| Author |
Message |
Tom Biggs (Tom_Biggs) (67.8.176.101)
Rating: N/A
Votes: 0 (Vote!) | | Posted on Sunday, April 04, 2004 - 11:51 pm: | |
I've have GMC 4151 (Silversides) with a 4-speed manual transmission. The manual calls for avaition-grade SAE 50 oil. What oils are normally used for this transmission and where can these be found?
Tom Biggs |
doug (68.83.22.144)
Rating: N/A
Votes: 0 (Vote!) | | Posted on Monday, April 05, 2004 - 12:44 am: | |
straight 40 wt.....same as you should run in the crankcase |
FAST FRED (65.150.247.121)
Rating: N/A
Votes: 0 (Vote!) | | Posted on Monday, April 05, 2004 - 6:03 am: | |
I use straight 30 , as was the recomendation when the coach was new.(4 speed Spicer)
The ENGINE , needs 40wt now by Da Book ,
but the tranny is the same as always.
I have added 20% Red Line Synthetic to slow down any wear from shifting.
100% synthetic was too hard to hold without all new seals and gaskets.
Works for me,
FAST FRED |
Nick Morris (Nick3751) (65.117.139.135)
Rating: N/A
Votes: 0 (Vote!) | | Posted on Monday, April 05, 2004 - 7:28 am: | |
Tom,
Where are you I've got a 3751 and would love to talk to ya more especailly if your local to NW Ohio. |
Tom Biggs (Tom_Biggs) (67.8.176.101)
Rating: N/A
Votes: 0 (Vote!) | | Posted on Monday, April 05, 2004 - 7:42 pm: | |
I'm running Delo 40wt in the crankcase.
Aeroshell W100, which has equivalent viscosity to SAE 50 has the same dispersancy and antifoam properties as aircraft grade oil recommended in the operating manual. Is there an arguemnt to use something other than what is recommended in the manual?
The remaining question is what is in the gearbox now (i.e. synthetic) and is it compatible with petroleum based lubricants.
(Nick, I'm located in Central Florida and while I am new to this Silversides and busses in general, I'd be happy to share my small amount of knowlesge and the fun / frustrations of owning a 56 year old coach. There are a few pictures of 4151-293 on the Yahoo Silversides list.)
Tom Biggs |
Johnny (4.174.67.107)
Rating: N/A
Votes: 0 (Vote!) | | Posted on Monday, April 05, 2004 - 8:27 pm: | |
I'd avoid synthetic oils in older syncronized (which I don't THINK this would be) manual trannies. I've been told (by someone I trust completely) that it's actually TOO slippery, & the synchros don't work properly. |
Phil Dumpster (24.16.243.37)
Rating: N/A
Votes: 0 (Vote!) | | Posted on Tuesday, April 06, 2004 - 8:20 am: | |
These are non-synchro transmissions. In fact, they may even being sliding mesh as opposed to constant mesh. Just about everything that went into the Silversides was still 1930's era technology, built in a hurry to replace and augment the equipment which was abused during the war.
I'd use the synthetic IF the seals were good enough to hold it. You'll want to do everything you can to protect those gears since replacing them with identical replacements probably isn't an option. |
DonTX/KS (66.82.9.24)
Rating: N/A
Votes: 0 (Vote!) | | Posted on Tuesday, April 06, 2004 - 1:48 pm: | |
I second that Phil. I became a believer in synthetics when I switched my Kenworth tranny and both differentials to synthetic. They all had temp probes on them of course, and the operating temps of diff and tranny all went down, dramatically, like running 30 degrees cooler! Takes friction to produce heat. I would recommend changing seals if they won't hold it, I never had any problem with leaking se3als with the change to synthetics. |
Phil Dumpster (24.16.243.37)
Rating: N/A
Votes: 0 (Vote!) | | Posted on Wednesday, April 07, 2004 - 1:44 am: | |
Johnny, the person who told you that is a victim of the misconception that sychros work on friction between the synchronizer cones. They don't, they work on the viscosity of the lubricant. If they worked on friction between the cones, they'd wear out in no time as that would require metal-on-metal contact.
As long as the synthetic lubricant being substituted has a similar viscosity, the synchros should work fine. Synthetic lubes tend to have greater penetrating power for the same viscosity, which is why seals may become a concern.
The synchronizer cones have spiral cut grooves on their working surfaces. Each half has the groove cut in the opposite direction. For thick gloppy 90 weight gear oil (which, incidentally, has finely ground clay in it to thicken it up, which is what gives it that obnoxious odor) somewhat coarse grooves are used, while those units designed to use ATF as a lubricant have very fine grooves.
When the two halves of the synchro are brought together at different speeds, the lubricant is forced to travel between the grooves. This restriction creates a resistance which then causes the freewheeling shaft to speed up or slow down to match the driven shaft. As they approach the same speed, the dog (gear-shaped cog) then slides into its mating hole in the gear and the shift is completed.
Using a thicker lubricant will speed up the synchronizer action. Some folks use 140 weight lube for this reason. Thinner lubricants will slow down this action. The lubricating ability of the fluid involved makes no difference as long as it prevents metal-on-metal contact.
Synchros aren't used on very large transmissions (like in semis) because the rotational masses are too large for them to be effective. Gear changes would take too long to complete, and double clutching would be required anyway to speed it up to acceptable levels. |
Nick Morris (Nick3751) (65.117.139.135)
Rating: N/A
Votes: 0 (Vote!) | | Posted on Wednesday, April 07, 2004 - 7:20 am: | |
I had a 1/2 ton ford with a 5 speed in it that was supposed to use atf fluid. However, unknow to me it got some 80 weight put in it by a freind trying to help. The thing winned continually untill I drained it and put the atf back in it. Just kinda backs up Phils statement. |
Tom Biggs (Tom_Biggs) (67.8.176.101)
Rating: N/A
Votes: 0 (Vote!) | | Posted on Wednesday, April 07, 2004 - 7:08 pm: | |
Phil is probably right when he mentions that it would hard to find replacement parts for the Silverside transmission. I called the previous owner who tells me the he filled the transmission with aviation grade SAE 50 per the manual.
For the time being, I am going to assume that the seals are a bit tired and continue with the same lubricant. I ordered a case of AeroShell online yesterday. Shipping drove the price up to considerably, but until I find a local distributor to deal with, the transmission needs topping. |
TWO DOGS (65.179.193.56)
Rating: N/A
Votes: 0 (Vote!) | | Posted on Wednesday, April 07, 2004 - 7:33 pm: | |
go to the little airport close by |
Johnny (4.174.112.38)
Rating: N/A
Votes: 0 (Vote!) | | Posted on Wednesday, April 07, 2004 - 9:33 pm: | |
The person who told me this has been wrenching for almost 35 years. He has run literally dozens of race cars in his life. I trust him absolutely 100%. I also saw it personally: the tranny I compared it in did not like being bang-shifted with synthetic oil in it, & was noticeably "notchier" even driving normally. With regular 80W-90 gear oil, it's fine.
However, I'm not sure, but I think I recall hearing somewhere that this particular tranny (Mopar A-833 4-speed) does NOT have grooves on the synchros. |