
Posts: 38
Joined: Fri Nov 01, 2013 9:12 am
Top

Re: What is normal torque converter slip?

Postby Philip » Thu Feb 27, 2014 5:48 pm

The fuel line from the filter to the front of the injection pump is not a one piece line. It is two pieces with the connection behind the pump.

There is also a cover on the back side of the pump. It is sealed with an O-ring. It could be leaking also.
93 W350 Club/cab w/duals, buckets & console, B&W flatbed, G56, 6 spd, 3:07 rears, gages, HX40/16, 4" exhaust, 6X.018 sticks, rear air ride suspension
User avatar
Philip
14mm rotor
 
Posts: 1954
Joined: Mon Jan 08, 2007 10:50 am
Location: Indiana
Top

Re: What is normal torque converter slip?

Postby CumminsPower59 » Fri Feb 28, 2014 6:38 am

What Philip said. I would check the return line just to be safe too. It's small/thin, I could see the possibility of one cracking or something...
Ike

91 W350 SRW, 3.07's, NV4500, 370's, THD LPPP, Super HX40, 2nd gen IC swap, BHAF, Isspro's, 2" lift, 285's on 3rd gen 17"'s.
04 VW Jetta Wagon TDI 5speed
CumminsPower59
14mm rotor
 
Posts: 3203
Joined: Mon Feb 25, 2008 8:04 am
Location: The Hawkeye State of 'Murica!
Top

Re: What is normal torque converter slip?

Postby SNOOT » Fri Feb 28, 2014 11:13 am

Put a 3200rpm gov spring in that thing...
1993 W350
User avatar
SNOOT
14mm rotor
 
Posts: 609
Joined: Tue Mar 11, 2008 8:05 pm
Location: Seattle, WA.
Top


Return to Transmission

Who is online

Users browsing this forum: No registered users and 11 guests